Which organ is the most important organ in the body? Most people would say the heart or the brain, completely overlooking the gastrointestinal tract (GI tract). Though definitely not the most attractive organs in the body, they are certainly among the most important. The 30+ foot long tube that goes from the mouth to the anus is responsible for the many different body functions which will be reviewed in this chapter. The GI tract is imperative for our well being and our lifelong health. A non-functioning or poorly functioning GI tract can be the source of many chronic health problems that can interfere with your quality of life. In many instances the death of a person begins in the intestines.
The old saying "you are what you eat" perhaps would be more accurate if worded "you are what you absorb and digest". Here we will be looking at the importance of these two functions of the digestive system: digestion and absorption.
The Gastrointestinal System is responsible for the breakdown and absorption of various foods and liquids needed to sustain life. Many different organs have essential roles in the digestion of food, from the mechanical disrupting by the teeth to the creation of bile (an emulsifier) by the liver. Bile production of the liver plays an important role in digestion: from being stored and concentrated in the gallbladder during fasting stages to being discharged to the small intestine.
In order to understand the interactions of the different components we shall follow the food on its journey through the human body. During digestion, two main processes occur at the same time;
- Mechanical Digestion: larger pieces of food get broken down into smaller pieces while being prepared for chemical digestion. Mechanical digestion starts in the mouth and continues into the stomach.
- Chemical Digestion: starts in the mouth and continues into the intestines. Several different enzymes break down macromolecules into smaller molecules that can be absorbed.
The GI tract starts with the mouth and proceeds to the esophagus, stomach, small intestine (duodenum, jejunum, ileum), and then to the large intestine (colon), rectum, and terminates at the anus. You could probably say the human body is just like a big donut. The GI tract is the donut hole. We will also be discussing the pancreas and liver, and accessory organs of the gastrointestinal system that contribute materials to the small intestine.
Layers of the GI Tract
The GI tract is composed of four layers also known as Tunics. Each layer has different tissues and functions. From the inside out they are called: mucosa, submucosa, muscularis, and serosa.
Mucosa: The mucosa is the absorptive and secretory layer. It is composed of simple epithelium cells and a thin connective tissue. There are specialized goblet cells that secrete mucus throughout the GI tract located within the mucosa. On the mucosa layer there are Villi and Micro Villi.
Submucosa: The submucosa is relatively thick, highly vascular, and serves the mucosa. The absorbed elements that pass through the mucosa are picked up from the blood vessels of the submucosa. The submucosa also has glands and nerve plexuses.
Muscularis: The muscularis is responsible for segmental contractions and peristaltic movement in the GI tract. The muscularis is composed of two layers of muscle: an inner circular and outer longitudinal layer of smooth muscle. These muscles cause food to move and churn with digestive enzymes down the GI tract.
Serosa: The last layer is a protective layer. It is composed of avascular connective tissue and simple squamous epithelium. It secretes lubricating serous fluid. This is the visible layer on the outside of the organs.
- 1. Salivary glands
- Parotid gland, submandibular gland, sublingual gland
- Exocrine gland that produces saliva which begins the process of digestion with amylase
- 2. Tongue
- Manipulates food for chewing/swallowing
- Main taste organ, covered in taste buds
- 3. Teeth
- 4. Liver
- Produces and excretes bile required for emulsifying fats. Some of the bile drains directly into the duodenum and some is stored in the gall bladder.
- Helps metabolize proteins, lipids, and carbohydrates.
- Urea, chief end product of mammalian metabolism, is formed in liver from amino acids and compounds of ammonia.
- Breaks down insulin and other hormones.
- Produces coagulation factors.
- 5. Gallbladder
- 6. Pancreas
- Exocrine functions: Digestive enzyme secretion.
- Stores zymogens (inactive enzymes) that will be activated by the brush border membrane in the small intestine when a person eats protein (amino acids).
- Trypsinogen – Trypsin: digests protein.
- Chymotypsinogen – Chymotrypsin: digests proteins.
- Carboxypeptidases: digests proteins.
- Lipase-lipid: digests fats.
- Amylase: digests carbohydrates.
- Endocrine functions: Hormone secretion.
- Somatostatin: inhibits the function of insulin. Produced if the body is getting too much glucose.
- Glucagon: stimulates the stored glycogen in the liver to convert to glucose. Produced if the body does not have enough glucose.
- Insulin: made in the beta cells of the Islets of Langerhans of the pancreas. Insulin is a hormone that regulates blood glucose.
- 7. Vermiform appendix
- There are a few theories on what the appendix does.
- Vestigal organ
- Immune function
- Helps maintain gut flora
The Digestive System
The first step in the digestive system can actually begin before the food is even in your mouth. When you smell or see something that you just have to eat, you start to salivate in anticipation of eating, thus beginning the digestive process.
Food is the body's source of fuel. Nutrients in food give the body's cells the energy they need to operate. Before food can be used it has to be broken down into tiny little pieces so it can be absorbed and used by the body. In humans, proteins need to be broken down into amino acids, starches into sugars, and fats into fatty acids and glycerol.
During digestion two main processes occur at the same time:
- Mechanical Digestion: larger pieces of food get broken down into smaller pieces while being prepared for chemical digestion. Mechanical digestion starts in the mouth and continues in to the stomach.
- Chemical Digestion: several different enzymes break down macromolecules into smaller molecules that can be more efficiently absorbed. Chemical digestion starts with saliva and continues into the intestines.
The digestive system is made up by the alimentary canal, or the digestive tract, and other abdominal organs that play a part in digestion such as the liver and the pancreas. The alimentary canal is the long tube of organs that runs from the mouth (where the food enters) to the anus (where indigestible waste leaves). The organs in the alimentary canal include the mouth( for mastication),esophagus, stomach and the intestines. The average adult digestive tract is about thirty feet (30') long. While in the digestive tract the food is really passing through the body rather than being in the body. The smooth muscles of the tubular digestive organs move the food efficiently along as it is broken down into absorb-able atoms and molecules. During absorption, the nutrients that come from food (such as proteins, fats, carbohydrates, vitamins, and minerals) pass through the wall of the small intestine and into the bloodstream and lymph. In this way nutrients can be distributed throughout the rest of the body. In the large intestine there is re absorption of water and absorption of some minerals as feces are formed. The parts of the food that the body passes out through the anus is known as feces.
Digestion begins in the mouth. A brain reflex triggers the flow of saliva when we see or even think about food. Saliva moistens the food while the teeth chew it up and make it easier to swallow. Amylase, which is the digestive enzyme found in saliva, starts to break down starch into simpler sugars before the food even leaves the mouth. The nervous pathway involved in salivary excretion requires stimulation of receptors in the mouth, sensory impulses to the brain stem, and parasympathetic impulses to salivary glands.
Swallowing your food happens when the muscles in your tongue and mouth move the food into your pharynx. The pharynx, which is the passageway for food and air, is about five inches (5") long. A small flap of skin called the epiglottis closes over the pharynx to prevent food from entering the trachea and thus choking. For swallowing to happen correctly a combination of 25 muscles must all work together at the same time. Salivary glands also produce an estimated three liters of saliva per day.
|Enzyme||Produced In||Site of Release||pH Level|
|Salivary amylase||Salivary glands||Mouth||Neutral|
|Pancreatic amylase||Pancreas||Small intestine||Basic|
|Maltase||Small intestine||Small intestine||Basic|
|Peptidases||Small intestine||Small intestine||Basic|
|Nucleic Acid Digestion:|
The esophagus (also spelled oesophagus/esophagus) or gullet is the muscular tube in vertebrates through which ingested food passes from the throat to the stomach. The esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. It connects the pharynx, which is the body cavity that is common to both the digestive and respiratory systems behind the mouth, with the stomach, where the second stage of digestion is initiated (the first stage is in the mouth with teeth and tongue masticating food and mixing it with saliva).
After passing through the throat, the food moves into the esophagus and is pushed down into the stomach by the process of peristalsis (involuntary wavelike muscle contractions along the G.I. tract). At the end of the esophagus there is a sphincter that allows food into the stomach then closes back up so the food cannot travel back up into the esophagus.
The esophagus is lined with mucus membranes, and uses peristaltic action to move swallowed food down to the stomach.
The esophagus is lined by a stratified squamous epithelium, which is rapidly turned over, and serves a protective effect due to the high volume transit of food, saliva, and mucus into the stomach. The lamina propria of the esophagus is sparse. The mucus secreting glands are located in the submucosa, and are connective structures called papillae.
The muscularis propria of the esophagus consists of striatedmuscle in the upper third (superior) part of the esophagus. The middle third consists of a combination of smooth muscle and striated muscle, and the bottom (inferior) third is only smooth muscle. The distal end of the esophagus is slightly narrowed because of the thickened circular muscles. This part of the esophagus is called the lower esophageal sphincter. This aids in keeping food down and not being regurgitated.
The esophagus has a rich lymphatic drainage as well.
The stomach is a thick walled organ that lies between the esophagus and the first part of the small intestine (the duodenum). It is on the left side of the abdominal cavity, the fundus of the stomach lying against the diaphragm. Lying beneath the stomach is the pancreas. The greater omentum hangs from the greater curvature.
A mucous membrane lines the stomach which contains glands (with chief cells) that secrete gastric juices, up to three quarts of this digestive fluid is produced daily. The gastric glands begin secreting before food enters the stomach due to the parasympathetic impulses of the vagus nerve, making the stomach also a storage vat for that acid.
The secretion of gastric juices occurs in three phases: cephalic, gastric, and intestinal. The cephalic phase is activated by the smell and taste of food and swallowing. The gastric phase is activated by the chemical effects of food and the distension of the stomach. The intestinal phase blocks the effect of the cephalic and gastric phases. Gastric juice also contains an enzyme named pepsin, which digests proteins, hydrochloric acid and mucus. Hydrochloric acid causes the stomach to maintain a pH of about 2, which helps kill off bacteria that comes into the digestive system via food.
The gastric juice is highly acidic with a pH of 1-3. It may cause or compound damage to the stomach wall or its layer of mucus, causing a peptic ulcer. On the inside of the stomach there are folds of skin call the gastric rugae. Gastric rugae make the stomach very extendable, especially after a very big meal.
The stomach is divided into four sections, each of which has different cells and functions. The sections are: 1) Cardiac region, where the contents of the esophagus empty into the stomach, 2) Fundus, formed by the upper curvature of the organ, 3) Body, the main central region, and 4) Pylorus or atrium, the lower section of the organ that facilitates emptying the contents into the small intestine. Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the: 1) Cardiac or esophageal sphincter, dividing the tract above, and 2) Pyloric sphincter, dividing the stomach from the small intestine.
After receiving the bolus (chewed food) the process of peristalsis is started; mixed and churned with gastric juices the bolus is transformed into a semi-liquid substance called chyme. Stomach muscles mix up the food with enzymes and acids to make smaller digestible pieces. The pyloric sphincter, a walnut shaped muscular tube at the stomach outlet, keeps chyme in the stomach until it reaches the right consistency to pass into the small intestine. The food leaves the stomach in small squirts rather than all at once.
Water, alcohol, salt, and simple sugars can be absorbed directly through the stomach wall. However, most substances in our food need a little more digestion and must travel into the intestines before they can be absorbed. When the stomach is empty it is about the size of one fifth of a cup of fluid. When stretched and expanded, it can hold up to eight cups of food after a big meal.
There are many different gastric glands and they secret many different chemicals. Parietal cells secrete hydrochloric acid and intrinsic factor; chief cells secrete pepsinogen; goblet cells secrete mucus; argentaffin cells secrete serotonin and histamine; and G cells secrete the hormone gastrin.
Vessels and nerves
- Arteries: The arteries supplying the stomach are the left gastric, the right gastric and right gastroepiploic branches of the hepatic, and the left gastroepiploic and short gastric branches of the lineal. They supply the muscular coat, ramify in the submucous coat, and are finally distributed to the mucous membrane.
- Capillaries: The arteries break up at the base of the gastric tubules into a plexus of fine capillaries, which run upward between the tubules, anatomizing with each other, and ending in a plexus of larger capillaries, which surround the mouths of the tubes, and also form hexagonal meshes around the ducts.
- Veins: From these the veins arise, and pursue a straight course downward, between the tubules, to the submucous tissue; they end either in the lineal and superior mesenteric veins, or directly in the portal vein.
- Lymphatics: The lymphatics are numerous: They consist of a superficial and a deep set, and pass to the lymph glands found along the two curvatures of the organ.
- Nerves: The nerves are the terminal branches of the right and left urethra and other parts, the former being distributed upon the back, and the latter upon the front part of the organ. A great number of branches from the celiac plexus of the sympathetic are also distributed to it. Nerve plexuses are found in the submucous coat and between the layers of the muscular coat as in the intestine. From these plexuses fibrils are distributed to the muscular tissue and the mucous membrane.
Disorders of the Stomach
Disorders of the stomach are common. There can be a lot of different causes with a variety of symptoms. The strength of the inner lining of the stomach needs a careful balance of acid and mucus. If there is not enough mucus in the stomach, ulcers, abdominal pain, indigestion, heartburn, nausea and vomiting could all be caused by the extra acid.
Erosions, ulcers, and tumors can cause bleeding. When blood is in the stomach it starts the digestive process and turns black. When this happens, the person can have black stool or vomit. Some ulcers can bleed very slowly so the person won't recognize the loss of blood. Over time, the iron in your body will run out, which in turn, will cause anemia.
There isn't a known diet to prevent against getting ulcers. A balanced, healthy diet is always recommended. Smoking can also be a cause of problems in the stomach. Tobacco increases acid production and damages the lining of the stomach. It is not a proven fact that stress alone can cause an ulcer.
Histology of the human stomach
Like the other parts of the gastrointestinal tract, the stomach walls are made of a number of layers.
From the inside to the outside, the first main layer is the mucosa. This consists of an epithelium, the lamina propria underneath, and a thin bit of smooth muscle called the muscularis mucosa.
The submucosa lies under this and consists of fibrous connective tissue, separating the mucosa from the next layer, the muscularis externa. The muscularis in the stomach differs from that of other GI organs in that it has three layers of muscle instead of two. Under these muscle layers is the adventitia, layers of connective tissue continuous with the omenta.
The epithelium of the stomach forms deep pits, called fundic or oxyntic glands. Different types of cells are at different locations down the pits. The cells at the base of these pits are chief cells, responsible for production of pepsinogen, an inactive precursor of pepsin, which degrades proteins. The secretion of pepsinogen prevents self-digestion of the stomach cells.
Further up the pits, parietal cells produce gastric acid and a vital substance, intrinsic factor. The function of gastric acid is twofold 1) it kills most of the bacteria in food, stimulates hunger, and activates pepsinogen into pepsin, and 2) denatures the complex protein molecule as a precursor to protein digestion through enzyme action in the stomach and small intestines. Near the top of the pits, closest to the contents of the stomach, there are mucous-producing cells called goblet cells that help protect the stomach from self-digestion.
The muscularis externa is made up of three layers of smooth muscle. The innermost layer is obliquely-oriented: this is not seen in other parts of the digestive system: this layer is responsible for creating the motion that churns and physically breaks down the food. The next layers are the square and then the longitudinal, which are present as in other parts of the GI tract. The pyloric antrum which has thicker skin cells in its walls and performs more forceful contractions than the fundus. The pylorus is surrounded by a thick circular muscular wall which is normally tonically constricted forming a functional (if not anatomically discrete) pyloric sphincter, which controls the movement of chyme.
Control of secretion and motility
The movement and the flow of chemicals into the stomach are controlled by both the nervous system and by the various digestive system hormones.
The hormone gastrin causes an increase in the secretion of HCL, pepsinogen and intrinsic factor from parietal cells in the stomach. It also causes increased motility in the stomach. Gastrin is released by G-cells into the stomach. It is inhibited by pH normally less than 4 (high acid), as well as the hormone somatostatin.
Cholecystokinin (CCK) has most effect on the gall bladder, but it also decreases gastric emptying. In a different and rare manner, secretin, produced in the small intestine, has most effects on the pancreas, but will also diminish acid secretion in the stomach.
Gastric inhibitory peptide (GIP) and enteroglucagon decrease both gastric motility and secretion of pepsin. Other than gastrin, these hormones act to turn off the stomach action. This is in response to food products in the liver and gall bladder, which have not yet been absorbed. The stomach needs only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as a storage for food.
The small intestine is the site where most of the chemical and mechanical digestion is carried out. Tiny projections called villi line the small intestine which absorbs digested food into the capillaries. Most of the food absorption takes place in the jejunum and the ileum.
The functions of a small intestine is, the digestion of proteins into peptides and amino acids principally occurs in the stomach but some also occurs in the small intestine. Peptides are degraded into amino acids; lipids (fats) are degraded into fatty acids and glycerol; and carbohydrates are degraded into simple sugars.
The three main sections of the small intestine are the duodenum, the jejunum, the ileum.
- The duodenum
In anatomy of the digestive system, the duodenum is a hollow jointed tube connecting the stomach to the jejunum. It is the first and shortest part of the small intestine. It begins with the duodenal bulb and ends at the ligament of Treitz. The duodenum is almost entirely retro peritoneal. The duodenum is also where the bile and pancreatic juices enter the intestine.
- The jejunum
The jejunum is a part of the small bowel, located between the distal end of duodenum and the proximal part of ileum. The jejunum and the ileum are suspended by an extensive mesentery giving the bowel great mobility within the abdomen. The inner surface of the jejunum, its mucous membrane, is covered in projections called villi, which increase the surface area of tissue available to absorb nutrients from the gut contents. It is different from the ileum due to fewer goblet cells and generally lacks Peyer's patches.
- The ileum
Its function is to absorb vitamin B12 and bile salts. The wall itself is made up of folds, each of which has many tiny finger-like projections known as villi, on its surface. In turn, the epithelial cells which line these villi possess even larger numbers of micro villi. The cells that line the ileum contain the protease and carbohydrate enzymes responsible for the final stages of protein and carbohydrate digestion. These enzymes are present in the cytoplasm of the epithelial cells. The villi contain large numbers of capillaries which take the amino acids and glucose produced by digestion to the hepatic portal vein and the liver.
The terminal ileum continues to absorb bile salts, and is also crucial in the absorption of fat-soluble vitamins (Vitamin A, D, E and K). For fat-soluble vitamin absorption to occur, bile acids must be present.
The large intestine (colon) extends from the end of the ileum to the anus. It is about 5 feet long, being one-fifth of the whole extent of the intestinal canal. It's caliber is largest at the commencement at the cecum, and gradually diminishes as far as the rectum, where there is a dilatation of considerable size just above the anal canal. It differs from the small intestine in by the greater caliber, more fixed position, sacculated form, and in possessing certain appendages to its external coat, the appendices epiploicæ. Further, its longitudinal muscular fibers do not form a continuous layer around the gut, but are arranged in three longitudinal bands or tæniæ.
The large intestine is divided into the cecum, colon, rectum, and anal canal. In its course, describes an arch which surrounds the convolutions of the small intestine. It commences in the right iliac region, in a dilated part, the cecum. It ascends through the right lumbar and hypochondriac regions to the under surface of the liver; here it takes a bend, the right colic flexure, to the left and passes transversely across the abdomen on the confines of the epigastric and umbilical regions, to the left hypochondriac region; it then bends again, the left colic flexure, and descends through the left lumbar and iliac regions to the pelvis, where it forms a bend called the sigmoid flexure; from this it is continued along the posterior wall of the pelvis to the anus.
There are trillions of bacteria, yeasts, and parasites living in our intestines, mostly in the colon. Over 400 species of organisms live in the colon. Most of these are very helpful to our health, while the minority are harmful. Helpful organisms synthesize vitamins, like B12, biotin, and vitamin K. They breakdown toxins and stop proliferation of harmful organisms. They stimulate the immune system and produce short chain fatty acids (SCFAs) that are required for the health of colon cells and help prevent colon cancer. There are many beneficial bacteria but some of the most common and important are Lactobacillus Acidophilus and various species of Bifidobacterium. These are available as "probiotics" from many sources.
Pancreas, Liver, and Gallbladder
The pancreas, liver, and gallbladder are essential for digestion. The pancreas produces enzymes that help digest proteins, fats, and carbohydrates, the liver produces bile that helps the body absorb fat, and the gallbladder stores the bile until it is needed. The enzymes and bile travel through special channels called ducts and into the small intestine where they help break down the food.
The pancreas is located posterior to the stomach and in close association with the duodenum.
In humans, the pancreas is a 6-10 inch elongated organ in the abdomen located retro peritoneal. It is often described as having three regions: a head, body and tail. The pancreatic head abuts the second part of the duodenum while the tail extends towards the spleen. The pancreatic duct runs the length of the pancreas and empties into the second part of the duodenum at the ampulla of Vater. The common bile duct commonly joins the pancreatic duct at or near this point.
The pancreas is supplied arterially by the pancreaticoduodenal arteries, themselves branches of the superior mesenteric artery of the hepatic artery (branch of celiac trunk from the abdominal aorta). The superior mesenteric artery provides the inferior pancreaticoduodenal arteries while the gastroduodenal artery (one of the terminal branches of the hepatic artery) provides the superior pancreaticoduodenal artery. Venous drainage is via the pancreatic duodenal veins which end up in the portal vein. The splenic vein passed posterior to the pancreas but is said to not drain the pancreas itself. The portal vein is formed by the union of the superior mesenteric vein and splenic vein posterior to the body of the pancreas. In some people (as many as 40%) the inferior mesenteric vein also joins with the splenic vein behind the pancreas, in others it simply joins with the superior mesenteric vein instead.
The function of the pancreas is to produce enzymes that break down all categories of digestible foods (exocrine pancreas) and secrete hormones that affect carbohydrates metabolism (endocrine pancreas).
The pancreas is composed of pancreatic exocrine cells, whose ducts are arranged in clusters called acini (singular acinus). The cells are filled with secretory granules containing the precursor digestive enzymes (mainly trypsinogen, chymotrypsinogen, pancreatic lipase, and amylase) that are secreted into the lumen of the acinus. These granules are termed zymogen granules (zymogen referring to the inactive precursor enzymes.) It is important to synthesize inactive enzymes in the pancreas to avoid auto degradation, which can lead to pancreatitis.
The pancreas is near the liver, and is the main source of enzymes for digesting fats (lipids) and proteins - the intestinal walls have enzymes that will digest polysaccharides. Pancreatic secretions from ductal cells contain bicarbonate ions and are alkaline in order to neutralize the acidic chyme that the stomach churns out. Control of the exocrine function of the pancreas are via the hormone gastrin, cholecystokinin and secretin, which are hormones secreted by cells in the stomach and duodenum, in response to distension and/or food and which causes secretion of pancreatic juices.
The two major proteases which the pancreas are trypsinogen and chymotrypsinogen. These zymogens are inactivated forms of trypsin and chymotrypsin. Once released in the intestine, the enzyme enterokinase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin. The free trypsin then cleaves the rest of the trypsinogen and chymotrypsinogen to their active forms.
Pancreatic secretions accumulate in intralobular ducts that drain the main pancreatic duct, which drains directly into the duodenum.
Due to the importance of its enzyme contents, injuring the pancreas is a very dangerous situation. A puncture of the pancreas tends to require careful medical intervention.
Scattered among the acini are the endocrine cells of the pancreas, in groups called the islets of Langerhans. They are:
Insulin-producing beta cells (50-80% of the islet cells) Glucagon-releasing alpha cells (15-20%) Somatostatin-producing delta cells (3-10%) Pancreatic polypeptide-containing PP cells (remaining %)
The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, by either cytoplasmic processes or by direct apposition.
The liver is an organ in vertebrates, including human. It plays a major role in metabolism and has a number of functions in the body including glycogen storage, plasma protein synthesis, and drug detoxification. It also produces bile, which is important in digestion. It performs and regulates a wide variety of high-volume biochemical reaction requiring specialized tissues.
The liver normally weighs between 1.3 - 3.0 kilograms and is a soft, pinkish-brown "boomerang shaped" organ. It is the second largest organ (the largest being the skin) and the largest gland within the human body. Its anatomical position in the body is immediately under the diaphragm on the right side of the upper abdomen, The liver lies on the right side of the stomach and makes a kind of bed for the gallbladder.
The liver is supplied by two main blood vessels on its right lobe: the hepatic artery and the portal vein. The hepatic artery normally comes off the celiac trunk. The portal vein brings venous blood from the spleen, pancreas, and small intestine, so that the liver can process the nutrients and byproducts of food digestion. The hepatic veins drain directly into the inferior vena cava.
The bile produced in the liver is collected in bile canaliculi, which merge from bile ducts. These eventually drain into the right and left hepatic ducts, which in turn merge to form the common hepatic duct. The cystic duct (from the gallbladder) joins with the common hepatic duct to form the common bile duct. Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the duodenum together at the ampulla of Vater. The branching's of the bile ducts resemble those of a tree, and indeed term "biliary tree" is commonly used in this setting.
The liver is among the few internal human organs capable of natural regeneration of lost tissue: as little as 25% of remaining liver can regenerate into a whole liver again. This is predominantly due to hepatocytes acting as unipotential stem cells. There is also some evidence of bio potential stem cells, called oval cell, which can differentiate into either hepatocytes or cholangiocytes (cells that line bile ducts).
The various functions of the liver are carried out by the liver cells or hepatocytes.
- The liver produces and excretes bile, required for dissolving fats. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder
- The liver performs several roles in carbohydrate metabolism:
- gluconeogenesis (the formation of glucose from certain amino acids, lactate or glycerol)
- Glycogenolysis (the formation of glucose from glycogen)
- Glycogenesis (the formation of glycogen from glucose)
- The breakdown of insulin and other hormones
- The liver is responsible for the mainstay of protein metabolism.
- The liver also performs several roles in lipid metabolism:
- cholesterol synthesis
- The production of triglycerides (fats)
- The liver produces coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, Protein S and antithrombin.
- The liver breaks down hemoglobin, creating metabolites that are added to bile as pigment
- The liver breaks down toxic substances and most medicinal products in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor.
- The liver converts ammonia to urea.
- The liver stores a multitude of substances, including glucose in the form of glycogen, vitamin B12, iron, and copper.
- In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd weeks of gestation, the bone marrow has almost completely taken over that task.
- The liver is responsible for immunological effects; the reticuloendothelial system of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the portal system.
The gallbladder is a pear shaped organ that stores about 50 ml of bile (or "gall") until the body needs it for digestion. The gallbladder is about 7-10cm long in humans and is dark green in appearance due to its contents (bile), not its tissue. It is connected to the liver and the duodenum by the biliary tract.
The gallbladder is connected to the main bile duct through the gallbladder duct (cystic duct). The main biliary tract runs from the liver to the duodenum, and the cystic duct is effectively a "cul de sac", serving as entrance and exit to the gallbladder. The surface marking of the gallbladder is the intersection of the midclavicular line (MCL) and the trans pyloric plane, at the tip of the ninth rib. The blood supply is by the cystic artery and vein, which runs parallel to the cystic duct. The cystic artery is highly variable, and this is of clinical relevance since it must be clipped and cut during a cholecystectomy.
The gallbladder has an epithelial lining characterized by recesses called Aschoff's recesses, which are pouches inside the lining. Under the epithelium there is a layer of connective tissue, followed by a muscular wall that contracts in response to cholecystokinin, a peptide hormone synthesized in the duodenum.
The gallbladder stores bile, which is released when food containing fat enters the digestive tract, stimulating the secretion of cholecystokinin (CCK). The bile emulsifies fats and neutralizes acids in partly digested food. After being stored in the gallbladder, the bile becomes more concentrated than when it left the liver, increasing its potency and intensifying its effect on fats.
The human anus is situated between the buttocks, posterior to the perineum. It has two anal sphincters, one internal, the other external. These hold the anus closed until defecation occurs. One sphincter consists of smooth muscle and its action is involuntary; the other consists of striated muscle and its action is voluntary. In many animals, the anus is surrounded by anal sacs. Role of the anus is when the rectum is full, the increase in intra-rectal pressure forces the walls of the anal canal apart allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincters of the anus allow the feces to be passed by muscles pulling the anus up over the exiting feces.
Conditions Affecting the Esophagus
There are two different types of conditions that may affect the esophagus. The first type is called congenital: meaning a person is born with it. The second type is called non-congenital: meaning the person develops it after birth. Some examples of these are:
Tracheoesophageal fistula and esophageal atresia
Both of these conditions are congenital. In Tracheoesophageal fistula there is a connection between the esophagus and the wind pipe (trachea) where there shouldn't be one. In Esophageal atresia the esophagus of a newborn does not connect to the stomach but comes to a dead end right before the stomach. Both conditions require corrective surgery and are usually detected right after the baby is born. In some cases, it can be detected before the baby is born.
Esophagitis is inflammation of the esophagus and is a non-congenital condition. Esophagitis can be caused by certain medications or by infections. It can also be caused by gastroesophageal reflux disease (gerd), a condition where the esophageal sphincter allows the acidic contents of the stomach to move back up into the esophagus. Gastroesophageal reflux disease can be treated with medications, but it can also be corrected by changing what you eat.
Conditions Affecting the Stomach and Intestines
Everybody has experienced constipation or diarrhea in their lifetime. With constipation, the contents of the large intestines don't move along fast enough and waste material stays in the large intestines so long that almost all water is extracted out of the waste and it becomes hard. With diarrhea you get the exact opposite reaction: waste moves along too fast and the large intestines can't absorb the water before the waste is pushed through. Common flora bacteria assists in the prevention of many serious problems. Here are some more examples of common stomach and intestinal disorders:
Appendicitis is the inflammation of the appendix, the finger-like pouch that extends from the cecum. The most common symptoms are abdominal pain, loss of appetite, fever, and vomiting. Children and teenagers are the most common victims of appendicitis, which must be corrected by surgery. While mild cases may resolve without treatment, most require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, mortality is high, mainly due to peritonitis and shock.
Celiac disease is a disorder in which a person's digestive system is damaged by the response of the immune system to a protein called gluten, which is found in rye, wheat, and barley, and also in foods like breakfast cereal and pizza crust. People who have celiac disease experience abdominal pain, diarrhea, bloating, exhaustion, and depression when they eat foods with gluten in them. They also have difficulty digesting their food. Celiac disease runs in families and becomes active after some sort of stress, like viral infections or surgery. The symptoms can be managed by following a gluten free diet. Doctors can diagnose this condition by taking a full medical history or with a blood test.
Diverticulitis is a common disease of the bowel, in particular the large intestine. Diverticulitis develops from diverticulosis, which involves the formation of pouches (diverticula) on the outside of the colon. Diverticulitis results if one of these diverticula becomes inflamed. In complicated diverticulitis, bacteria may subsequently infect the outside of the colon if an inflamed diverticula bursts open. If the infection spreads to the lining of the abdominal cavity (peritoneum), this can cause a potentially fatal peritonitis. Sometimes inflamed diverticula can cause narrowing of the bowel, leading to an obstruction. Also, the affected part of the colon could adhere to the bladder or other organ in the pelvic cavity, causing a fistula, or abnormal communication between the colon and an adjacent organ.
Gastritis and Peptic ulcers
Usually the stomach and the duodenum are resistant to irritation because of the strong acids produced by the stomach. But sometimes a bacteria called Helicobacter pylori or the chronic use of drugs or certain medications, weakens the mucous layer that coats the stomach and the duodenum, allowing acid to get through the sensitive lining beneath. This can cause irritation and inflammation of the lining of the stomach, which is called gastritis, or cause peptic ulcers, which are holes or sores that form in the lining of the stomach and duodenum and cause pain and bleeding. Medications are the best way to treat this condition.
Gastrointestinal infections can be caused by bacteria such as Campylobacter, Salmonella, E. coli, or Shigella. They can also be caused by viruses or by intestinal parasites like amebiasis and Giardiasis. The most common symptoms of gastrointestinal infections are abdominal pain and cramps, diarrhea, and vomiting. These conditions usually go away on their own and don't need medical attention.
Inflammatory Bowel Disease
Inflammatory bowel disease is the chronic inflammation of the intestines, which usually affects older children, teens and adults. There are two major types, ulcerative colitis and Crohn'sdisease and indeterminate colitis, which occurs in 10-15% of patients. Ulcerative colitis usually affects just the rectum and large intestine, while Crohn's disease can affect the whole gastrointestinal tract from mouth to anus along with some other parts of the body. Patients with these diseases also suffer from extraintestinal symptoms including joint pain and red eye, which can signal a flare of the disease. These diseases are treated with medications and if necessary, Intravenous or IV feeding, or in the more serious cases, surgery to remove the damaged areas of the intestines.
A polyp is an abnormal growth of tissue (tumor) projecting from a mucous membrane. If it is attached to the surface by a narrow elongated stalk it is said to be pedunculated. If no stalk is present it is said to be sessile. Polyps are commonly found in the colon, stomach, nose, urinary bladder and uterus. They may also occur elsewhere in the body where mucous membranes exist like the cervix and small intestine.
Disorders of the Pancreas, Liver, and Gallbladder
Disorders of the pancreas, liver, and gallbladder affect the ability to produce enzymes and acids that aid in digestion. examples of these disorders are.
Cystic fibrosis is a chronic, inherited illness where the production of abnormally thick mucous blocks the duct or passageways in the pancreas and prevents the digestive fluids from entering the intestines, making it difficult for the person with the disorder to digest protein and fats, which cause important nutrients to pass through without being digested. People with this disorder take supplements and digestive enzymes to help manage their digestive problems.
Hepatitis is a viral condition that inflames a person's liver which can cause it to lose its ability to function. Viral hepatitis, like hepatitis A, B, and C, is extremely contagious. Hepatitis A, which is a mild form of hepatitis, can be treated at home, but more serious cases that involve liver damage, might require hospitalization.
Acute or chronic inflammation if the gallbladder causes abdominal pain. 90% of cases of acute cholecystitis are caused by the presence of gallstones. The actual inflammation is due to secondary infection with bacteria of an obstructed gallbladder, with the obstruction caused by the gallstones. Gallbladder conditions are very rare in kids and teenagers but can occur when the kid or teenager has sickle cell anemia or in kids being treated with long term medications.
Cholestasis is the blockage in the supply of bile into the digestive tract. It can be "intrahepatic" (the obstruction is in the liver) or "extrahepatic" (outside the liver). It can lead to jaundice, and is identified by the presence of elevated bilirubin level that is mainly conjugated.
This is when a gallstone blocks either the common bile duct or the duct leading into it from the gallbladder. This condition causes severe pain in the right upper abdomen and sometimes through to the upper back. It is described by many doctors as the most severe pain in existence, between childbirth and a heart attack. Other symptoms are nausea, vomiting, diarrhea, bleeding caused by continual vomiting, and dehydration caused by the nausea and diarrhea. Another more serious complication is total blockage of the bile duct which leads to jaundice, which if it is not corrected naturally or by surgical procedure can be fatal, as it causes liver damage. The only long term solution is the removal of the gallbladder.
As we age, the amount of digestive enzymes produced by the body drops way down. This leads to decreased and slower digestion, slower absorption of nutrients and increased accumulation of fecal mater in the intestinal tract. Undigested food material and metabolic waste can also build up due to slow elimination, starting a series of health problems.
When digestion slows, it turns the intestines into a toxic environment. Helpful organisms cannot live in toxic environments. When the beneficial organisms die they are replaced by harmful organisms, such as yeasts and parasites, the most common being Candida albicans. This leads to changes in the intestinal wall which produce leaky gut syndrome, which allows many toxic chemicals to be introduced into the bloodstream. As a result, the entire toxic load of the body is increased, causing a bigger burden on the liver, kidneys and other body organs. When this happens the organs that are normally used for eliminating waste and supplying nutrients to the GI tract become a large dump for waste. This problem can be made worse by the use of prescriptions and over-the-counter medications, antibiotics, and a diet that is too low in fiber or contains 'junk food'.
Most people never think about their GI tract. We are concerned about what the outside of our bodies look like, but we completely ignore the inside. Because our bodies a very resilient, deterioration of the digestive system can go on for years with no symptoms or side-effects. When symptoms finally do appear they are usually very non-specific, and include: decreased energy, headaches, diarrhea, constipation, heartburn, and acid reflux. Over the years these symptoms become more serious, including: asthma, food allergies, arthritis, and cancer.
Poor digestion, poor absorption, and bacterial imbalance can be traced to many chronic conditions. Every organ in the body receives nutrients from the GI tract; if the GI tract is malfunctioning then the whole body suffers.
It is possible to return good health to your GI tract by improving digestion, consuming the right amount of fiber, and cutting out junk food and refined sugars.
You can improve the function of the intestines by taking fiber supplements and vitamins (especially B12 and vitamin K). Some doctors suggest herbal or vitamin enemas to cleanse and relieve constipation and to help stimulate peristaltic movement which will help to move the bowels.
Irritable Bowel Syndrome
Irritable Bowel Syndrome (IBS) is a disorder with symptoms that are most commonly bloating, abdominal pain, cramping, constipation, and diarrhea. IBS causes a lot of pain and discomfort. It does not cause permanent damage to the intestines and does not lead to serious diseases such as cancer. Most of the people affected with IBS can control their symptoms with stress management, diet, and prescription medication. For others IBS can be debilitating, they may be unable to go to work, travel, attend social events or leave home for even short periods of time.
About 20 percent of the adult population has some symptoms of IBS, making it one of the most common intestinal disorders diagnosed by physicians. It is more common in men than women and in about 50 percent of people affected it starts at about age 35.
Researchers have not found out what exactly causes IBS. One idea is that people with IBS have a large intestine (colon) that is sensitive to certain foods and stress. The immune system may also be involved. It has also been reported that serotonin is linked with normal GI functioning. 95 percent of the body's serotonin is located in the GI tract (the other 5 percent is in the brain). People with IBS have diminished receptor activity, causing abnormal levels of serotonin in the GI tract. Because of this, IBS patients experience problems with bowel movement, motility, and the sensation having more sensitive pain receptors in their GI tract. Many IBS patients suffer from depression and anxiety which can make symptoms worse.
There is no cure for IBS, but medications are an important part of relieving symptoms. Fiber supplements or laxatives are helpful for constipation. Anti diarrhoeals such as Imodium can help with diarrhea. An antispasmodic is commonly prescribed for colon muscle spasms. Antidepressants and pain medication are also commonly prescribed. 
Gastrointestinal Stromal Tumor
Gastrointestinal Stromal Tumors or GIST is an uncommon type of cancer in the GI tract (esophagus, stomach, small intestine, and colon). These types of cancers begin in the connective tissue like fat, muscles, nerves, cartilage, etc.
GIST originates in the stroma cells. Stroma cells are strung along the GI tract and are part of the system that helps the body to know when to move food through the digestive system. Over half of GISTs occur in the stomach. Most cases occur in people between the ages of forty and eighty, but they can also occur in a person of any age.
All GISTs of any size or location have the ability to spread. Even if a GIST is removed, it can reappear in the same area, or may even spread outside of the GI tract.
In the early stages, GIST is hard to diagnose because early-stage symptoms cannot be recognized. In the later stages a person can have vague abdominal pain, vomiting, abdominal bleeding that shows up in stool or vomit, low blood counts causing anemia, and having an early feeling of being full, causing a decrease in appetite.
GIST is now recognized as an aggressive cancer that is able to spread to other parts of the body. People who have been diagnosed with GIST should get treatment as soon as possible.
Food allergies occur when the immune system thinks that a certain protein in any kind of food is a foreign substance and will try to fight against it.
Only about eight percent of children and two percent of adults actually have a food allergy. A person can be allergic to any kind of food, but the most common food allergies are to nuts, cow's milk, eggs, soy, fish, and shellfish. Most people who have a food allergy are allergic to fewer than four different foods.
The most common signs of food allergies are hives, swelling, itchy skin, itchiness, tingling or swelling in the mouth, coughing, trouble breathing, diarrhea, and vomiting. The two most common chronic illness that are associated with food allergies are eczema and asthma.
Food allergies can be fatal if they cause the reaction called anaphylaxis. This reaction makes it hard for the person to breathe. This can be treated by an epinephrine injection.
GERD, Heartburn, Acid Reflux
GERD, or Gastroesophageal Reflux Disease occurs when the lower esophageal sphincter is not able to close properly. When this happens, contents from the stomach, called reflux, leak back into the esophagus and the stomach.
When the stomach refluxes, stomach acid touches the lining of the esophagus and causes it to have a burning feeling in the throat or the chest. This is what heartburn is. When you taste the fluid in the back of your throat, it is called acid indigestion. It is common for a person to get occasional heartburn, but when it occurs more than twice a week it can be considered to be GERD. GERD can occur in people of all ages including infants.
Some symptoms of GERD include having a pain in your chest, hoarseness, having trouble swallowing, or having the feeling of food being stuck in your throat. The main symptoms are having persistent heartburn and acid regurgitation. GERD can also cause bad breath and a dry cough.
No one knows why people get GERD. Some things that could contribute to GERD are alcohol use, pregnancy, being overweight and smoking. Certain foods might also contribute like citrus fruits, caffeine, spicy, fatty, and dried foods, and also mint flavorings.
Over-the-counter antacids or medications that help stop acid production and help the muscles empty the stomach are commonly used to treat GERD.
Not everyone is on the same schedule for having a bowel movement. Depending on the person, a "normal" schedule can range anywhere from three times a day to three times a week. If you start having bowel movements less than your own personal schedule, then you might be getting the signs of constipation.
Constipation is when you have trouble having bowel movements. The stool is very hard, making it difficult to pass and causing a person to strain. You may even feel like you have to have a bowel movement even after you have already had one.
When you digest food, the waste products go through your intestines by the muscles contracting. When in the large intestine, most of the water and salt from the waste products are reabsorbed because they are needed by the body for our everyday functions. You can become constipated if too much water is absorbed, or if waste products move too slowly.
Not getting enough fluids, a low fiber diet, age, not being physically active, depression, stress and pregnancy can all contribute to constipation. Medications and narcotics can also cause a person to get constipated. Chronic constipation may be a symptom of a liver problem such as a urea cycle disorder.
The best way for a person to treat constipation is to make sure that they are getting enough fluids as well as fiber in their diet. By doing this, the bulk of their stool is increased and made softer, so that it can move through the intestines more easily. Being more active and increasing daily exercise also helps keep bowel movements regulated.
Hemorrhoids (also known as haemorrhoids, emerods, or piles) are varicosities or swelling and inflammation of veins in the rectum and anus.
Two of the most common types of hemorrhoids are external and internal hemorrhoids.
- External hemorrhoids are those that occur outside of the anal verge (the distal end of the anal canal). They are sometimes painful, and can be accompanied by swelling and irritation. Itching, although often thought to be a symptom from external hemorrhoids, is more commonly due to skin irritation.
- If the vein ruptures and a blood clot develops, the hemorrhoid becomes a thrombosed hemorrhoid.
- Internal hemorrhoids are those that occur inside the rectum. As this area lacks pain sensory receptor|receptors, internal hemorrhoids are usually not painful and most people are not aware that they have them. Internal hemorrhoids, however, may bleed when irritated.
- Untreated internal hemorrhoids can lead to two severe forms of hemorrhoids: prolapsed and strangulated hemorrhoids.
- Prolapsed hemorrhoids are internal hemorrhoids that are so distended that they are pushed outside of the anus.
- If the anal sphincter muscle goes into spasm and traps a prolapsed hemorrhoid outside of the anal opening, the supply of blood is cut off, and the hemorrhoid becomes a strangulated hemorrhoid.
Bleeding in the Gastrointestinal tract
Bleeding in the gastrointestinal tract doesn't always mean you have a disease, it's usually a symptom of a digestive problem. The cause of the bleeding may not be that serious, it could be something that can be cured or controlled such as hemorrhoids. However, locating the source of the bleeding is very important. The gastrointestinal tract contains many important organs like the esophagus, stomach, small intestine, large intestine or colon, rectum, and anus. Bleeding can come from one or more of these area from a small ulcer in the stomach, or a large surface like the inflammation of the colon. Sometimes a person doesn't even know they are bleeding. When this happens, it is called hidden, or occult bleeding. Simple tests can detect hidden blood in the stool.
What Causes Bleeding in the Digestive Tract
Esophageal bleeding may be caused by Mallory-Weiss syndrome which is a tear in the esophagus. Mallory-Weiss syndrome is usually caused by excessive vomiting or may be caused by childbirth, a hiatal hernia, or increased pressure in the abdomen caused by coughing. Various medications can cause stomach ulcers or inflammations. Medications containing aspirin or alcohol, and various other medications(mainly those used for arthritis) are some examples of these.
Benign tumors or cancer of the stomach may also cause bleeding. These disorders don't usually produce massive bleeding. The most common source of bleeding usually occurs from ulcers in the duodenum. Researchers believe that these ulcers are caused by excessive stomach acid and a bacteria called Helicobacter Pylori.
In the lower digestive tract, the most common source of bleeding is in the large intestine, and the rectum. Hemorrhoids are the most common cause of bleeding in the digestive tract. Hemorrhoids are enlarged veins in the anal area which produces bright red blood that you see in the toilet or on the toilet paper.
How do you Recognize Bleeding in the Digestive Tract
The signs of bleeding in the digestive tract vary depending on the site and severity of the bleeding. If the blood is coming from the rectum, it would be bright red blood. If it was coming from higher up in the colon or from the small intestine, the blood would be darker. When the blood is coming from the stomach, esophagus, or the duodenum, the stool would be black and tarry.
If the bleeding is hidden, or occult, a person may not notice changes in the stool color. If extensive bleeding occurs, a person may feel dizzy, faint, weak, short of breath, have diarrhea or cramp abdominal pain. Shock can also occur along with rapid pulse, drop in blood pressure, and difficulty urinating. Fatigue, lethargy, and pallor from anemia will settle in if the bleeding is slow. Anemia is when the bloods iron-rich substance, hemoglobin, is diminished.
Common Causes of Bleeding in the Digestive Tract
- Gastritis (inflammation)
- Inflammation (ulcerative colitis)
- Colo rectal Polyps
- Colo rectal Cancer
- Duodenal Ulcer
- Enlarged Veins
- Esophagitis (inflammation of the esophagus)
- Mallory-Weiss Syndrome
Iron and beets can also turn the blood red or black giving a false indication of blood in the stool.
How Bleeding in the Digestive Tract is Diagnosed
To diagnose bleeding in the digestive tract the bleeding must be located and a complete history and physical are very important. Here are some of the procedures that diagnose the cause of bleeding.
An endoscopy is a common diagnostic technique that allows direct viewing of the bleeding site. Since the endoscope can detect lesions and confirm the absence or presence of bleeding, doctors often use this method to diagnose acute bleeding, the endoscope can also be used to treat the cause of bleeding as well.
The endoscope is a flexible instrument that can be inserted through the mouth or rectum. The instrument allows the doctors to see inside the esophagus, stomach, duodenum(esophagoduodenoscopy), sigmoid colon(sigmoidoscopy), and rectum(rectoscopy, to collect small samples of tissues, take pictures, and stop the bleeding. There is a new procedure out using a long endoscope that can be inserted during surgery to locate a source of bleeding in the small intestine.
Capsule endoscopy helps doctors to see and examine the lining of the middle part of the gastrointestinal tract, which includes the three parts of the small intestine (duodenum, jejunum, ileum). The capsule is a small pill sized video camera called an endoscope. It has its own lens and light that transfers the images to a monitor so the doctor can view them outside of the body. This process is also referred to as small bowel endoscopy, capsule endoscopy, or wireless endoscopy.
The most common reason for doing a capsule endoscopy is to look for the causes of bleeding that is coming from the small intestine. It is also able to help detect ulcers, tumors, and Crohn's disease.
Angiography is a technique that uses dye to highlight blood vessels. This procedure is used when the patient is bleeding badly enough that it allows the dye to leak out of the blood vessels and identifies the bleeding site. In some situations, Angiography allows the patient to have medication injections that may stop the bleeding.
Radionuclide scanning is a non-invasive screening technique used for locating sites of acute bleeding, especially in the lower GI tract. This procedure injects small amounts of radioactive material that either attach to the persons red blood cells or are suspended in the blood. Special pictures are taken that allows doctors to see the blood escaping. Barium x-rays, angiography, and radionuclide scans can be used to locate sites of chronic occult bleeding.
How to Recognize Blood in the Stool and Vomit
- Bright red blood coating the stool
- Dark blood mixed with the stool
- Black or tarry stool
- Bright red blood in the vomit
- Grainy appearance in vomit
Symptoms of Acute Bleeding
- Shortness of breath
- Cramp abdominal pain
- Feeling light headed
Symptoms of Chronic Bleeding
- Shortness of breath
A colonoscopy is a test to look at the inside of your colon. Everyone should have a colonoscopy by the time they are 50 to check for diseases of the colon. Colonoscopy is best known for its use in early detection of colorectal cancer, the second leading cause of cancer deaths in the United States. Colon cancer develops from growths like polyps within the intestinal wall. These growths often take 5-10 years to develop usually without symptoms. You are at a higher risk to have this disease if you have a close relative who has had it. If you are going to develop a polyp, you will probably do so after age 50. So the American College of Gastroenterology (the digestive specialists) recommends screening examinations every 5 years for early detection and removal of these cancer-causing growths after that age. Don't make excuses! It's not so bad and it may save your life!
Bob had a history of chronic pain in his intestinal area, and wasn't sure what it was. His doctor suspected what it was and gave Bob antibiotics, which helped. It so happened that whenever Bob ate popcorn or nuts he would get this pain. Sometimes it would just go away... other times he had to go on antibiotics. The doctor ordered some tests, and told Bob he would have to stay away from nuts, popcorn, tomatoes, strawberries, and anything else with seeds or hard parts; something in his bowels couldn't tolerate those foods. Bob ate a pretty healthy diet so he couldn't understand what was happening. A few years later, Bob had another series of painful episodes. The pain was so great Bob could hardly stand, let alone go to work. This time the doctor did more tests and found out that his lower intestine was almost blocked. Surgery was ordered. What did Bob have?
- An inflammation if the intestines caused by infestation with Entameba histolytica (a type of ameba) and characterized by frequent loose stools flecked with blood and mucus
- An enzyme produces in the pancreas and salivary glands that help in the digestions of starches.
- A bitter, alkaline, brownish-yellow or greenish-yellow fluid that is secreted by the liver, stored in the gallbladder, and discharged into the duodenum and aids in the emulsification, digestion, and absorption of fats. Also called gall.
- Biotin is used in cell growth, the production of fatty acids, metabolism of fats, and amino acids. It plays a role in the Krebs Cycle. Biotin is also helpful in maintaining a steady blood sugar level. It is often recommended for strengthening hair and nails.
- A vitamin important for the normal formation of red blood cells and the health of the nerve tissues. Undetected and untreated B12 deficiency can lead to anemia and permanent nerve and brain damage
- Candida Albicans
- Found in animals and in man. Has been isolated from the skin and mucosa of man, but has also been recovered from leaves, flowers, water, and soil. Reported to be allergenic. A common cause of superficial infection, oral and vaginal infection, sepsis, and disseminated disease. Cells from the organism are usually not airborne and are considered to be normal component of the flora of the mouth and other mucous membranes on the body.
- Chemical digestion
- Is a chemical breakdown of food when being in the mouth (oral cavity). Is the digestive secretions of saliva that moistens food and introduces gastric juices and enzymes that are produced in the stimulation to certain macronutrients, such as, carbohydrates. In this, the mouth saliva carries an enzyme called amylase for breaking down carbohydrates.
- Cholecystokinin (CCK)
- Cholecystokinin (also called pancreozymin), this is a hormone in the small intestinal cells (intestinal mucosa) that is produced in response to food. This hormone regulates the release of secretions of many organs that aid digestion, such as, bicarbonate from the pancreas to reduce the acidity of digestive juices like the chyme that enters the small intestine form the stomach that contains hydrochloric acid (HCL).
- The lipoproteins first formed after absorption of lipids form food.
- The thick semi fluid mass of partly digested food that is passed from the stomach to the duodenum.
- Crohn's Disease
- Described as skip lessions in the large and small bowel it is a malabsorption disorder that can affect the gastrointestinal tract for the mouth to the anus.
- When an amino acid group breaks off an amino acid that makes a molecule of ammonia and keto acid.
- A mixture of two immiscible (unblendable) substances.
- The stomach mucosa secretes a hormone gastrin that increases the release of gastric juices.
- GI tract
- Gastrointestinal Tract, The tube that extends from the mouth to the anus in which the movement of muscles and release of hormones and enzymes digest food.
- The chemical substance hydrochloric acid is the water-based solution of hydrogen chloride (HCI) gas. It is a strong acid, the major component of stomach acid and of wide industrial use.
- Lactobacillus Acidophilus
- Important resident inhabitant of the human small and large intestines, mouth, and vagina. Secretes natural antibiotic substances which strengthen the body against various disease-causing microbes
- Leaky gut syndrome
- Abnormal level of intestinal permeability
- Lingual lipase
- An enzyme produced only in infancy to aid digestion of long-chain fatty acids.
- An enzyme produced by microorganisms that split the fat molecules into fatty acids which create flavor
- Mechanical digestion
- The crushing of the teeth and rhythms made by the movement of the tongue, the teeth aid in tearing and pulverizing food, while the tongue helps with peristalsis (movement), of food down the esophagus.
- A product of lipids and bile assist in lipid absorption.
- On the villi in the small intestine is mivrovilli, these projections called brush border microvilli secrete specific enzymes for disaccharide hydrolysis, these further aid the absorption of the carbohydrate by yielding a monosaccharide that then can go through portal circulation to liver circulation to be further processed into immediate use for energy or glycogen storage.
- The wavelike muscular contractions of the intestine or other tubular structure that propel the contents onward by alternate contraction and relaxation.
- The process of reproduction or division of cells
- Protein enzyme
- Only produced during infancy and is a gastric protease and functions with calcium to clot with milk proteins casein, to slow the movement of milk so that digestion is prolonged.
- chemical messenger in the brain that affects emotions, behavior, and thought
- To create something, such as chemicals in the body, from simpler, raw materials
- Ulcerative Colitis
- A minute projection arising from a mucous membrane, especially one of the vascular projections of the small intestine.
- Vitamin K
- A substance that promotes the clotting of blood
Case Study Answer Bob has diverticulitis. The doctor was afraid that if he had another bad infection that scar tissue would eventually block his colon completely and burst, which would necessitate a colostomy. Bob ended up having to have surgery to remove the damaged part of his colon. The doctor removed almost 18 inches of Bob's large intestine. Bob is doing fine now and most importantly, he can now eat his favorite food - nuts! Note: Sometimes a diet rich in fiber can help you avoid this dreaded problem. Sometimes, like in Bob's case, the predisposition to have this problem runs in the family. All of his siblings and his father suffered from this same ailment. Stress is another factor that can exacerbate this disease. So.. don't worry, be happy and eat fiber!
1: Chen Ts, Chen PS. Intestinal autointoxication: A gastrointestinal leitmotive: Journal Clinical Gastroenterology
2: Ernst E. Colonic irrigation and the theory of autointoxication: A triumph of ignorance over science. Journal of Gastroenterology
3: Alvarez WC. Origin of the so-called auto-intoxication symptoms.
4: Donaldson AN. Relation of constipation to intestinal intoxication.
5: Kenney JJ. Fit for Life: Some notes on the book and its roots. Nutrition Forum
6: Use of enemas is limited. FDA consumer
7: Amebiasis associated with colonic irrigation - Colorado. Morbidity and Mortality Weekly Report
8: Istre GR and others. An outbreak of amebiasis spread by colonic irrigation at a chiropractic clinic
9: Benjamin R and others. The case against colonic irrigation
10: Eisele JW, Reay DT. Deaths related to coffee enemas
11: Jarvis WT. Colonic Irrigation. National Council Against Health Fraud.
12: National Digestive Disease Information Clearinghouse (NDDIC)
Diagram showing the small intestine
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This clicker case is designed to lead students to a conceptual understanding of oxidative phosphorylation (and, by analogy, photosynthesis). Students begin with a pre-class handout that presents background information on DNP, a weight-loss drug that wa...
A Different Kind of Stress
Protein folding and trafficking is essential for normal cell function, and when it goes awry it can lead to various chronic conditions, including fatty liver disease, diabetes, and Parkinson's. The narrative of this case study follows two undergraduate...
A Family in Need: In-Class Case Study on Cancer Genetics
This case is designed as an in-class, problem-based learning activity for students to learn about several innovative medical applications of molecular biology. Students assume the role of a second-year medical student assigned to work with a pediatric ...
A Family in Need: Internet-Enhanced Case Study on Cancer Genetics
This problem-based learning case was designed for students to learn about several innovative medical applications of molecular biology. Students assume the role of a second-year medical student assigned to work with a pediatric oncologist who has just ...
A Healthy Retirement?
Nancy has been looking forward to her retirement and a chance to entertain and travel with her husband Jim. But she hasn’t been feeling well. She’s often tired, and recently she’s been experiencing a burning sensation in her lower che...
A Metabolic Storm
This "clicker" case presents the true story of a 20-year-old athlete who developed a life threatening reaction to anesthesia during a simple elective surgical procedure. His response was unexpected, but not unusual for individuals who possess an inheri...
A Need for Needles - Acupuncture
In this case study, students evaluate information about the use of acupuncture and consider the possibilities of alternative therapies while at the same time questioning their effectiveness. To complete the case, students collect information from Inter...
A Pain in the Gut
This interrupted case study in gastric physiology follows the story of Frank, a businessman under a lot of stress who has a car accident while driving home from work one night. Frank has low blood insulin levels and high blood sugar levels that his doc...
A Perfect Storm in the Operating Room
In this interrupted case study, a high school biology student shadows her uncle, an anesthesiologist, at a hospital for a school assignment. She witnesses a patient who has an unusual reaction to his anesthesia and nearly dies. As they try to dia...
A Recipe for Invention
In this case study, designed to help break down stereotypes about scientists and engineers, students research the personal and professional lives of researchers in their field. The case was designed for use in high school to graduate courses in a varie...
A Right to Her Genes
In this true story, students examine the case of a woman with a family predisposition to cancer who is considering genetic testing. Students learn about various aspects of DNA testing and determine how to counsel the woman. The case was designed for an...
A Rigorous Investigation
In this directed case study, students investigate the cause of death in an incident that occurs late at night in a research lab. The overall goal of the case is to make the abstract concepts involved in cellular respiration more accessible to students....
A Search for the Right Answer
In this role-playing case study on Parkinson’s disease, students learn about brain injury and brain repair mechanisms, the physical and psychological effects of a degenerative disease on a patient and her family, the ethics of fetal tissue resear...
A Sickeningly Sweet Baby Boy
When a newborn develops symptoms eerily similar to those of an older sibling who died shortly after birth, his Mennonite parents are understandably alarmed. They soon discover that their son has Maple Syrup Urine Disease (MSUD), a recessively inherited...
A Simple Plan
This case study introduces students to Dr. E.L. Trudeau, who performed a seminal early experiment validating the germ theory of infection. Part I introduces Trudeau's Rabbit Island experiment, which is simple and easy for beginning or non-major student...
A Struggle for Power in China: The Three Gorges Dam
The Three Gorges Dam in China is one of the world's largest hydroelectric dams, providing energy for millions of people. However, the dam's construction forever altered the Yangtze River ecosystem and the lives of local residents. In this case study, s...
A Tale of Three Lice
This “clicker case” explores the questions of when hominins lost their body hair and began wearing clothing by examining the surprising phylogeny of human head, body, and pubic lice. Students are led through the scientific process as they a...
A Trip to the Beach
This interrupted case study, designed for an introductory biology or environmental science course, introduces students to the complexity of ecosystems by examining changes in trophic interactions and abiotic factors in a freshwater ecosystem as a resul...
A Whale of a Tale?
For years whale evolution was characterized by speculation and limited evidence. Evolution critics even focused on whales as a means to criticize evolutionary theory. Now whale evolution represents one of the best examples of "macroevolution." This "cl...
A Yellow-Bellied Lawyer?
This interrupted case study tells the story of Michael, a Harvard law graduate with a stressful job and a seemingly heavy drinking problem. Students are provided with background information, medical history, and lab results in order to guide them towar...
This case introduces students to HIV, its life cycle, treatment, and problems associated with treatment options. The case, which incorporates critical thinking skills, active learning, self-directed study, and peer-to-peer learning, was developed for u...
Acids, pH, and Buffers
In this “clicker case,” a three-year-old girl gets into the medicine cabinet and ingests an unknown number of aspirin tablets. Her brother calls 911 and the girl is taken to a nearby hospital, where she is treated. The case is used to discu...
African Illness: A Case of Parasites?
This case is based on a British patient presenting to a hospital with an array of symptoms after returning from an African safari. Students learn about potential causes of the symptoms based on the patient's potential exposure to parasites endemic to A...
Agony and Ecstasy
This “clicker case” follows Susan, an intern at a local hospital, who has admitted a patient she discovers has used the drug Ecstasy. The girl becomes delirious, and Susan begins to suspect that she may be suffering from water intoxication....
As the carbon dioxide concentration of our atmosphere increases and our climate warms, the hay fever season seems to be getting longer and more severe. In this case study, students assume the a role of a public relations specialist contracted to commun...
AIDS and the Duesberg Phenomenon
Renowned virologist and member of the prestigious National Academy of Science, Peter Duesberg has argued that AIDS is not caused by HIV, but is the result of recreational and anti-HIV drugs. In this PBL case, students read Duesberg’s 1999 a...
Aliens on Earth?
The discovery of a bacterium capable of substituting arsenic for phosphorus in its DNA was announced with much fanfare in 2010. It was immediately and very publicly critiqued by researchers posting their analyses of the paper on their blogs. The author...
All or Nothing
In this interrupted case study, students pose as an intern of a neuromuscular/skeletal specialist and discover how sarin and myasthenia gravis influence muscle function. Students are given background information about the patients and their situations,...
Am I a Girl, or a Boy?
A baby is born with ambiguous genitalia to parents from the Dominican Republic and is determined to be a female based on general appearance. At the child's 12-year-old checkup, the parents and the child are distraught as they report to the pediat...
When chronic pain forces a top student to withdraw from college, biology instructor Dr. Sharpe learns that medications (in this case, Vioxx) may be removed from the market for many reasons, including safety concerns. As the case unfolds, students learn...
This problem-based case focuses on the female menstrual cycle and early stages of pregnancy of an unwed teenager. Working in small groups, students identify the learning issues for each part of the story and research answers to their questions. They ar...
An Antipodal Mystery
The discovery of the platypus had the scientific world in an uproar and kept it tantalized for decades. Here was the strangest animal ever seen. How was one to classify it? It had fur. So, was it a mammal? But then what to make of its duck-like bill? A...
An End to Ulcers?
This “clicker case” teaches students about the scientific method by following the story of the discovery of the cause of human gastric ulcers by two Australian biomedical scientists. Students see how the researchers followed up an unusual o...
An Infectious Cure
This four-part interrupted case on phage therapy was developed for a freshmen non-majors course in molecular biology. The case begins with a story inspired by real events where Europeans imposed a treatment for cholera on the unwilling population of an...
An Unusual Case of Animal Reproduction
This case study in human reproduction follows Andrea, a college biology student who discovers she is pregnant with twins, but is not sure who the father is. Students are presented with a variety of signs, symptoms, and physiological information that th...
And Baby Makes Four
This case study is based on stories reported in the media and is used to examine biological and ethical dimensions of assisted reproductive technologies, specifically egg donation and gestational surrogacy. The case follows an Indian woman as she...
And Now What, Ms. Ranger?
Intelligent Design continues to be a hot political and educational topic in some parts of the country. This discussion case study uses the dramatic setting of a public school board as it considers whether district science teachers should be made to rea...
Andrea: The Death of a Diabetic
In chronicling the life and death of a woman who developed diabetes as a teenager, this case study explores such basic science topics as metabolism, hormones, cell receptors, eye anatomy, and immunology as well as issues in nutrition, exercise, stem ce...
Anencephaly in Yakima
This case study explores the recent (2010 - 2016) outbreak of neural tube defects, specifically anencephaly, in a rural three-county region of Washington state, particularly Yakima, WA. The case study focuses on the biological aspects of teratogens tha...
Animals on Treadmills
This group-based, interrupted case study challenges students' perceptions of "useful" scientific research. We present student groups with the methods used in two scientific studies that have been heavily scrutinized in the popular media. Both research ...
Another Can of Bull?
This case is a “clicker” adaptation of a similarly titled case by Merle Heidemann and Gerald Urquhart of Michigan State University, “A Can of Bull?” The story introduces students to basic principles of metabolism and energy thro...
This case study presents a fictitious bio-terrorist plan to release anthrax in the United States. Students are assigned character roles and, through research, role-playing, and teamwork, develop a plan to minimize or avert the attack. The case is appro...
Resistance to antibiotics arose very shortly after these "wonder drugs" were first introduced. This case study examines resistance to the most commonly used antibiotics, penicillin and its derivatives. In particular, it examines a recent st...
Antibiotic Resistance in a Russian Prison
In this case study, students will have the opportunity to model the spread of tuberculosis and development of antibiotic resistance in a hypothetical prison environment. After reading a brief handout and viewing a short video, students play a simulatio...
Anyone Who Had a Heart
After undergoing a fertility procedure, a 37-year-old woman and her husband are expecting twins. The delivery goes smoothly, but it soon becomes apparent that, while the baby boy appears normal, the baby girl has a heart problem and is cyanotic. In thi...
Apple and Linguine
This flipped case study is suited for general education undergraduate level biology. Students prepare ahead of time for class by viewing a video created by the authors that reviews the basics of nutrition and digestion; in class, students then engage i...
Are We Too Clean?
This case study focuses on the relationship between the microbiome (the suite of species that live in or on the human body) and autoimmune and allergic diseases. At the center of the case is Amelia, a young woman living with Crohn's disease. As the cas...
Atkins or Fadkins?
When Mitchell reveals that he is going on a low-carb diet, Janine tries to talk him out of it, telling him that he’s too thin as it is and doesn’t need to loose any weight. Designed to accompany a nonmajors unit on human anatomy and physiol...
Baby Doe v. The Prenatal Clinic
This "clicker case" presents a fictionalized story about a couple ("John" and "Jane") whose new baby is born with Down syndrome; the parents are suing the prenatal clinic where Jane received her care, blaming the clinic for the baby’s condition. ...
The ethics of human experimentation are explored in this case about the infamous syphilis studies performed at the Tuskegee Institute from the 1930s to the 1960s. Sponsored by the U.S. Public Health Service, 399 African American men with syphilis were ...
Bad Fish, Bad Bird
This "clicker case" is based on the General Biology edition of James Hewlett’s “Bad Fish” case in our collection. The case follows the story of biologist Dr. Westwood, who is accidentally poisoned, first while traveling in Asia and th...
Bad Fish: General Biology Edition
In this version, developed for a course in general biology, the protagonist of the case, Dr. Westwood, survives an accidental poisoning-not once, but twice. Students read about each incident, applying what they learn in each part of the case to the lat...
Banana Split: To Eat or Not to Eat
This case focuses on the banana, the most popular fruit in the world. In the first part of the case, students are introduced to the history of "Banana Republics" and the biological constraints to banana production, including the devastating funga...
Between the Living and the Dead
As Jen pores over her introductory biology textbook, she falls asleep and enters a nightmarish world in which bacteria and viruses dwarf human beings. This engagingly written case explores the differences between viruses and bacteria while teaching abo...
Bioengineering the Pancreas
This case study applies problem-based learning to the field of biotechnology. Students assume the role of newly-hired bioengineers at a fictitious biotech company, Bio-Art. Students work individually to complete background research in the basic biology...
Bioluminescence and 16th-century Caravaggism
This case study looks at the probable connection between bioluminescence and Caravaggio's painting style in the 16th century in order to explore the mechanism of bioluminescence and its role in animal evolution and modern medicine. Recent studies have ...
Blood Suckers! A Case Study on Evolution and Speciation
This directed case study in PowerPoint format focuses on the London Underground Mosquito, Culex molestus, and its potential relationship to the common mosquito, Culex pipiens, in order to explore the topics of evolution, reproductive ...
Bloodline: A Human Genetics Case
In this "clicker" case, based on a TV drama about a family secret that only knowledge of genetics can solve, students apply what they have read and heard about genetic diseases to determine familial relationships and predict the chance that a family me...
Bonding with the Tutor: How to Stick Together in Chemistry
This case study presents the story of "Nick," a student who has been assigned the task of writing a research paper describing the fundamentals of chemical bonds and how they relate to human life. When Nick experiences difficulty remembering information...
This directed case study follows two college roommates, Darrell and Anthony, who have just returned to school after winter vacation. They share that their ageing fathers are concerned about their declining faculties and are amused by their fathers' eff...
Bringing Back Baby Jason
This dilemma case, designed for use in an undergraduate genetics course, explores the basic genetic concepts underlying the cloning process as well as the ethical, medical, political, economic, and religious issues surrounding human cloning. While the ...
Bringing Home More than a Medal
This case study was inspired by the Zika virus outbreak that occurred around the time of the 2016 Olympic Games. Many athletes were fearful of attending because of the link between Zika virus infection and microcephaly in infants. This concern, however...
BSL-4: Authorized Personnel Only
This case study is based on the 2014 Ebola epidemic that spread to multiple highly populated countries in West Africa, making it the largest and most devastating outbreak in the history of the virus. The storyline, inspired by a compilation of factual ...
But I'm Too Young!
In this “clicker case,” students are introduced to Abby, a college student who has been diagnosed with ovarian cancer. As they follow Abby’s plight, students learn about basic cellular and genetic mechanisms that are responsible for c...
Butterflies in the Stomach
Why is the North American population of monarch butterflies declining? In 1999, a study published in the journal Nature suggested that a variety of genetically modified corn was killing these iconic butterflies. While it was later shown that t...
This case study uses an interactive activity to illustrate density dependence in ecology classes. We developed a "hunt" using paper butterflies with warning signals on the upper side of the wings and symbols that indicate if a butterfly is noxious unde...
CAMEL Question: Can Applied Math Extend Life?
This directed case study examines differences between the exponential and logistic growth models in biology and how they are applied to solve real life problems. The narrative follows a student returning to the United States as he tries to assess his p...
This PowerPoint-driven case study follows the progress of three undergraduate students as they attempt to model the rapid spread of an influenza outbreak to determine whether their local newspaper's claim that "40% of the campus has the flu" is accurat...
Can a Genetic Disease Be Cured?
In this discussion case, parents must decide whether or not to enroll their sons in an experimental treatment program designed to alleviate the symptoms of muscular dystrophy. The case explores the genetics and physiology of the disease as well as the ...
Cancer Cure or Conservation
This case is based on the controversy that surrounded harvesting of the Pacific yew from 1989 to 1997 to develop paclitaxel (Taxol), a revolutionary anti-cancer drug. The case was designed to expose students to basic conservation biology concepts by ex...
Caribou Conservation Conundrum
As a Government of Canada biologist, "Rachael Mercer" faces the task of advising the Environment Minister on whether a proposed wolf cull should be carried out to conserve threatened caribou populations in the Northern Alberta oilsands region. The Albe...
Cat vs. Bird: Another Look at Complexity in Conservation
This clicker case is an adaptation of a case by Loren Byrne that told the true story of a Texas man who killed a cat that was killing piping plovers (see "Complexity in Conservation: The Legal and Ethical Case of a Bird-Eating Cat and its Human Killer,...
Cauldron of Democracy
This case study explores the controversy surrounding Yellowstone bison (Bison bison) and the relationship between wildlife management and pluralist democracy. In the late 1960s Yellowstone National Park suspended the policy of strictly managin...
Cell Phone Use and Cancer
In this case study, students analyze a scientific study, first by analyzing news articles reporting on the research and then by reading the original research article. In working through the case, students identify the basic elements of a scientific stu...
This case study is designed to teach introductory biology majors about the role of the pituitary in controlling hormones. It could easily be applied or modified to fit a variety of other courses, including a non-majors introductory biology course or an...
Chemical Eric - The Clicker Version
This “clicker case” is a modified version of a case originally published in the National Center for Case Study Teaching in Science case collection in 2006, “Chemical Eric: Dealing with the Disintegration of Central Control,” by...
Chemical Eric Can't See
This autobiographical case study presents the story of Eric as he learns that he has a genetic eye disease, which progresses to the point that he becomes legally blind. The story is true and, in this respect, similar to another case by the same author ...
Chickens and Humans and Pigs, Oh My!
Influenza is a common topic in the popular press and a point of interest for many students. This case study was written to promote interdisciplinary connections between upper division virology and immunology classes. Students that participa...
This case describes the pioneering work of Ignaz Semmelweis and his efforts to remedy the problem of childbed fever in mid-19th century Europe. Its purpose is to teach students about the scientific method by "dissecting" the various steps involve...
Chimpanzee Droppings Lead Scientists to Evolutionary Discovery
This interrupted case study focuses on the research of Dr. Beatrice Hahn, who investigates DNA sequences in chimpanzee droppings in order to explore the origins of the human immunodeficiency virus (HIV). Students first consider the types of data that c...
Classic Experiments in Molecular Biology
All introductory biology textbooks, and many sophomore-level genetics textbooks as well, describe several classic experiments in molecular biology. This interrupted case study takes students through two of these classic experiments, namely, those by Gr...
Cloning Man's Best Friend
The Cleaver family of television fame faces a dilemma—whether or not to clone their recently deceased dog Spot. Written for a high school introductory biology class, the case provides students with an opportunity to discuss animal cloning and its...
Closing the Gap
In this problem-based learning/role playing case, students apply their knowledge of the biology of HIV/AIDS and antiretroviral therapy to developing foreign aid policy for the HIV/AIDS crisis in sub-Saharan Africa. The case was created for a non-majors...
Coffee and Cigarettes
This analysis case explores second-hand smoke and its impact on the decision to institute a smoking ban in the outdoor seating area of a popular coffee bar. In working through the case, students discuss the medical, ethical, legal, and societal i...
Conversations with Fireflies
This case explores the aggressive mimicry behavior of the femme fatale firefly - female fireflies in the genus Photuris that mimic the flash pattern of females in the genus Photinus in order to lure Photinus males to their de...
Cow of the Future
In this case developed for an introductory general microbiology course, students consider concepts of bacterial genetics as they act as consultants to a foundation interested in funding innovative products. Students take the role of advising "the baron...
Cracking the Case
In this directed case study, students shadow Dr. Lee in diagnosing two patients with osteoporosis. The students are given patient history and an initial panel of test results, which they discuss in small groups. After diagnosis, they are asked specific...
Crazy About Cryptids! An Ecological Hunt for Nessie and Other Legendary Creatures
Who wouldn't want to go in search of a creature like Bigfoot, Yeti, or the Loch Ness Monster? Using the science of ecology, students do exactly that in this case study that encompasses a variety of case study teaching formats. Working in gr...
Cross-Dressing or Crossing-Over?
In this “clicker case,” students learn about sex determination, meiosis, and chromosomal “crossing over” through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 As...
This "clicker case" about female mimicry in spawning salmon was developed for an introductory-level, non-majors biology course to help address one of the most common misconceptions that students have about natural selection, namely, that only the "stro...
This PowerPoint-driven, flipped case study begins with a short video about a woman suffering from cystic fibrosis (CF) in the 1970s, a friend of the lead author's, whom she met in college and who died in her twenties. Hooked by this personal story, stu...
The incidence of Clostridium difficile infection (CDI), including severe infection, has increased in both institutional settings and the general community. This case study presents the story of an elderly woman who spent time in a hospital and...
Dark Skin, Blond Hair
This interrupted case is based on a genome wide association study (GWAS) that identified the genetic variation causing some inhabitants of the Solomon Islands to have blond hair. The case illustrates the connection between genotype and phenotype, and a...
Darwin's Finches and Natural Selection
In this "clicker case," students learn about natural selection through the research of Peter and Rosemary Grant and colleagues on the finches of the Galapagos Islands. Students are presented with data in the form of graphs and asked to determine what i...
Decoding the Flu
This "clicker case" was designed to develop students' ability to read and interpret information stored in DNA. Making use of personal response systems ("clickers") along with a PowerPoint presentation, students follow the story of "Jason," a student in...
In this case study, a forensic anthropologist must determine the age and sex as well as look for signs of trauma to a skeleton found in a shallow grave in a state park. Students simulate the actual procedures used in a forensics lab and learn to identi...
Diabetes and Insulin Signaling
Cellular signaling, otherwise known as signal transduction, is the mechanism by which cellular context and environmental situation are used to regulate or adjust cellular behavior. Multicellular organisms use cellular signaling to coordinate responses ...
Diagnosis of a Congenital Disorder
This progressive disclosure case study explores the medically-related issues of a female infant born with the congenital disorder Sirenomelia, more commonly known as "Mermaid Syndrome." The case starts with a high-risk mother participating in prenatal ...
Differential Diagnosis and Treatment of an Autoimmune Response
There are a number of medical disorders that mimic each other and accordingly prove problematic for diagnosis, including autoimmune disorders (rheumatoid arthritis and systemic lupus erythematosus), bacterial infections (syphilis), and arthropod borne ...
Disappearing Marine Iguanas
In this interrupted case study, students apply the scientific method to probe possible reasons behind declining marine iguana populations in the Galapagos Islands. Initially students are given rudimentary information and encouraged to generate wide-ran...
Disease Along the River: A Case Study and Cholera Outbreak Game
This case study centers on an active teaching game that simulates a cholera outbreak among five villages along a river, similar to the Haitian outbreak of 2010. By enacting the behaviors of fictional villagers, students learn how trade, travel, sanitat...
Do Corridors Have Value in Conservation?
This case study discusses conservation corridors as a means to reduce the problems of population size and isolation in a fragmented habitat. In an interrupted format, students learn what a corridor is, consider how nature preserves and corridors functi...
Does the Matrix Matter?
In this case study, students apply principles of landscape ecology, experimental design, and data interpretation to examine alternative explanations for how birds respond to forest fragmentation and landscape matrix. Using an interrupted format, the ca...
Dolphin Deaths: A Case Study in Environmental Toxicology
This case study examines a variety of biological factors that may have been involved in the 2013 dolphin "unusual mortality event" (UME) on the East Coast of the United States. The story follows a news reporter and four different scientists who are pre...
Don’t Lose Your Head!
This whimsical case introduces students to the topic of dorsal/ventral (DV) axis formation in amphibians. After the recent birth of a good-sized clutch of eggs, Heather Pipiens is pleased to see that most of her little larvae are doing fine, but alarme...
Dr. Collins and the Case of the Mysterious Infection
In this case study, Dr. Collins must diagnose and prescribe treatment for a young patient with a serious infection. Students receive pieces of the case in a progressive disclosure format and answer questions about bacterial infection, antibiotics, and ...
Driving Can Be Dangerous to Your Health
In this interrupted case study, students read about an older woman named Barbara who becomes ill after driving with her husband 19 hours from Florida to visit their son’s family. Barbara experiences an asthma attack and then more serious breathin...
Dust to Dust
Tom and his grandfather, a retired high school chemistry teacher, are talking about a National Geographic television documentary titled “Waking the Baby Mammoth.” As students read the dialogue that ensues, they learn how carbon, an essentia...
Earthquakes Damage Cells, Too
Cholera is a commonly explored disorder when teaching transmembrane transport. Expanding on this theme, this case study also introduces intracellular and extracellular signal transduction, the physiological basis of rehydration treatments, and provides...
Eating Himself to Death
This case study was developed for an introductory biology course with the goal of integrating content (specifically, structure/function, signaling pathways, and homeostasis) while reinforcing general critical thinking skills and the scientific method (...
Eating PCBs from Lake Ontario - The Clicker Version
This is a “clicker” adaptation of another case in our collection, “Eating PCBs from Lake Ontario: Is There an Effect or Not?” (2001), written by the same author. It encourages students to examine how scientific results get prese...
Ecology of Individuals: Using Game Theory to Understand Animal Behavior
This case study is based on the game theory developed by John Maynard Smith where two behavioral strategies ("Hawks" and "Doves") compete over a contested resource. During this 50- to 75-minute case, students experience "hands-on"' the change in freque...
This case encourages students to explore various aspects of alternative and complementary medicine that might be helpful in treating a woman who is suffering from scoliosis. The case was developed for use in a variety of settings, ranging from an intro...
Energy Up, Weight Down?
When Jill’s roommate Nancy starts using a nutritional product to improve her energy and lose weight, Jill goes searching for information about it. Her search leads her to nutrition labels, websites and, as she digs deeper, the results of scientif...
Equal Time for Intelligent Design?
Whether Intelligent Design should be taught in a science classroom is a serious problem. This case study tackles the issue head-on by using intimate debate, a pedagogical structure in which small student groups are subdivided into opposing student pair...
Escape from Planet Soma
In this case, students assume the role of a fictitious space explorer captured by aliens. To win their release, they must correctly explain the neurophysiology underlying some of the punishments used by the aliens to deter attempts at escape. The purpo...
Evolution and Plasticity in Guppies
This case study focuses on the relationship between evolution and plasticity using a hands-on, inquiry-based approach. Students view examples from the literature that illustrate the difference between nature and nurture, or the relative contributions o...
Evolution in Action
This case study is based on Dr. Richard Lenski’s ongoing studies of evolution in E. coli. Students are introduced to prokaryotic biology and to Lenski’s studies based on serial broth cultures of E. coli, which have been mo...
This case examines the biological, ecological, social, political, and economic factors surrounding exotic species as well as the role of resource managers in shaping public policy on environmental issues. In addition to conservation ecology courses, th...
Eyes Without a Face
Although blind since childhood as the result of an accident, Lucy has never given up hope that one day she might see again. So, when her ophthalmologist tells her about a study being conducted at the University Medical Center that might help her regain...
Face the Fats
This clicker case introduces students to the biochemistry of lipids through the story of Pete, a college student who begins to consider his nutritional fat intake after watching a commercial for the cholesterol-lowering drug Vytorin. In this case, stud...
This case study is targeted to the middle school science student and written especially with female students in mind. Using an interdisciplinary approach, it combines content from physical science and areas of biology (bacteriology, pathology) to tell ...
Life has changed for the rural residents of Farmville County since the arrival of four concentrated animal feeding operations (CAFOs); the air has an odor, wildlife has decreased, and illnesses are on the rise. One of the town's residents has become ac...
It's Mother's Day and Dolly, a high school senior, is making a Mediterranean salad for her mom, who is a college chemistry major and who likes to take every opportunity to teach Dolly what she has learned in school. Today is no exception, as she guides...
Fecal Coliforms in Antarctica
In this interrupted case study, students explore the environmental consequences of Antarctic research as they design experiments to assess the impact of disposing untreated sewage from a research station into the ocean. Students review experimental met...
This case study uses the example of ionic foot baths to examine how placebo treatments can affect our health and wellness. Inspired by a student’s real visit to a spa, the story begins with a description of the experience of an ionic foot bath, a...
Fishing for Answers in the Gulf of Mexico's Dead Zone
This “clicker case” addresses the eutrophication of aquatic systems caused by human activities. "Susan" is a biology student working at a seafood restaurant on the Gulf of Mexico. She discovers that the restaurant doesn't serve locally caug...
FOXP2 and Speech
FOXP2 was first identified as a human language gene when a mutated version of the gene was found to cause speech problems in the KE family in London. In 2009, a research team transferred the cloned FOXP2 gene into mice and demonstrated that the FOXP2 t...
From Cow Juice to a Billion Dollar Drug, With Some Breakthroughs in Between
Before the discovery of insulin in 1921, being diagnosed with Type 1 diabetes was a death sentence. Despite the successful management of diabetes with purified animal insulin, potentially severe side effects were abundant, and alternative ways to produ...
From Gummy Bears to Celery Stalks: Diffusion and Osmosis
This is an interrupted case study that intersperses information about diffusion and osmosis with content review and knowledge application questions, as well as a simple experiment that can be conducted without the use of a laboratory. This case study i...
From Prairies to Corn Fields for Fuel
With increasing U.S. government support for biofuel production in the late 2000s came increased pressure to convert more land to cornfields for ethanol. To make way for more corn, millions of acres of prairie grassland were plowed under, destroying an ...
From Twiggy to Tubby
This case study explores the topics of diffusion, osmosis, membrane transport, and the physiological significance of glucose and insulin in the human body. The story begins with a high school athlete, Timmy, who is incredibly efficient at metabolizing ...
Gender: In the Genes or in the Jeans?
How are males and females different? Most people have a sex that is consistent on all levels: genetic, gonadal, internal genitals, external genitals. But sometimes there are discrepancies. This case explores the biology of human sexual differentiation ...
Genetic Testing and Breast Cancer
In this dilemma case, the central character, Kathy, must decide whether or not to be tested for known mutations in the breast cancer genes. Students assume the roles of members of Kathy’s book club and, using a jigsaw technique, explore the advan...
Genetics and a Transcontinental Romance
Annika is a PhD student from Sweden who spends two years in the Solomon Islands to complete her fieldwork. During her stay in the South Pacific she experiences a few surprises related to the hair color not only of the locals, but also of her own baby g...
Giant Pandas, Hormones, and the Evolution of a Lazy Bear
This clicker case study looks at the role of hormone cascades in homeostatic control of metabolism in a charismatic organism, the Giant Panda. The case explores how Giant Pandas have adapted to a nutritionally poor food resource, bamboo, through ...
Giving Birth to Someone Else's Children?
Most students have heard about situations in which the paternity of a child is questioned, but maternity? This case was designed for introductory biology students and asks them to develop hypotheses to explain how a mother cannot be geneticall...
Global Climate Change: Evidence and Causes
This “clicker case” begins by assessing students’ impressions of global climate change and the role that human activities play in recent global warming trends. Students assume the role of an intern working for a U.S. senator. They nee...
Global Climate Change: Impact and Remediation
This “clicker case” is a continuation of another case in our collection, “Global Climate Change: Evidence and Causes,” in which students assumed the role of an intern working for a U.S. senator so that they could advise the sena...
Global Climate Change: What Does it Look Like?
In this interrupted case study, Ph.D.-paleoclimatologist-turned-TV-meteorologist Sara Fahrenheit finds herself projected into a future climate that reminds her of the Early Eocene: it's hot, it's humid, and seems tropical. The story is a vehicle for te...
Glowing Plants on Kickstarter
This case study is centered on a real scenario from 2013 in which the Kickstarter fundraising platform included a fundraising proposal from a group wanting to use synthetic biology to make glowing plants. The proposal raised controversy because the Glo...
The Aedes aegypti mosquito is the major vector for transmission of numerous viral diseases, including yellow fever, dengue, and now, Zika. Interestingly, different subspecies of A. aegypti are known to exist in close proximity but wit...
Grandma's TUM-my Trouble
An elderly woman living independently with some help from her family is brought to the local emergency room because she is confused and vomiting. While her son suspects a stroke, a quick battery of laboratory tests indicates that her current probl...
Grazing in Vernal Pools
This case study in restoration ecology utilizes two peer reviewed articles that ask a similar question about the effects of grazing in temporary wetlands, yet the articles have different conclusions about these effects. Students are challenged to...
Helicobacter pylori and the Bacterial Theory of Ulcers
This case is an account of the events that led Drs. Robin Warren and Barry Marshall to the bacterial theory of ulcers. The two physicians refused to accept the standard explanations for what they had observed and instead developed an alternative hypoth...
This case deals with the genetics of the hemophilic condition that afflicted the royal families of Europe. Students trace the pedigrees of the descendants of Queen Victoria and the passage of the recessive X-linked trait from ancestor to ancestor...
Hidden in Plain Sight
This case study tells the story of John and Mary, two first-year college students learning about biodiversity while on a trip to Costa Rica where they become interested in studying butterflies (Astraptes fulgerator). Designed for use in a flip...
Hidden in Plain Sight
As nonliving entities, viruses face specific challenges when replicating in a host. Avoiding the host immune system is something that every virus aims for in order to successfully reproduce itself and infect another host. Many viruses repli...
Holes in the Matter
This case centers on a fictional group of young adults who studied abroad together in Scotland as college students. A number of them develop disease symptoms and die a few years after the trip. The cause of death is determined to be a prion disease. Ap...
Hot and Bothered
This interrupted case study is a story about Carrie and her infant daughter Hayden who share similar symptoms: weight loss, metabolic abnormalities, and endocrine glands that just won't quit - as well as autoimmune complications. Students will eventual...
How a Cancer Trial Ended in Betrayal
In this case study, students learn about the complexities and issues associated with clinical trials. After reading a newspaper story about a fraudulently conducted clinical trial involving a treatment for skin cancer, students simulate their own small...
How Do Scallops Swim?
Scallops are bivalve mollusks that live on the seabed. This way of life makes them susceptible to predation and so they have evolved the ability to escape by swimming. This interrupted case study is based on a few observations and simple experiments wh...
How Many More Thymes? A Case of Phytochemical Defense
This clicker case addresses several concepts related to the evolutionary ecology of herbivore defenses. A survey of several different studies that investigated chemical defenses in Thymus vulgaris (thyme) gives students the opportunity to deve...
How to Remove Makeup
This case study explores how intermolecular forces affect the solubility of substances. The story line presents a scenario in which specialists in a marketing department are investigating three types of makeup removers. They want to generate a short pr...
Hunting the Black Rhino
This case study was developed to teach students the importance of understanding the behavior of wildlife, explore the difficulty in making management decisions when the public is invested in a species, and to help students develop critical thinking and...
Hunting the Ebola Reservoir Host
This one-hour introduction to the study of infectious diseases uses recent research on the Ebola reservoir host to motivate students to consider the characteristics of a viral host species and how it can be identified. Presented in the form of an inter...
I Can Quit Anytime I Want
This “clicker case” explores the biological basis for the temporary euphoria that accompanies drug use as well as certain aspects of the biological basis of drug dependency. The case is called a clicker case because it is designed for use w...
I Don't Need a Flu Shot!
In this “clicker case,” Ryan, a college student, receives an email from the campus health education office urging students to get a flu shot. Ryan thinks it is too late since he just had the stomach flu, and besides, even if he did catch it...
I Heart Running: A Case Study on Tachycardia in Sam the Runner
"I Heart Running" is a case study in which students diagnose the cause of exercise-induced tachycardia in an otherwise healthy, 27-year-old female. The patient, Sam, is a long-distance runner and realizes that her exercising heart rate reaches over 200...
I Scream for Ice Cream
Lactose intolerance, caused by a lack of persistent lactase enzyme expression, is a trait commonly observed in adult humans, with varying geographic prevalence depending on dietary habits in different cultures. This case study follows a diverse group o...
Identical Twins, Identical Fates?
This case tells the story of Elise, a college freshman whose identical twin sister has recently been diagnosed with schizophrenia. Elise is concerned about her own risk for developing this disease. Through her research and interactions with a physician...
I'm Looking Over a White-Striped Clover
This case is an exploration of the process of natural selection using white clover (Trifolium repens) as an example. In general, two forms of white clover can be found around the world in various habitats. One type is able to produce cyanide i...
Impacts of Climate Change on Pinyon Pine Cone Production
In this interrupted case study, students explore how changing climate may affect cone production in pinyon pine (Pinus edulis). Students begin by learning about mast seeding, a common reproductive strategy among many perennial plant species, a...
Improving on Nature?
In 1958, black bass were introduced into Lake Atitlan in the highlands of western Guatemala as a way to attract tourism and boost the local economy, but unforeseen complications resulted in an ecological disaster. Developed for an introductory course i...
In Sickness and in Health
In this interrupted case study, Greg and Olga, a young couple planning a family, have decided to see a genetic counselor because of a family history of genetic disease. Students construct a pedigree from the information presented in the case; then, on ...
Is Iron Fertilization Good for the Sea?
This case study describes experiments to seed the ocean with iron to encourage algae growth. It explores how human activities contribute to greenhouse effects and global warming, proposals to potentially counteract these effects and make the ocean more...
Is That Pill You're Taking Safe?
This dilemma cased is based on the actual development, FDA approval, and market withdrawal of dexfenfluramine, a drug used in the late 1990s in combination with phentermine for weight loss. The case is set up as a mock trial, with students taking the r...
Is the Data Dirty or Clean?
This case study challenges students to differentiate between anecdotal evidence and science-based evidence related to human health. The case uses a "flipped" approach in which students watch two preparatory videos prior to attending class. The fir...
It Takes a Lot of Nerve
In this two-part case study on the nervous system, students learn about neural pathways. The case scenarios are drawn from real life and require students to explain the physiological mechanisms at work. The first scenario is designed for freshmen level...
It’s a Crocodile! No, a Fish! No, a Dolphin!
It is not uncommon to hear creationists argue that evolution is not science because no one saw it happen, or for students to wonder how we can know anything about the physiology or behavior of organisms that went extinct hundreds of millions of years a...
It’s All Greek to Me: Genetics Edition
Stephania and Nikolaus Stamos are concerned about their baby daughter. They take her to her pediatrician, who immediately notices that the once bright and active child is small for her age, pale, lethargic, and has a swollen abdomen. Students examine t...
It's All Greek to Me: Physiology Edition
Stephania and Nikolaus Stamos are concerned about their baby daughter. They take her to her pediatrician, who immediately notices that the once bright and active child is small for her age, pale, lethargic, and has a swollen abdomen. Students exam...
It's Just Stress, Right?
Ellie is a struggling college student on the brink of failing her physiology course; not surprisingly, she exhibits many classic signs of stress. However, a visit to the health clinic reveals that she may be suffering from more than just stress. In thi...
It's Like Pulling Teeth
In this interrupted case study, a middle-aged man is having his wisdom teeth surgically removed. He decides to have a general anesthetic, but is unaware of the reaction he will have to halothane. His skeletal muscles go rigid and his body temperature r...
I've Fallen Over and I Can't Get Up
Greg Myron is playing the last football game of his career as the high school’s star running back. As the clock counts down the final seconds, Greg rushes 70 yards down field until he is tackled out of bounds. When the kicking team comes out to t...
Jim and the Forgotten Embryos
The goal of this case study is to expose students to the basics of embryonic stem cells, their therapeutic uses, and the controversy surrounding embryonic stem cells through the story of a college student, Jim Allison, who becomes paralyzed after a car...
Joel E. Greengiant Learns About Peas
This case study follows purveyors of peas, Joel E. and Jolene Greengiant, as they learn about the origin, biochemistry, genetics and eventual artificial selection of sweet (wrinkled) peas, all in the context of evolutionary biology. This integrative ap...
In this interdisciplinary case, students meet Josie, the main character, who suffers from a variety of symptoms. Students must grapple with the conflicting data presented, which ultimately leads them to a diagnosis of either porphyria or schizophrenia....
Just a Spider Bite?
This case relates the story of two fictional college students, Kristen and Brent, who discover that they are infected with Staphylococcus aureus. Brent recovers after using an antibiotic, but Kristen does not. It is later confirmed through tes...
In this interrupted case, students examine the concept of unconsciousness and develop an understanding of how clinicians diagnose death. Developed for a freshman course in human biology, the case focuses on brain death, but raises related issues, inclu...
Katrina's Troubled Waters
This case study explores some of the health issues brought to light during the flooding in New Orleans caused by Hurricane Katrina. The case encourages students to think about a variety of problems that can occur when humans are exposed to unsanitary f...
Keeping up with the Joneses
This interrupted case study in cardiovascular physiology focuses on Suzie, a determined young woman who is training hard for the upcoming figure skating season. But family dynamics combined with high aspirations of competing in the Olympic Games have n...
Kill the Aliens: Controlling Leafy Spurge
The majority of people in the world interact with nature in an urban setting. Management issues in urban parks tend to be more challenging than in “natural” parks for a variety of reasons, including heavy use, proximity to housing, local ad...
This case study takes place at a fictional biotechnology company developing herbicides against invasive plant species. The case study focuses on five herbicides with different effects on photosynthesis. Students play the role of lab interns and explore...
King Tut's Family Secrets
This "clicker case" is based on several articles published in 2010 that determined the genealogy of the ancient Egyptian pharaoh Tutankhamun based on microsatellite DNA analysis. The case begins with a description of the seven royal mummies found in Va...
Knot Your Typical Weed
Japanese knotweed (Fallopia japonica) is an invasive plant that can be very hard to eliminate. This PowerPoint-driven case study briefly describes this plant and asks students to identify possible solutions for its control when a homeowner dis...
Kudz-who? and Other Questions of Invasive Species
It is now well known that non-native species have the potential to be harmful to an ecosystem, but that wasn't always the case, and getting rid of non-native invasive species is usually a difficult task. This brief, interrupted case study tells the sto...
Lady Tasting Coffee
In the 1920s, biologist and statistician Ronald Fisher met a woman who claimed she could taste whether a cup of tea was prepared by adding milk before or after the tea. Fisher’s essay about the tea party may be one of the first cases published to...
Let's Get This Course Started
The first day of class is often a reading of the syllabus, even when active learning approaches are used throughout the rest of the term. This interrupted case uses the first day to model the expectations of a course that uses case method approaches. S...
Lewis and Clark Reloaded
Frank and Joe are 24-year-old fraternal twins who share similar interests, including cycling. The brothers decide to attempt their first long-distance bicycling trip, retracing the journey of early American explorers Lewis and Clark to the Northwest.&n...
Life on Mars
This case explores the question of whether there was ever life on Mars and in doing so explores how we define life. The backdrop for the case is the 1996 revelation by NASA of evidence of life on Mars. Through a fictionalized account of the events, the...
Life, The Final Frontier
Designed for high school and college-level introductory biology courses, the goal of this "clicker case" is to get students to think about what it means for something to be alive by defining the characteristics of living organisms and applying these to...
Little Girl Lost: A Case Study on Defective Cellular Organelles
This case study introduces students to the structure and function of cellular organelles and seeks to show their importance by discussing diseases and disorders that can result when an organelle does not function as it should. The storyline follows a f...
This case presents a fanciful story about the origin of the eukaryotic cell, a major milestone in the evolution of life. The characters of the story are Mito, Chlora, Flag, ER, Nuc, Golgi, Ves, and Ly, all members of an extended cellular family. Writte...
Living in a Genomic World
This directed case study was developed in order to present genomic data to students, allow them to interpret the impact of genetic variations on phenotype, and to explore precision medicine. Students are introduced to "Josie," a college sophomore who d...
Living on the Edge
This case study describes the daily osmotic struggle for survival faced by hummingbirds. The narrative is written from the viewpoint of a human observer who sees an Anna's hummingbird feeding on flowers outside of her window. She notices that the...
Living the Sweet Life
In this directed case study, students assist Dr. Gupta in his endocrinology clinic in diagnosing three patients having problems with blood glucose regulation. In Part I, students are given patient backgrounds and results from laboratory tests generated...
Living With Her Genes
When a 30-year-old genetic counselor learns that her 38-year-old sister has developed early onset familial Alzheimer’s disease (EOFAD), a dominantly inherited disorder that led to their father's death at age 42, she struggles with whether to unde...
Lost in the Desert!
Students learn about the interconnectedness of the body, with a particular focus on the skin as one of the most important homeostatic organ systems, in this case study in which the protagonist sets out on a three-hour drive across the Arizona desert to...
Lost in the Desert! Hebrew Translation
In this directed case study, translated from the original English into Hebrew, students read about a man who sets out on a three-hour drive across the Arizona desert to meet his fiancee in California but never shows up at his final destination. S...
Lost? Ask a Turtle
This case study examines the events surrounding the hatching and migration of loggerhead sea turtles, specifically what mechanisms they use to head towards the ocean (once hatched) and where and how they migrate once in the ocean. The story is wr...
Love Potion #10
In this case study, students are asked to consider whether there is evidence to adequately support a series of scientific claims made in an advertisement for pheromones. The case teaches students about the scientific method and the process of science. ...
This clicker case was designed to teach students about basic enzyme structure, mechanisms of enzyme inhibition, and mechanisms of drug resistance. The story follows Oliver Casey, a patient afflicted with Chronic Myelogenous Leukemia (CML). CML is cause...
Make a Life to Save a Life
In this “clicker case,” students learn about meiosis through the real-life story of a couple who used pre-implantation genetic screening to select an embryo that was a genetic match for an older sibling with leukemia, and thus able to provi...
Making It Fit: Using Excel to Analyze Biological Systems
In this case, students read about a biologist who needs to determine how to analyze age-at-length data, a common situation in fisheries biology. The fictional Dr. Latimer is tasked with fitting non-linear models to the data, and the case develops as he...
Mathematics in Conservation
This interrupted case study teaches probability theory and transmission genetics through their application to the conservation of the endangered Florida panther. An endangered population is unlikely to survive simply due to its small population size. B...
In this case study on multi-drug resistant (MDR) tuberculosis, students consider ways in which to preserve health as a human right without subjecting already marginalized communities susceptible to the disease to further discrimination. Students learn ...
In this PowerPoint-based clicker case, developed for use in either a general biology or general genetics class, students are introduced to the life and work of Gregor Mendel. The initial slides set up the story as we see Mendel, who is ill, remin...
This interdisciplinary case study introduces us to the Greens, a family with a recently diagnosed autistic child. Autism is one of several disorders grouped within the acronym ASD, or autism spectrum disorders. Autistic children have problems with comm...
Microbial Pie, or What Did You Feed the Neighbors?
The Emergency Room seems busier than usual, and the cases coming in are all too similar. Everyone seems to be suffering from the same symptoms - abdominal pain, vomiting, and bloody diarrhea. Once the hospital staff identify the bacteria ca...
Mildred Using Plants
The format for this case is unusual. The PowerPoint of the "case" provides an in-class framework for working through all of the activities associated with the case. These activities are explained in the teaching notes. The teaching no...
Mini Cases in Psychoactive Drugs and Their Effects on the Brain
Designed for an upper-level psychology class titled Brain & Behavior, this series of mini-cases can be used in any undergraduate course that covers the major classes of commonly abused legal and illicit psychoactive drugs from a biological...
Mini Cases on Choosing Appropriate Statistical Tests for Ecological Data
This set of mini cases on the ecology of eastern cottontail rabbits is designed to give students practical experience using statistics in a scientific context. Given a dataset and experimental design, groups of students are asked to play the part of a ...
This interdisciplinary case study uses the format of a progressive disclosure to explore certain advances in biotechnology and evaluate them within the framework of societal needs, concerns and pressures. When faced with a heart valve transplant,...
Mom Always Liked You Best
This interrupted case study is based on a journal article on the parenting behavior of American coots. Working through the case, students develop hypotheses and design experiments to test their hypotheses as they are given pieces of the case in an inte...
Monday on the Metabolic Ward
This case is a variation of a longer case in our collection titled "Murder or Medical Mishap? Death on the Metabolic Ward," which has a "murder-mystery" aspect to it. In both versions of the case, students assume the role of pre-med students part...
More Than Just a Cough: Exploring the Role of the Cytoskeleton in Fertility
This interrupted case study explores the role of cytoskeletal structures on human health, specifically on respiratory function, sperm motility, and female fertility. It follows the story of a couple struggling to conceive a child and the doctors workin...
More Than Meets the Eye
The classic example of a human trait that behaves in a clear Mendelian fashion is human eye color. The gene that controls it exists in two forms: a dominant brown allele and a recessive blue allele. But the genetics of eye color is more complex than ty...
Mother's Milk Cures Cancer?
This case study on the immune system, cell cycle regulation, and cancer biology explores the role that serendipity plays in new discoveries in science, how scientific research is funded, and the personal and professional implications of unexpectedly fi...