Nutrition: Medical School Crash Course

Nutrition Medical School Crash Course™

AudioLearn.com

Table of Contents Preface ..............................................................................................................................................1 Chapter 1: The Gastrointestinal Tract and Digestion ............................................................................3 GI Tract Basics ......................................................................................................................................... 3 Structure of the GI Tract ......................................................................................................................... 5 Embryonic Development ........................................................................................................................ 5 Histology of the GI Tract ......................................................................................................................... 6 Functions of the GI Tract ......................................................................................................................... 7 GI Diseases .............................................................................................................................................. 7 Digestion ................................................................................................................................................. 8 Key Takeaways ...................................................................................................................................... 10 Quiz ....................................................................................................................................................... 10 Chapter 2: The Major Macronutrients............................................................................................... 14 Carbohydrates ...................................................................................................................................... 14 Fats ....................................................................................................................................................... 16 Protein .................................................................................................................................................. 18 Key Takeaways ...................................................................................................................................... 19 Quiz ....................................................................................................................................................... 20 Chapter 3: Vitamins and Minerals ..................................................................................................... 23 Important Vitamins ............................................................................................................................... 23 Minerals ................................................................................................................................................ 25 Key Takeaways ...................................................................................................................................... 26 Quiz ....................................................................................................................................................... 27 Chapter 4: Dietary Recommendations for Adults .............................................................................. 30 Basic Healthy Eating Recommendations ............................................................................................... 30 Understanding Food Labels .................................................................................................................. 31 US Eating Patterns ................................................................................................................................ 32 Recommendations to Alter Poor Eating Habits .................................................................................. 32 Caloric Intake Depending on Age and Size ............................................................................................ 33 Dietary Reference Intakes ..................................................................................................................... 34 Key Takeaways ...................................................................................................................................... 35

Quiz ....................................................................................................................................................... 35 Chapter 5: The Biochemistry of Hunger and Satiety ........................................................................... 38 Overview of Hunger and Nutritional Needs .......................................................................................... 38 The GI Brain Connection ....................................................................................................................... 39 Peripheral Factors ................................................................................................................................. 40 The Biochemistry of Hunger ................................................................................................................. 41 Key Takeaways ...................................................................................................................................... 42 Quiz ....................................................................................................................................................... 42 Chapter 6: Body Weight and Nutrition .............................................................................................. 45 Obesity and Nutrition ........................................................................................................................... 45 The Underweight State ......................................................................................................................... 47 Key Takeaways ...................................................................................................................................... 49 Quiz ....................................................................................................................................................... 49 Chapter 7: Pediatric Nutrition........................................................................................................... 52 Basic Nutritional Recommendations ..................................................................................................... 52 Caloric Intake for Children .................................................................................................................... 52 Nutrition in the Very Young .................................................................................................................. 53 Childhood Obesity................................................................................................................................. 54 Key Takeaways ...................................................................................................................................... 55 Quiz ....................................................................................................................................................... 55 Chapter 8: Nutrition in Pregnancy..................................................................................................... 59 Eating Basics in Pregnancy .................................................................................................................... 59 Nutrition in Gestational Diabetes ......................................................................................................... 60 Nutrition and Morning Sickness ............................................................................................................ 61 Pica in Pregnancy .................................................................................................................................. 61 Listeria in Pregnancy ............................................................................................................................. 61 Key Takeaways ...................................................................................................................................... 61 Quiz ....................................................................................................................................................... 62 Chapter 9: Nutrition and Human Disease States ................................................................................... 65 Nutrition and Cancer............................................................................................................................. 65 Diabetes Mellitus and Nutrition ............................................................................................................ 65 Hypertension and Nutrition .................................................................................................................. 68 Heart Disease and Nutrition.................................................................................................................. 69

Key Takeaways ...................................................................................................................................... 69 Quiz ....................................................................................................................................................... 69 Chapter 10: Performance and Exercise Nutrition ............................................................................... 73 Exercise Nutrition Basics ....................................................................................................................... 73 Strength Training Nutrition ................................................................................................................... 74 Cardio Workout .................................................................................................................................... 74 Minerals and Exercise ........................................................................................................................... 75 Key Takeaways ...................................................................................................................................... 76 Quiz ....................................................................................................................................................... 76 Chapter 11: Nutritional Deficiencies and Disorders ........................................................................... 79 Malnutrition .......................................................................................................................................... 79 Anorexia Nervosa .................................................................................................................................. 80 Celiac Disease ....................................................................................................................................... 81 Key Takeaways ...................................................................................................................................... 83 Quiz ....................................................................................................................................................... 83 Chapter 12: Food Safety and Food Technology .................................................................................. 86 Food Safety Facts .................................................................................................................................. 86 Storing Food .......................................................................................................................................... 86 Food Technology ................................................................................................................................... 87 Genetically-Modified Food ................................................................................................................... 88 Key Takeaways ...................................................................................................................................... 88 Quiz ....................................................................................................................................................... 88 Summary ......................................................................................................................................... 92 Course Questions and Answers ........................................................................................................ 94

Preface This course is intended to cover the basics of nutrition from both a clinical and non-clinical standpoint.

The study of nutrition starts with a discussion of the gastrointestinal tract and how it functions. It goes on to cover topics of nutrition as they relate to physical and mental health. All of these topics are discussed in this course as they relate to the nutrition of healthy and unhealthy human hosts.

The first chapter of the course will include a discussion of the gastrointestinal tract and its basic anatomy. The anatomy is closely linked to the functions of digestion and absorption—both things that are necessary for food to make it from the mouth to the cells of the body.

The second chapter of the course will cover the basic macronutrients, which include carbohydrates, protein, and fat. All food consumed comes from a combination of each of these types of food groups and each is necessary for better health and development.

Vitamins and mineral will be the discussion of the third chapter of the course. There are numerous vitamins and about twenty minerals that are essential to eat in the diet because they cannot be synthesized by the body and must be gotten through eating health foods.

Chapter four will include a discussion of dietary recommendations for healthy adults. In order to proceed through adulthood and into a healthy old age, people need to follow certain health recommendations from the number of calories to be consumed to the type of food each person should eat.

The topic of chapter five will involve the biochemistry of satiety and hunger. Both of these sensations are highly biochemically-mediated in the body and are less under psychological control than most people think.

Chapter six of the course is intended to be a discussion of body weight and nutrition. While obesity is the more common of the extremes in body weight, low body weight can also impact a person and this will be discussed in this chapter.

The discussion in chapter seven of the course will be on pediatric nutrition. Children and babies have special nutritional needs that will be discussed as they apply mainly to healthy children who need excellent nutrition for growth and development.

Chapter eight will be devoted to discussing nutrition in pregnancy. Women in pregnancy have certain nutritional needs that must be satisfied to have the birth of a healthy baby. Eating in pregnancy is more than just “eating for two” and this will be discussed in this chapter.

The focus of the discussion in chapter nine of the course will be on nutrition and the various common disease states in humans. The special nutritional needs in cancer patients, patient with high blood pressure, patients with diabetes, and patients with heart disease will be covered in this chapter.

Chapter ten will be a discussion on performance and exercise nutrition. There are special nutritional needs for the exercising person and especially for the person who is an endurance athlete that will be covered in this chapter.

The focus of discussion in chapter eleven will be nutritional deficiencies and nutritional disorders.

Things like malnutrition, anorexia nervosa, and celiac disease will be covered as these are common nutritional disorders seen in humans.

1

The twelfth and final chapter of the course will include a brief discussion on food safety and food technology. There are specific ways to store and cook food that will help ensure food safety. There are also advances in food technology that have made for a wider variety and selection of foods eaten by humans.

2

Chapter 1: The Gastrointestinal Tract and Digestion The study of nutrition starts with an understanding of the structure and function of the gastrointestinal tract. The gastrointestinal tract or GI tract refers to the parts of the body that begin with the mouth and end with the anus. The major function of the GI tract is digestion, although you’ll see that it has other functions as well. The anatomy of the GI tract and the basics of the digestion of nutrients is the main focus of this chapter.

GI Tract Basics The GI tract is not just one organ but is instead an organ system that consists of several interrelated organs beginning with the mouth and ending with the anus. It is also referred to as the alimentary canal or gut. The vast majority of the GI tract is simply a tube that holds the contents of what a person has eaten, while other parts are solid organs that aid in the digestive process, such as the pancreas and liver.

Figure 1 indicates what the digestive system looks like:

Figure 1 A unique feature of the GI tract is that it contains millions of bacteria inside mostly the lower part of the GI tract that are symbiotic with the human host. Bacteria digest cellulose and other indigestible ingested food and make molecules as part of their metabolism that are used by the host. These bacterial colonies are known as the “gut flora”.

The main organs of the human GI tract are the esophagus, stomach, and intestinal tract, which together make up both the upper and lower gastrointestinal tract. The ancillary organs of the GI tract include the tongue, salivary glands, gallbladder, liver, and pancreas. Embryologically, all of these organs come from

3

the foregut, midgut, and hindgut. The entirety of the GI tract is about nine meters in length when stretched to its full length but is shorter when it functions because of peristalsis, etc.

There are several major hormones associated with the GI tract, including ghrelin, cholecystokinin, secretin, and gastrin. These can be intracrine enzymes or autocrine enzymes. Intracrine enzymes are those that act inside a working cell, while autocrine enzymes act through cell signaling within the same organ. These are different from the endocrine hormones that act over long distances and paracrine hormones that act between cells that are next to each other.

Ghrelin is a small peptide hormone made by certain cells of the GI tract. It acts on the CNS, particularly the hypothalamus. It is released when the stomach is empty and stops being released when the stomach is stretched or full. It increases hunger, increases gastric acid secretion, and increases GI motility in order to prepare the system for the intake of food.

Figure 2 shows the balance of ghrelin and leptin on hunger and satiety:

Figure 2 Cholecystokinin used to be called pancreozymin. It is a peptide hormone responsible for increasing the digestive capabilities of both protein and fat. It is secreted by specialized cells of the duodenum and triggers the release of bile and digestive enzymes from the gallbladder and pancreas. It acts as a hunger suppressant as well.

Secretin is also secreted by the duodenum but is secreted by the S cells of the duodenum (in the intestinal glands). It regulates the homeostasis of water in the body by influencing secretions of the liver, pancreas, and stomach.

Gastrin, on the other hand, is produced by the G cells in the pyloric antrum of the stomach and duodenum. It stimulates gastric motility and is stimulated to be released by certain peptides present in the stomach lumen.

4

Structure of the GI Tract The GI tract is divided into an upper GI tract and a lower GI tract. The upper GI tract begin with the buccal cavity (the mouth), which leads to the pharynx (the throat), esophagus, stomach and duodenum.

The particular demarcation that separates the upper and lower GI tracts is called the “suspensory muscle of the duodenum”. This is where the embryonic foregut and midgut change places. Any hemorrhage that happens above the muscle is considered to be upper GI bleeding and any bleeding below that level is considered to be lower GI bleeding.

There are four main parts of the duodenum, which isn’t functionally just one structure. The four parts of the duodenum include the bulb, the descending duodenum, the horizontal duodenum, and the ascending duodenum. The suspensory muscle is attached to the ascending duodenum and allows it to be suspended by the diaphragm. After the suspensory muscle, the lower gastrointestinal tract and the jejunum starts.

The lower GI tract includes the jejunum, the ileum, and the colon. Basically, this includes much of the small intestine and the entire large intestine. Technically, the parts of the small intestine include the duodenum, the jejunum, and the ileum. The large intestine, on the other hand, consists of four major parts: the anal canal, rectum, colon, and cecum, with the cecum being the most proximal part of this structure.

The start of the small intestine is the duodenum, which takes the partially digested food from the stomach. It has a large absorptive surface so that it can absorb nutrients once they’ve been fully digested. The duodenum is about 25 cm long, and mixes the pancreatic juices and bile with the chyme that comes through the pyloric sphincter. There are Brunner’s glands in the duodenum, which make a mucoid alkaline secretion that turns the acidic chyme into a more basic mixture, this allows the enzymes in the duodenum to work better at a pH that is more optimal.

The jejunum is the middle part of the small intestine. It is about 2.5 meters in length, and has both circular folds and villi that increase its absorptive surface. It is the main part of the GI tract involved in the absorption of macronutrients. The ileum is about three meters in length and is responsible for the absorption of bile acids and vitamin B12. It also has villi but isn’t as much of an absorbing structure when compared to the duodenum and the jejunum.

The large intestine contains the cecum and appendix, followed by the ascending colon on the right side.

The right colic flexure is where it bends near the liver to form the transverse colon (which passes underneath the diaphragm). The left colic flexure is the bend on the left side of the body (near the spleen), where the colon becomes the “descending colon”. After this is the sigmoid colon, a short section of colon near the rectum. This opens out into the rectum and anus, which are the last and most distal parts of the intestine.

Embryonic Development The gut is derived from embryonic endoderm and is initially created on the sixteenth day of embryonic development. This is when the disc-shaped embryo folds ventrally into a tube-like structure. A small piece of the yolk sac is pinched off to form the gut. The yolk sac eventually regresses and disappears, except for the part that may later become a Meckel’s diverticulum in a fully developed human.

5

Three segments come out of this embryonic gut, called the foregut, the midgut, and the hindgut. These develop a blood supply and parts of it will expand to form wider structures, like the colon and the stomach. The foregut represents the esophagus, the stomach, the first and second parts of the duodenum, the gallbladder, the liver, and the pancreas.

The midgut begins in the lower duodenum and extends down to the first two-thirds of the transverse colon. It is basically defined as being that part of the intestinal tract that is supplied by the superior mesenteric artery. The hindgut starts at the last third of the transverse colon and ends at the anal canal.

It is supplied exclusively by the inferior mesenteric artery.

Histology of the GI Tract The gastrointestinal tract has a relatively consistent pattern of having four major layers to its lining. The inner layer is the mucosa, which is the part that has contact with the lumen of the gut. This layer comes in direct contact with the chyme as it is passing through the gut. There are three layers to the mucosa: the epithelium (inside layer that is mainly absorptive and secretory), the lamina propria (which is a connective tissue layer), and the muscularis mucosa (the smooth muscle layer).

Figure 3 shows the different layers of the GI tract:

Figure 3 The submucosa is just outside the mucosa. It consists of blood vessels, connective tissue, nerves, and lymphatic vessels that supply the other layers of the GI tract lining. It contains an enteric nerve plexus and a submucosal plexus, located just inside the muscular layer. The muscular layer is outside of the

6

submucosa and has both an outer longitudinal layer of smooth muscle and an inner circular layer of smooth muscle.

Between the two layers of muscle in the muscular layer is a myenteric plexus, which is a nerve plexus that controls peristalsis. There are pacemaker cells that activate the peristalsis. These cells are called the myenteric interstitial cells of Cajal. They control the intrinsic peristaltic activity of the GI tract and are modulated by the sympathetic and parasympathetic nervous systems.

The adventitia and serosa are the outermost layers of the lining of the GI tract. They contain mainly connective tissue. The part of the intestinal tract that remains inside the peritoneum are covered with serosa. These include everything from the stomach to the cecum (and appendix), the transverse colon, the sigmoid colon, and the rectum. The mesentery is attached to this.

Those parts of the GI tract that are retroperitoneal are covered not with serosa but with adventitia.

They are relatively fixed in position when compared to the other parts of the GI tract. These parts include the esophagus, pylorus of the stomach, last part of the duodenum, anal canal, ascending colon, and descending colon.

Functions of the GI Tract As soon as food is eaten, the digestive process begins and, within half an hour, half of the stomach contents will empty into the intestines, with a total emptying time of about two hours. The eventual transit time from stomach through the colon is about twelve to fifty hours. This is a wide variation among different people. The main function of the GI Tract is the breakdown and absorption of consumed food.

The GI tract is an important immune system organ as well. Its surface area is three times that of the skin, making it highly in contact with potential pathogens. The mucosal barrier provides an adequate barrier against potential pathogens. Besides being a physical barrier, the GI tract has an extensive amount of gut-associated lymph tissue or GALT. Things like the low pH of the stomach and the mucus, which contains a great deal of IgA antibodies, are things that keep microorganisms at bay. Saliva and bile acids also play an immune system function.

Symbiotic bacteria also play a role in the immune function of the GI tract. There are many types of bacterial organisms in the GI tract that help break down molecules that aren’t otherwise digested by the body. They make the intestinal gas that produces flatulence. They assist in the uptake of water from the intestinal milieu back into the bloodstream and are responsible for the absorption of sodium and other nutrients that didn’t get taken up by the small intestine. In general, about 80 percent of the GI tract’s bacteria are helpful and 20 percent are potentially harmful but are kept at bay by the healthy microbiota.

GI Diseases The GI tract normally functions well and is relatively healthy. Situations where the GI tract is not healthy include various types of infections of the GI tract, inflammatory diseases in the GI tract, and certain cancers of the GI tract.

There is a wide variety of pathogens that can cause gastroenteritis, which is both an infectious disease and inflammatory condition of the GI tract. Most gastroenteritis cases are caused by foodborne

7

illnesses that inflame the lining of the intestinal tract, resulting in nausea, vomiting, crampy abdominal pain, and diarrhea. Gastroenteritis is the most common GI condition in the world.

Cancer can affect any part of the GI tract, from the mouth to the anus. The most common cancer of the GI tract is colon cancer, which has an incidence of about 40.1 per 100,000 men and women per year in the US and other developed countries. Appendicitis can be purely inflammatory in nature or can be caused by an infection of the cecum.

Various inflammatory diseases can affect the intestinal tract. Crohn’s disease can cause inflammation of any part of the GI tract and ulcerative colitis affects only the colon, although both are autoimmune GI diseases. Celiac disease involves the inability to tolerate gluten in the diet. It mainly affects the small intestinal tract. This, too, is an autoimmune disease. Diverticular disease, like appendicitis, is both inflammatory and infectious. It mainly affects the colon but can be in the small intestine as well.

Functional gastrointestinal disorders include irritable bowel syndrome, functional constipation, and chronic functional abdominal pain. These have an underlying problem with the nervous system supply to the GI tract but there are no obvious pathologic findings associated with these diseases. They affect millions of people and are notoriously difficult to treat.

Digestion The main role of the GI tract when it comes to nutrition is digestion. This involves taking food that is unable to be absorbed by the mucosa and breaking it down into smaller subunits that can be easily absorbed into the bloodstream. The actual digestion starts in the mouth and continues to the duodenum. Most of the actual absorption occurs in the small intestinal lumen.

There are two types of digestion that happen in the GI tract. The first is called “mechanical digestion”, which is the physical breakdown of food so that digestive enzymes can act on it. Mechanical digestion begins in the mouth with the chewing of food. The second is called “chemical digestion” and involves the action of enzymes. The first enzyme that acts chemically on food is amylase, which is found in the saliva.

Figure 4 shows the salivary glands that provide saliva to the mouth:

Figure 4 8

Saliva also contains mucus and hydrogen carbonate, which needs to be present in order to maintain a pH that will help amylase work. After chewing and saliva act on the food, it enters the esophagus as a bolus and travels to the stomach by means of peristaltic action.

Gastric juices also take part in chemical digestion but not completely in an enzymatic way. The contents of gastric juice is mainly pepsin and hydrochloric acid, which are protected from actually damaging the mucosa itself by the action of mucus secreted by cells in the stomach lining. Mechanical digestion takes place in the stomach as well because there is peristalsis that further separates the food boluses into a smooth liquid called chyme.

Chyme enters the duodenum after the pyloric sphincter in the distal part of the stomach opens to let it into the narrower duodenal lumen. Digestive enzymes from both the liver and pancreas act chemically on the chyme constituents to make the food even more digestible. Bile acids primarily act on the fats in the consumed food, while pancreatic enzymes act on the proteins and carbohydrates.

About 95 percent of the digested food is absorbed in the small intestine, with the rest absorbed in the colon. Water and vitamins are mainly absorbed by the large intestine with the help of symbiotic bacteria. In fact, both vitamin K and biotin are made by the symbiotic bacteria in the large intestine and are absorbed there as well. Anything not digested and absorbed is passed as waste through the act of defecation.

There are three main phases of digestion. The cephalic phase is first, followed by the gastric phase and the intestinal phase. The cephalic phase begins before food is even consumed and starts with just thoughts, smells, and the sight of food. This stimulates the medulla oblongata and the hypothalamus in the brain, which send signals by means of the vagus nerve, which releases acetylcholine, triggering the release of gastric acid.

The gastric phase of digestion lasts about three to four hours and is stimulated by food and distention of the stomach. The pH of the stomach is partially buffered by food so the pH isn’t as high as it is during the cephalic phase of digestion. More gastric juices are secreted by the release of acetylcholine, which is the main digestive neurotransmitter involved in the action of the stomach on food.

The intestinal phase of digestion has two separate parts. The first is the excitatory part and the second is the inhibitory part. It begins in the duodenum when food passes through the pyloric sphincter.

Intestinal gastrin is released because of the distention of the duodenum and sympathetic fibers are activated, causing the pyloric sphincter to close so that just the right amount of food leaves the stomach at any given point in time.

Protein digestion happens in both the stomach and the duodenum. There are three main enzymes responsible for this digestion: pepsin, trypsin, and chymotrypsin (with pepsin being the only one that acts in the stomach). Exopeptidases and dipeptidases in the duodenum break down small peptides into amino acids, which are then absorbed by the small intestinal lining. Digestive enzymes from the pancreas are not secreted as complete enzymes but are instead secreted as zymogens (pre-enzymes) that are further modified in the duodenal lumen to become active enzymes.

Fat digestion starts in the mouth with chemical digestion by lingual lipase in the saliva. It breaks down short-chain fatty acids into diglycerides. The rest of fat digestion happens in the small intestines.

Pancreatic lipase helps break down fats and bile acids emulsify fats so they can be better absorbed by the intestinal lining.

9

Carbohydrates start out as starches and are broken down into single sugar molecules, such as glucose, galactose, lactose, and fructose. Salivary and pancreatic amylase are responsible for this digestive process, along with lactase, which breaks down milk sugar (a disaccharide found in dairy products).

Lactose intolerance stems from not making enough lactase. This affects up to 65 percent of US adults, who experience abdominal symptoms when they consume dairy products.

There are several hormones that aid in the digestive process in humans. Gastrin is produced by the stomach, which then secretes pepsinogen (the zymogen of pepsin) and hydrochloric acid by the parietal cells in the stomach wall. Secretin is made in the duodenum and signals sodium bicarbonate secretion in the duodenal lumen. Cholecystokinin is also secreted in the duodenum and triggers the release of pancreatic enzymes/bile acids.

The fat in chyme triggers cholecystokinin to be secreted. GIP or gastric inhibitory peptide is made by the duodenum, causing the induction of insulin secretion and a decrease in stomach peristalsis. Motilin is made in the duodenum, and stimulates both intestinal motility and pepsin production.

The pH of the system plays a big role in digestion. The pH of the mouth, hypopharynx, and esophagus is about 6.8, which is perfect for the activity of salivary amylase, which begins carbohydrate digestion. The acidic environment of the stomach causes denaturation of proteins and acts to kill pathogens that may harm the host. The pH of the duodenum and the rest of the small intestine goes up to accommodate the activity of the enzymes that function inside these parts of the intestinal tract.

Key Takeaways •

The gastrointestinal tract starts with the mouth and ends with the anus.

•

Food is taken in and digested, starting with mouth enzymes, until the molecular components are small enough to be digested.

•

Most of the absorption in the GI tract happens in the small intestine, which has a large absorptive surface area.

•

There are digestive enzymes in the mouth, stomach, and duodenum, which aid in the breakdown of food products.

Quiz 1. A molecule that acts by signaling cells through cell receptors within the same organ but not necessarily next to one another is called what? a. Autocrine b. Intracrine c. Endocrine d. Paracrine Answer: a. Autocrine signaling involves signaling through cell reception within the same organ but not necessarily between cells that are next to one another.

10

2. Ghrelin acts to increase the sensation of hunger in the CNS. What organ of the body is most stimulated by this hormone in order to cause hunger? a. Pituitary gland b. Hypothalamus c. Amygdala d. Parotic glands Answer: b. Ghrelin increases the sensation of hunger by acting on the hypothalamus, which is the center for hunger sensations in the brain.

3. Which GI hormone acts mainly to suppress hunger? a. Ghrelin b. Secretin c. Gastrin d. Cholecystokinin Answer: d. Cholecystokinin does many things in the GI tract, including having the ability to suppress hunger.

4. What is the most distal part of the large intestine in humans? a. Anal canal b. Rectum c. Colon d. Cecum Answer: a. The anal canal is the most distal part of the large intestine in humans.

5. What is the approximate length of the duodenum in humans? a. Ten centimeters b. Fifteen centimeters c. Twenty-five centimeters d. Forty centimeters Answer: c. The duodenum is about twenty-five centimeters in total length in humans.

6. Which part of the GI tract is most involved with the absorption of the various macronutrients consumed by the body? a. Stomach

11

b. Ileum c. Duodenum d. Jejunum Answer: d. The jejunum has a very large surface area (in the mucosa) and is responsible for the absorption of macronutrients. The other structures will be involved in absorption but to a much lesser degree.

7. What is the function of the Brunner glands in the GI tract? a. They secrete digestive enzymes in the small intestine. b. They make an alkaline mucus in the duodenum. c. They secrete an acid substance in the stomach lining. d. They secrete IgA antibodies in the intestinal tract.

Answer: b. The Brunner glands are located in the duodenum and secrete an alkaline mucus that helps the digestive enzymes function better in the duodenal milieu.

8. About what percent of the microbiota of the large intestine is considered healthy bacteria? a. Fifty percent b. Seventy percent c. Eighty percent d. Ninety-nine percent Answer: c. About eighty percent of the bacteria of the large intestine are considered healthy bacteria, with the remaining microorganisms being potentially harmful to the body.

9. There are many diseases that can affect the GI tract. Which is the most common GI disease in the world? a. Colon cancer b. irritable bowel syndrome c. Ulcerative colitis d. Gastroenteritis Answer: d. There are many types of foodborne gastroenteritis, which makes it the most common gastrointestinal disease in the world. It is more common in developing countries where sanitation is poor.

10. Which enzyme acts in the stomach to start the cleavage of proteins into smaller peptides? a. Trypsin

12

b. Chymotrypsin c. Amylase d. Pepsin Answer: d. Pepsin can be found in the stomach and it serves to break down proteins into smaller polypeptides that enter the duodenum for further processing by other enzymes.

13