Ch. 3 part 2

SUMMARY OF CHAPTER 3

3.1 Cells join together to make up tissues, tissues unite to form organs, and organs work together in organ systems. Cells are the basic structural units of the human body. Almost all cells contain the same organelles, but cell structure varies according to the type of job cells must perform. Epithelial, connective, muscle, and nervous tissues are the four primary types of tissues in the human body. Each organ system both affects and is affected by nutrient intake. 3.2 Metabolism refers to all the chemical reactions involved in maintaining life, including the synthesis (anabolism) of new compounds and the breakdown (catabolism) of carbohydrates, fats, and proteins to yield energy in the form of adenosine triphosphate (ATP). Some nutrients (e.g., vitamins and minerals) are important regulators of metabolic reactions. 3.3 From the cells of the GI tract, water-soluble nutrients are absorbed into capillaries and fat-soluble nutrients are absorbed into lymph vessels, which eventually connect to the bloodstream. Blood delivers nutrients and oxygen to cells and picks up waste as it circulates around the body. 3.4 In the urinary system, the kidneys are responsible for filtering the blood, removing body waste, and maintaining the chemical composition of the blood. 3.5 The nervous system allows for communication and regulation. Vitamin B-12 is part of the insulation that surrounds neurons. Transmission of nerve impulses relies on sodium and potassium. Neurotransmitters are made from amino acids. 3.6 The endocrine system produces hormones—protein-based chemical messengers—to regulate metabolic reactions and the levels of nutrients in the blood. 3.7 With assistance from the skin and the gastrointestinal tract, the immune system protects the body from pathogens. Optimal immune system function relies on protein; essential fatty acids; vitamins A, C, and D; some B vitamins; and the minerals iron, zinc, and copper. 3.8 The GI tract consists of the mouth, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus. *Spaced along the GI tract are sphincters that regulate the flow of food matter. Peristalsis is the movement of food matter along the GI tract. Nerves, hormones, and other substances control the activity of sphincters and peristaltic muscles. *Digestive enzymes are secreted by the mouth, stomach, small intestine, and pancreas. Some protein and fat are digested in the stomach. In the large intestine, no further digestion by human enzymes takes place, but bacterial enzymes do break down some dietary components. *The liver, gallbladder, and pancreas participate in digestion and absorption. Enzymes from the pancreas and bile from the liver enter the small intestine and help in digesting protein, fat, and carbohydrate. *Most absorption occurs through the cells of the villi, which line the small intestine. Absorptive processes include passive diffusion, facilitated diffusion, active transport, phagocytosis, and pinocytosis. The large intestine absorbs water, a few minerals, and some products of microbial fermentation. Any remaining undigested materials are eliminated in the feces. 3.9 Limited stores of nutrients are present in the blood for immediate use. Some nutrients, such as minerals and fat-soluble vitamins, can be stored extensively in bone, adipose, and liver tissues. Excessive storage of nutrients can be toxic. Conversely, breakdown of vital tissues can supply nutrients in times of need, but continued breakdown eventually leads to ill health. 3.10 Common GI tract diseases, such as heartburn, constipation, and irritable bowel syndrome, can be treated with a combination of dietary changes and medications.

lipase

Fat-digesting enzyme produced by the salivary glands, stomach, and pancreas.

epiglottis

flap that folds down over the trachea during swallowing.; prevents the bolus of swallowed food from entering the trachea (windpipe)

laxatives

medication or other substance that stimulates evacuation of the intestinal tract.

cecum

pouch at the first part of the large intestine that houses many bacteria.

microbiota

Community of microorganisms living in a particular region; with regard to our discussion of probiotics, the community of microorganisms coexisting on and within the human body. The large intestine is home to a large population of bacteria (over 500 different species) which are collectively called the microbiota.

gastroesophageal reflux disease (GERD)

Disease that results from stomach acid backing up into the esophagus. The acid irritates the lining of the esophagus, causing pain. When suffering from persistent heartburn or GERD, see a doctor if you have difficulty swallowing or pain when swallowing. heartburn that has persisted for more than 10 years. initial onset of heartburn after age 50. heartburn that resists treatment with medications. sudden, unexplained weight loss. chest pain. blood loss or anemia. blood in stool or vomit.

process of swallowing

During swallowing, food lands on the epiglottis, folding it down to cover the opening of the trachea. Breathing also stops automatically. These responses ensure that swallowed food will only travel down the esophagus. If food instead travels down the trachea, choking may occur (the victim will not be able to speak, cough, or breathe).

ulcer

Erosion of the tissue lining, usually in the stomach or the upper small intestine. As a group these are generally referred to as peptic ulcers.

microvilli

Extensive folds on the muscosal surface of the absorptive cells.

mechanical digestion

In the digestive system, food is broken down mechanically and chemically. Mechanical digestion takes place as soon as you begin chewing your food and continues as muscular contractions simultaneously mix and move food through the length of the GI tract.

causes of IBS (difficult to pinpoint!)

It is difficult to pinpoint an exact cause for IBS. Alterations in some of the hormones that regulate the movement of food matter through the GI tract may be to blame. Also, inflammatory responses in the GI tract could be involved for some people with IBS. Recent studies demonstrate alterations in the activity of gut microorganisms in people with IBS. As mentioned in Section 3.8, gut microorganisms produce compounds that affect many body systems. Perhaps IBS leads to changes in the microbiota, or perhaps imbalances in the gut microbiota trigger the range of problems that plague people with IBS.

probiotics

Live microorganisms that, when administered in adequate amounts, confer health benefits on the host. find these probiotic microorganisms in some forms of fluid milk, fermented milk, and yogurt, and in pill form

facilitated diffusion

Movement of a substance across a semipermeable membrane from an area of higher solute concentration to an area of lower solute concentration. This type of transport does not require energy, but it does require a carrier. Some compounds require a carrier protein to follow a concentration gradient into absorptive cells. This type of absorption is called facilitated diffusion. Fructose is one example of a compound that makes use of such a carrier to allow for facilitated diffusion.

large intestine

Physiologically, the large intestine differs from the small intestine in that there are no villi or digestive enzymes. The absence of villi means that little absorption takes place in the large intestine in comparison to the small intestine. Nutrients absorbed from the large intestine include water, some vitamins, some fatty acids, and the minerals sodium and potassium. Unlike the small intestine, the large intestine has a number of mucus-producing cells. The mucus secreted by these cells functions to hold the feces together and protect the large intestine from the bacterial activity within it.

gluten

Poorly digested protein found in wheat, barley, and rye. for those who have celiac disease or gluten sensitivity Gluten is a type of protein found in certain grains: wheat, rye, and barley.

digestion

Process by which large ingested molecules are mechanically and chemically broken down to produce basic nutrients that can be absorbed across the wall of the GI tract.

digestive system

System consisting of the gastrointestinal tract and accessory structures (liver, gallbladder, and pancreas). This system performs the mechanical and chemical processes of digestion, absorption of nutrients, and elimination of wastes. provide us with usable nutrients. The processes of digestion and absorption take place in a long tube that is open at both ends and extends from the mouth to the anus. This tube is called the gastrointestinal (GI) tract (Fig. 3-9). The open space inside the GI tract is called the lumen.

culprits, causes, risk factors of IBS

The majority of people who suffer from IBS perceive that their symptoms are related to food, but there is little evidence of actual food allergies or intolerances. When it comes to specific foods, poorly digested carbohydrates are a prime suspect (see the discussion of FODMAPs in "What the Dietitian Chose" at the end of this chapter).9, 10 Fructose, sugar alcohols, and other carbohydrates may lead to diarrhea or excessive gas if they reach the large intestine undigested. Depression and stress are also associated with IBS; up to 50% of sufferers report a history of verbal or sexual abuse.

pharynx

The organ of the digestive tract and respiratory tract located at the back of the oral and nasal cavities, commonly known as the throat.

causes of constipation

There are many possible causes for constipation. The muscular movement of feces through the GI tract is regulated by neurological and hormonal signals, so disorders of the nervous system or muscular function could alter bowel motility. A physical obstruction in the GI tract could also be to blame. Constipation may be a side effect of certain medications (e.g., antacids) or dietary supplements (e.g., iron or calcium). More often, however, constipation arises due to inadequate dietary fiber and/or fluid intake or poor toileting habits.

saliva

Watery fluid, produced by the salivary glands in the mouth, which contains lubricants, enzymes, and other substances

gastric juice

While in the stomach, the food is mixed with gastric juice, which contains water, hydrochloric acid, and enzymes. (Gastric is a term pertaining to the stomach.) The acid in the gastric juice halts the biological activity of proteins, converts inactive digestive enzymes to their active form, partially digests food protein, and makes dietary minerals soluble so that they can be absorbed.

trachea

airway that extends from the throat, down the neck, to the lungs. Also called the windpipe.

peristalsis

coordinated muscular contraction used to propel food down the gastrointestinal tract.

lumen

hollow opening inside a tube, such as the GI tract

jejunum

middle segment of the small intestine; approximately 4 feet in length

irritable bowel syndrome (IBS)

An estimated 10% to 15% of adults have irritable bowel syndrome (IBS), characterized by a combination of bloating, abdominal pain, and irregular bowel function (diarrhea, constipation, or alternating episodes of both). It is about twice as common in women as it is in men. The disease leads to about 3.5 million visits to primary care providers in the United States each year. Although it does not lead to cancer or other serious digestive problems, the physical discomfort and anxiety of IBS can significantly impact quality of life.

gallbladder

An organ attached to the underside of the liver; site of bile storage, concentration, and eventual secretion. The liver, gallbladder, and pancreas work with the GI tract and are considered accessory organs to the process of digestion (review Fig. 3-9). These accessory organs are not part of the GI tract through which food passes, but they play necessary roles in the process of digestion. These organs secrete digestive fluids into the GI tract and facilitate the digestion of food into absorbable nutrients.

proton pump inhibitors (PPIs)

A medication that inhibits the ability of gastric cells to produce acid. Proton pump inhibitors (PPIs) are medications that inhibit the ability of gastric cells to secrete hydrogen ions and thus reduce acid production. Low doses of this class of medications may be available without a prescription. Because stomach acid is important for the absorption of vitamin B-12, prolonged use of PPIs could impair vitamin B-12 status. Examples: Omeprazole (Prilosec®) Lansoprazole (Prevacid®) Rabeprazole (Aciphex®) Esomeprazole (Nexium®)

pinocytosis

A process in which a cell forms an indentation, and fluid enters the indentation and is engulfed by the cell.

absorptive cells

Also known as enterocytes; the intestinal cells that line the villi and participate in nutrient absorption Each individual villus (singular) is made up of many absorptive cells (also called enterocytes), and the mucosal surface of each of these cells is folded even further into microvilli. T

chemical digestion

Chemical digestion refers to the chemical breakdown of foods by acid and enzymes secreted into the GI tract. Enzymes are a key part of digestion. Each enzyme is specific to one type of chemical process. organs of the digestive system are able to fine-tune the production of each type of digestive enzyme in response to the nutritional makeup and amount of food consumed. Overall, the enzymes of the digestive system work together to hasten the breakdown of ingested food into absorbable nutrients

H2 blockers

H2 blockers impede the stimulating effect of histamine on acid-producing cells in the stomach. Examples: Cimetidine (Tagamet®) Nizatidine (Axid®) Famotidine (Pepcid®)

symptoms of hemorrhoids

Hemorrhoids can develop unnoticed until a strained bowel movement precipitates symptoms. Itching (caused by moisture in the anal canal), swelling, and irritation are the most common symptoms. Pain, if present, is usually aching and steady. Bleeding may result from a hemorrhoid and appear in the toilet as a bright red streak in the feces. The sensation of a mass in the anal canal after a bowel movement is a symptom of an internal hemorrhoid that protrudes through the anus.

diagnosis of celiac disease

If celiac disease is suspected, the first step in making a formal diagnosis is a blood test for the presence of antibodies to gluten. This may be followed by one or more biopsies of the small intestine to confirm the pathological defects. There is also a genetic test for celiac disease, but having the gene does not always predict development of the disease.

causes of gallstones

These stones are caused by a combination of factors, with excess weight being the primary modifiable risk factor, especially among women. Other factors include genetic background (e.g., Native Americans), advanced age (> 60 years), pregnancy, reduced activity of the gallbladder (contracts less than normal), altered bile composition (e.g., too much cholesterol or not enough bile salts), diabetes, and eating pattern (e.g., low-fiber diets). In addition, gallstones may develop during rapid weight loss or prolonged fasting (as the liver metabolizes more fat, it secretes more cholesterol into the bile).

villi

fingerlike protrusions into the small intestine that participate in digestion and absorption of food. The lining of the small intestine is called the mucosa and is folded many times; within these folds are fingerlike projections called villi. These "fingers" are constantly moving, which helps them trap food to enhance absorption.

esophagus

tube in the GI tract that connects the pharynx with the stomach. no digestion or absorption occurs in the esophagus; it serves merely to transport food from the mouth to the stomach. The cells of the esophagus secrete mucus to lubricate the passage of food, but no digestive enzymes are produced.

pyloric sphincter

Ring of smooth muscle between the stomach and the small intestine. located at the base of the stomach, controls the rate at which the chyme is released into the small intestine (Fig. 3-13). There is very little absorption of nutrients from the stomach, except for some water and alcohol.

transverse colon

Segment of the large intestine that carries feces from the ascending colon, from right to left across the top of the abdomen, to the descending colon.

primary nutrients absorbed in large intestine

Sodium Potassium Some fatty acids Gases Water (10% to 30% of total)

sigmoid colon

Last segment of the large intestine that carries feces from the descending colon to the rectum.

NSAIDS

NSAIDs Nonsteroidal anti-inflammatory drugs; include aspirin, ibuprofen (Advil®), and naproxen (Aleve®).

umami

brothy, meaty, savory flavor in some foods. Monosodium glutamate enhances this flavor when added to foods.

Diarrhea

increased fluidity, frequency, or amount of bowel movements (i.e., three or more loose stools per day). defined as increased fluidity, frequency, or amount of bowel movements compared to a person's usual pattern. Most cases of diarrhea are of short duration and result from viral or bacterial infections. These microorganisms produce substances that cause the intestinal cells to secrete fluid rather than absorb fluid. Another form of diarrhea can be caused by consumption of substances that are not readily absorbed, such as sorbitol, a sugar alcohol found in sugarless gum (see Section 4.3) or large amounts of a high-fiber source such as bran. When consumed in large amounts, the unabsorbed substance draws water into the intestines, leading to diarrhea.

small intestine

. Most of the digestion and absorption of food occurs in the small intestine. As chyme moves from the stomach into the first part of the small intestine, it is still very acidic. r, if the small intestine were coated with mucus, digestion and absorption would be very limited. Therefore, the pancreas and intestinal cells secrete bicarbonate to neutralize the acid. The neutral pH also optimizes the activity of the digestive enzymes that work in the small intestine. Muscular contractions move the chyme through the small intestine and thoroughly mix food particles with digestive juices (review Fig. 3-12). These juices contain many enzymes that break down carbohydrates, protein, and fat into absorbable units. The combined folds, villi, and microvilli in the small intestine increase its surface area 600 times beyond that of a simple tube has a smaller diameter than the large intestine but is actually longer in length than the large intestine

treatment of hemorrhoids

A physician may suggest a variety of self-care measures for hemorrhoids. Pain can be lessened by applying warm, soft compresses or sitting in a tub of warm water for 15 to 20 minutes. Dietary recommendations are the same as those for treating constipation, emphasizing the need to consume adequate fiber and fluid. Over-the-counter remedies, such as Preparation H®, can also offer relief from symptoms.

heartburn treatment

If left untreated, heartburn can damage the lining of the esophagus, leading to chronic esophageal inflammation and an increased risk of esophageal cancer. Heartburn sufferers should follow the general recommendations given in Table 3-4. For occasional heartburn, quick relief can be found with over-the-counter antacids. Taking antacids will reduce the acid in the stomach but will not stop the acid reflux. For more persistent (few days a week or everyday) heartburn or GERD, H2 blockers or proton pump inhibitors (PPIs) may be needed (see the "Medicine Cabinet" feature in this section). PPIs provide long-lasting relief by reducing stomach acid production and should be taken before the first meal of the day because they take longer to work. Medications that improve GI motility may also be useful. If the proper medications are not effective at controlling GERD, surgery may be needed to strengthen the weakened esophageal sphincter

absorption of nutrients

Once absorbed, water-soluble compounds such as glucose and amino acids are transported by the capillaries to the hepatic portal vein, which leads directly to the liver. Most fats are absorbed into the lymph vessels, which eventually empty into the bloodstream Any undigested food that reaches the end of the small intestine must pass through the ileocecal sphincter on the way to the large intestine. This sphincter prevents the contents of the large intestine from reentering the small intestine.

descending colon

Segment of the large intestine that carries feces from the transverse colon, down the left side of the abdomen, to the sigmoid colon.

prebiotic

Selectively fermented ingredient that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefits upon the host. Prebiotics are substances that increase growth of probiotic microorganisms. One example is fructooligosaccharides

amylase

Starch-digesting enzyme produced by the salivary glands and the pancreas.

duodenum

First segment of the small intestine that receives chyme from the stomach and digestive juices from the pancreas and gallbladder. This is the site of most chemical digestion of nutrients; approximately 10 inches in length. first 10 in of the small intestine

lower esophageal sphincter

circular muscle that constricts the opening of the esophagus to the stomach after food enters the stomach. Also called the gastroesophageal sphincter or the cardiac sphincter.

constipation

condition characterized by difficult and/or infrequent bowel movements (i.e., fewer than three bowel movements per week). Individuals vary, but in general, normal bowel frequency ranges from three times per day to three times per week. Constipation, a condition characterized by difficult or infrequent evacuation of the bowels, is commonly reported by adults. As you learned in Section 3.8, the primary role of the large intestine is to absorb fluid. If fecal material moves too slowly through the large intestine, so much fluid is absorbed that the feces become dry, hard, and difficult to pass.

mouth

. Besides chewing food to reduce it to smaller particles, the mouth also senses the taste of the foods we consume. The tongue, through the use of its taste buds, identifies foods on the basis of their specific flavor(s). Sweet, sour, salty, bitter, umami, and oleogustus comprise the primary taste sensations we experience.

symptoms and complaints of celiac disease

. Malabsorption leads to a variety of GI complaints: diarrhea, bloating, cramps, and flatulence. In fact, it is common for celiac disease to be misdiagnosed as IBS. However, the pathology underlying celiac disease has far worse consequences than IBS. Over time, malabsorption of nutrients can lead to fatigue, weight loss (or poor growth in children), anemia, infertility, and even bone loss

bile acids

A compound produced by the liver. Bile acids are the main component of bile, which aids in emulsification of fat during digestion in the small intestine.

enterohepatic circulation

A continual recycling of compounds such as bile acids between the small intestine and the liver. Interestingly, some of the bile constituents can be "recycled" in a process known as enterohepatic circulation: components of bile are reabsorbed from the small intestine, returned to the liver via the portal vein, and reused.

anal sphincters

A group of two sphincters (inner and outer) that help control expulsion of feces from the body

perforation

A hole made by boring or piercing. With reference to the gastrointestinal tract, the hole is in the wall of the esophagus, stomach, intestine, rectum, or gallbladder. Complications include bleeding and infection.

bile

A liver secretion stored in the gallbladder and released through the common bile duct into the first segment of the small intestine. It is essential for the digestion and absorption of fat. . Components of the bile enable large portions of fat to break into smaller bits so that they can be suspended in water

more ulcer stuff

A peptic ulcer occurs when the lining of the esophagus, stomach, or small intestine is eroded by the acid secreted by stomach cells (Fig. 3-19). A disruption of the layer of mucus that usually protects the stomach allows acid and protein-digesting enzymes to damage the stomach lining. Acid can also erode the lining of the esophagus and the first part of the small intestine, the duodenum. This can cause pain, blood loss, and even perforation. At any given time, about 4.5 million people in the United States are affected by peptic ulcers. In young people, most ulcers occur in the small intestine, whereas in older people, they are most common in the stomach. How do you know if you have a peptic ulcer? Some people experience no symptoms at all, but most notice stomach pain about 2 hours after eating. Stomach acid acting on a meal irritates the ulcer after most of the meal has moved from the site of the ulcer. Other symptoms may include weight loss, lack of appetite, nausea and vomiting, or bloating. Vomiting blood or what looks like coffee grounds and the appearance of black, tarry stools are signs of bleeding in the GI tract. Any evidence of GI bleeding warrants immediate medical attention.

mucus

A thick fluid secreted by many cells throughout the body. It contains a compound that has both carbohydrate and protein parts. It acts as a lubricant and means of protection for cells.

heartburn

About half of North American adults experience occasional heartburn, also known as acid reflux (Fig. 3-18). This gnawing pain in the upper chest is caused by the movement of acid from the stomach into the esophagus. Unlike the stomach, the esophagus has very little mucus to protect it, so acid quickly erodes the lining of this organ. Acid reflux symptoms may include pain, nausea, gagging, cough, or hoarseness. The recurrent and therefore more serious form of the problem is called gastroesophageal reflux disease (GERD). GERD is diagnosed when symptoms occur two or more times per week. Heartburn is caused by relaxation of the gastroesophageal sphincter. Typically, it should be relaxed only during swallowing, but in individuals with GERD, it is relaxed at other times as well. Increased pressure against the lower esophageal sphincter (e.g., as a result of pregnancy or obesity) heightens risk for heartburn. The hormonal changes of pregnancy also tend to relax the lower esophageal sphincter. For some people, slow movement of gastric contents from the stomach to the small intestine complicates the problem.

primary nutrients absorbed in stomach

Alcohol (20% of total) Water (minor amount)

causes and risk factors of hemorrhoids

Anyone can develop a hemorrhoid, and about half of adults over age 50 do. Diet, lifestyle, and heredity may contribute to the problem. For example, a low-fiber diet can lead to hemorrhoids as a result of straining during bowel movements. If you think you have a hemorrhoid, you should consult your primary care provider. Rectal bleeding, although usually caused by hemorrhoids, may also indicate other problems, such as cancer.

prevention and treatment of gallstones

Attacks due to gallstones are characterized by intermittent pain in the upper right abdomen, gas and bloating, nausea or vomiting, or other health problems. Medications are available to dissolve gallstones, but these take a long time to work, and the recurrence of gallstones after therapy is common. Therefore, surgical removal of the gallbladder is the most common method for treating gallstones (500,000 surgeries per year in the United States). The best prevention strategy is to avoid becoming overweight, especially for women. Avoiding rapid weight loss (> 3 pounds per week), limiting animal protein and focusing more on plant protein intake (especially nuts), and following a high-fiber diet can help as well. Regular physical activity is also recommended, as are moderate to no caffeine and alcohol intake

primary nutrients absorbed in small intestine

Calcium, magnesium, iron, and other minerals Glucose Amino acids Fats Vitamins Water (70% to 90% of total) Alcohol (80% of total) Bile acids

how stomach prevents itself from being digested by the acid and enzymes it produces

First, the stomach has a thick layer of mucus that lines and protects it. Second, the production of acid and enzymes also requires the release of a specific hormone (gastrin). This release happens primarily when we are eating or thinking about eating. Last, as the concentration of acid in the stomach increases, hormonal control causes acid production to taper off.

other treatments for diarrhea

For diarrhea caused by infection, dietary changes (besides increased fluid intake) are usually not necessary. Some health care providers recommend temporarily decreasing intake of caffeine, fat, fiber, and poorly absorbed carbohydrates, but other sources show that maintaining a regular diet speeds recovery. Foods containing probiotics may assist recovery. For diarrhea caused by a poorly absorbed substance, such as excess sugar alcohols or lactose, avoidance of the offending substance is the key to relief.12

gluten-free diet (ASK THE RDN!)

For individuals with celiac disease and nonceliac wheat sensitivity, avoiding gluten is a health priority. It will likely correct gastrointestinal complications and a range of other symptoms such as fatigue and body pain. Weight loss, however, is not one of the benefits of a gluten-free diet. only reason a gluten-free diet might induce weight loss is because it can be restrictive. For the person who regularly overconsumes bread, pasta, pizza, and baked goods, eliminating all sources of gluten could limit these food choices, thus leading to weight loss. Important point: Weight loss is the result of a calorie deficit, not the lack of gluten. Now, with the increased availability of gluten-free options in grocery stores and restaurants, you will soon realize that a gluten-free diet may not be that restrictive after all. you may actually gain weight on a gluten-free diet. For a person with celiac disease, as the small intestine heals, nutrient absorption will increase and appetite will likely improve. In addition, many gluten-free products contain more calories than their wheat-based counterparts. To compensate for losses of taste and texture, some gluten-free products incorporate extra fat or sugar. For example, a typical slice of whole-grain wheat bread is about 80 kcal; some brands of gluten-free bread provide as many as 140 kcal per slice. Keep in mind that the "Gluten-Free" claim does not make a food healthy! grains are an important part of a balanced eating pattern. They provide calories, of course, but they also supply dietary fiber and essential vitamins and minerals. Wheat flour is fortified with thiamin, niacin, riboflavin, folic acid, and iron. So, if you are planning to try a gluten-free diet, work with a registered dietitian nutritionist to ensure that your eating pattern meets your nutrient needs. Choose whole gluten-free grains and unprocessed fruits and vegetables to replace wheat and balance calories to avoid weight gain.

gallstones

Gallstones are a major cause of illness and surgery, affecting 10% to 20% of U.S. adults. Gallstones are pieces of solid material that develop in the gallbladder when substances in the bile—primarily cholesterol (80% of gallstones)—form crystal-like particles. They may be as small as a grain of sand or as large as a golf ball

motility

Generally, the ability to move spontaneously. In this context, it refers to movement of food through the GI tract.

treatment of IBS

Given the diversity of symptoms and possible causes, therapy must be individualized. Medications that target nerves or alter the bacterial population in the GI tract may help people who suffer from frequent diarrhea. For IBS patients whose primary complaint is constipation, medications are available to stimulate peristalsis or block abdominal pain. Medications may be expensive, and some have side effects. Therefore, dietary strategies to cope with IBS are of great interest. At least half of patients with IBS experience improvements with a low-FODMAP dietary pattern. For several weeks, they eliminate (or greatly reduce) their intake of foods containing FODMAPs, including wheat, onions, legumes, and dairy products. Then, foods are gradually added back to the dietary pattern to determine which can be tolerated and which should be avoided long term. Probiotics and peppermint oil have been shown to decrease symptoms of IBS and improve overall quality of life.11 The patient should limit or eliminate caffeine-containing foods and beverages. Low-fat and more frequent, small meals may help because large meals can trigger contractions of the large intestine. Other strategies include a reduction in stress, psychological counseling, and antidepressant medications. Hypnosis has been shown to relieve symptoms in severe cases. Following an eating pattern that eliminates certain foods or entire food groups can limit nutritional adequacy. Indeed, research indicates that intakes of some nutrients, including calcium and vitamin A, are inadequate among people with IBS. An experienced registered dietitian nutritionist is a valuable resource to help a person with IBS identify problem foods and plan a nutritionally adequate dietary pattern.

treatment/management of celiac disease

If celiac disease is suspected, the first step in making a formal diagnosis is a blood test for the presence of antibodies to gluten. This may be followed by one or more biopsies of the small intestine to confirm the pathological defects. There is also a genetic test for celiac disease, but having the gene does not always predict development of the disease. Strict dietary avoidance of food products containing wheat, rye, and barley is the only proven way to manage the disease.15 On food labels, food manufacturers must identify the presence of wheat (one of eight major food allergens). However, rye and barley are not as easy to spot. Therefore, people following a gluten-free diet must learn to carefully interpret the list of ingredients to identify sources of gluten. Within the grains group, rice, potato flour, cornmeal, buckwheat, arrowroot, and soy are gluten free, but ingredients such as wheat, rye, barley, bran, graham flour, semolina, spelt, and malt are sources of gluten and must be avoided. Oats do not traditionally contain gluten, but contamination in the field or during food processing could introduce gluten into this grain as well. People with celiac disease quickly learn that wheat, barley, and rye can be hidden ingredients in any food group. Wheat and its derivatives are used to thicken sauces and condiments, as flavoring agents in dairy products and many other processed foods, and in breading for deep-fried vegetables and meats. It is helpful that many food manufacturers now voluntarily disclose the presence or absence of gluten in their products. However, not all products clearly identify gluten. Dining out is yet another challenge: even a dusting of wheat flour can have adverse effects for a person with celiac disease. After several weeks on a gluten-free diet, the small intestine lining regenerates, GI symptoms subside, and nutrient absorption improves. So far, the gluten-free diet is the only proven way to manage celiac disease, but research on other treatments is underway. Food scientists are working toward developing strains of wheat, barley, and rye that do not contain gluten. From a gastroenterological perspective, other approaches are to supply digestive enzymes that will break down the gluten proteins before they stimulate an autoimmune response and to use polymers that will bind to gluten in the GI tract and prevent it from being absorbed. From an immunological perspective, researchers are looking at medications that could block immune responses that damage the small intestine.

phagocytosis and pinocytosis:

In a further means of active absorption, absorptive cells literally engulf compounds (phagocytosis) or liquids (pinocytosis). A cell membrane forms an indentation and when particles or fluids move into the indentation, the cell membrane surrounds and engulfs them. This process is used when an infant absorbs immune substances from human milk

liver stuff

In addition to bile, the liver releases a number of other substances that travel with the bile to the gallbladder and end up in the small intestine and eventually in the large intestine for excretion. The liver functions in this manner to remove unwanted substances from the blood.

treatment of constipation

Increasing dietary intakes of fiber and fluid are usually safe and effective strategies for treating mild cases of constipation.7 Whole grain breads and cereals, beans, and dried fruits are excellent sources of fiber. Fiber stimulates peristalsis by drawing water into the large intestine and helping to form a bulky, soft fecal output. Additional fluid should be consumed to facilitate fiber's action in the large intestine. Also, people with constipation may need to develop more regular bowel habits. When people regularly ignore their normal bowel reflexes (e.g., because it is inconvenient to interrupt occupational or social activities), feces can become hard and dry. Allowing the same time each day for a bowel movement can help to train the large intestine to respond routinely. Regular physical activity can also stimulate the GI tract to function normally.8 In more severe cases, laxatives can alleviate constipation. Some laxatives work by irritating the intestinal nerve junctions to stimulate peristalsis, while others that contain fiber draw water into the intestine to enlarge fecal output. The larger output stretches the peristaltic muscles, making them rebound and then constrict. Regular use of laxatives, however, should be supervised by a primary care provider. Overall, if laxatives are necessary, the bulk-forming fiber laxatives, such as psyllium husk, are the safest to use.8

anus

Last portion of the GI tract; serves as an outlet for the digestive system.

ileum

Last segment of the small intestine; approximately 5 feet in length.

feces

Mass of water, fiber, tough connective tissues, bacterial cells, and sloughed intestinal cells that passes through the large intestine and is excreted through the anus; also called stool. What remains in the feces, besides water and undigested fiber, is tough connective tissues (from animal foods); bacteria from the large intestine; and some body wastes, such as parts of dead intestinal cells.

psyllium

Mostly soluble type of dietary fiber found in the seeds of the plantago plant; common ingredient in bulk-forming laxatives, such as Metamucil®.

passive diffusion

Movement of a substance across a semipermeable membrane from an area of higher solute concentration to an area of lower solute concentration. This type of transport does not require a carrier and does not require energy. When the nutrient concentration is higher in the lumen of the small intestine than in the absorptive cells, the difference in nutrient concentration drives the nutrient into the absorptive cells by diffusion. Fats, water, and some minerals are examples of nutrients that move down a concentration gradient to be absorbed by passive diffusion.

active absorption

Movement of a substance across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This type of transport requires energy and a carrier In addition to the need for a carrier protein, some nutrients also require energy input to move from the lumen of the small intestine into the absorptive cells. This mechanism makes it possible for cells to take up nutrients even when they are consumed in low concentrations (i.e., against a concentration gradient). Some sugars, such as glucose, are actively absorbed, as are amino acids.

treatment of peptic ulcers

Nonsteroidal anti-inflammatory drugs (NSAIDs) are medications for painful inflammatory conditions such as arthritis. Aspirin, ibuprofen, and naproxen are the most commonly used types. NSAIDs reduce the mucus secreted by the stomach. Newer medications, called "COX-2 inhibitors" (e.g., celecoxib [Celebrex®]), have been used as a replacement for NSAIDs because they are less likely to cause stomach ulcers. They do offer some advantages over NSAIDs, but they may not be totally safe for some people, especially those with a history of cardiovascular disease or strokes. The primary risk associated with an ulcer is the possibility that it will erode entirely through the stomach or intestinal wall. The GI contents could then spill into the body cavities, causing a massive infection. In addition, an ulcer may damage a blood vessel, leading to substantial blood loss. For these reasons, it is important to never ignore the early warning signs of ulcer development, which include a persistent gnawing or burning near the stomach that may occur immediately following a meal or awaken you at night. Today, a combination approach is used for ulcer therapy.6 People infected with H. pylori are given antibiotics and stomach acid-blocking medications (see the "Medicine Cabinet" feature in this section). There is a 90% cure rate for H. pylori infections in the first week of this treatment. Recurrence is unlikely if the infection is cured, but an incomplete cure almost certainly leads to repeated ulcer formation. Are dietary changes effective for prevention or treatment of peptic ulcers? Many people think that eating spicy or acidic foods can cause ulcers. Contrary to popular belief, these foods do not cause ulcers. However, once an ulcer has developed, these foods may irritate damaged tissues. Thus, for some people, avoidance of spicy or acidic foods may help to relieve symptoms. In the past, milk and cream were thought to help cure ulcers. Clinicians now know that milk and cream are two of the worst foods for a person with ulcers because the calcium in these foods stimulates acid secretion and actually inhibits ulcer healing. Overall, medical treatment of H. pylori infection has so revolutionized ulcer therapy that dietary changes are of minor importance. People with ulcers should refrain from smoking and minimize the use of NSAIDs. Current dietary therapy approaches simply recommend avoidance of foods that tend to worsen ulcer symptoms

celiac disease and NCWS trends for future

Overall, the prevalence and awareness of celiac disease and NCWS seem to be on the rise. A cause for the increased prevalence has not been pinpointed, but some scientists speculate that changes in wheat production or widespread use of wheat in the food supply may be to blame. Others suspect that an infection or exposure to some environmental toxin could lead to gluten sensitization.

ascending colon

Segment of the large intestine that carries feces from the cecum, up the right side of the abdomen, to the transverse colon.

rectum

Terminal section of the large intestine where feces are held prior to expulsion. feces or stool remains in the last portion of the large intestine, the rectum, until muscular movements push it into the anus to be eliminated. The presence of feces in the rectum stimulates elimination. The anus contains two anal sphincters (internal and external), one of which is under voluntary control (external sphincter). Relaxation of this sphincter allows for elimination

the immune response of celiac disease

The autoimmune response that occurs after exposure to gluten targets the cells of the small intestine, causing a flattening of the villi, which thereby reduces the absorptive surface (Fig. 3-21). The production of some digestive enzymes is decreased, and the ability of the small intestine to absorb nutrients is impaired

summary of these digestive disorders

The conditions discussed here can be very serious, possibly leading to malnutrition, internal bleeding, and life-threatening infections. It is important to seek competent medical advice if you or someone you know suspects a GI disorder. However, you should feel empowered to know that you can control some risks and complement medical treatment with nutrition and other lifestyle changes. Overall, keeping body weight within a healthy range, meeting recommendations for fiber and fluid intake, and avoiding tobacco and overuse of NSAID medications are useful strategies that can help you cope with several common disorders of the GI tract.

pancreas

The pancreas has both endocrine and digestive functions. As a gland of the endocrine system, the pancreas manufactures hormones—insulin and glucagon—that are secreted into the blood to regulate blood glucose levels (review Fig. 3-8). As an organ of the digestive system, it produces "pancreatic juice," a mixture of water, bicarbonate, and a variety of digestive enzymes capable of breaking apart carbohydrates, proteins, and fats into small fragments. Bicarbonate is a base that neutralizes the acidic chyme as it moves from the stomach into the duodenum. As noted earlier, the small intestine does not have a protective layer of mucus because mucus would impede nutrient absorption. Instead, the neutralizing capacity of bicarbonate from the pancreas protects the walls of the small intestine from erosion by acid, which would otherwise lead to the formation of an ulcer

absorption

The process by which substances are taken up from the GI tract and enter the bloodstream or the lymph.

ileocecal sphincter

The ring of smooth muscle between the end of the small intestine and the beginning of the large intestine.

strains of bacteria

The strains bifidobacteria and lactobacilli are typically associated with health, whereas clostridia are considered problematic. Some of the products of bacterial metabolism in the large intestine, which include various fatty acids and gases, can be absorbed and exert health effects in other areas of the body. Foods containing certain live microorganisms, such as lactobacilli, have been linked to some health benefits, such as improving intestinal-tract health. These microorganisms are called probiotics because, once consumed, they take up residence in the large intestine and confer health benefits

causes of peptic ulcers

The two chief culprits of peptic ulcer disease are infection of the stomach by the acid-resistant bacteria Helicobacter pylori (H. pylori) and heavy use of medications that impair mucus production by the stomach. Conditions that cause excessive stomach acid production also play a role. In addition, cigarette smoking is known to cause ulcers, increase ulcer complications such as bleeding, and lead to ulcer treatment failure. H. pylori bacteria is found in more than 80% of patients with stomach and duodenal ulcers.5 The bacteria is common but results in ulcer disease in only 10% to 15% of those infected. Although the mechanism by which H. pylori causes ulcers is not well understood, treatment of the infection with antibiotics heals the ulcers and prevents their recurrence. Two Australian physicians were awarded the Nobel Prize in 2005 "for their discovery of the bacterium H. pylori and its role in gastritis and peptic ulcer disease."

Celiac disease (sometimes called celiac sprue)

affects about 1% of the U.S. population. Development of celiac disease depends on two factors: a genetic predisposition and dietary exposure to a protein called gluten. Protein-digesting enzymes in the GI tract break down some of the bonds in gluten, but digestion is incomplete. These partially digested proteins can be absorbed into the cells lining the small intestine. When people with a genetic predisposition for celiac disease are exposed to these small proteins from gluten, they experience an inflammatory reaction. Although many people think celiac disease is a food allergy, it is actually an autoimmune response: the immune system attacks and destroys its own cells.

intervention for diarrhea

goal of nutrition therapy for any form of diarrhea is to prevent dehydration. Increasing intake of water and electrolytes is the first line of defense against dehydration. Prompt treatment of dehydration—within 24 to 48 hours—is critical, especially for infants and older adults (see Section 19.2 and Section 20.2). Diarrhea that lasts more than 7 days in adults should be investigated by a primary care provider as it can be a sign of a more serious intestinal disease, especially if there is also blood in the stool.

chyme

mixture of stomach secretions and partially digested food. mixing that takes place in the stomach produces a watery food mixture, called chyme, which slowly leaves the stomach a teaspoon (5 milliliters) at a time and enters the small intestine. Following a meal, the stomach contents are emptied into the small intestine over the course of 1 to 4 hours.

mucus

site of production: Mouth, esophagus, stomach, small intestine, large intestine purpose: Protects GI tract cells Lubricates food as it travels through the GI tract

enzymes

site of production: Mouth, stomach, small intestine, pancreas purpose: Promote digestion of carbohydrates, fats, and proteins into forms small enough for absorption (examples: amylases, lipases, proteases)

hormones

site of production: Stomach, small intestine, pancreas purpose: Stimulate production and/or release of acid, enzymes, bile, and bicarbonate Help regulate movement of food matter through the GI tract

bile

site of production: liver (stored in gallbladder) purpose: Aids fat digestion in the small intestine by suspending fat in water using bile acids, cholesterol, and phospholipids

saliva

site of production: mouth purpose: Contains enzymes that make a minor contribution to starch and fat digestion Lubrication of food for swallowing

bicarbonate

site of production: pancreas, small intestine purpose: Neutralizes stomach acid when it reaches the small intestine

intrinsic factor

site of production: stomach purpose: Facilitates absorption of vitamin B-12 in the small intestine

acid

site of production: stomach purpose: Promotes digestion of protein Destroys pathogens Solubilizes some minerals Activates some enzymes

nonceliac wheat sensitivity (NCWS)

sometimes called gluten sensitivity or gluten intolerance. Some people experience symptoms of celiac disease after ingestion of gluten, but they do not have the small intestine pathology of celiac disease, nor do they express the antibodies typical of celiac disease. One or more of a variety of immune-related conditions with symptoms similar to celiac disease that are precipitated by the ingestion of gluten in people who do not have celiac disease. Some reports indicate that for each person who is diagnosed with celiac disease, as many as six others have NCWS. Aside from GI symptoms, patients with NCWS may also report fatigue, headache, muscle and joint pain, and/or sleep disorders. Symptoms subside with a gluten-free diet but reappear when gluten is reintroduced. The medical community recognizes NCWS as a verifiable condition, but the immunological mechanism that causes it is not well understood. There is no diagnostic test for the condition at this time—only the effectiveness of the gluten-free diet in alleviating symptoms. Many questions remain: Is NCWS a permanent condition? Is there a level of gluten intake that would not trigger symptoms? It seems that there are multiple immunological reactions to gluten that are predicted by different genetic traits.

Hemorrhoids (piles)

swollen vein in the rectum or anus. Hemorrhoids, also called piles, are swollen veins of the rectum and anus. The blood vessels in this area are subject to intense pressure, especially during bowel movements. Added stress to the vessels from pregnancy, obesity, prolonged sitting, violent coughing or sneezing, or straining during bowel movements (particularly with constipation) can lead to a hemorrhoid.

oleogustus

taste for fat. The presence of fatty acids in foods stimulates taste receptors in the mouth; this sensation is unpleasant.

stimuli for digestion of food

taste of food, or the anticipation of it, signals the rest of the GI tract to prepare for the digestion of food. Once in the mouth, mechanical and chemical digestion begins. Salivary glands produce saliva, which functions as a solvent so that food particles can be further separated and tasted. In addition, saliva contains a starch-digesting enzyme, salivary amylase (see Section 4.4 for more on starch-digesting enzymes) and a fat-digesting enzyme, lipase (see Section 5.4). Mucus, another component of saliva, is a lubricant that makes it easier to swallow a mouthful of food. The food then travels to the esophagus.

gastrointestinal (GI) tract

the main sites in the body used for digestion and absorption of nutrients. It consists of the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Also called the digestive tract.

more on small intestine absorption

the small intestine absorbs only 70% to 90% of the fluid it receives, which includes large amounts of GI-tract secretions produced during digestion (Table 3-3). The remnants of a meal also contain some minerals and some fiber. Because water is removed from the large intestine, its contents become semisolid by the time they have passed through the first two-thirds of it