What are some different parts of the body that you think might belong to the digestive system that might cause discomfort if not treated properly?

What are some different parts of the body that you think might belong to the digestive system that might cause discomfort if not treated properly?

Which parts of the digestive system do you think are the most common to cause humans some sort of discomfort? Explain and give examples.

What do you think some common causes of digestive system discomfort might be? Explain and give examples.

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The foods we eat—apples, pepperoni pizzas, leafy green salads—taste good to us, but cannot be used by the body as they are. The nutrition the cells of the body need to keeping growing and working must be in a simple form: amino acids, simple sugars, and fatty acids. It is the job of the digestive system to take the complex organic molecules of the foods we ingest—proteins, carbohydrates, and fats—and break them down into their simple building blocks. This process is called digestion. Once digestion has occurred, the simple molecules (nutrients) are absorbed from the digestion system by the cardiovascular and lymphatic systems and transported to cells throughout the body.
DESIGN: PARTS OF THE DIGESTIVE SYSTEM
The digestive system may be broken into two parts: a long winding muscular tube, accompanied by accessory digestive organs and glands. That open-ended tube, known as the alimentary canal or digestive tract, is composed of various organs. These organs are, in order from the head downward, the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The rectum and anus form the end of the large intestine. The accessory digestive organs and glands that help in the digestive process include the tongue, teeth, salivary glands, pancreas, liver, and gall bladder.
The walls of the alimentary canal from the esophagus through the large intestine are made up of four tissue layers or mucous membranes. The innermost layer is the mucosa, coated with mucus, a thick, sticky fluid. This layer of tissue protects the alimentary canal from chemicals and enzymes (proteins that speed up the rate of chemical reactions) that break down food and from germs and parasites that might be in that food. Around the mucosa is the submucosa, which contains blood vessels, nerves, and lymph vessels. Wrapped around the submucosa are two layers of muscles that help move food along the canal. The outermost layer, the serosa, is moist, fibrous tissue that protects the alimentary canal and helps it move against the surrounding organs in the body.
The mouth
Food enters the body through the mouth, or oral cavity. The lips form and protect the opening of the mouth, the cheeks form its sides, the tongue forms its floor, and the hard and soft palates form its roof. The hard palate is at the front; the soft palate is in the rear. Attached to the soft palate is a fleshy, fingerlike projection called the uvula (from the Latin word meaning “little grape”). Two U-shaped rows of teeth line the mouth–one above and one below. Three pairs of salivary glands open at various points into the mouth.
The Tongue
The tongue is a muscular organ attached to the base of the mouth by a fold of mucous membrane. On the upper surface of the tongue are small projections called papillae (singular, papilla), many of which contain taste buds. Most of the tongue lies within the mouth, but its base extends into the pharynx. Located at the base of the tongue are the lingual tonsils, small masses of lymphatic tissue that serve to prevent infection.
Teeth
Humans have two sets of teeth: deciduous and permanent. The deciduous teeth (also known as baby or milk teeth) start to erupt through the gums in the mouth when a child is about six months old. By the age of two, the full set of twenty teeth has developed. Between the ages of six and twelve, the roots of these teeth are reabsorbed into the body and the teeth begin to fall out. They are quickly replaced by the thirty-two permanent adult teeth. (The third molars, the wisdom teeth, may not erupt because of inadequate space in the jaw. In such cases, they become impacted or embedded in the jawbone and must be removed surgically.)
Teeth are classified according to shape and function. Incisors, the chisel-shaped front teeth, are used for cutting. Cuspids or canines, the pointed teeth next to the incisors, are used for tearing or piercing. Bicuspids (or premolars) and molars, the back teeth with flattened tops and rounded, raised tips, are used for grinding.
Each tooth consists of two major portions: the crown and the root. The crown is the exposed part of the tooth above the gum line; the root is enclosed in a socket in the jaw. The outermost layer of the crown is the whitish enamel. Made mainly of calcium, tooth enamel is the hardest substance in the human body. Underneath the enamel is a yellowish bonelike material called dentin. It forms the bulk of the tooth. Within the dentin is the pulp cavity, which receives blood vessels and nerves through a narrow root canal at the base of the tooth.
The Salivary Glands
Three pairs of salivary glands produce saliva, a watery substance, on a continuous basis to keep the mouth and throat moist. The largest pair, the parotid glands, is located just below and in front of the ears. The next largest pair, the submaxillary or submandibular glands, is located in the lower jaw. The smallest pair, the sublingual glands, is located under the tongue.
Ducts or tiny tubes carry saliva from these glands into the mouth. Ducts from the parotid glands open into the upper portion of the mouth; ducts from the submaxillary and sublingual glands open into the mouth beneath the tongue.
The salivary glands are controlled by the autonomic nervous system, a division of the nervous system that functions involuntarily (meaning that the processes it controls occur without conscious effort on the part of an individual). The glands produce about 1.5 pints (700 milliliters) of saliva each day, which is much less than what was once thought. Although the flow is continuous, the amount varies. Food (or anything else) in the mouth increases the amount produced. Even the sight or smell of food will increase the flow of saliva.
Saliva is mostly water (about 99 percent), with waste products, antibodies, and enzymes making up the small remaining portion. At mealtimes, saliva contains large quantities of digestive enzymes that help break down food. Saliva also controls the temperature of food (cooling it down or warming it up), cleans surfaces in the mouth, and kills certain bacteria present in the mouth. In addition, it protects the enamel of the teeth and the tissues lining the mouth from the corrosive effects of stomach acid when a person feels sick and vomits.
The pharynx
The pharynx, or throat, is a short muscular tube extending about 5 inches (12 centimeters) from the mouth and nasal cavities to the esophagus and trachea (windpipe). The pharynx serves two separate body systems: the digestive system (by allowing the passage of solid food and liquids) and the respiratory system (by allowing the passage of air).
The esophagus
The esophagus, sometimes referred to as the gullet, is a muscular tube connecting the pharynx and stomach. It is approximately 10 inches (25 centimeters) in length and 1 inch (2.5 centimeters) in diameter. Within the thorax (the area of the body between the neck and the abdomen), the esophagus lies behind the trachea. At the base of the esophagus where it connects with the stomach is a strong ring of muscle called the lower esophageal sphincter. Normally, this circular muscle is contracted, preventing the contents of the stomach from moving back into the esophagus.
The stomach
The stomach is located on the left side of the abdominal cavity just under the diaphragm (a membrane of muscle separating the chest cavity from the abdominal cavity). It has a volume ranging from less than one quart (one liter) when empty, to as much as four quarts (four liters) when full. These dimensions vary from person to person, depending on body type. When empty, the stomach is shaped like the letter J and its inner walls are drawn up into long soft folds called rugae (singular, ruga). When the stomach expands, the rugae flatten out and disappear.
The dome-shaped portion of the stomach to the left of the lower esophageal sphincter is the fundus. The large central portion of the stomach is the body. The part of the stomach connected to the small intestine (the curve of the J) is the pylorus. The pyloric sphincter is a muscular ring that regulates the flow of material from the stomach into the small intestine by variously opening and contracting. That material, a soupy mixture of partially digested food and stomach secretions, is called chyme.
The stomach wall contains three layers of smooth muscle. These layers contract in a regular rhythm–usually three contractions per minute–to mix and churn stomach contents. Mucous membrane lines the stomach. Mucus, the thick, gooey liquid produced by the cells of that membrane, helps protect the stomach from its own secretions. Those secretions–acids and enzymes–enter the stomach through millions of shallow pits that open onto the surface of the inner stomach. Called gastric pits, these openings lead to gastric glands, which secrete about 2 to 3 quarts (2 to 3 liters) of gastric juice each day.
Gastric juice contains two chemicals that help to digest food: hydrochloric acid and pepsin. Pepsin is an enzyme that breaks down proteins; hydrochloric acid kills microorganisms and breaks down cell walls and connective tissue in food. The acid is strong enough to burn a hole in carpet, yet the mucus produced by the mucous membrane prevents it from dissolving the lining of the stomach. Even so, the cells of the mucous membrane wear out quickly: the entire stomach lining is replaced every three days. Mucus also aids in digestion by keeping food moist.
The small intestine
The small intestine is the body’s major digestive organ. Looped and coiled within the abdominal cavity, it extends about 20 feet (6 meters) in humans older than five years from the stomach to the large intestine. It can vary from 13 feet to 22 feet in length. At its junction with the stomach, the small intestine measures about 1.5 inches (4 centimeters) in diameter. By the time it meets the large intestine, its diameter has been reduced to 1 inch (2.5 centimeters). Although much longer than the large intestine, the small intestine is called “small” because its overall diameter is smaller.
The small intestine is divided into three regions or sections. The first section, the duodenum, is the initial 10 inches (30 centimeters) closest to the stomach. Chyme from the stomach and secretions from the pancreas and liver empty into this section. The middle section, the jejunum, measures about 8.2 feet (2.5 meters) in length. Digestion and the absorption of nutrients occur mainly in the jejunum. The final section, the ileum, is also the longest, measuring about 11 feet (3.5 meters) in length. The ileum ends at the ileocecal valve, a sphincter that controls the flow of chyme from the ileum to the large intestine.
The inner lining of the small intestine is covered with tiny fingerlike projections called villi (giving it an appearance much like the nap of a plush soft towel). The villi, which themselves are covered with even smaller structures called microvilli, greatly increase the intestinal surface area available for absorbing digested material. The small intestine contains between 2,200 and 5,000 square feet (200-460 square meters) of absorptive area–600 times the area of a smooth-walled tube of equal length.
Within each villus (singular of villi) are blood capillaries and a lymph capillary called a lacteal. Digested food molecules are absorbed through the walls of the villus into both the capillaries and the lacteal. At the bases of the villi are the openings of intestinal glands, which secrete a watery intestinal juice. This juice contains digestive enzymes that convert food materials into simple nutrients the body can readily use. On average, about 2 quarts (2 liters) of intestinal juice are secreted into the small intestine each day.
As with the lining of the stomach, a coating of mucus helps protect the lining of the small intestine. Yet again, the digestive enzymes prove too strong for the delicate cells of that lining. They wear out and are replaced about every two days.
The large intestine
Extending from the end of the small intestine to the anus, the large intestine measures about 5 feet (1.5 meters) in length and 3 inches (7.5 centimeters) in diameter. It almost completely frames the small intestine. The large intestine is divided into three major regions: the cecum, colon, and rectum.
The word cecum comes from the Latin word caecum, meaning “blind.” Shaped like a rounded pouch, the cecum lies immediately below the area where the ileum empties into the large intestine. Attached to the cecum is the slender, fingerlike appendix, which measures about 3.5 inches (9 centimeters) in the average adult–although appendices twice this length have been reported. Composed of lymphoid tissue, the appendix has no vital function in present-day humans, although it is thought to contribute to the immune system. It can be removed without any damage to the body, and for that reason, scientists refer to it as a vestigial organ (an organ that is reduced in size and function when compared with that of evolutionary ancestors).
Sometimes used to describe the entire large intestine, the colon is actually the organ’s main part. It is divided into four sections: ascending, transverse, descending, and sigmoid. The ascending colon travels upward from the cecum along the right side of the abdominal cavity until it reaches the liver. It then makes a turn, becoming the transverse colon, which travels horizontally across the abdominal cavity. Near the spleen on the left side, it turns downward to form the descending colon. At about where it enters the pelvis, it becomes the S-shaped sigmoid colon.
After curving and recurving, the sigmoid colon empties into the rectum, a fairly straight 6-inch-long (15-centimeter) tube ending at the anus, the opening to the outside. Two sphincters (rings of muscle) control the opening and closing of the anus.
Roughly 1.5 quarts (1.5 liters) of watery material enters the large intestine each day. No digestion takes place in the large intestine, only the reabsorption or recovery of water. Mucus produced by the cells in the lining of the large intestine help move the waste material along. As more and more water is removed from that material, it becomes compacted into soft masses called feces. Feces are composed of water, cellulose and other indigestible material, and dead and living bacteria. The remnants of worn red blood cells give feces their brown color. Only about 3 to 7 ounces (85 to 200 grams) of solid fecal material remains after the large intestine has recovered most of the water. That material is then eliminated through the anus, a process called defecation. It takes the large intestine between 12 and 25 hours to carry out its part of the process of digestion.
The pancreas
The pancreas is a soft pink triangular-shaped gland that measures between 6 and 10 inches (15 to 25 centimeters) in length in adult humans. It lies behind the stomach, extending from the curve of the duodenum to the spleen. While a part of the digestive system, the pancreas is also considered a part of the endocrine system because it produces two hormones, insulin and glucagon.
Primarily a digestive organ, the pancreas produces pancreatic juice that helps break down all three types of complex food molecules in the small intestine. The enzymes contained in that juice include pancreatic amylase, pancreatic lipase, trypsinogen, and chymotrypsinogen. Amylase breaks down starches into such simple sugars as maltose (malt sugar). Lipase breaks down fats into simpler fatty acids and glycerol (an alcohol). Trypsinogen is the inactive form of the enzyme trypsin, which breaks down proteins into amino acids. Trypsin is so powerful that if it were produced directly in the pancreas, it would digest the organ itself. To prevent this, the pancreas produces trypsinogen, which is then changed in the duodenum to its active form. Chymotrypsinogen is similar to trypsinogen; it is an inactive form of an enzyme called chymotrypsin, which also digests proteins.
Pancreatic juice is collected from all parts of the pancreas through microscopic ducts. These ducts merge to form larger ducts, which eventually combine to form the main pancreatic duct. This duct, which runs the length of the pancreas, then transports pancreatic juice to the duodenum of the small intestine.
Because of the importance of the enzymes produced by the pancreas, damage to this organ is potentially life-threatening. Puncturing of the pancreas (as might happen in an automobile accident or athletic injury) is considered a medical emergency and requires immediate treatment.
The liver
The largest glandular organ in the body as well as the heaviest organ, the liver weighs between 3.5 and 6 pounds (1.7 and 3.0 kilograms) in human adults. It lies on the right side of the abdominal cavity just beneath the diaphragm. In this position, it overlies and almost completely covers the stomach. Deep reddish brown in color, the liver is shaped roughly like a boomerang. It is divided into four unequal-sized lobes: two large right and left lobes in front and two smaller lobes visible only from the back.
The liver is an extremely important organ. Researchers have discovered that it performs over 200 different functions in the body. Among its many functions are processing nutrients, making plasma proteins and blood-clotting chemicals, detoxifying (transforming into less harmful substances) alcohol and drugs, storing vitamins and iron, and producing cholesterol. The liver is also one of the few internal organs in humans that can regenerate lost or destroyed tissue; as little as 25 percent of a human liver can regrow into a full-sized liver.
One of the liver’s main digestive functions is the production of bile. A watery greenish-yellow liquid, bile consists mostly of water, bile salts, bile pigments, cholesterol, and assorted lipids or fats. Liver cells produce roughly 1 quart (1 liter) of bile each day. The bile leaves the liver through the common hepatic duct. This duct unites with the cystic duct from the gall bladder to form the common bile duct, which delivers bile to the duodenum.
In the small intestine, bile salts act like a detergent; they emulsify fats, breaking them down from large globules into smaller droplets that stay suspended in the watery fluid in the small intestine. Bile salts are not enzymes and therefore do not digest fats. By breaking down the fats into smaller units, bile salts aid the fat-digesting enzymes present in the small intestine.
The gall bladder
The gall bladder is a small pouchlike green organ located on the undersurface of the right lobe of the liver. It measures 3 to 4 inches (7 to 10 centimeters) in length. The gall bladder’s function is to store bile, of which it can hold about 1.2 to 1.7 ounces (35 to 50 grams).
The liver continuously produces bile. When digestion is not occurring, bile backs up the cystic duct and enters the gall bladder. While holding the bile, the gall bladder removes water from it, making it more concentrated–up to five times its original strength. When fatty food enters the duodenum once again, the gall bladder is stimulated to contract and spurt out the stored bile.
WORKINGS: HOW THE DIGESTIVE SYSTEM FUNCTIONS
The digestive system breaks down food into useful forms through mechanical and chemical means. Mechanical digestion refers to the physical breaking up of food into small pieces, such as by chewing. The smaller pieces are then acted upon by digestive enzymes, which change complex chemical molecules into much simpler molecules the body can easily utilize. The stage of digestion involving enzymes is called chemical digestion.
Digestive activities in the mouth
Food taken into the mouth is broken down by both mechanical and chemical means. Through the process of mastication or chewing, the teeth physically break down the tough tissues of meats and the fibers in plants into smaller particles. The tongue helps move the food around the mouth, allowing the different sets of teeth variously to cut, tear, or grind the food. The jaw muscles, some of the strongest muscles in the body, help the teeth break down food in seconds.
Stimulated by the presence of something appetizing in the mouth, the salivary glands secrete an increased amount of saliva (the sensations of sight, taste, and smell also increase saliva flow). As saliva is mixed with the food, salivary amylase (an enzyme in saliva) begins the chemical digestion of carbohydrates or starches, changing them into the simple sugar maltose.
As the food is broken down into pieces by the teeth and mixed with saliva, the tongue rolls these pieces into a moist soft mass or ball called a bolus. Only after food has been compacted into a bolus of proper texture and consistency can swallowing occur.
Swallowing
Swallowing is both a voluntary and involuntary action. Once food has been properly chewed and mixed with saliva to create a bolus, the tongue forces the bolus toward the back of the mouth and into the pharynx. This is a voluntary action; the individual has total control over moving the bolus while it is in the mouth. When the bolus presses against the soft palate, the soft palate and the uvula rise to close off the nasal passages to prevent the bolus from entering them.
Once the bolus enters the pharynx, however, swallowing becomes an automatic reflex action and cannot be stopped. The larynx, the upper part of the trachea that contains the vocal cords, rises. As it does so, a flaplike piece of tissue at the top of the larynx called the epiglottis folds down to cover its opening. This closure prevents the bolus from passing into the trachea or windpipe.
Sometimes, when a person laughs or talks while eating or drinking, the uvula and the epiglottis may not cover their openings quickly enough. If the uvula does not rise in time, bits of food or liquid may squirt upward into the nose. If the epiglottis does not fold down, bits of food or liquid may enter the trachea, an unpleasant sensation that causes the person to cough (a protective reflex) until the food or liquid is expelled from the trachea.
Once material reaches the esophagus, the circular muscles in the walls of the esophagus begin alternately to contract and relax in a wavelike manner, pushing the bolus further and further downward. This series of wavelike muscular motions is known as peristalsis (or peristaltic contractions). Material is pushed down the esophagus regardless of the person”s position: standing up, sitting, lying down, or upside down. Gravity helps move the bolus along, but peristalsis occurs even in the zero gravity of space.
A typical moist bolus takes about nine seconds to travel through the esophagus. Drier boluses take longer. Boluses of warm food increase the strength of the muscular contractions, while boluses of cold food weaken them. Liquids often pass through this muscular tube in just seconds, faster than the accompanying peristaltic waves. When the bolus or liquid reaches the lower esophageal sphincter, it presses against the sphincter, causing it to open. The swallowed material then passes into the stomach.
Digestive activities in the stomach
Gastric juices begin to flood the stomach even before food arrives. The sight, smell, taste, or even thought of food triggers the central nervous system to send nerve impulses to the gastric glands, which respond by secreting gastric juice. Once food does arrive in the stomach and touches its lining, the cells in the lining release gastrin, a hormone. Gastrin in turn stimulates the production of even greater amounts of gastric juice.
As food fills the stomach, its walls begin to stretch. This stretching initiates the process of mechanical digestion in the stomach. The muscles in the walls begin to contract, compressing and pummeling the food, breaking it apart physically. At the same time, the food is mixed with gastric juices, and chemical digestion begins. Pepsin, the protein-digesting enzyme in gastric juice, starts to break down complex proteins. Little digestion of carbohydrates or fats takes place in the stomach because the acids in gastric juice interfere with the activity of the enzymes that break down these nutrients. Water, alcohol, and such drugs as aspirin, however, are absorbed through the walls of the stomach into the bloodstream.
Once the food has been well mixed and broken down into chyme, peristalsis begins in the lower portion of the stomach. The chyme is moved downward into the pylorus. With each contraction of the stomach walls, the pyloric sphincter opens just a little, allowing a bit of chyme to squirt into the duodenum of the small intestine. When the duodenum is filled and its wall stretched, a nerve impulse is sent to the stomach to slow down its activity. It takes about four hours for the stomach to empty completely after receiving a well-balanced meal. If that meal contains large quantities of fatty foods, however, then the process could take six or more hours. Emotional stress, heat or exercise stress, and certain prescription medications may also cause the stomach to empty more slowly than usual.
Digestive activity in the small intestine
When chyme from the stomach enters the small intestine, it contains proteins and carbohydrates that have been only partially digested. Fats have been hardly digested at all. Over a three- to six-hour period, as chyme moves through the twists and coils of the small intestine, chemical digestion speeds up and intensifies. By the time chyme reaches the end of the small intestine, eighty percent of all digestion in the body has taken place.
The presence of chyme in the duodenum stimulates the secretion of intestinal juice. Cells in the lining of the duodenum are also stimulated to produce hormones that in turn stimulate the pancreas to produce pancreatic juice and the liver to produce bile. The gall bladder is also stimulated to release its store of concentrated bile. Both substances enter the duodenum and combine with intestinal juice to digest or break down proteins, carbohydrates, and fats.
Peristalsis, the wavelike muscular contractions that push food down the esophagus during swallowing, also takes place within the small intestine, mixing the chyme with the intestinal juices and moving it through the organ. Although water and nutrients are absorbed all along the length of the small intestine, most of this absorption occurs in the jejunum. In this section, digested carbohydrates, fats, proteins, and most of the vitamins, minerals, and iron are absorbed. These nutrients pass through the walls of the microvilli and villi into the blood capillaries and lacteals (lymph capillaries). The blood capillaries eventually drain into veins that connect with the portal vein, which transports the nutrient-rich blood to the liver. The lacteals, carrying nutrients from digested fats, eventually drain into larger lymph vessels that connect with the venous system.
By the time the digested material enters the ileum, the last section of the small intestine, all that remains is some water, such indigestible food matter as plant fibers, and bacteria. This material then enters the large intestine through the ileocecal valve, which closes to prevent the material from flowing backward.
Digestive activities in the large intestine
The large intestine does not produce any digestive enzymes; therefore, no digestion takes place. It functions mainly to absorb water and a few minerals from the waste products of digestion. Peristalsis in the large intestine occurs very slowly: material takes between twelve and twenty-four hours to pass through this part of the digestive tract.
Millions of bacteria living in the large intestine feed on the waste products. In doing so, they produce vitamin K and some B vitamins that are absorbed through the wall of the large intestine into the bloodstream and then transported to the liver. The bacteria also produce intestinal gas–methane and hydrogen sulfide–that gives feces their characteristic odor. The amount of that gas, properly known as flatus, may increase if certain foods rich in carbohydrates (such as beans, cabbage, broccoli, lentils, onions, milk, certain types of cheese, and sweet potatoes) are eaten.
When powerful peristaltic contractions force the feces or compacted waste products from the sigmoid colon into the rectum, the wall of the rectum stretches. This stretching triggers the defecation reflex. Signals from the spinal cord cause the walls of the sigmoid colon and rectum to contract and the anal sphincters to relax. Feces are then eliminated through the anus. The outer sphincter muscle can be controlled voluntarily, allowing an individual to delay defecation when necessary.
People often feel the need to defecate soon after finishing a meal. This phenomenon is called the gastrocolic reflex. It occurs because the stretching of the stomach at the end of the meal and the passage of partially digested food into the small intestine trigger nerve endings in the sigmoid colon, which in turn moves the waste products of the previous meal into the rectum.
AILMENTS: WHAT CAN GO WRONG WITH THE DIGESTIVE SYSTEM
Many ailments or maladies can afflict the digestive system. Although it is remarkably resistant to abuse, it is still vulnerable and can break down. Some ailments are relatively minor, such as canker sores in the mouth. Others are severe and life-threatening, such as cancers that can target almost every part of the digestive system.
As an individual ages, the activity of the digestive system slows down. Fewer digestive juices are produced and secreted. Peristalsis slows down. The sensations of taste and smell are weaker, and eating becomes less appealing. When less food is ingested, the body receives fewer nutrients. All body systems are then weakened and become susceptible to disease.
The following are just a few of the legion of ailments that can beset the many parts of the digestive system.
DIGESTIVE SYSTEM DISORDERS
Anorexia nervosa (an-ah-REK-see-ah ner-VO-sa): Eating disorder usually occurring in young women (about 10 percent of cases occur in men) that is characterized by an abnormal fear of becoming obese, a persistent aversion to food, and severe weight loss.
Appendicitis (ah-pen-di-SIGH-tis): Inflammation of the vermiform appendix.
Biliary atresia (BILL-ee-a-ree ah-TREE-zee-ah): Condition in which the ducts that transport bile from the liver to the duodenum fail to develop in a fetus.
Bulimia (boo-LEE-me-ah): Eating disorder characterized by eating binges followed by self-induced vomiting or laxative abuse.
Cirrhosis (si-ROW-sis): Chronic disease of the liver in which normal liver cells are damaged and then replaced by scar tissue.
Crohn’s disease (CRONES di-ZEEZ): Disorder that causes inflammation and ulceration of all the layers of the intestinal wall, particularly in the small intestine.
Diverticulosis (di-ver-ti-cue-LOW-sis): Condition in which the inner lining of the large intestine bulges out through its muscular wall; if the bulges become infected, the condition is called diverticulitis.
Gallstones (GAUL-stones): Solid crystal deposits that form in the gall bladder.
Hepatitis (hep-a-TIE-tis): Inflammation of the liver, caused mainly by viruses, but also by certain types of bacteria, toxic chemicals, and heavy use of alcohol.
Lactose intolerance (LAK-tose in-TOL-er-ance): Inability of the body to digest significant amounts of lactose, the predominant sugar in milk.
Ulcer (digestive) (UL-sir): Any sore that develops in the lining of the lower esophagus, stomach, or duodenum.
Ulcerative colitis (UL-sir-a-tiv ko-LIE-tis): Disorder that causes inflammation and ulceration of the inner lining of the large intestine and rectum.
Appendicitis
Appendicitis is an inflammation of the appendix. It is the most common abdominal emergency found in children and young adults. Because of the position of the appendix at the bottom of the cecum, scientists believe one of the main causes of appendicitis is an invasion of bacteria following blockage of the appendix by ulcers or fecal matter. When infected with bacteria, the appendix may become swollen and filled with pus. It may then eventually rupture. Symptoms of appendicitis include pain that begins above or around the navel. The pain, which may be severe or only achy, then moves into the right corner of the abdomen. In this position, the pain often becomes more steady and severe.
A doctor can often diagnose appendicitis by pressing on an area on the right side of the abdomen below the navel. The most effective way to confirm the diagnosis is a computed tomography (CT) scan. If left untreated, appendicitis is usually fatal. The treatment for the condition is an immediate appendectomy or surgical removal of the inflamed and ruptured appendix.
Biliary atresia
Biliary atresia is a rare condition in which the ducts that transport bile from the liver to the duodenum fail to develop in a fetus. The condition is the most common fatal liver disease in children. Biliary atresia affects between 15,000 and 20,000 infants in the United States each year, girls slightly more often than boys, and Asian Americans or African Americans more often than Caucasians. Half of all liver transplants are done for this reason. No cause for this birth defect has as yet been found.
In a child with this condition, bile begins to back up into the liver and eventually into the rest of the body. The child becomes jaundiced (its skin turns yellow). The abdomen then begins to swell and the child becomes progressively sicker. If left untreated, liver failure and death will occur within two years.
Surgery is the only treatment for biliary atresia. The surgeon must find a way to create an adequate duct or pathway for the bile to drain from the liver into the intestine. This operation is called a Kasai procedure, named for the Japanese surgeon who introduced it. Even if the surgery is successful, however, persistent disease in the liver will gradually destroy the organ. A liver transplant currently offers the best hope for this condition.
Cavities
A dental cavity, also known as dental caries or tooth decay, is the destruction of the enamel or outer surface of a tooth. It is a common health problem in developed countries, second only to the common cold. About 90 percent of children and adults worldwide have experienced dental caries. Tooth decay results from the action of bacteria that live in plaque, which is a sticky whitish film that forms on teeth. Plaque is composed of a protein in saliva, sugars from foods, and bacteria. The bacteria use the sugars and starches from food particles in the mouth to produce acid that dissolves tooth enamel, creating cavities or holes. If the decay reaches the dentin (the bony material between the outer enamel and the inner pulp of the tooth), the tooth becomes sensitive to temperature and touch. If the decay reaches the pulp cavity, inflammation and pain (toothache) develop.
If left untreated, the decay can eventually destroy the entire tooth. A dentist is able to treat most cases of tooth decay by removing all decayed parts of the tooth and then filling the cavity with a hard material, which may be either a metal alloy of some kind or a composite material made of powdered glass and resin. Many people prefer composite fillings because they look like the natural tooth. If the decay has attacked the pulp, the dentist may perform a root canal treatment, removing the pulp and filling the inside chamber. If the larger part of a tooth has to be removed, the dentist covers the tooth with a crown.
Cirrhosis
Cirrhosis is a chronic (long-term) disease in which the cells of the liver are damaged and then replaced by scar tissue. The disease obviously affects the liver’s ability to perform its many functions. The condition is irreversible; it worsens over time and may lead to death. Twice as common in men as in women, cirrhosis is the tenth leading cause of disease-related death for men and the twelfth for women in the United States. About 27,000 Americans die each year from cirrhosis.
Long-term alcoholism is the primary cause of cirrhosis in the United States. About 15 percent of people who drink heavily for more than 10 years will develop alcoholic cirrhosis. Throughout the digestive system, alcohol interferes with the absorption of nutrients. Alcohol provides calories but no essential nutrients to the body. It also robs the body of vitamins and minerals necessary to maintain proper cell function. Because alcohol is detoxified within the liver, a constant level of alcohol in the organ severely affects it. Cirrhosis may also result from exposure to dry cleaning solvents and other toxic chemicals, or from viral infections like hepatitis B and hepatitis C.
During the early stages of cirrhosis, the liver enlarges. The palms of the hands then turn red. Other symptoms include changes in the color and shape of the fingernails, swelling of the breasts in men, constipation or diarrhea, a sweetish or pungent breath odor, fluid accumulating in the abdomen, dull abdominal pain, fatigue, loss of appetite, nausea, vomiting, weakness, and weight loss. If left untreated, the symptoms increase and worsen, leading to liver failure and death.
The primary treatment for cirrhosis is to correct the condition causing it. A person suffering from cirrhosis must not consume alcohol. A balanced diet low in salt, which helps regenerate healthy liver cells and lowers the risk of fluid collecting in the abdomen, must be followed. In patients with advanced cirrhosis, a liver transplant may be necessary.
Diverticulosis and diverticulitis
Diverticulosis is a condition, most common in middle-aged or elderly adults, in which the inner layer of the large intestine bulges out through the outer, muscular layer. These bulges are called diverticula. When they become infected and inflamed, the resulting condition is known as diverticulitis. About 95 percent of cases of diverticulitis in Western countries involve the sigmoid colon.
Diverticula occur most frequently in individuals whose diets are low in fiber. Since the amount of fecal matter produced is low, the large intestine must narrow itself and contract forcefully to move the smaller feces along to the rectum. Over time, this pattern of contraction weakens the muscular wall, allowing diverticula to develop.
Diverticulitis occurs when a hardened piece of stool, undigested food, or bacteria become lodged in the diverticula. Blood supply to the area is disrupted and infection sets in. Symptoms of diverticulitis include pain in the lower left side of the abdomen and fever. A blood test usually indicates a high level of white blood cells. Abscesses (walled-off pockets of infection) may develop within the wall of the intestine. A CT scan is 98 percent accurate in diagnosing diverticulitis.
Diverticulitis is quite treatable. Usually, the intestine is “rested” by preventing the individual from eating or drinking anything by mouth. Medications (usually antibiotics) to fight the infection are also given. Once the condition is brought under control, the individual must adhere to a high-fiber diet.
If the condition is severe and surgery is needed to remove a portion of the intestine filled with abscesses, a colostomy is performed. This procedure involves pulling the end of the remaining intestine through the abdominal wall and attaching it to a bag on the outside. Because the intestine no longer connects with the rectum, the individual’s feces pass out of the intestine into the bag. The colostomy may be temporary (until healing has occurred) or it may be permanent.
Gallstones
Gallstones are solid crystal deposits that form in the gall bladder. They can vary in size from as small as a grain of sand to as large as a golf ball. Eighty percent of all gallstones are composed of cholesterol, a fatlike substance produced by the liver. Cholesterol gallstones form when the liver produces more cholesterol than the intestinal juices can liquefy. The other 20 percent of gallstones are small dark stones made of the pigments and calcium salts found in bile.
Gallstones are the fifth most common reason adults are hospitalized in the United States. They usually develop in adults between the ages of twenty and fifty, with women twice as likely to develop gallstones as men. The condition of developing gallstones tends to run in families. Mexican Americans and Native Americans are also more likely to develop gallstones. In addition, high levels of estrogen (female hormones), insulin (the hormone that regulates sugar levels), and cholesterol in the body increase the risk of developing gallstones. A diet high in fat and low in fiber, the use of birth control pills, heavy drinking, and smoking may also play a part.
Gallstones may block the common bile duct, preventing bile from flowing into the duodenum. A gallstone in the cystic duct may cause the gall bladder to become inflamed. Symptoms of a gallbladder attack include pain that begins in the abdomen and moves to the chest and back, chills and sweating, nausea and vomiting, and gas and belching.
Gallstones of a small size may pass out of the body through the urine. So they may more easily pass out, doctors may use high-frequency sound waves to break up the gallstones. To treat painful severe cases, doctors may surgically remove the gall bladder and gallstones. Special medications can be used to dissolve cholesterol gallstones if the patient is too weak for surgery; however, the gallstones usually recur after nonsurgical treatment.
Heartburn
Heartburn is the common name for a burning sensation in the chest at the level of the breastbone that can extend to the neck, throat, and face. It is caused by a backflow of the stomach’s acids through the lower esophageal sphincter into the esophagus, leading to inflammation. More than one third of the population suffers from this disorder, formally known as acid reflux.
Normally the lower esophageal sphincter is tightly closed and opens only to allow food to pass from the esophagus into the stomach. Many different factors, however, may cause the sphincter to open inappropriately or fail to close completely. Fatty or greasy foods, spicy foods, citrus fruits, carbonated beverages, tomatoes, cigarettes, alcohol, chocolate, caffeine, and certain medications can relax the sphincter, increasing reflux. In some cases heartburn is caused by emotional stress or tension. A large meal, obesity, and pregnancy increase the pressure inside the abdomen, pushing the contents of the stomach into the esophagus.
Heartburn can be prevented by avoiding those foods, drugs, or stressful situations that trigger the disorder. Mild cases of heartburn can be treated with over-the-counter antacids, which decrease the acidity in the stomach. People who are not helped by over-the-counter antacids usually benefit from prescription drugs known as proton-pump inhibitors, which block the production of stomach acid. Surgery to correct a defective or damaged sphincter may be necessary in severe cases.
Hepatitis
Hepatitis is an often fatal disease that causes inflammation of the liver. There are various types of hepatitis, most of which are caused by a virus. The viral forms include hepatitis A, B, C, D, E, and G. The assorted symptoms marking hepatitis include jaundice (yellowing of the skin), darkening of the urine, nausea, vomiting, fever, weakness, loss of appetite, abdominal and joint pain, flu-like symptoms, and cirrhosis (scarring of the liver).
Alcoholic hepatitis is a noninfectious type of hepatitis. Alcohol, a poison if taken in more than modest amounts, is detoxified in the liver. Too much alcohol causes the liver to become inflamed. The liver cannot function properly and eventually turns to useless fat. If the poisoning continues, cirrhosis develops.
Two viral forms of hepatitis are most common: A and B. Hepatitis A (commonly known as infectious hepatitis) is spread through direct contact with contaminated feces, food, or water. Once infected, an individual usually recovers within two months. A vaccine is now available that will protect against hepatitis A for life.
Hepatitis B (commonly called serum hepatitis) is much more severe, causing between 500,000 and 1,200,000 deaths around the world each year. It is transmitted by sexual activity, blood transfusions, getting tattoos, and the use of shared syringes by drug users. A pregnant woman infected with hepatitis B can transmit the disease to her unborn child. Hepatitis B may destroy the liver through cirrhosis or it may lead to cancer of the liver. Fortunately, there is a vaccine that offers lifetime protection against hepatitis B.
Hepatitis C causes acute (rapidly developing) and chronic (long-term) disease. It is spread mainly through blood transfusions. Medical researchers believe hepatitis C may be caused by several different viruses. As with hepatitis B, hepatitis C may lead to cirrhosis of the liver and eventually liver cancer. No vaccine has yet been developed to prevent hepatitis C.
Inflammatory bowel disease
Inflammatory bowel disease (IBD) is a disorder that causes inflammation and ulceration (development of ulcers) in the small and large intestine. The two main forms of IBD are ulcerative colitis and Crohn’s disease.
Ulcerative colitis, which occurs mainly in people between the ages of fifteen and forty, affects the inner lining of the large intestine and rectum. It is a rare disorder, affecting about 1 person in every 10,000 in the United States. Inflammation usually begins in the rectum and spreads upward into the entire large intestine. Diarrhea, cramping or abdominal pain, fever, and weight loss result. Ulcers (tiny open sores) develop in the intestinal lining, and blood and pus appear in the feces. If the disorder becomes widespread through the large intestine, the risk of cancer increases. Although the cause of ulcerative colitis is not yet known, some evidence points to the involvement of genetic factors in the disease. The only cure for advanced cases is the surgical removal of the large intestine. Anti-inflammatory drugs help to keep the disorder under control in less severe cases.
Crohn’s disease, named for the American doctor who described it in 1932, is a lifelong illness that often begins as early as the teen years and may recur frequently over a person’s lifetime. Also called regional enteritis, Crohn’s disease affects between 400,000 and 600,000 persons in Canada and the United States. It causes the inflammation of all the layers of the intestinal wall, particularly in the small intestine. In turn, the inflammation brings about ulcerations in the intestinal wall. Crohn’s disease can also affect the large intestine, mouth, esophagus, and stomach. The disease is marked by diarrhea, abdominal pain, weight loss, and fever. In children, it may cause growth failure. The cause of Crohn’s disease has yet to be found, as well as a cure. Medications to control diarrhea, abdominal pain, and inflammation are the main forms of treatment. Surgery to remove or repair a section of the intestine is sometimes required.
Ulcers (digestive)
A digestive ulcer is any sore that develops in the lining of the stomach or duodenum (sores in the lower esophagus occur less frequently). Because these sores form in areas where gastric juice is present, they are generally referred to as peptic ulcers (pepsin is an enzyme in gastric juice). Peptic ulcers found in the stomach are more specifically called gastric ulcers. Those in the duodenum are called duodenal ulcers. Of the two, duodenal ulcers are the most common type, accounting for about 80 percent of all digestive ulcers. They tend to be smaller than gastric ulcers and heal more quickly. Any ulcer that heals leaves a scar.
The symptoms of gastric ulcers include feelings of heartburn, nausea, weight loss, bloody vomit, black or tarry-looking feces, and stomach pain. That pain is often described as gnawing, dull, aching, or resembling hunger pangs. About one-third of those individuals suffering from gastric ulcers are awakened by pain at night.
The symptoms of duodenal ulcers differ slightly from those of gastric ulcers. They include heartburn, stomach pain that is relieved by eating or antacids, and a burning sensation at the back of the throat. Pain is most often felt two to four hours after a meal. Citrus juices, coffee, and aspirin bring on pain more quickly. About 50 percent of individuals suffering from duodenal ulcers are awakened by pain at night.
Before the 1980s, physicians believed ulcers were caused by several factors–including stress and a poor diet–that resulted in excess stomach acid. Medical research has since shown that a certain bacterium known as Helicobacter pylori, which can live undetected in the mucous membrane of the digestive tract, is the culprit in 75 percent of cases. This bacterium irritates and weakens the lining, making it more susceptible to damage by gastric juice. The frequency of H. pylori infections in the general population rises with age, from 20 percent in 20-year-olds to 80 percent in 80-year-olds.
The discovery of H. pylori does not mean that emotional or physical stress does not play a role in the development of digestive ulcers. In addition to people under emotional stress, people being treated for severe burns or head injuries are at increased risk of developing digestive ulcers.
Treatment for peptic ulcers includes antibiotics to eliminate the bacterium and other drugs to reduce the amount of gastric juice secreted in the stomach. The most effective combination is two antibiotics plus one proton-pump inhibitor, often supplemented by a bismuth compound such as Pepto-Bismol. Very few ulcers fail to respond to the medications that are currently used to treat them.
TAKING CARE: KEEPING THE DIGESTIVE SYSTEM HEALTHY
The body is wholly dependent on the digestive system to provide it with the nutrients–fluids, carbohydrates, proteins, lipids, vitamins, and minerals–it needs to continue to function. If the digestive system fails to do this because it is not functioning properly, the entire body suffers.
A healthy lifestyle will keep the digestive system healthy. This recommended lifestyle includes following a proper diet, exercising regularly, maintaining a healthy weight, not smoking, drinking alcohol only in moderation, and reducing the levels of emotional stress in one’s life.
The “My Plate” nutrition guide developed by the U.S. Departments of Agriculture and Health and Human Services in 2011 provides easy-to-follow guidelines for a proper diet. In general, foods that are low in fat (especially saturated fat), low in cholesterol, and high in fiber are good choices. Fiber is especially important in maintaining the workings of the intestines. The My Plate program recommends a daily intake of 30 percent grains, 30 percent vegetables, 20 percent fruits and 20 percent protein, with a very limited amount of fats. Drinking fluids, especially water, helps move material through the digestive system.
Long-term ingestion of cigarette fumes, excessive alcohol, and spicy foods can cause serious damage to the digestive system. Toxins that are taken into the body by way of the mouth are absorbed by the digestive tract and transported to the liver, which can suffer permanent damage. Many medications, particularly aspirin and other over-the-counter pain relievers, can irritate or injure the lining of the esophagus, stomach, and intestines. Medicines in pill or capsule form should always be taken with plenty of water.
Proper storage and preparation of food is also an important part of keeping the digestive system healthy. According to the Centers for Disease Control and Prevention (CDC), each year 76 million Americans will suffer an episode of “food poisoning,” which is the everyday expression for foodborne illness. Many cases of foodborne illness cause only mild nausea or vomiting; however, others are characterized by fever, severe abdominal cramps, diarrhea, and dehydration. CDC statistics indicate that 5,000 people die each year in the United States from food poisoning.
Harmful bacteria are the most common cause of foodborne illness, but food can also be contaminated by viruses or parasites. To prevent food poisoning, people should refrigerate cold foods promptly; cook hot foods to the proper temperature, using a meat thermometer to measure the internal temperature; wash hands before and after handling raw meat or fish, and wash hands after using the bathroom; wash cooking utensils and cutting boards before and after use in hot soapy water; and never eat food that looks or smells “off” or unsafe.
Teeth are an important yet often overlooked part of the digestive system. They begin the entire process of digestion. Oral hygiene is therefore a primary concern. The best way to prevent tooth decay is to brush the teeth at least twice a day, preferably after every meal and snack, and to minimize eating sugary foods. The teeth should also be flossed daily to help prevent gum disease.
Minor irritations of the digestive system are common. Occasional diarrhea, nausea or vomiting, constipation, or excessive gas can be expected. Often, these minor problems are treated with nonprescription drugs. If these or any digestive problems persist, however, they should not be ignored and medical attention should be sought.
PAVLOV AND HIS SALIVATING DOG
Ivan Petrovich Pavlov (1849-1936) was a Russian physiologist (person who studies the physical and chemical processes of living organisms) who conducted pioneering research into the digestive activities of mammals. His now-famous experiments with a dog (“Pavlov’s dog”) to show how the central nervous system affects digestion earned him the Nobel Prize for Medicine or Physiology in 1904.
Interested in the actions of digestion and gland secretion, Pavlov set up an ingenious experiment. In a laboratory, he severed a dog’s throat (Pavlov was a skillful surgeon and the animal was unharmed). When the dog ate food, the food dropped out of the animal’s throat before reaching its stomach. Through this simulated feeding, Pavlov discovered that the sight, smell, and swallowing of food were enough to cause the secretion of gastric juice. He demonstrated that the stimulation of the vagus nerve (the tenth cranial nerve, one of the major nerves of the brain) influences the actions of the gastric glands.
In another famous study, Pavlov set out to determine whether he could turn unconditioned (naturally occurring) reflexes or responses of the central nervous system into conditioned (learned) reflexes. He had noticed that laboratory dogs would sometimes salivate merely at the approach of laboratory assistants who fed them. Pavlov then decided to ring a bell each time a dog was given food. After a while, he rang the bell without feeding the dog. He discovered that the dog salivated at the sound of the bell even though food was not present. Through this experiment, Pavlov demonstrated that unconditioned reflexes (salivation and gastric activity) could become conditioned reflexes that were triggered by a stimulus (the bell) that previously had had no connection with the event (in this case, eating).
A VIEW OF THE STOMACH
William Beaumont (1785-1853) was an American surgeon who served as an army surgeon during the War of 1812 (1812-15) and at various posts after the war. It was at one of these posts that he saw what perhaps no one before him had seen: the inner workings of the stomach.
In 1822, while serving at Fort Mackinac in northern Michigan, Beaumont was presented with a patient named Alexis St. Martin (1794-1880). The French Canadian trapper, only nineteen at the time, has been accidentally shot in the stomach. The bullet had torn a deep chunk out of the left side of St. Martin’s lower chest. At first, no one thought he would survive, but amazingly he did. His wound never completely healed, however, leaving a 1 inch-wide (2.5 centimeter-wide) opening. This opening, called a fistula, allowed Beaumont to put his finger all the way into St. Martin’s stomach.
Beaumont decided to take advantage of the opening into St. Martin’s side to study human digestion. In 1825 he hired St. Martin, who could no longer work as a trapper, as his handyman. Beaumont started his study of digestion by taking small chunks of food, tying them to a string, then inserting them directly into the young man’s stomach. At irregular intervals, he pulled the food out to observe the varying actions of digestion. Later, using a handheld lens, Beaumont peered into St. Martin’s stomach. He observed the ways in which the human stomach behaves at various stages of digestion and under differing circumstances. He also extracted a sample of the digestive juices from St. Martin’s stomach for chemical analysis. Beaumont found that the stomach juices would digest pieces of food even outside the stomach, thus proving that digestion is primarily a chemical process rather than a mechanical one.
Beaumont conducted almost 240 experiments on St. Martin between 1825 and 1833. In 1833 he published his findings in Experiments and Observations on the Gastric Juice and the Physiology of Digestion, a book that provided invaluable information on the digestive process. St. Martin returned to Canada, where he died in 1880 in his late seventies.
BULIMIA
Bulimia is an eating disorder that occurs chiefly in women in their teens and twenties, although some experts think that as many as 15 percent of bulimics are male. Bulimia comes from the Greek word boulimos, meaning “great hunger.” Individuals who are bulimic go on eating binges (often gorging on junk food), then purge their bodies of the food by making themselves vomit or by taking large amounts of laxatives (medicines or foods that stimulate bowel movements).
During an eating binge, bulimics favor high-carbohydrate foods: candy, donuts, cookies, cakes, cereal, bread, soft drinks, and ice cream. At one sitting, bulimics consume more calories than they normally would in an entire day. They usually eat quickly and messily during a binge, stuffing the food in their mouths and gulping it down.
The self-induced vomiting after a binge can cause damage to the stomach and esophagus. Acid in the vomit from the stomach can irritate the throat, damage the salivary glands, and erode tooth enamel. Blood vessels in the eyes can burst. The overuse of laxatives can cause muscle cramps, stomach pains, dehydration, and even poisoning. Over time, bulimia causes vitamin deficiencies and an imbalance of critical body fluids. Seizures and kidney failure can ultimately result.
Bulimics know that their eating habits are abnormal. They often suffer from depression, especially after a binge. Bulimics may also suffer from anxiety and low self-esteem. Some medical researchers believe bulimia is related to an imbalance in the brain chemical serotonin, which influences mood. Most research on bulimia, however, focuses on psychological factors. Treatment for bulimia generally involves psychotherapy and sometimes the use of antidepressant medications.
WORMS IN THE BODY
Tapeworms are parasites (organisms that live in or on other kinds of organisms) that live in the intestinal tracts of some animals. There are three major species of tapeworms that can infect humans. They are typically acquired from eating raw or undercooked beef, pork, or freshwater fish.
Tapeworm eggs are passed along in feces. When improperly treated human sewage is used to fertilize pastures or crops, pigs and cattle can become infected with the eggs. They can also become infected from drinking contaminated water. Freshwater fish become infected when human feces contaminate their water source.
The tapeworm eggs develop into larvae in the infected animals and fish. When humans eat the meat from those animals and fish without properly cooking it, they become infected. The tapeworm travels to the intestine, attaching itself to the inner lining by hooks on its head. If not treated, the tapeworm may stay in the intestine for years, absorbing nutrients through its outer covering. It may grow up to 30 feet (9 meters) in length.
Most individuals infected with a tapeworm have no symptoms. Some, however, may experience pain in the upper abdomen, diarrhea, unexplained weight loss, and weakness. A tapeworm’s eggs or worn body parts that appear in an individual’s feces are often the only sign of an infection.
Tapeworms are easily treated with a single oral dose of medication. Practicing good hygiene and avoiding raw or undercooked meat or fish are important steps in preventing a tapeworm infection. These foods should be thoroughly cooked to a temperature of more than 135°F (57°C). Smoking or drying meat or fish will not destroy tapeworm eggs.
ANOREXIA NERVOSA
Anorexia nervosa is a psychiatric diagnosis referring to an eating disorder that usually occurs in young women, although about 10 percent of anorectics in developed countries are young men. There are between eight and thirteen cases per 100,000 persons per year diagnosed in the United States and Canada. Anorexia comes from the Greek word anorektos, meaning “without appetite.” The problem for patients diagnosed with anorexia is not that they do not feel hunger but rather that they have a distorted body image. Anorectics do not eat because they fear gaining weight. They see themselves as fat even when they are severely underweight.
Some anorectics refuse to eat at all; others eat only small portions of fruit or vegetables. A few live only on diet drinks. In addition to fasting, anorectics may exercise strenuously to keep their weight low.
The body of a person with this disorder is severely affected. Skin becomes dry and flaky; muscles begin to waste away; bones stop growing and become brittle; menstrual periods cease; and the heart weakens. Because the body has almost no fat to keep it warm, fine downy hair grows on the face, back, and arms. Muscle cramps, dizziness, tiredness, and even brain damage or kidney and heart failure may occur. An estimated 10 to 20 percent of anorectics die, either from the effects of starvation on the cardiovascular system or by committing suicide.
Medical researchers believe that anorexia is caused by a combination of biological, psychological, and social factors. Low self-esteem, fear of losing control, and fearing growing up are common characteristics of anorectics. The emphasis on thinness in Western culture since the 1970s is believed to contribute to the disorder.
Hospitalization combined with psychotherapy and family counseling is often needed to treat anorexia; however, the long-term prognosis is not favorable for many patients. A study conducted in 2002 reported that fewer than half of patients diagnosed with anorexia recover fully; one-third improve somewhat; but 20 percent remain chronically ill.
WHAT IS LACTOSE INTOLERANCE?
Lactose is the primary carbohydrate or sugar in milk. Normally, the enzyme lactase, produced by the cells in the lining of the small intestine, breaks down lactose into simple sugars that can be absorbed into the bloodstream. In individuals who are lactose-intolerant, however, the cells have stopped producing lactase. This shutdown usually occurs in late childhood. Interestingly, lactose intolerance is not a disease; in fact, it was the normal condition of human adults for most of evolutionary history. Certain human populations underwent a change in their genetic material about 6,000 years ago, however–a change that enables the body to bypass the normal shutdown of lactase production. This genetic difference thus allows members of these populations (including most Western Europeans and people of Western European ancestry) to continue consuming fresh milk and other milk products throughout their lives.
When lactose-intolerant persons drink milk or eat small amounts of other dairy products, they can suffer discomfort from nausea, gas cramps, bloating, and diarrhea. Undigested lactose brings about these symptoms because it provides a source of energy for the bacteria that inhabit the large intestine. The gassiness and other symptoms are the result of the bacteria’s fermentation of the milk sugar.
Between 30 and 50 million Americans are lactose-intolerant; however, lactose intolerance varies widely according to race, from 25 percent of European Americans over the age of 40 to 75-90 percent of Asian Americans, African Americans, and Native Americans. Men and women are affected equally.
Lactose intolerance is not a dangerous condition. It is usually treated by making changes in the diet, such as using yogurt and fermented cheeses rather than unfermented dairy products; substituting special milk for lactose-intolerant people; or using soy milk rather than regular milk. Most people with lactose intolerance should also take a calcium supplement to keep their bones strong.
WORDS TO KNOW
Alimentary canal (al-i-MEN-tah-ree ka-NAL): Also known as the digestive tract, the series of muscular structures through which food passes while being converted to nutrients and waste products; includes the oral cavity, pharynx, esophagus, stomach, large intestine, and small intestine.
Amylase (am-i-LACE): Any of various digestive enzymes that convert starches to sugars.
Appendix (ah-PEN-dix): Small, apparently useless organ extending from the cecum.
Bile: Greenish yellow liquid produced by the liver that neutralizes acids and emulsifies fats in the duodenum.
Bolus (BO-lus): Rounded mass of food prepared by the mouth for swallowing.
Cecum (SEE-kum): Blind pouch at the beginning of the large intestine.
Chyle (KILE): Thick, whitish liquid consisting of lymph and tiny fat globules absorbed from the small intestine during digestion.
Chyme (KIME): Soupylike mixture of partially digested food and stomach secretions.
Colon (KOH-lun): Largest region of the large intestine, divided into four sections: ascending, transverse, descending, and sigmoid (colon is sometimes used to describe the entire large intestine).
Colostomy (kuh-LAS-tuh-mee): Surgical procedure in which a portion of the large intestine is brought through the abdominal wall and attached to a bag to collect feces.
Defecation (def-e-KAY-shun): Elimination of feces from the large intestine through the anus.
Dentin (DEN-tin): Bonelike material underneath the enamel of the teeth, forming the main part of the tooth.
Duodenum (doo-o-DEE-num or doo-AH-de-num): First section of the small intestine.
Emulsify (e-MULL-si-fie): To break down large fat globules into smaller droplets that stay suspended in water.
Enamel (e-NAM-el): Whitish, hard, glossy outer layer of the teeth.
Enzymes (EN-zimes): Proteins that speed up the rate of chemical reactions.
Epiglottis (ep-i-GLAH-tis): Flaplike piece of tissue at the top of the larynx that covers its opening when swallowing is occurring.
Esophagus (e-SOF-ah-gus): Muscular tube connecting the pharynx and stomach.
Feces (FEE-seez): Solid body wastes formed in the large intestine.
Flatus (FLAY-tus): Gas generated by bacteria in the large intestine.
Gastric juice (GAS-trick JOOSE): Secretion of the gastric glands of the stomach, containing hydrochloric acid, pepsin, and mucus.
Ileocecal valve (ill-ee-oh-SEE-kal VALV): Sphincter or ring of muscle that controls the flow of chyme from the ileum to the large intestine.
Ileum (ILL-ee-um): Final section of the small intestine.
Jejunum (je-JOO-num): Middle section of the small intestine.
Lacteals (LAK-tee-als): Specialized lymph capillaries in the villi of the small intestine.
Larynx (LAR-ingks): Organ between the pharynx and trachea that contains the vocal cords.
Lipase (LIE-pace): Digestive enzyme that converts lipids (fats) into fatty acids.
Lower esophageal sphincter (LOW-er i-sof-ah-GEE-al SFINGK-ter): Strong ring of muscle at the base of the esophagus that contracts to prevent stomach contents from moving back into the esophagus.
Mucosa (mew-KOS-uh): Mucous membrane; a layer of tissue that lines the cavities and passages of the body and secretes a thick, sticky fluid known as mucus.
Palate (PAL-uht): Roof of the mouth, divided into hard and soft portions, that separates the mouth from the nasal cavities.
Papillae (pah-PILL-ee): Small projections on the upper surface of the tongue that contain taste buds.
Peristalsis (per-i-STALL-sis): Series of wavelike muscular contractions that move material in one direction through a hollow organ.
Pharynx (FAR-inks): Short, muscular tube extending from the mouth and nasal cavities to the trachea and esophagus.
Plaque (PLACK): Sticky whitish film on teeth formed by a protein in saliva that combines with sugary substances in the mouth.
Pyloric sphincter (pie-LOR-ick SFINGK-ter): Strong ring of muscle at the junction of the stomach and the small intestine that regulates the flow of material between them.
Rugae (ROO-jee): Folds of the inner mucous membrane of organs, such as the stomach, that allow those organs to expand.
Trypsin (TRIP-sin): Digestive enzyme that converts proteins into amino acids; inactive form is trypsinogen.
Uvula (U-vue-lah): Fleshy projection hanging from the soft palate that raises to close off the nasal passages during swallowing.
Vestigial organ (ves-TIJ-ee-al OR-gan): Organ that is reduced in size and function when compared with that of evolutionary ancestors.
Villi (VILL-eye): Tiny, fingerlike projections on the inner lining of the small intestine that increase the rate of nutrient absorption by greatly increasing the intestine’s surface area.

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