The digestive system consists of organs--the mouth, esophagus, stomach, and small and large intestines--and glands--salivary glands, liver, gall bladder, and pancreas. The glands secrete digestive juices containing enzymes that chemically break down food into smaller, more absorbable molecules. In addition to providing the body with the nutrients and energy it needs to function, the digestive system also separates and disposes of waste products ingested with the food.
Digestive disorders in infancy
Malformation of any one of the digestive organs can disrupt digestive functions. Surgery is required to correct most of these conditions. The intake of food can be disrupted by orofacial clefts, commonly known as cleft lip and palette or palate. This condition is usually corrected by surgery within the first three months following birth, and may be corrected within the first days after birth. Infants with cleft lip or palate may have difficulty feeding because they are unable to suck efficiently enough to nurse or bottle feed. Special bottles that direct the flow of formula to the back of the mouth are used in these cases.
Another congenital disorder, an abnormal closure in an opening of one of the digestive system organs called atresia, requires surgery as soon as possible after birth to allow normal function of the digestive system. Abnormal closures may also affect the intestines. An imperforate anus is completely closed off, and surgery to create an opening is required immediately after birth.
Abnormal narrowing of a digestive system passageway, stenosis, typically affects the stomach or intestines. In pyloric stenosis, the pyloric sphincter between the stomach and small intestine is too small to allow food to pass through it. A symptom of pyloric stenosis is projectile vomiting following every feeding, usually within 15 to 30 minutes. Most infants with pyloric stenosis begin to exhibit projectile vomiting sometime between two weeks and four months. The vomiting may develop gradually while the parents and pediatrician try various strategies for relieving a newborn's "spitting up." Pyloric stenosis may occur as often as one in every 250 births, and is most common in male, white, first-born babies. Like most narrowing or closures of digestive system organs, pyloric stenosis is serious and must be corrected with surgery. Similarly, in anal stenosis, the anus is too small to allow the passage of fecal material.
Infants with chronic vomiting may also have a condition that results when the esophogeal sphincter, the valve between the esophagus and stomach, allows the stomach contents to flow back into the esophagus. This problem, usually outgrown within the first year, can be alleviated by burping the infant frequently and by leaving the infant in an upright or semi-upright position for at least 30 minutes following a feeding. For bottlefed babies, thickening the formula with baby cereal may help.
Digestive disorders in toddler, preschool, and school years
After the first few months of life, the most common causes of digestive disorders are infections caused by a virus or, less commonly, bacteria or parasites. An intestinal infection, referred to as gastroenteritis, is spread by unsanitary water or food supplies. A pediatrician should be consulted when a young child experiencing abdominal pain exhibits any of these warning signs: vomits blood or greenish bile; exhibits strenuous or repeated vomiting, or vomiting that lasts more than 24 hours; complains of harsh abdominal pain or has a swollen abdomen; exhibits symptoms of dehydration, such as decreased or lack of urination; is unable to take fluids; or seizure.
When an infant or young child is vomiting, it is important to keep his head turned to the side or face down over a basin or towel to minimize the possibility that the vomitus (material being vomited) be inhaled into the lungs. A key concern whenever a young child is vomiting and unable to keep anything in her stomach is dehydration. About one to two hours after the last vomiting episode, offer the child a few sips of cool water. Follow this every half hour with a few sips of water or other clear liquid such as sugar water or gelatin water (one-half to one teaspoon of sugar or flavored gelatin in about four ounces of water). There are also commercial electrolyte solutions that your pediatrician may prescribe to counteract the potential for dehydration during a bout with vomiting. Gradually return the child to a normal diet over the next 24 hours, while continuing to encourage his intake of fluids. If your child is unable to keep fluids down, and continues to vomit for more than 24 hours, notify your pediatrician. He may order diagnostic blood, urine, and other tests. In rare instances, a hospital stay may be required.
After age five, emotional upset--either distress or excitement--sometimes triggers abdominal pain and even vomiting. If your child exhibits recurring abdominal pain and vomiting accompanied by change in behavior, emotional triggers for the digestive problems should be considered. Your pediatrician, your child's teacher, or a child psychologist can help diagnose the root of the emotional upset.
Inguinal hernia, present in 5% of all children and more commonly in boys than girls, occurs when an opening in the lower abdominal wall allows the child's intestine to squeeze through. Most hernias are not painful, and they are discovered when the child, parent, or pediatrician notices a bulge in the groin area. A hernia develops when the large sac that surrounds the abdominal organs, known as the peritoneum, does not close properly prior to birth. Openings in the peritoneum can allow small section of the intestine to push through into the groin (in boys or girls) or the scrotum (in boys).
In a small percentage of hernias, the section of intestine becomes trapped, causing a condition known as incarcerated hernia. When there is tenderness or swelling associated with a hernia, it may be incarcerated. All hernias require medical attention, but the presence of pain or swelling make it urgent that you seek treatment.
Digestive disorders in adolescence
Eating disorders , such as anorexia nervosa and bulimia nervosa , affect mostly young women in adolescence. Not digestive disorders per se, eating disorders can contribute to physical problems centerd in the digestive system.
Stomach ulcers are sores that form in the lining of the stomach. Ulcers are rare in children and uncommon in adolescents. People who are at most risk for ulcers are those who smoke, middle-age and older men, chronic users of alcohol, and those who take anti-inflammatory drugs, such as aspirin and ibuprofen.
NORMAL FUNCTION OF THE DIGESTIVE SYSTEM
Food is taken into the mouth where the teeth break it down into smaller pieces. The tongue rolls these pieces into balls (boluses). The sensations of sight, taste, and smell cause the salivary glands, located in the mouth, to produce saliva which then pours into the mouth to soften the food. Amylase, a type of enzyme in the saliva, begins the breakdown of carbohydrates (starch) into simple sugars. Ptyalin, one of the main amylase enzymes found in the mouth, is also secreted by the pancreas.
The moistened and partially digested food is maneuvered to the back of the mouth (pharynx) by the tongue, where it is then swallowed. In the throat, rings of muscles force the food into the esophagus, which moves the food from the throat to the upper part of the stomach with wavelike muscular contractions. Known as peristalsis, this muscle action consists of the alternate contraction and relaxation of the smooth muscles of the esophagus. At the junction of the esophagus and stomach, the powerful esophageal sphincter muscle acts as a valve to keep food, stomach acids, and bile from flowing back into the esophagus and mouth.
Digestion in the stomach
Chemical digestion begins in the stomach, where food is broken down by the action of gastric juice containing hydrochloric acid and a protein- digesting enzyme called pepsin. The stomach lining also secretes mucus to protect itself from being irritated by the gastric juices. The gastric juices break the food into smaller molecules, which, in turn, stimulate the stomach lining to release the hormone gastrin into the bloodstream.
Stomach muscles churn the food into a fine semi-liquid paste called chyme. The pyloric sphincter between the stomach and the duodenum (the first section of the small intestine) controls the flow of chyme from the stomach.
The small intestine or small bowel is a long, narrow tube about 20 ft (6 m) long. Coiled and twisted between the stomach and the large intestine, the small intestine's lining, the mucosa, contains millions of glands that aid in the digestive and absorptive processes. Muscle action moves the chyme toward the large intestine through the three sections of the small intestine-the duodenum, the jejunum, and the ileum. Upon entering the duodenum, chyme undergoes further enzymatic digestion and is subjected to pancreatic juice, intestinal juice, and bile. There are three enzymes in pancreatic juice which digest carbohydrates, fats, and proteins. The gall bladder secretes bile containing bile salts and other substances that help to emulsify (dissolve) fats which are otherwise insoluble in water.
Chyme passing from the duodenum next reaches the 3-ft (1-m) jejunum of the small intestine, where the digested breakdown products of carbohydrates, fats, proteins, and most of the vitamins, minerals, and iron are absorbed. The inner lining of the small intestine is composed of up to five million tiny, finger-like projections called villi. The villi increase the rate of absorption of the nutrients into the bloodstream by extending the surface of the small intestine to about five times that of the surface area of the skin. The last section of the small intestine is the ileum.
Absorption and elimination in the large intestine
The large intestine, or colon, is wider and heavier then the small intestine, but much shorter-only about 4 ft (1 .2 m) long. It rises up on one side of the body (the ascending colon), crosses over to the other side (the transverse colon), descends (the descending colon), forms an S-shape (the sigmoid colon), reaches the muscular rectum, about 5 in (113 cm) long, where the feces is expelled through the anus, which has a large muscular sphincter that controls the passage of waste matter. Fecal matter contains undigested food, bacteria, and cells from the walls of the digestive tract.
The gallbladder lies under the liver and is connected by various ducts to the liver and the duodenum. its main function is to store bile until it is concentrated enough to be used by the small intestine. Bile contains cholesterol dissolved in the bile acids.
The pancreas, in its digestion function, secretes pancreatic juices when food reaches the small intestine. In its endocrine function, a group of cells within the pancreas secrete the hormone insulin. Insulin targets liver and muscle cells, and allows them to take excess sugar from the blood and store it in the form of glycogen.
For Your Information
- Maryon-Davis, Alan and Steven Parker. Food and Digestion. New York: F. Watts, 1990.
- Peikin, Steven R. Gastrointestinal Health. New York: HarperCollins, 1991.
- Thompson, W. Grant. The Angry Gut: Coping with Colitis and Crohn's Disease. New York: Plenum Press, 1993.
Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.