Structure and Function

The digestive system is also known as the gastrointestinal system or G.I. system. The main purpose of the digestive system is to break down food into small enough pieces to be absorbed into the bloodstream and used by the body. The digestive system begins at the mouth and ends at the anus, with many structures and organs connected to the 30-foot tube.

Food and fluids enter the body through the mouth. The teeth chew and grind food into pieces small enough to be swallowed. Saliva mixes with the food and begins breaking down nutrients. The food is pushed to the back of the mouth by the tongue. The food then enters the pharynx. As the food is swallowed, it enters the esophagus (food tube). The esophagus is a long tube that passes through the chest and connects to the stomach. Digestion is the breakdown of food into a form usable by the body. Digestion begins in the mouth and continues in the stomach. The stomach is a pouch situated just below the diaphragm on the left side of the abdomen. In the stomach, food is mixed with stomach acid. The partially digested food then passes into the small intestine.

The first section of the small intestine is called the duodenum; it is where food is mixed with the last of the digestive juices. Digestive juices are produced in the liver and pancreas. In the second and third sections of the small intestine, the jejunum and ileum, digestion of food is completed and nutrients are absorbed into the bloodstream. Waste products and water are then moved into the large intestine, also called the colon. Here in the colon, extra water is absorbed into the body. Formed stool is stored in the rectum until a bowel movement occurs. Stool is eliminated through the anus.

Age-Related Changes

Changes in the digestive system of the older person can be troublesome. Teeth become thin, brittle and sensitive. Missing or decayed teeth can make chewing difficult. Less saliva is produced, causing a dry mouth, diminished taste and difficulty swallowing dry food. Taste buds also decrease with age. Less acid is produced in the stomach. Absorption of calcium and some vitamins is diminished. Normal muscle activity in the stomach and intestines can be slowed, resulting in poor digestion of food and constipation. The liver decreases in size and fewer enzymes are produced, which makes metabolism and detoxification of medications more complex. Bile production decreases and gallstones may develop. The membrane lining the entire system becomes thinner and more fragile. Social isolation can result in poor appetite and unbalanced meals. Care must be taken to enhance the dining experience and to make it a socially pleasant event.

Drugs that Affect the Digestive System

1. Antacids are over-the-counter agents that neutralize stomach acid. They work in a variety of ways including decreasing acid, strengthening muscle tone in part of the stomach, or forming a gas that may be burped up and eliminated. Side effects may include poor appetite, constipation and/or diarrhea.
2. Antibiotics prevent or treat infections. Side effects may include allergic reaction, nausea, vomiting, diarrhea and/or constipation.
3. Antiulcer drugs are used to reduce acid production. There are two primary categories: 
   1. Histamine receptor blockers promote healing of ulcers and work with antacids to reduce the acidity of the stomach. Side effects may include dizziness, headaches, drowsiness and/or diarrhea. 
   1. Proton pump inhibitors inhibit the acid pump in the stomach permanently. Side effects may include headache, diarrhea and/or abdominal pain.
4. Laxatives/cathartics change the consistency of stool, speed the passage of stool through the digestive system and aid in the elimination of stool. Long-term, excessive use of laxatives may result in permanent damage to the digestive system. 
   1. Stimulant laxatives increase muscle contraction of the intestine and stimulate stool to move through the digestive system faster. Side effects may include muscle weakness, pruritus, cramps and/or electrolyte imbalance. 
   1. Saline laxatives draw water into the intestines and increase water content in the stool. Side effects may include nausea, vomiting, cramping and/or electrolyte imbalance. 
   1. Bulk-forming laxatives absorb water and then expand, increasing the bulk and water content of stool. Side effects may include abdominal cramps, diarrhea and/or obstruction. 
   1. Lubricant laxatives produce a slick barrier between the intestinal wall and the stool. This prevents water from being absorbed from the stool. Side effects may include cramping, poor absorption of nutrients and fat-soluble vitamins, and nausea. 
   1. Osmotic laxatives distend the bowel from fluid accumulation and promote movement of stool through the colon. Side effects may include nausea, vomiting, cramping and/or electrolyte imbalance. 
   1. Stool softeners are mild laxatives that are used to soften stool. Side effects may include cramping and/or rash.
5. Digestants are digestive enzymes that promote digestion of food by replacing enzymes that are lacking in the digestive system. Digestants are usually taken before or while eating a meal. Side effects may include indigestion, nausea, cramping and/or diarrhea. Digestants should be taken with food, or the body will destroy the drug. Digestive enzymes include pancreatin (Creon) and pancrelipase (Cotazym, Pancrease).
6. Drugs used to control muscle spasms of the stomach or intestines are called antispasmodic and anticholinergic agents. antidiarrheal medications also work in similar ways. They work by depressing the nerve stimulation of the muscles in the digestive tract, sometimes called an anticholinergic effect. They slow the motility of the intestinal muscle. Antispasmodics may also be used to relieve smooth muscle spasms in other organs such as the urinary bladder or gallbladder. Side effects may include dry mouth, constipation, urinary retention, blurred vision, change in heart rate, headache, dizziness and/ or fever. Antidiarrheal medications reduce water in the stool and slow the motility of the G.I. tract. Side effects may include rapid heart rate, dizziness, drowsiness and/or fatigue. Physical dependence on the medication is possible.
7. Antiemetics prevent and treat nausea and vomiting. These drugs work on the central nervous system to control the vomiting center in the brain. Side effects may include restlessness, depression, dizziness, constipation, diarrhea and/or respiratory depression. Common antiemetic drugs include prochlorperazine (Compazine), promethazine (Phenergan) and metoclopramide (Reglan).

Most medications are given through the gastrointestinal tract and therefore enter the same system as food. Food-drug interactions are common, and the more medications a person takes, the more likely it is that an interaction will occur. This type of interaction may increase, decrease or cancel out the effect of a medication. It may also increase or decrease the likelihood of side effects. A medication may be prescribed to be taken with food to provide a desired effect. The person providing direction and monitoring should be aware of possible interactions