Office of Health Education & Promotion

Nicole Valentine - Mosaic

The Digestive System

The main structure of the digestive system is a long passageway, open at both ends, called the alimentary canal or the gastrointestinal tract. In adults, this tract or passageway is about 29 feet long. Food is broken down or digested by mechanical (chewing) and chemical means, and then absorbed through the walls of the intestinal tract. Food actually undergoes three kinds of processing in the body: digestion, absorption, and metabolism.

Food enters the digestive tract through the mouth and the process of digestion begins immediately. The mouth, like all of the digestive tract, is lined with mucous membranes which lubricates food passing through it. Three pairs of salivary glands contain mucus and a digestive enzyme called salivary amlyase. This enzyme begins the chemical digestion of carbohydrates.

Food moves from the mouth to the pharynx, a tubelike structure made of muscle and lined with mucous membrane. The pharynx functions as part of the respiratory and digestive systems; air must pass through the pharynx on its way to the lungs, and food must pass through it on its way to the stomach.

The esophagus, or foodpipe, is the muscular, mucus-lined tube that connects the pharynx with the stomach.

Food then travels to the stomach, passing through a sphincter, which keeps food from regurgitating back into the esophagus. Contraction of the smooth muscle of the stomach’s walls results in peristalsis, which mechanically moves chyme, a semisolid mixture of food and gastric juices, down the digestive tract.

From here, chyme moves to the small intestines, about 20 feet in length, where it is absorbed by thousands of villi, fingerlike folds that are a rich network of blood capillaries. These villi absorb products of carbohydrate and protein digestion. With the help of bile produced from the liver and stored in the gallbladder, lipid or fat materials are also mechanically broken down and then absorbed from the chyme passing through the small intestine.

Although an exocrine gland, the pancreas plays an important role in digestion. Pancreatic juice contains enzymes that digest all three major kinds of food – carbohydrates, fats, and proteins.

The large intestine, about 5 feet long, forms the lower portion of the digestive tract. Undigested and unabsorbed food materials enters the large intestine, and the chyme changes to fecal matter as water and salts are reabsorbed. Material in the large intestine that has not been digested is acted upon by bacteria to aid in this process. Bacteria here are also responsible for the synthesis of vitamin K, which is needed for normal blood clotting and for the production of some of the B-complex vitamins. Normal passage of material through the large intestine takes about 3 to 5 days.

Elimination of fecal matter from the rectum then occurs through the anus.

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The Skeletal System
The Muscular System
The Nervous System
The Digestive System
The Respiratory System

The Endocrine System
The Lymphatic System
The Urinary System
The Reproductive System