HUMAN BODY SYSTEMS Skeletal Muscular Circulatory Lymphatic Digestive Excretory Endocrine Reproductive Skin Respiratory

The digestive system is responsible for processing food, breaking it down into usable proteins, carbohydrates, minerals, fats, and other substances, and introducing these into the bloodstream so that they can be used by the body. The digestive, or alimentary, tract begins at the mouth, where the teeth and tongue begin the breakdown of food, aided by saliva secreted by the salivary glands. DIGESTIVE SYSTEM The chewed food, combined with saliva, is swallowed, carrying it in peristaltic (contractile) waves down the esophagus to the stomach. In the stomach, the food combines with hydrochloric acid which further assists in breaking it down. Click on this picture!

When the food is thoroughly digested, the fluid remaining, called chyme, is passed through the pylorus sphincter to the small intestine and large intestines. Within the long, convoluted intestinal canals, the nutrients are absorbed from the chyme into the bloodstream, leaving the unusable residue. This residue passes through the colon (where most of the water is absorbed into the bloodstream) and into the rectum where it is stored prior to excretion. This solid waste, called feces, is compacted together and, upon excretion, passes through the anal canal and the anus. Along the way through the digestive tract, the pancreas, spleen, liver, and gallbladder secrete enzymes which aid in the digestive process.

The mouth is a responsible for chewing and swallowing food. The mouth cavity is located just below the nasal cavity and is formed by the palatine bones and the palatine processes of the maxilla on top and by the mandible on bottom. At the opening of the mouth cavity are the lips - muscular structures which are covered with thin, membranous skin. The lips occlude the mouth opening during chewing to keep food and liquid within, and help manipulate food during chewing. Within the mouth cavity, the teeth extend down from their maxillary sockets and up from their mandibular sockets to form the dental arcade. The muscles of the tongue assist in manipulating food and swallowing.

The stomach is one of the primary organs of the digestive system. It is located in the middle of the abdominal cavity and extends from the lower end of the esophagus to the duodenum. The chewed food paste enters the stomach from the esophagus. The cardiac gastric glands lubricate the food as it comes in. The stomach secretes hydrochloric acid and the enzymes which help digest the carbohydrates, proteins and fats in food. The stomach is lined with a durable mucous lining which protects it from the gastric juices so that the stomach itself is not digested.

The liver is the largest of the body's glands and is responsible for several important functions. Located mostly on the right side of the abdominal cavity, just above the duodenum, the liver aids in the digestion of fats by secreting bile into the duodenum. The liver also destroys red blood cells, forms urea for the excretion of nitrogenous wastes, forms fibrinogen, used in blood coagulation, stores glycogen, helps in the metabolism and storage of vitamins, and produces protective and antitoxic substances, among its many functions.

The small intestine is responsible for completing digestion and for absorbing the usable food products into the lymphatic system and bloodstream. The small intestine itself consists of a coiled, narrow tube (1-2 inches in diameter), between 19 and 22 feet (about 6-7 meters) long, in the lower abdomen, below the stomach. The large intestine is a broad, corrugated tube which accepts the by-products of digestion from the small intestine and passes it along to be excreted, continuing to process the material on the way. Any unabsorbed food materials are stored in the large intestine until the body can partially reabsorb water from it, then passing the remains along to the anus for elimination.