FUNCTIONS OF THE GASTRO INTESTINAL TRACT
The gastrointestinal system includes the gastrointestinal tract (mouth, pharynx, oesophagus, stomach, small intestine, large intestine, including rectum) and the glandular organs (salivary glands, liver, gallbladder and pancreas) that are not part of the tract but secrete substances into it via ducts connecting these organs to the tract. The overall function of the gastrointestinal system is to process ingested foods into molecular forms that can be transferred, along with salts and water, from the external environment to the body's internal environment, where they can be distributed to cells by the circulatory system.
Fig shows depicts the anatomy of the gastrointestinal system. The liver overlies the gallbladder and a portion of the stomach, and the stomach overlies part of the pancreas.
The entire oesophagus functions as one tissue during swallowing. As the bolus of food is moved voluntarily from the mouth to the pharynx, the upper sphincter relaxes, the food moves into the oesophagus, and the lower esophageal sphincter relaxes to receive the food. Peristaltic waves move the bolus down the oesophagus and into the stomach.
The alimentary tract provides the body with a continual supply of water, electrolytes and nutrients. To achieve this requires
1. Movement of food through the alimentary tract.
2. Secretion of digestive juices and digestion of the food.
3. Absorption of the digestive products, water and the various electrolytes.
4. Circulation of blood through the gastro intestinal organs to carry away the absorbed substances and
5. Control of all these functions by the nervous and hormonal system.
The small and large intestines serve as organs of digestion, absorption and excretion. Digestion is initiated in the mouth and stomach and is continued in the duodenum and jejunum with the aid of secretions from the liver, pancreas and small intestine. Absorption occurs primarily in the jejunum; the only substances absorbed in the terminal ileum are fats, bile salts and vitamin B12. The large intestine or colon exists for the purpose of absorbing water and excreting the faecal mass.