3.Human Physiology
3.3 Digestion and absorption
Digestion
Dr V Malathi
Digestion
Digestion is the mechanical and chemical break down of food into small organic fragments. During the process of digestion large complex proteins, polysaccharides, and lipids molecules are reduced to simple molecules such as simple sugar, acids acids and fatty acids before they can be absorbed by the intestinal epithelial cells.
Main Organs of the Digestive System
“Digestive-system” by Leysi24 via Wikimedia commons is licensed under CC BY 3.0
- Mouth: Digestion of food begins in the mouth. The food is chewed and mixed with saliva in the mouth so as to break it down into a form that can be easily swallowed and digested.
- Esophagus: It is the muscular tube that connects the mouth to the stomach. The food moves from the mouth through esophagus by a wave-like muscle contraction process called .
- Stomach: The food is further broken down in the stomach using stomach acids and enzymes. The food is now turned into a semi-liquid form called.The stomach links the esophagus to the duodenum. The empty stomach is only about the size of fist, but can stretch to hold as much as 4 liters of food and fluid, and then return to its resting size when empty. There are four main regions in the stomach: the cardia, fundus, body, and pylorus.
- The cardia (or cardiac region) : This is the point where the esophagus connects to the stomach and through which food passes into the stomach.
- Fundus : is located inferior to the diaphragm, above and to the left of the cardia. It is the dome-shaped .
- Body : This is the main part of the stomach and is located below the fundus.
- Pylorus : This is funnel-shaped. The pylorus connects the stomach to the duodenum. The wider end of the funnel is called the pyloric antrum, This connects to the body of the stomach. The narrower end is called the pyloric canal, which connects to the duodenum. The pyloric sphincter is located at the bottom of the stomach, between the stomach and the duodenum. It controls stomach emptying. In the absence of food, the stomach deflates inward, and its mucosa and submucosa fall into a large fold called a ruga.
- Small Intestine: The small intestine includes the the duodenum, jejunum, and ileum. Most of the digestion and absorption of nutrients occurs in the small intestine. It is the longest part of the alimentary canal, the small intestine is about 3.05 meters (10 feet) long in a living person. The diameter of the small intestine is about 2.54 cm (1 in).The folds and projections of the lining of the small intestine gives an enormous surface area of about 200 m2
- Large Intestine: The large intestine runs from the appendix to the anus and includes the cecum, colon, and rectum. The water and salts from the material that has not been digested are absorbed in the large intestine. The large intestine is responsible for forming and expelling feces. The large intestine frames the small intestine on three sides and has a diameter mo