Digestive system physiology summary

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

Digestive System Physiology The digestive system consists of the tube through which food (and digested products pass (mouth, esophagus, stomach, small intestine, large intestine, rectum and anus) as well as accessory organs (liver, pancreas, salivary glands, gall bladder) that produce substances (e.g., enzymes, bile) that assist in digestion. There are four main functions (actions is probably a better way to describe these four things) of the digestive system. 1) Motility contraction of smooth muscle lining the esophagus, stomach and intestine helps to move food stuff through the digestive system from mouth to anus. 2) Digestion this is the process whereby food is broken down into its constituent molecules (i.e., proteins broken down into amino acids; carbohydrates broken down into simple sugars; lipids broken down into free fatty acids and monoglycerides). 3) Secretion this is the secretion of substances that aid digestion from the digestive organs or accessory glands into the lumen of the stomach or intestine. 4) Absorption this refers to the uptake of digestive break down products (i.e., amino acids, small peptides, simple sugars, free fatty acids, monoglycerides) from the lumen of the digestive system into the blood. Most absorption takes place in the small intestine. A few substances (i.e., aspirin; alcohol) can be taken up across the stomach while the large intestine is predominately involved in water reabsorption. Entry of food into the esophagus is regulated by the upper esophageal sphincter while entry of food into the stomach is regulated by the lower esophageal sphincter (which also prevents backflow of food from the stomach to the esophagus. Digestion of carbohydrates begins in the mouth as the salivary glands release salivary amylase into the mouth. This begins the process of carbohydrate digestion. However, salivary amylase is inactivated in the acidic environment of the stomach. The Stomach and Intestine The stomach is divided into three regions the fundus (the top portion of the stomach located above (in a human) the lower esophageal sphincter), the body (the main central region of the stomach) and the antrum (the region closest to the small intestine). The small intestine is divided into three regions the duodenum (the region closest to the stomach), the jejunum (the middle region) and the ileum (the region closest to the large intestine). www.notesolution.com
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