Small Intestine

The partly digested food enters the small intestine where it is completely digested by intestinal, pancreatic and bile enzymes. Digested food is broken down into the final products of amino acids, glucose, fatty acids and glycerol, and monosaccharide (glucose, fructose and etc.) The small intestine is made up of 2 sections: the duodenum and the ileum.  (Some text may refer to it as being divided into 3 parts). The inner surface of the small intestine is lined with finger like projections called villi.

Theses villi increase the surface area of the small intestine thus creating a larger area for digestion and absorption.

Each villi is lined with other finger like projections called the micro villi.  This further increases the surface area of the small intestine.

The duodenum is the place where most of the chemical digestion takes place. Enzymes from the pancreas, a large glandular organ close to the stomach, enter the small intestine at the duodenum and supplement the intestinal enzymes in the digestion. Bile (a liquid containing salts, pigment and cholesterol) is created by the liver and stored in the gall bladder, a saclike structure close to the liver.  Bile also enters the small intestine at the duodenum and assists in the digestion of fats by breaking fats into emulsified fats (smaller droplets of fat).

A list of the enzymes found in the small intestine and their location and purpose is shown below:

Enzyme Food stuff End product Point of action
Salivary Amylase Starch Maltose Mouth
Pancreatic Amylase Starch Maltose Duodenum
Intestinal Amylase Starch Maltose Ileum
Maltase Maltose Glucose Ileum
Lactase Lactose(milk sugar) Glucose and Galactose Ileum
Sucrase Sucrose Glucose and Fructose Ileum
Pepsin Protein Polypeptides Stomach
Trypsin Protein Polypeptides Duodenum
Peptidase Polypeptides Amino acids Duodenum
Milk Protein Milk Protein Renin Stomach
Bile (no enzymes) Fats Fat droplets Duodenum
Lipase Fat droplets Fatty acids and Glycerol Duodenum

The ileum is the site of digestion for carbohydrates as can be seen above. Most of the absorption also takes place in this area. This brings us to our next section.

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