Small intestine

The small intestine is part of the gastrointestinal tract.

Function of the small intestine

The small intestine follows the stomach and is composed of the duodenum, jejunum and ileum. Its function is to continue the digestion of foods, and particularly to absorb nutrients.

The intestine secretes intestinal juice, which is neutral or slightly basic and contains the enzymes required to convert chyme (the food digested by the stomach) into chyle, which only contains nutrients.

Foods are absorbed by these passing from the lumen of theintestine to the inside by la crossing the intestinal wall. Glucose and sugars in general, amino acids, short chain fatty acids and glycerol pass into blood vessels. Long chain fatty acids and triglycerides pass into lymph vessels. Water, minerals and vitamins can pass into either of these vessels.

Structure of the small intestine

The smallintestine is an average of 6 metres in length and increases the contact surface area between nutrients and the wall to by up to 250 square meters. It is the presence of folds at different levels which make this increase possible: co-operating valvules (folds in the mucosa) covered by intestinal villi (folds in intestinal connective tissue) and also cellular micro-villi (folds in the enterocyte plasma membrane).

Peristaltic movement of food occurs as a result of the circular and longitudinal muscle layers.