Most digestion and absorption of food occurs in the small intestine. The small intestine is a narrow, twisting tube that occupies most of the lower abdomen between the stomach and the beginning of the large intestine. It extends about 20 feet in length. The small intestine consists of three parts: the duodenum, the jejunum, and the ileum.
The Duodenum
The duodenum plays an important role in the emptying of stomach contents into the small intestine. The Duodenum is the site of complete digestion of all four biological molecules and final breakdown of molecules digested by the mouth and stomach. The walls of the duodenum secrete peptidase and maltase along with the hormones CCK and secretin. This in turn acts as a signal for the release of bile from the liver and digestive enzymes from the pancreas. The process of enzymatic breakdown of food in the duodenum begins.
Absorption of iron occurs primarily in the duodenum and upper jejunum. Apart from iron, amino acids, gylcerol, Calcium, fatty acids, monoglycerides, vitamin A and B, monosaccharides, and disaccharides are absorbed in the duodenum.
Absorption of iron occurs primarily in the duodenum and upper jejunum. Apart from iron, amino acids, gylcerol, Calcium, fatty acids, monoglycerides, vitamin A and B, monosaccharides, and disaccharides are absorbed in the duodenum.
The Jejunum
There are small projections in the wall of the jejunum called villi. These villi are covered with smaller projections called microvilli. The villi increase the surface area of the jejunum and allows more absorption of nutrients in this part of the small intestine. Simple sugars, water soluble vitamins (except vitamin C and some Bs) and amino acids made from the food is passed from the villi into the blood stream while the fat is passed into the lymph capillaries. The rest of the food passes into the ileum.
The Ileum
The last absorption of nutrients from the food takes place here—amino acids (protein digestion), fat-soluble vitamins , fatty acids (the end products of fat digestion), cholesterol, sodium, potassium alcohol, and B12. The unabsorbed and undigested food then passes from the ileum into the beginning of the large intestine.