Intestines absorbs collective amount of ingested fluid and fluid secreted in gastrointestinal secretions. Throughout the inner wall of small intestine many folds called valvulae conniventes (also known as folds of kerckring) present, which increase the surface area for absorption. The valvulae conniventes covered by small protrusions known as villi (singular ‘Villus’). Figure 12.4 shows the longitudinal section of the villus.

Figure 12.4: Longitudinal section of the villus.

Absorption of Monosaccharides: Absorption of glucose and galactose occur through active transport. Sodium pump on the cell membrane helps in its active transport. Fructose is absorbed by facilitated diffusion. Glucose, galactose and fructose are absorbed into the blood capillaries. Galactose is the most rapidly transported monosaccharide.
Absorption of amino acids: Amino acids are absorbed by active transport coupled with active sodium transport. They also enter the blood stream.

Absorption of fatty acids and glycerol: Fatty acids and glycerol are insoluble in water thus they can’t enter in blood stream directly. In intestinal lumen, bile salts and phospholipids incorporates fatty acids and glycerol into small, spherical water soluble droplets known as micelles. Fat soluble vitamins and sterols along with fatty acids and glycerol are absorbed by diffusion by the help of micelles into intestinal cells, where they are resynthesized in the endoplasmic reticulum and are converted into small droplets known as chylomicrons. Latter most of them released into lymph present in lacteals (lymphatic capillaries).