Absorption of water: Osmosis helps in the absorption of water in small intestine through epithelial cells surface and villi into the blood capillaries. In order to maintain the osmolality, electrolytes and digested food absorb along with water.

Absorption of electrolytes: Sodium can move in and out of epithelial cells by diffusion process and in mucosal cells it moves by active transport. Many others ions such as potassium, calcium, magnesium, iron and phosphate absorbed by active transport. Whereas chloride ions can be absorbed through diffusion or active transport. Vitamin D and parathyroid hormone enhance the absorption of calcium.

Absorption of vitamins: Most water soluble vitamins (Vitamin B complex, Vitamin C, Vitamin P) absorbed by diffusion. Castle’s intrinsic factors play an important role in reabsorption of vitamin B12.

Assimilation and egestion:
Finally, all absorbed nutrients transported by blood and lymph further transferred to blood circulation. With the help of blood nutrients reach to target body cells, where it become integral component of protoplasm and used for energy, growth and repair. This process is known as assimilation.
The excess of monosaccharide stores in liver and muscles in the form of glycogen by the process called glycogenesis. Excess of amino acids are converted into glucose and then to fat through an irreversible reaction and then stored. Most of the fats stored in subcutaneous layers and mesenteries.
Another important step is egestion, the process by which undigested food materials eliminated through anus in the form of faeces. Egestion occurs by peristalsis movement. After absorption of water in colon, chyme converted into semisolid faeces. When faeces enters into rectum, wall of rectum feels distension which induces desire of defecation due to a defecation reflex. Due to this reflex peristalsis initiated in the sigmoidal colon and reaches to anus through rectum. Involuntary action of internal anal sphincter and voluntary action of external anal sphincter thus helps in defecation.