When the digested food substance reaches the ileum, enzymes are secreted from its walls. There are Protein splitting trypsin, carbohydrates spliting amylase, moltase, sucrase, lactase and fat splitting lipase enzymes. As a result, rest of the undigested protein, carbohydrate and fat are converted into amino acid, glucose (monosaccharide) and fatty acid and glycerol respectively.
Absorption: Digested liquid and simple food i.e. glucose and amino acids are absorbed by the capillaries of the villi of the small intestine and the fatty acid and glycerol being absorbed by the lacteal ducts of the villi. Excess glucose reaches the liver through hepatic portal vein. Here glucose is transformed into glycogen and is stored. Excess amino acid being transformed into urea is discharged as excreta through the kidney and the fatty food stored at different places of the body as fat.
Egestion: After the absorption of digested food, the undigested part of the food reaches the large intestine from the small intestine. Here water and mineral salts are absorbed. The rest of the waste material is stored in the rectum. Afterwards these are thrown out of the body through the cloacal aperture as faeces.