Absorption of different products of digestion becomes easier in ileum due to its enormously increased surface area . There is an apparently 600 folds increase in total internal surface area of small intestine due to presence of folds (3 times), villi (10 times) and microvilli (20 times). Enhanced surfaces area ensures more complete and quicker absorption of digestion products. Bile salts again play an important role in absorption of fat digestion products and fat soluble vitamins.
Assimilation is the ultimate process in which various nutrients are transported to different organs of the body for their actual metabolism and functions for which they are consumed.
Glucose and other monosaccharides are used for energy production by all cells, conversion in glycogen (stored carbohydrate of liver and muscles) and fats (in adipose tissue). Amino acids are utilized by all body cells for incorporation into different cellular proteins required for growth, cell division, synthesis of enzymes & hormones, tissue repair and some for energy productions. Fatty acids are mainly utilized for energy production, synthesis of stored lipids/body fats, milk fats and cell repair etc. Nitrogenous bases of nucleic acids are incorporated in synthesis of fresh nucleic acids during cell division and cellular metabolism.