How is the digestion of fats different from that of proteins and carbohydrates?
(1) Fat digestion occurs in the small intestine, and the digestion of proteins and carbohydrates occurs in the stomach
(2) Fats are absorbed into the cells as fatty acids and monoglycerides but are then modified for absorption into the blood; amino acids and glucose are not modified further
(3) Fats enter the hepatic portal circulation, but digested proteins and carbohydrates enter the lymphatic system
(4) Digested fats are absorbed in the large intestine, and digested proteins and carbohydrates are absorbed in the small intestine
(2) Absorption of fats: Fatty acids and glycerol being insoluble, cannot be absorbed into the blood after digestion and thus needs to be modified. They are first incorporated into small droplets called micelles which move into the intestinal mucosa. They are re-formed into very small protein coated fat globules called the chylomicrons which are transported into the lymph vessels (lacteals) in the villi. These lymph vessels ultimately release the absorbed substances into the blood stream.
Carbohydrates and proteins: Amino acids and glucose do not need any modification because they can be directly absorbed by active, passive and facilitated diffusion. (page-265).