Digestion and Absorption
Absorption and assimilation of proteins, carbohydrates and fats
- Absorption is the process by which nutrients pass from the alimentary canal into blood and lymph through its mucous membrane. 90% absorption of nutrients occurs in small intestine, 10% occurs in stomach and large intestine.
- All carbohydrates are absorbed as mono saccharides in stomach and jejunum. Glucose and galactose are absorbed by active transport. Fructose and mannose is absorbed by facilitated diffusion.
- Amino acid are absorbed by active transport and some are absorbed by facilitated transport. It occurs mainly in duodenum and jejunum. (95 - 98 %)
- Fatty acids are glycerol are insoluble in water, so they can't reach the bloodstream directly. They first incorporated into small, spherical water soluble droplets called micelles with the help of bile salts and phospholipids in the intestinal lumen. A micelle is an aggregate of many molecules.
- From the micelles fatty acids, glycerides, sterols and fat soluble vitamins are absorbed into intestinal cells by simple diffusion, where they resynthesised in ER and converted into very small fat droplets called Chylomicrons. Chylomicron are released from intestinal cells into lymph present in lymphotic capillaries, the lacteals.
- 90 % of all water absorption occurs in small intestine by osmosis from the lumen of the small intestine through epithelial cells and into the blood capillaries in the villi.
- Alcohol is lipid soluble, it begins to be absorbed in the stomach. But in the small intestine it is absorbed more rapidly than stomach. Sodium is absorbed from small intestine by active transport. Chloride can be absorbed either by active transport or diffusion. Calcium is mainly absorbed in duodenum.
- Assimilation in ears incorporation of absorbed food materials into cells as their integral and homogeneous components and are used for energy, growth and repair.
- Aminoacids are not stored but are taken up by the cells for the synthesis of proteins. Proteins are used for growth, repair etc. Excess amino acids can be converted into glucose and then to fat and are thus stored. During amino acid conversion to glucose, the amino acids are deaminated. (removal of amino group - NH2). The liver is cheif site for deamination.
- Excess glucose, fructose and galactose are usually stored in liver (reaches here by hepatic portal vein) and muscle cells in the form of glycogen (glycogenesis). Some glucose is changed as fats and stored as such.
- The fat is stored in the fat deposits of body such as subcutaneous layers, mesenteries etc. The stored fat is a readily available source of fuel for the cell.
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