Zoology · Ch 5 — Digestion and Absorption
Absorption of Digested Products
Absorption of Digested Products
How Absorption Happens
Absorption is the process by which the end products of digestion cross the intestinal mucosa into the blood or the lymph. Different substances use different routes:
- Simple diffusion -- small amounts of monosaccharides such as glucose, amino acids, and some electrolytes (like chloride ions) move down their own concentration gradient, needing no energy.
- Facilitated transport -- glucose and amino acids are also absorbed with the help of carrier proteins that ferry them across the membrane.
- Osmosis -- water absorption depends on the osmotic gradient created by absorbed solutes.
- Active transport -- amino acids, monosaccharides like glucose, and electrolytes such as sodium ions are also absorbed against their concentration gradient, a process that requires energy.
Absorbing Fats
Fatty acids and glycerol do not dissolve in water, so they cannot be absorbed straight into the blood. They are first packaged into tiny droplets called micelles, which move into the intestinal mucosal cells. There they are reassembled into very small, protein-coated fat globules called chylomicrons, which pass into the lymph vessels (the lacteals) running up the centre of each villus. These lymph vessels eventually carry the absorbed fat into the bloodstream.
Absorption Along the Canal
Absorption takes place at several points along the alimentary canal, though the small intestine does by far the greatest share of it.
Table: Summary of Absorption in Different Parts of the Digestive System
| Mouth | Stomach | Small Intestine | Large Intestine |
|---|---|---|---|
| Certain drugs coming in contact with the mucosa of the mouth and the lower side of the tongue are absorbed into the blood capillaries lining them. | Absorption of water, simple sugars, and alcohol etc. takes place. | Principal organ for absorption of nutrients. Digestion is completed here, and the final products of digestion such as glucose, fructose, fatty acids, glycerol and amino acids are absorbed through the mucosa into the bloodstream and lymph. | Absorption of water, some minerals and drugs takes place. |
After Absorption: Assimilation and Egestion …
| Mouth | Stomach | Small Intestine | Large Intestine |
|---|---|---|---|
| Certain drugs coming in contact with the mucosa of mouth and lower side of the tongue are absorbed into the blood capillaries lining them. | Absorption of water, simple sugars, and alcohol etc. takes place. | Principal organ for absorption of nutrients. The digestion is completed here and the final products of digestion such as glucose, fructose, fatty acids, glycerol and amino acids are absorbed through the mucosa into … |