6.5 Absorption and Assimilation of Digested Food
1. Ileum is the major site of nutrient absorption.
2. Soluble nutrients are absorbed by simple diffusion, facilitated diffusion or active transport.
Adaptive characteristics of the digestive system
1. The wall of the small intestine is covered with epithelial cells that are specialized to complete the digestive process.
2. The small intestine in adults is a long and narrow tube about 6 metre long, is the longest section of the alimentary canal.
3. The small intestine contains small finger-like projections of tissue called villi which increase the surface area of the intestine and contain specialized cells that transport substances into the bloodstream.
4. Specific feature of the villi:
(a) there are numerous in number. This feature increases the internal surface area of the intestinal walls making available a greater surface area for absorption.
(b) they have moist and thin wall, one cell thick, which enables a shorter diffusion path.
(c) the epithelial cells contain microvilli which provide a large surface area for more rapid absorption.
(d) contain network of blood capillaries for the absorption and efficient transport of digested food.
(e) contain lacteals for more efficient absorption of fatty acids and glycerol into the blood stream.
5. The absorbed food substances are transported to the various body tissues or organs to be assimilated or to be stored for later use.