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Above: The ileum is the site of absorption of water and digested food materials.
Site of absorption of water and digested food materials.
The inner surface of the ileum is structurally adapted for absorption of digested food materials.
The inner surface of the ileum consists of folds. Each fold consists of many villi. Each villus is involved in the absorption of digested nutrients, e.g. glucose, amino acids, fatty acids and glycerol.
Structural adaptations of ileum for absorption
1. Large surface area for absorption of digested food materials.
Inner surface of the small intestines is folded into many folds. Each fold bears numerous minute (about 1 mm long) finger-like projections, villi, which extend into the intestinal cavity.
Epithelial cells on the villi have numerous, tiny finger-like projections on their cell membranes called microvilli.
Increases surface area for absorption of digested food materials.
2. Steep concentration gradient maintained for diffusion of digested food materials.
Each villus is well surrounded by a branching network of blood capillaries.
Both the blood and lymph vessels continuously transport absorbed nutrients away from the small intestines.
Hence, a steep concentration gradient is maintained between blood vessels and the ileum.
Absorption of monosaccharides and amino acids
Simple sugars (eg glucose) and amino acids diffuse through the villi walls and into the blood capillaries.
Glucose and amino acids are also absorbed by active transport. This occurs when there is a lower concentration of digested food substances in the lumen of the small intestines than in the blood capillaries.
Blood transports simple sugars and amino acids from the small intestine to the liver and then to other parts of the body.
URL: https://www.youtube.com/watch?v=uNGzmqgJKNg
Absorption of fatty acids and glycerol
Both fatty acids and glycerol are insoluble in water.
Fatty acids and glycerol diffuse into the epithelium where they recombine to form fats.
Fats enter the lacteal (lymph capillary) and mix with lymph to form a milky fluid called chyle. Note: Absorption of fatty acids and glycerol cannot occur by active transport.
Chyle is eventually discharged into a vein leading into the heart.
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