Structure Of The Villi

The surface of The endothelium of the ileum is greatly increased by numerous finger-like villi (singular:villus) which projects into the lumen.
The surface areas is further increased by numerous micro villi, which projects from the cells lining the surface of the villi.

The epithelium of the villus is very thin, one cell thick, which enables the end product of digestion to diffuse through the wall of the villus easily.
Each villus has a rich supply of blood capillaries. One set of capillaries originated from arterioles in the intestinal wall.
It Carries oxygenated blood to the villus.
Another set of capillary vary deoxygenated blood from the villus into the venules which lead to the hepatic portal vein.

At the center of each villus is a blind tube called lacteal.
The tube contains transparent fluid called Lymph.
The lacteal pours it content into the lymphatic vessels.
The villi contain smooth muscles which enable them to contract and expand to.bring them in contacts with digested food.
Monosaccharides, mainly glucose; and amino acids are absorbed by diffusion and active transport across epithelial lining of the villi into the network of capillaries beneath.
These capillaries drain their contents into hepatic portal vein from where the glucose and amino acids are carried to the liver.

Fatty acids and glycerol are absorbed into the columnar epithelial cells lining the villi where they are resynthesized onto neutral fat.
These are absorbed into they lymph in the lacteals of the villi as a white emulsion of minute globules.
This passes into the lymphatic system which opens into the veins which distributes the fat through the blood vascular system.

Inorganic salts, vitamins and water are absorbed in the small intestine.
More water absorbed in the colon whose wall is much folded for this purpose.

The lining of the rectum secrets large amount of mucus which lubricates it for easy defecation or egestion of indigestible food as semi-solid faeces.
The characteristic colour and smell of the faeces is due to the bile pigment.