Anatomical Model, Intestinal Villi Model

Villi exist to increase the surface area available for food absorption; this area has been estimated at approximately eleven square yards. Also, under some conditions, food may pass through the small intestine rapidly; the villi make the most of the time that the digested material is in contact with the intestine.
The intestinal villi (1) project from the surface of the mucous membrane over the folds and between them. They have cores of lamina propria (8), which is composed of loose connective tissue. Each villus contains a vascular capillary network (3), a central lacteal (7), and nerve fibers. The second consists of the vascular system; here, one arteriole (5) enters each villus splitting into capillaries and is collected by venules (4).
The crypts of Lieberkühn (6) open between the villi. They produce enzymes, mucus and possibly a hormone. There are goblet cells (21) in the crypts among the columnar epithelium (20). Goblet cells may also be found in the epithelium (2) in the villi. At the bottom of the crypts, the Paneth cells (22) may be located; although there are several theories their function is unknown
at the present time. They are special cells that contain zinc. The muscularis mucosae (10, 11) possess no distinguishing characteristics. The muscularis consists of an inner circular (10) and outer longitudinal layer (11), and it thins out as it approaches the large intestine. The submucosa (13) distinguishes the blood and lymph vessels. The serosa (16) is composed of visceral peritoneum. Efferent nerve fibers from Auerbach’s plexus (18) are muscle-oriented and Meissner’s plexus (19) are submucosa-oriented. Between them, they serve the smooth muscle of the intestinal wall. The visceral afferent nerves conduct the impulses from the intestine to the central nervous system. Complete absorption into the blood stream is a complex biochemical process. Briefly, the simple sugars, minerals, amino acids, vitamins, and some glycerol pass through the epithelial cells (2) of the villi into the capillaries (3).
The lymph vessels (7) in the villi receive the products of fat digestion and transport them through the mucosal cells into the lymph. Not all fats are absorbed at equal rates or to an equal degree.