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The villi are structures especially adapted to the work of absorption, and they are found only in the small intestine. The mucous membrane in all parts of the canal, however, is capable of taking up some of the digested materials. Villi. 2. Small glands, called crypts. Small artery. 2. Lacteal. 3. Villus showing termination of the lacteal. 4. Villus showing capillaries. 5.
In what different ways is the small intestine especially adapted to the work of absorption? What are the parts of a villus? What are the lacteals? Account for the name. What part is played by the capillaries and the lacteals in the work of absorption? How does their work differ? What changes, if any, take place in water, common salt, fat, proteids, and carbohydrates during absorption?
Villus showing both the lacteal and the capillaries. 6. Small vein. 7. Layer of epithelial cells. *Work of Capillaries and Lacteals.*—The capillaries and lacteals act as receivers of material as it passes through the layer of epithelial cells covering the mucous membrane. The lacteals take up the digested fats, and the capillaries receive all the other kinds of nutrients.
At B are shown little projections of the intestinal wall, called villi extending into this food and covered by a membrane. Inside of these villi are blood-vessels, C, and it will be thus seen that the membrane, B, separates two liquids, one containing the dissolved food outside the villus, and the other containing blood inside the villus.
Each villus contains a loop of blood-vessels, and another vessel, the lacteal, so called from the Latin word lac, milk, because of the milky appearance of the fluid it contains. The villi are adapted especially for the absorption of fat. They dip like the tiniest fingers into the chyle, and the minute particles of fat pass through their cellular covering and gain entrance to the lacteals.
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