. Adventures with animals and plants. Biology. 198 Honjo a Co?nplex A?iimal Uses Food unit iv Absorption is more than simple diffu- sion through a Hfeless membrane. The cells that absorb take an active part in the absorption as is shown by the fact that they use more oxygen and produce more carbon dioxide while they are ab- sorbing. Absorption by the small intestine. If you were to slit open the small intestine along its length and examine the inside with a powerful magnifying glass, you would find it moist and pink like the lining of your cheeks. But in other re- spects it would be different.
. Adventures with animals and plants. Biology. 198 Honjo a Co?nplex A?iimal Uses Food unit iv Absorption is more than simple diffu- sion through a Hfeless membrane. The cells that absorb take an active part in the absorption as is shown by the fact that they use more oxygen and produce more carbon dioxide while they are ab- sorbing. Absorption by the small intestine. If you were to slit open the small intestine along its length and examine the inside with a powerful magnifying glass, you would find it moist and pink like the lining of your cheeks. But in other re- spects it would be different. The inside of your mouth is smooth; the lining of the small intestine is wrinkled into deep folds, sometimes one third of an inch deep. If you rubbed your hand over the folds and if your sense of touch were delicate enough you would discover that the folds feel like a soft brush or like plush, for they are covered with micro- scopic, hairlike projections. These are called villi (vilPeye), plural of villus. They are soft because they are made of delicate cells. They sway back and forth, now lengthening, now shortening. They and the folds increase the lining surface enormously. It has been estimated that the surface of this narrow tube is more than five times as great as the skin sur- face of your whole body. Study the drawing of a villus (Fig. 206) to see how the digested foods can diffuse through the thin layer of mucous membrane cov- ering the villus and go into the tiny blood vessels just underneath. Once the food is in the blood vessels it can be car- ried to larger and larger vessels and sent to every part of the body. In the center of the villus is a lacteal (lack'tee-al) into which the fatty acids and glycerin go. Capillaries Lacteal {lymphatic) Mucous membrane. Muscle cells Vein Artery Fig. 206 One of the villi of the sjnall intestine cut through lengthwise. How many kinds of tnbes does the villus contain? Can you see the opening of one intestinal gland alongside the vi
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Keywords: ., bookcentury1900, bookpublisherbostondcheath, booksubjectbiology
