Lecture05 - Lecture 05: Chapter 3 - Digestion, Absorption,...

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Lecture 05: Chapter 3 - Digestion, Absorption, and Transport (continued) ABSORPTION : the passage of nutrients from the GI tract into either the blood or the lymph One meal: Within 3-4 hours, on the order of 4 x 10 23 molecules are absorbed, half of which come from carbohydrate digestion and the remainder from protein and lipid digestion + many vitamin and mineral molecules. 10-foot length of small intestine has a surface area equal to about 1,000 square yards (the surface area of a tennis court). Nutrients absorbed across this surface are swept away in the bloodstream, and carried to the liver and other parts of the body. Anatomy of the Absorptive System : Figure 3-10 Inner surface of the small intestine is highly folded and contoured into thousands of fingerlike projections called villi (singular = villus ). A single villus is composed of hundreds of cells , each of which is covered with tiny hairlike projections called microvilli . In the crevices between the villi lie crypts : tubular glands that secrete enzyme-rich intestinal juices into the small intestine. Each villus is lined with a thin sheet of muscle that keeps it in constant motion, waving like the tentacles of a sea anemone, so that the villus can trap nutrient particles. Its many microvilli then can absorb digested nutrients from the particle, as further enzymatic digestion of the particle continues. Nutrient Absorption : Figure 3-9. The membranes surrounding the cells of the microvilli possess a variety of enzymes, "pumps", and carriers that are specialized for recognizing the different kinds of nutrients
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Lecture05 - Lecture 05: Chapter 3 - Digestion, Absorption,...

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