Answer to Question 1
The intestinal tract lining is composed of a single sheet of cells, and the sheet pokes out into millions of finger-shaped projections called villi. Each villus has its own capillary network and a lymph vessel so that as nutrients move across the cells, they can immediately mingle into the body fluids. Every villus cell has a brush-like covering of tiny hairs, called microvilli, which can trap nutrient particles.
The lining of the small intestine, villi and all, is wrinkled into thousands of folds, making its absorbent surface area enormous. If the folds and the villi that cover them were spread out flat, the total area would equal the size of a tennis court. The billions of cells of that surface, although they weigh only 4 to 5 pounds total, absorb enough nutrients in a few hours a day to nourish the other 150 or so pounds of body tissues.
Answer to Question 2
The liver produces about one liter of bile each day. Bile, made up of water, bile salts, bile pigments, and cholesterol, is slightly alkaline, which helps neutralize acidic chyme in the intestinal tract.
Bile is stored in the gallbladder and released through the common bile duct into the small intestine when fat arrives there. The bile emulsifies the fat, making it ready for enzyme action. Bile emulsifies fat-soluble vitamins and aids in their absorption with other fats. The bile pigments and cholesterol are waste products and are eventually eliminated from the body.
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