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the endocrine portion of pancreas pours out the hormone insulin which promotes the transport of glucose into the tissue cells. With the drop in sugar-level, secretion of insulin also decreases. On the other hand, where blood-sugar level falls below normal, other regulatory mechanisms come into play. These promote breakdown of glycogen in the liver and the release of glucose into the blood decrease glucose utilization, mobilize lipids from the cells and enhance glucose-absorption from the intestine.
The liver plays a pivotal role in the carbohydrate me. tabolism. Here, much, of the glucose is removed and synthesized into glycogen. If in abundance, some of the glucose is converted into fat and stored. When the glucose-supply is low, liver breaks down glycogen to glucose. Under some conditions, liver can synthesize glucose from non-carbohydrate sources. During starvation, first the glycogenreserves are exhausted. Then the fat-deposits are called upon. Finally the tissue-proteins are broken down and their amino-acids used for producing glucose and energy.
Protein Metabolism
Apparently the body goes to a great deal of wasted effort. Proteins are first broken dwon into amino-acids by the digestive processes, absorbed into the blood-stream, delivered to the cells and then build back into proteins again. However this round-about procedure is necessary for two reasons : first, the food-protein molecules are too large to pass through cell-membranes, and second, the food proteins are not the (chemically) right proteins for the human body. All the proteins of all living organisms on earth, though differing from species to species, are built up from the same basic set of building materials viz. about twenty odd different amino-acids. Thus after the foodproteins are broken into their components, no matter from where they originally come from-a plant or an animalthey can be synthesized into human proteins.
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