Homeostasis is the maintenance of relatively constant internal conditions. Homeostatic mechanisms keep physiological conditions within a certain range that is conducive to life. This definition is necessarily broad since homeostasis pervades all aspects of life and functions in any number of ways on a variety of organ systems. In fact, every organ systems functions, in some way, in some way, through homeostatic mechanisms, including the nervous system, respiratory system, circulatory system, and immune system. Even behavior has homeostatic significance. Homeostasis then is one of the major things in biology.
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Two hormones, insulin and glucagon, which are both secreted by the pancreas, are responsible for glucose homeostasis. Insulin acts to reduce the levels of blood glucose, and glucagon has the opposite effect, causing an increase in blood glucose. The pancreas contains different populations of secretory cells. Approximately 1 million cell clusters called islets of Langerhans exists in the pancreas. Each islet is composed of alpha cells that produce glucagon, beta cells that produce insulin, and delta cells that produce somatostatin, a hormone that inhibits secretion of glucagons and insulin. Digestive enzymes are secreted by pancreas cells that surround the islets. see figure 41.3.
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After eating a meal, blood glucose levels increase, and within minutes, insulin is released from beta cells in the pancreas. The immediate effect (in seconds or minutes) of insulin is to increase the rate of glucose update from the blood into target cells- primarily liver and muscle cells. Once inside cells, glucose molecules can be metabolized or linked together to produce glycogen, a storage form of glucose. As blood glucose levels fall below the normal range, glucagons is released by alpha cells of the pancreas in response.
Causes and consequences of abnormal glucose homeostasis.
Too much insulin reduces blood sugar, and serious effects or generally related to brain damage, as this organ uses glucose almost exclusively as an energy source.
