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Unformatted text preview: Neural Regulation of Blood Sugar- Because glucose is the ideal source of energy for tissues, especially the brain and muscle, it is closely monitored by the brains hypothalamic centers to keep it at a constant level of 100mg/dL, but using hormonal control (as discussed rather thoroughly above) and by controlling physical behavior. The main portion of the hypothalamus that detect blood glucose changes are special neurons in the glucostatic center that have such a high metabolic rate (lots of O 2 consumption) that a slight change in glucose in their cytoplasm correlates to change in blood Glucose o When low blood sugar is detected, the hypothalamic-feeding center is activated to increase appetite and food intake, which creates a temporary hyperglycemia, which causes insulin release, which allows tissues to be flooded with glucose. o When there is high blood sugar, the hypothalamic-satiety centers are activated, which suppresses appetite and allows absorption to take place in the digestive system o When food is present in the stomach, the neurons there act on the hypothalamus to decrease food intake by releasing CCK from the duodenum. Leptin, a fat hormone, provides long-term suppression of food intake.- The hypothalamus also plays an important role in releasing hormones when the glucose level is too low o When the HTGC senses low blood glucose between meals, it directly activates the HT controls centers for the Symp NS which releases norepinephrine from nerves and epinephrine from the adrenal medulla. These catecholamines increase glycogenolysis in the liver and lipolysis in the adipose tissues (to provide glycerol for glycogenolysis) o Growth Hormone acts on fat cells to mobilize FAs and Glycerol, as well as to make the adipose tissue more sensitive to catecholamine release. GH also acts on muscle tissues to take up more AAs and use less Glu so that there is a higher reserve for the brain o Cortisol is necessary for the actions of GH on fat cells and mobilizes AAs and stimulates their utilization in gluconeogenesis. It is also important in maintaining Gluc reserves for the brain and sparing its use in muscle. o Adrenal Hormones- The adrenal glands are paired endocrine glands (the medulla and cortex) that sit right on the kidney and laugh at them. They are concerned with preparing the body for and protecting it from stress. - The adrenal medulla is part of the sympathetic nervous system and can be compared to a ganglion. Its secretory cells (chromaffin cells) can be compared to a postganglionic fiber. They synthesize the catecholamines Epinephrine (adrenaline) 80% of the time, and norepinephrine (noradrenaline) 20% of the time, both of which are derived from tyrosine (Tyr L-Dopa Dopamine NorEpi Epi)....
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- Spring '08