 Glucose metabolism for the endocrine system. Common sense tells us that blood glucose levels must be maintained within homeostatic levels for good health. We manage this somewhat through conscious efforts, such as maintaining balanced nutrient intake and regular exercise. But the bulk of work for this equilibrium is done unconsciously through negative feedback systems within the body. This learning activity examines some of those hormones involved in glucose homeostasis. Seven hormones help control glucose metabolism. Growth hormone. GH, also called somatotropin, is an amino acid based hormone made by cells of the anterior pituitary gland. The main action of GH is to stimulate cells to enlarge and divide. Because it is a growth hormone, it is anabolic in promoting protein synthesis. GH increases the rate of fat usage by cells and decreases the rate at which cells use carbohydrates for energy. Thyroxine. Thyroxine is made by the follicular cells of the thyroid gland. The follicular cells need iodides to produce thyroxine. This hormone helps to regulate the metabolism of lipids, proteins, and carbohydrates in cells. Thyroxine enhances protein synthesis and lipid mobilization and stimulates the cells' use of carbohydrates as an energy source. Cortisol. Cortisol is a catabolic steroid hormone made by cells of the middle layer of the adrenal cortex gland. It is a glucocorticoid that affects glucose metabolism. Cortisol works to elevate the blood glucose level when it drops, such as between meals or after heavy exercise. Cortisol increases glucose levels by a process called gluconeogenesis. Basically, new glucose is made by the liver from non-carbohydrate sources, namely amino acids and glycerol from triglycerides. In order to have amino acids and glycerol available for gluconeogenesis, cortisol inhibits protein synthesis and promotes the release of fatty acids from fat deposits. These fatty acid molecules are an energy source to preserve the already low levels of available glucose. Abnormally high concentrations of cortisol are used to reduce inflammation. Glucogen. This amino acid-based hormone is made by the alpha cells of the islets of Langerhans, which are endocrine portions of the pancreas. Glucogen stimulates the liver to decompose stored glycogen into glucose when blood glucose levels drop, which can happen between meals or after exertion. This process, called glycogenesis, helps to bring glucose levels back toward normal. Glucogen also helps in the process of gluconeogenesis. After all, glucogen's main function is to elevate glucose levels. Insulin. This amino acid-based hormone is synthesized by the beta cells of the endocrine portions of the pancreas. The anabolic hormone is a hypoglycemic hormone in that it lowers blood glucose levels when the glucose level is high, such as after a meal. It helps in facilitated diffusion processes in getting glucose into cells for energy production. Insulin stimulates the process called glycogenesis, which is the synthesis by liver cells of the polysaccharide-storage molecule glycogen from glucose. Insulin also increases protein synthesis and is antagonistic to gluconeogenesis. Somatostatin. Made by delta cells of the pancreas, this hormone controls the glucose metabolism by inhibiting secretions of insulin and glucogens. Epinephrine, norepinephrine. These fight-or-flight hormones tend to promote processes to increase blood glucose levels since fight-or-flight functions demand the expenditure of more energy. In conclusion, many hormones and processes help regulate glucose metabolism. The various chemical and neural controls and negative feedback loops help keep this most precious fuel source in good balance and supply. Congratulations! You have completed this learning activity, Glucose Metabolism for the endocrine system.