In addition, approximately 79 million people in the US are estimated to have pre-diabetes, a condition in which blood glucose levels are abnormally high, but not yet high enough to be classified as diabetes. It is estimated that up to 7 million more adults have the condition but have not been diagnosed. An increasingly common disease, diabetes mellitus has been diagnosed in more than 18 million adults in the United States, and more than 200,000 children. Hormones of the Pancreasĭisorders of the Endocrine System Diabetes Mellitusĭysfunction of insulin production and secretion, as well as the target cells’ responsiveness to insulin, can lead to a condition called diabetes mellitus. As blood glucose levels decrease, further insulin release is inhibited. The secretion of insulin is regulated through a negative feedback mechanism. Finally, insulin promotes triglyceride and protein synthesis. Moreover, it stimulates the liver to convert excess glucose into glycogen for storage, and it inhibits enzymes involved in glycogenolysis and gluconeogenesis. Insulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin. Red blood cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes do not require insulin for glucose uptake. ![]() The primary function of insulin is to facilitate the uptake of glucose into body cells. The activity of glucagon is regulated through a negative feedback mechanism rising blood glucose levels inhibit further glucagon production and secretion. Taken together, these actions increase blood glucose levels. ![]() Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol.This response is known as gluconeogenesis. It stimulates the liver to take up amino acids from the blood and convert them into glucose.The glucose is then released into the circulation for use by body cells. This response is known as glycogenolysis. It stimulates the liver to convert its stores of glycogen back into glucose.In response, the alpha cells of the pancreas secrete the hormone glucagon, which has several effects: Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged labor or exercise (Figure 2). Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels. Hormones regulate both the storage and the utilization of glucose as required. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose is required for cellular respiration and is the preferred fuel for all body cells. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. Blood glucose concentration is tightly maintained between 70 mg/dL and 110 mg/dL. Regulation of Blood Glucose Levels by Insulin and Glucagonįigure 2. ![]() Elevated blood glucose levels stimulate the release of insulin. The beta cell produces the hormone insulin and makes up approximately 75 percent of each islet.Glucagon plays an important role in blood glucose regulation low blood glucose levels stimulate its release. The alpha cell produces the hormone glucagon and makes up approximately 20 percent of each islet.The pancreatic islets each contain two major types of cells: (Micrograph provided by the Regents of University of Michigan Medical School © 2012) Cells and Secretions of the Pancreatic Islets ![]() The micrograph reveals pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. Its endocrine function involves the secretion of insulin (produced by beta cells) and glucagon (produced by alpha cells) within the pancreatic islets. The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the small intestine by the pancreatic duct.
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