Answer
The pancreas secretes several hormones that regulate/maintain blood glucose homeostasis . Insulin and glucose are the main players, but somatostatin (STS) and pancreatic polypeptide (PPP) have important supporting roles
Insulin is produced by the beta cells of the pancreas. Secretion is stimulated by the following factors;
1. Increase in blood glucose levels
2. Increase in acetylcholine release from parasympathetic fibers of the vagus nerve (CN X-- as occurs
during exercise.
3. The presence in the plasma of the amino acids arginine and leucine--post absorptively.
4. Glucagon, GIP, and hGh also increase insulin secretion
Insulin secretion is inhibited by somatostatin
Work Step by Step
Glucagon is secreted by the alpha cells of the pancreatic islets (Islets of Langerhans). If blood glucose concentration falls below the expected normal range ( hypoglycemia) glucagon acts on liver cells to increase the levels of plasma glucose:
It breaks down glycogen --glycogenolysis-- to make more glucose available in the blood
It promotes the synthesis of glucose from lactic acid, and the amino acids arginine and leucine--
gluconeogenesis
The result of increased glucose release from the hepatocytes is that blood sugar rises to normal levels.
If blood glucose gets higher than expected normal levels, and remains persistently high,
hyperglycemia develops.
Negative feed back. If hyperglycemia persists, the high blood glucose level acts to suppress the release of
glucagon in a negative feed-back loop.
Regulation of insulin secretion:
Insulin is secreted by the beta cells of the pancreatic islands. High blood glucose levels result in the stimulation of insulin release from the beta cells. Insulin acts in the following ways to reduce high blood glucose to normal levels.
a. It increases the facilitated diffusion of glucose into various body cells
b. It speeds the conversion of glucose to glycogen--glycogenesis
c. It increases the rate of uptake of amino acids and promotes protein synthesis
d. It speeds cellular uptake of fatty acids.
As more glucose leaves the blood for body cells, the blood glucose level naturally falls within normal the normal range. If the level continues to fall and reaches hypoglycemic levels, then a negative feed back effect kicks in.--hypoglycemia inhibits the release of insulin
Normal blood glucose levels varies throughout the day. A range (fasting) of 95-100 mg/DL is usually accepted as normal for adults under 60 years of age. Non-fasting range is about 135 mg/DL -- one hour after meal-- to 115 mg/DL, two hours after meal. These values may vary with circumstances and subjects.
