Pancreatic Hormones-Chemistry, Secretion, Functions and Regulations (Insulin and Glucagon).

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 The pancreas plays a central role in regulating blood glucose levels through the secretion of two crucial hormones: insulin and glucagon. These hormones work in opposition to each other to maintain glucose homeostasis in the body. Here's an overview of insulin and glucagon, including their chemistry, secretion, functions, and regulation:

1. Insulin:

  • Chemistry: Insulin is a peptide hormone composed of two polypeptide chains connected by disulfide bridges. It consists of 51 amino acids in humans.
  • Secretion: Insulin is synthesized and secreted by the beta cells of the pancreatic islets of Langerhans. Its secretion is primarily stimulated by rising blood glucose levels.
  • Functions:
    • Glucose Uptake: Insulin facilitates the uptake of glucose into cells, particularly muscle and adipose (fat) cells, by promoting the translocation of glucose transporters (GLUT4) to the cell membrane.
    • Glycogen Synthesis: Insulin stimulates glycogen synthesis in the liver and muscles, converting excess glucose into glycogen for storage.
    • Protein Synthesis: It promotes protein synthesis by increasing amino acid uptake and protein production in cells.
    • Lipid Storage: Insulin encourages the storage of excess glucose as triglycerides (fat) in adipose tissue.
    • Inhibition of Glucose Production: Insulin inhibits gluconeogenesis (the production of glucose from non-carbohydrate sources) in the liver.
  • Regulation: Insulin secretion is primarily regulated by blood glucose levels. When blood glucose rises (e.g., after a meal), beta cells release insulin to help cells take up glucose and lower blood sugar.

2. Glucagon:

  • Chemistry: Glucagon is a peptide hormone composed of 29 amino acids.
  • Secretion: Glucagon is synthesized and released by the alpha cells of the pancreatic islets of Langerhans. Its secretion is stimulated by low blood glucose levels and other factors, such as amino acids and stress.
  • Functions:
    • Glycogenolysis: Glucagon stimulates the breakdown of glycogen in the liver, releasing glucose into the bloodstream. This process is called glycogenolysis.
    • Gluconeogenesis: Glucagon promotes gluconeogenesis in the liver, increasing the production of glucose from non-carbohydrate sources, such as amino acids and glycerol.
    • Lipolysis: It stimulates the breakdown of triglycerides in adipose tissue, releasing fatty acids into the bloodstream for use as an energy source.
  • Regulation: Glucagon secretion is primarily regulated by blood glucose levels. When blood glucose drops (e.g., between meals or during fasting), alpha cells release glucagon to raise blood sugar levels by stimulating glucose production and release.

In summary, insulin and glucagon are the key pancreatic hormones responsible for maintaining glucose homeostasis. They work in opposition to regulate blood glucose levels, with insulin lowering blood sugar by promoting glucose uptake and storage, while glucagon raises blood sugar by promoting glucose production and release. The secretion of these hormones is tightly regulated by blood glucose levels to ensure that glucose levels remain within a narrow range, supporting overall metabolic health. Dysregulation of insulin and glucagon can lead to disorders like diabetes mellitus.


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