Insulin, Glucagon and other Pancreatic Hormones

Insulin

  • Name(s): Insulin

  • Chemical Class: Peptide hormone

  • What organ makes/secretes: Pancreas

  • What specific cell makes/secretes: Beta cells of the Islets of Langerhans

  • How does the specific cell make the hormone: Beta cells synthesize proinsulin, which is then converted into insulin and stored in secretory vesicles.

  • How does the hormone travel through the blood: Insulin is released into the bloodstream and circulates freely.

  • Target organ: Primarily liver, muscle, and adipose tissue.

  • Target cell: Cells with insulin receptors, especially muscle and fat cells.

  • Where it binds to its receptor: Insulin binds to insulin receptors (tyrosine kinase receptors) on target cells, activating signaling pathways.

  • What effect hormone has: Facilitates glucose uptake by cells, promotes glycogen synthesis, inhibits gluconeogenesis, and regulates lipid metabolism.

  • Hyposecretion: Leads to Type 1 Diabetes (Juvenile Diabetes) characterized by high blood glucose levels, resulting in symptoms like polyuria, polydipsia, and polyphagia.

  • Hypersecretion: Can lead to hypoglycemia, which may cause symptoms such as dizziness, confusion, and fainting.

  • What causes release (stimulus): Increased blood glucose levels, after a meal, and the presence of certain amino acids and glucagon.

  • What prevents release (inhibition): Low blood glucose levels, somatostatin (GHIH) from delta cells.

Glucagon

  • Name(s): Glucagon

  • Chemical Class: Peptide hormone

  • What organ makes/secretes: Pancreas

  • What specific cell makes/secretes: Alpha cells of the Islets of Langerhans

  • How does the specific cell make the hormone: Alpha cells synthesize proglucagon, which is processed into glucagon.

  • How does the hormone travel through the blood: Released into the bloodstream and circulates freely.

  • Target organ: Primarily liver.

  • Target cell: Hepatocytes (liver cells).

  • Where it binds to its receptor: Glucagon binds to glucagon receptors on target cells, activating a G-protein coupled receptor pathway.

  • What effect hormone has: Increases blood glucose levels by promoting glycogenolysis and gluconeogenesis in the liver.

  • Hyposecretion: Can lead to hypoglycemia, especially in those with conditions affecting glucose metabolism.

  • Hypersecretion: Can lead to hyperglycemia, often seen in Type 2 Diabetes due to increased insulin resistance.

  • What causes release (stimulus): Low blood glucose levels, sympathetic nervous system activation, certain amino acids.

  • What prevents release (inhibition): High blood glucose levels, insulin release.

Other Pancreatic Hormones

Somatostatin (GHIH)

  • Name(s): Somatostatin

  • Chemical Class: Peptide hormone

  • What organ makes/secretes: Pancreas

  • What specific cell makes/secretes: Delta cells of the Islets of Langerhans

  • How does the specific cell make the hormone: Delta cells synthesize pro-somatostatin, which is processed into somatostatin.

  • How does the hormone travel through the blood: Released into the bloodstream and circulates freely.

  • Target organ: Various organs including the pancreas, intestines, and pituitary gland.

  • Target cell: Cells with somatostatin receptors.

  • Where it binds to its receptor: Binds to specific somatostatin receptors, inhibiting hormone secretion.

  • What effect hormone has: Inhibits the release of other hormones (e.g., insulin, glucagon, and growth hormone).

  • Hyposecretion: Can lead to uncontrolled release of insulin and glucagon, potentially disrupting glucose homeostasis.

  • Hypersecretion: Can lead to decreased secretion of both insulin and glucagon, affecting blood glucose levels.

  • What causes release (stimulus): Increase in blood glucose and certain gut hormones.

  • What prevents release (inhibition): Low nutrient levels and certain feedback mechanisms from insulin and glucagon.