Biology – Control and coordination in mammals | e-Consult
Control and coordination in mammals (1 questions)
ADH, Glucagon, and Insulin: Mechanisms of Action and Regulation
These three hormones play crucial roles in maintaining blood glucose homeostasis. However, they differ significantly in their mechanisms of action and the stimuli that regulate their release.
ADH: ADH acts on the kidneys to increase water reabsorption. It binds to V2 receptors in the collecting ducts of the kidneys, which then activates adenylate cyclase, leading to an increase in cAMP levels. cAMP activates protein kinases, which then stimulate the insertion of aquaporins (water channels) into the apical membrane of the collecting duct cells. This increases water permeability and allows more water to be reabsorbed from the filtrate back into the bloodstream. ADH release is regulated by osmoreceptors in the hypothalamus, which detect changes in blood osmolarity. Increased osmolarity stimulates ADH release, while decreased osmolarity inhibits it.
Glucagon: Glucagon acts primarily on the liver to increase blood glucose levels. It binds to glucagon receptors on liver cells, activating adenylate cyclase and increasing cAMP levels. cAMP activates protein kinases, which then stimulate glycogenolysis (breakdown of glycogen into glucose) and gluconeogenesis (synthesis of glucose from non-carbohydrate sources). Glucagon release is stimulated by low blood glucose levels detected by alpha cells in the pancreas.
Insulin: Insulin promotes glucose uptake by cells and reduces blood glucose levels. It binds to insulin receptors on target cells (muscle, adipose tissue, liver), activating tyrosine kinase receptors. This triggers a signaling cascade that leads to the translocation of GLUT4 glucose transporters to the cell membrane, increasing glucose uptake. Insulin also stimulates glycogenesis in the liver and muscle and inhibits glycogenolysis and gluconeogenesis. Insulin release is stimulated by high blood glucose levels detected by beta cells in the pancreas.
Comparison and Contrast:
- Mechanism of Action: ADH acts on the kidneys, glucagon acts on the liver, and insulin acts on multiple tissues (muscle, adipose, liver).
- Effect on Blood Glucose: ADH indirectly affects blood glucose by influencing blood volume and concentration. Glucagon directly increases blood glucose, while insulin directly decreases blood glucose.
- Regulation: ADH release is regulated by osmoreceptors, glucagon release is regulated by low blood glucose, and insulin release is regulated by high blood glucose.