Insulin is a peptide hormone produced by the beta cells of the pancreatic islets. It plays a crucial role in regulating blood glucose levels in the body. The primary function of insulin is to lower blood glucose levels by promoting the uptake and utilization of glucose by various tissues, as well as inhibiting glucose production and release by the liver.The mechanism of action of insulin can be described in several steps:1. Insulin secretion: When blood glucose levels rise, such as after a meal, the pancreatic beta cells secrete insulin into the bloodstream.2. Insulin binding to its receptor: Insulin binds to insulin receptors on the surface of target cells, such as muscle, adipose fat , and liver cells. The insulin receptor is a transmembrane protein with tyrosine kinase activity.3. Receptor autophosphorylation and activation: Binding of insulin to its receptor induces a conformational change, leading to autophosphorylation of specific tyrosine residues on the receptor's intracellular domain. This autophosphorylation activates the receptor's tyrosine kinase activity.4. Activation of intracellular signaling pathways: The activated insulin receptor phosphorylates and activates various intracellular signaling proteins, such as the insulin receptor substrate IRS proteins. This leads to the activation of multiple downstream signaling pathways, including the PI3K-Akt and the Ras-MAPK pathways.5. Cellular responses: The activation of these signaling pathways results in various cellular responses, including: a. Glucose uptake: Insulin stimulates the translocation of glucose transporter 4 GLUT4 to the cell membrane in muscle and adipose tissue, allowing glucose to enter the cells. b. Glycogen synthesis: In the liver and muscle cells, insulin promotes glycogen synthesis by activating glycogen synthase, the enzyme responsible for converting glucose into glycogen. c. Lipogenesis: In adipose tissue, insulin promotes the synthesis of fatty acids and triglycerides, leading to the storage of excess glucose as fat. d. Protein synthesis: Insulin promotes protein synthesis in various tissues by increasing the uptake of amino acids and activating the mTOR signaling pathway, which stimulates protein synthesis and inhibits protein degradation.6. Inhibition of glucose production and release: Insulin inhibits gluconeogenesis the production of glucose from non-carbohydrate sources and glycogenolysis the breakdown of glycogen into glucose in the liver, reducing the release of glucose into the bloodstream.Overall, the mechanism of action of insulin involves binding to its receptor, activation of intracellular signaling pathways, and the induction of various cellular responses that promote glucose uptake, utilization, and storage, as well as inhibiting glucose production and release by the liver. This helps to maintain blood glucose levels within a narrow physiological range, preventing hyperglycemia high blood glucose or hypoglycemia low blood glucose .