Insulin is the central hormone responsible for maintaining glucose homeostasis. After a meal, pancreatic β-cells release insulin into the bloodstream, allowing tissues such as skeletal muscle and adipose tissue to absorb glucose efficiently. At the molecular level, insulin binds to the insulin receptor, a receptor tyrosine kinase located on the cell membrane. This activates intracellular signaling pathways, mainly the PI3K-AKT pathway, ultimately triggering the translocation of GLUT4 transporters to the plasma membrane. Once GLUT4 is inserted into the membrane, glucose uptake increases dramatically. In Type I diabetes, the problem is insulin deficiency. Autoimmune destruction of pancreatic β-cells progressively eliminates insulin production, preventing proper glucose uptake. Despite high blood glucose levels, cells remain in an energy-deprived state. Increased lipolysis and ketone body production may eventually lead to diabetic ketoacidosis. Type II diabetes develops differently. Insulin is initially present, often at elevated levels, but tissues become resistant to its signaling. Chronic inflammation, excess fatty acids, and defects in insulin signaling pathways impair the cellular response to insulin. Over time, pancreatic β-cells become exhausted, reducing insulin secretion further. Although both diseases cause hyperglycemia, their molecular origins are fundamentally different: Type I diabetes results from loss of insulin production, whereas Type II diabetes arises primarily from impaired insulin responsiveness. Persistent hyperglycemia promotes oxidative stress, endothelial dysfunction, and formation of advanced glycation end products (AGEs), contributing to long-term complications such as neuropathy, nephropathy, retinopathy, and cardiovascular disease. References:

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