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What Is Insulin?
Insulin is a peptide hormone produced by beta cells in the pancreatic islets of Langerhans. It consists of 51 amino acids arranged in two chains (A and B) connected by disulfide bonds. Discovered in 1921 by Banting and Best, insulin's discovery transformed diabetes from a fatal disease to a manageable condition.
Key Functions
- Lowers blood glucose by promoting cellular uptake
- Stimulates glycogen synthesis in liver and muscle
- Promotes fat storage and inhibits lipolysis
- Stimulates protein synthesis (anabolic)
- Required for life in Type 1 diabetes
Mechanism of Action
- Binds to insulin receptor (tyrosine kinase receptor)
- Activates PI3K/Akt signaling pathway
- Causes GLUT4 translocation to cell membrane
- Enables glucose entry into muscle and fat cells
Clinical Insulin Types
| Type | Onset | Peak | Duration | Examples |
|---|---|---|---|---|
| Rapid-acting | 15 min | 1-2 hr | 3-5 hr | Lispro, Aspart, Glulisine |
| Short-acting | 30 min | 2-4 hr | 6-8 hr | Regular (Humulin R) |
| Intermediate | 1-2 hr | 4-8 hr | 12-18 hr | NPH |
| Long-acting | 1-2 hr | Minimal | 24+ hr | Glargine, Detemir, Degludec |
Historical Significance
Insulin's discovery in 1921 is one of medicine's greatest achievements:
- First successfully extracted from animal pancreas
- Transformed Type 1 diabetes from fatal to manageable
- First protein to have its structure determined (Sanger, 1955)
- First human protein made by recombinant DNA (1978)
Critical Medical Information
Insulin is a life-saving prescription medication for diabetics. Misuse can cause severe hypoglycemia, coma, and death. It should only be used under medical supervision for diagnosed diabetes. Non-diabetic use (e.g., for bodybuilding) is extremely dangerous.
Summary
Insulin remains one of the most important peptide hormones in medicine, essential for millions of diabetics worldwide. Its discovery saved countless lives and its study continues to advance our understanding of metabolism. Modern insulin analogs have improved upon nature's design to better meet clinical needs.