Insulin

Kuvaus

Insulin is a 51-amino-acid polypeptide hormone composed of two chains (A and B) linked by disulfide bonds. It was the first protein to have its amino acid sequence determined (by Frederick Sanger in 1951) and the first hormone to be produced recombinantly for medical use.

• Molecular weight: ~5.8 kDa
• Primary structure: 21 amino acids (A chain) + 30 amino acids (B chain)
• Secretion trigger: Rise in blood glucose after meals (also stimulated by amino acids, incretins, parasympathetic stimulation)

Main Functions of Insulin

Insulin acts as the key anabolic hormone in the body. Its primary actions include:

Glucose Metabolism

• Increases glucose uptake in muscle and adipose tissue via translocation of GLUT4 transporters to the cell membrane
• Stimulates glycogen synthesis in liver and muscle
• Inhibits hepatic gluconeogenesis and glycogenolysis

Lipid Metabolism

• Promotes lipogenesis (fat storage) in adipocytes
• Inhibits lipolysis (fat breakdown) by suppressing hormone-sensitive lipase
• Reduces circulating free fatty acids

Protein Metabolism

• Enhances amino acid uptake and protein synthesis
• Inhibits protein breakdown (anti-catabolic effect)

Other Effects

• Potassium uptake into cells (used clinically in hyperkalemia treatment)
• Cell growth and differentiation (via IGF-1 receptor cross-talk)

Types of Insulin Used in Medicine

Modern insulin therapy uses recombinant human insulin or insulin analogs designed for different onset, peak, and duration profiles:

Rapid-Acting Insulin Analogs

• Insulin lispro (Humalog), aspart (NovoRapid), glulisine (Apidra)
• Onset: 10–20 min | Peak: 1–2 h | Duration: 3–5 h

Short-Acting (Regular) Insulin

• Human regular insulin (Humulin R, Actrapid)
• Onset: 30 min | Peak: 2–4 h | Duration: 6–8 h

Intermediate-Acting Insulin

• NPH insulin (Humulin N, Insulatard)
• Onset: 1–2 h | Peak: 4–12 h | Duration: 12–18 h

Long-Acting Basal Analogs

• Insulin glargine (Lantus, Basaglar, Toujeo), detemir (Levemir), degludec (Tresiba)
• Near-flat 24-hour profile (degludec up to 42 h duration)

Ultra-Rapid & Ultra-Long Formulations

• Faster aspart (Fiasp), URLi lispro (Lyumjev)
• Degludec + combinations

Clinical Uses of Insulin

Insulin therapy is essential in:

• Type 1 Diabetes — absolute insulin deficiency
• Type 2 Diabetes — progressive beta-cell failure or severe insulin resistance
• Gestational Diabetes — when diet fails
• Diabetic ketoacidosis / Hyperosmolar hyperglycemic state — IV insulin protocols
• Hyperkalemia — insulin + glucose to drive potassium into cells
• Critical illness — intensive insulin therapy in some ICU settings

Common Insulin Delivery Methods

• Multiple daily injections (basal + bolus regimen)
• Insulin pump (continuous subcutaneous insulin infusion — CSII)
• Inhaled insulin (Afrezza — ultra-rapid mealtime option)
• Closed-loop / hybrid closed-loop systems (artificial pancreas)

Side Effects & Risks of Insulin Therapy

• Hypoglycemia — most common and serious risk
• Weight gain (especially with higher doses)
• Injection-site lipohypertrophy or lipoatrophy
• Edema (especially when starting or intensifying therapy)
• Rare allergic reactions (less common with human analogs)

Insulin & Weight Management (2026 Perspective)

While insulin is anabolic and can promote fat storage, modern basal-bolus regimens + GLP-1 receptor agonists + SGLT2 inhibitors + newer insulins (degludec, ultra-rapid analogs) have significantly improved the ability to achieve good glycemic control with less weight gain or even weight neutrality/loss in many patients.

Always use insulin under medical supervision with proper education on dosing, carbohydrate counting, hypoglycemia recognition, and sick-day rules.

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