What insulin does, and why it must be injected
Insulin is the body's signal of plenty: released by the pancreas after a meal, it tells muscle and fat to pull glucose out of the blood and tells the liver to stop making more. In type 1 diabetes the cells that make it are destroyed, so glucose climbs to dangerous levels. The only treatment is to put insulin back — pure replacement of a missing hormone.
Insulin acts on a kinase-linked receptor on the cell surface, triggering glucose transporters to move to the membrane. Because it is a protein, swallowing it would simply mean digesting it — the gut breaks it into amino acids. So insulin is given by subcutaneous injection (or by pump), absorbed slowly from under the skin into the blood.
Copying the body's rhythm: basal and bolus
A healthy pancreas does two jobs: a steady low trickle all day and night (basal) and a sharp spike at each meal (bolus). Modern therapy copies this with two kinds of insulin engineered to have different half-lives. Rapid-acting insulins are taken at meals to cover the food; a long-acting insulin given once or twice daily provides the steady background. Mixing them lets the patient mimic a normal day.
Sketch of a day on basal-bolus insulin Blood glucose target: roughly 4-7 mmol/L fasting Long-acting (basal): 1 dose ~ flat 24-h coverage Rapid-acting (bolus): 1 dose with each meal Worked carb-counting bolus (illustrative): Insulin-to-carb ratio = 1 unit per 10 g carbohydrate Meal contains 60 g carbohydrate Meal bolus = 60 / 10 = 6 units rapid-acting Correction (illustrative): 1 unit lowers glucose ~ 2 mmol/L Pre-meal glucose 12, target 6 -> excess 6 mmol/L Correction = 6 / 2 = 3 units added Total dose = 6 + 3 = 9 units
Hypoglycaemia: the side effect that defines the drug
Insulin's great danger is its own success: give too much, or eat too little after a dose, and blood glucose falls too low. Hypoglycaemia is the most important adverse drug reaction of insulin — it causes sweating, shaking, confusion, and, if severe, seizures or coma. It is a side effect that is simply the drug's main action taken too far, so it can never be fully designed out; it can only be managed by careful dosing and patient education.
- Recognise the warning signs early: sweating, hunger, trembling, a racing heart.
- Treat at once with fast sugar — glucose tablets, juice, sweets — then a longer-acting snack.
- For a collapsed or unconscious person, glucagon (by injection) or intravenous glucose is the rescue, never food by mouth.