Diabetes mellitus (hyposecretion of insulin)

Low insulin disturbs the metabolism of carbohydrates and lipids. Because glucose cannot enter the cells:

• blood glucose rises (hyperglycaemia);
• the kidney cannot reabsorb all the glucose, so glucose appears in the urine (glucosuria);
• the glucose in the urine holds a lot of water with it (osmotically), so a large volume of urine is excreted (polyuria) → continual thirst (polydipsia);
• cells that cannot use glucose burn fats and proteins → weight loss, tiredness, and acidic ketone bodies in the blood; in severe, untreated cases the person falls into diabetic coma. Treatment: regular insulin injections (type 1), diet and exercise, and tablets that stimulate insulin release (type 2).

Hypoglycaemia (too much insulin or too little food) causes sweating, shaking and fainting; the person is helped by sugar, and in severe cases by glucagon.

Worked example 9 (glucose test). A fasting person's blood glucose is 70 mg/100 cm³ — slightly low, and glucagon is released. After a heavy meal it rises to 160 → insulin is released → it falls back to about 100. Another: blood glucose 250 mg/100 cm³ after fasting, with glucose in the urine and excessive thirst → diabetes mellitus.

Worked example 10. A body has 5 litres of blood and a normal level of 100 mg/100 cm³. How much glucose is in the blood? 5000 cm³ ÷ 100 × 100 mg = 5000 mg = 5 g. This small amount (about a teaspoon) shows how precisely it must be regulated.