Hormonal regulation of metabolism
Insulin is the main building (anabolic) hormone; glucagon, epinephrine and cortisol mostly break down stores (catabolic) to release fuel.
Six hormones and their effects
| Hormone (source) | Carbohydrate | Protein | Fat |
|---|---|---|---|
| Insulin (β-cells, pancreas) | ↓ blood glucose: ↑ uptake into muscle and adipose tissue, ↑ glycogen synthesis and glycolysis, ↓ gluconeogenesis | ↑ amino acid uptake and protein synthesis; ↓ protein breakdown | ↑ fat synthesis (lipogenesis) and storage; ↓ lipolysis |
| Glucagon (α-cells, pancreas) | ↑ blood glucose: ↑ glycogen breakdown and gluconeogenesis in liver | ↑ amino acid uptake by liver for gluconeogenesis | ↑ lipolysis; ↑ ketone body formation |
| Epinephrine (adrenal medulla) | ↑ blood glucose quickly: glycogen breakdown in liver and muscle | Little direct effect | ↑ lipolysis |
| Cortisol (adrenal cortex) | ↑ blood glucose: ↑ gluconeogenesis, ↓ glucose uptake by tissues | ↑ muscle protein breakdown; amino acids sent to liver | Supports lipolysis; excess moves fat to face and trunk |
| Thyroid hormones, T₃ and T₄ (thyroid) | ↑ glucose absorption, glycogenolysis and gluconeogenesis; ↑ BMR (basal metabolic rate) | Normal levels: ↑ protein synthesis (growth). Excess: protein breakdown | ↑ lipolysis; ↓ blood cholesterol |
| Growth hormone (anterior pituitary) | ↑ blood glucose (anti-insulin); ↓ glucose uptake by muscle | ↑ protein synthesis (anabolic, via IGF-1, insulin-like growth factor 1) | ↑ lipolysis; fat used as fuel |
Anabolic vs catabolic
Insulin is the only hormone that lowers blood glucose. The others raise it and are called counter-regulatory (anti-insulin) hormones.
Diabetes mellitus: when insulin action fails
| Change | Why (hormone link) |
|---|---|
| Type 1 vs type 2 | Type 1: β-cells are destroyed, so no insulin is made. Type 2: insulin is made but tissues respond poorly (insulin resistance). |
| High blood glucose (hyperglycaemia) | Muscle and adipose tissue take up less glucose; liver keeps making glucose because glucagon acts unopposed. |
| Glucose in urine, frequent urination | Blood glucose rises above the kidney's threshold; glucose in urine pulls water with it. |
| Weight loss, muscle wasting | Fat and muscle protein are broken down for fuel and gluconeogenesis. |
| Ketoacidosis (mainly type 1) | Unchecked lipolysis floods the liver with fatty acids, which become ketone bodies and make the blood acidic. |
Low glycaemic index foods such as whole grains, ragi, other millets and pulses release glucose slowly and need less insulin. Chromium is thought to help insulin act (evidence is mixed), zinc is needed to store insulin in β-cells, and thyroid hormones need iodine.
2 marks: “Name two hormones that raise blood glucose.” Glucagon and epinephrine (also cortisol, growth hormone and thyroid hormones).
5 marks: “Explain the role of insulin in metabolism.” Lowers blood glucose (uptake, glycogen synthesis, ↓ gluconeogenesis), builds protein, builds fat and blocks lipolysis. Lack causes diabetes.
10 marks: “Discuss the hormonal regulation of carbohydrate, protein and fat metabolism.” Tabulate six hormones against the three nutrients, contrast anabolic and catabolic hormones, and end with diabetes.
Insulin puts fuel in (store). Glucagon is called when glucose is gone (release).