Biology – Homeostasis in mammals | e-Consult

Insulin and glucagon are key hormones in maintaining blood glucose homeostasis. They act antagonistically to ensure blood glucose levels remain within a narrow range. Insulin is released when blood glucose is high, and glucagon is released when blood glucose is low.

Insulin's actions: Insulin promotes glucose uptake by both muscle and liver cells. In muscle cells, it stimulates the insertion of GLUT4 transporters into the cell membrane, facilitating glucose entry. Inside the muscle cell, glucose can be used for energy or stored as glycogen. In the liver, insulin stimulates glycogenesis, converting glucose to glycogen for storage. It also inhibits gluconeogenesis, preventing the liver from producing more glucose.

Glucagon's actions: Glucagon counteracts insulin's effects. When blood glucose is low, glucagon stimulates glycogenolysis in the liver, breaking down stored glycogen into glucose and releasing it into the bloodstream. It also stimulates gluconeogenesis in the liver, synthesizing glucose from non-carbohydrate sources like amino acids.

Defects in hormone secretion: A deficiency in insulin secretion (e.g., in Type 1 diabetes) leads to persistently high blood glucose levels (hyperglycemia). This is because glucose cannot enter cells effectively, and the liver continues to produce glucose. A deficiency in glucagon secretion is less common but would result in persistently low blood glucose levels (hypoglycemia). The body would struggle to release glucose from glycogen stores or synthesize new glucose, leading to a lack of energy for cells.