Understanding Blood Glucose Homeostasis and Diabetes
Understanding Diabetes and Blood Glucose
Diabetes is a group of disorders that affect the body’s ability to regulate blood glucose (sugar) levels. The term diabetes mellitus refers to conditions caused by problems with the hormone insulin, while diabetes insipidus is a separate disorder involving the regulation of water balance in the body.
- Type 1 diabetes: Occurs when the body’s immune system destroys insulin-producing cells in the pancreas.
- Type 2 diabetes: Develops when the body becomes resistant to insulin or does not produce enough insulin.
The Role of Homeostasis
Homeostasis is the system of maintaining a stable internal environment within a biological system. Human blood glucose homeostasis is the process by which the body maintains an optimal concentration of blood glucose, which is approximately 5mM. This process is vital, as deviations from this range cause two primary health problems:
- Hyperglycaemia: When blood glucose is too high.
- Hypoglycaemia: When blood glucose is too low, resulting in insufficient ATP to carry out life processes.
Regulation of High Blood Glucose
When blood glucose concentration increases above the normal range (approximately 4–8 mmol L⁻¹), such as after a carbohydrate-rich meal, the body responds as follows:
- Detection: Beta cells within the Islets of Langerhans in the pancreas detect the increase.
- Response: The pancreas releases insulin via exocytosis.
- Communication: The pancreas communicates with the hypothalamus, which acts as the control centre.
- Action: Insulin binds to receptors on liver, muscle, and fat cells.
- Effect: GLUT4 transport proteins facilitate glucose uptake, and insulin promotes glycogenesis (storing glucose as glycogen) while inhibiting gluconeogenesis.
As a result, blood glucose concentration decreases back to the normal range, preventing hyperglycaemia.
Regulation of Low Blood Glucose
When blood glucose concentration falls below the normal range, such as during exercise or fasting, the body initiates a counter-response:
- Detection: Alpha cells within the Islets of Langerhans detect the decrease.
- Response: The pancreas releases glucagon into the bloodstream.
- Action: Glucagon binds to receptors on liver cells, activating glycogen phosphorylase.
- Effect: Glycogenolysis occurs, breaking down stored glycogen into glucose, which is released into the bloodstream.
As blood glucose levels rise back toward the normal range, the effects of hypoglycaemia are prevented. Together, these insulin and glucagon pathways operate through negative feedback mechanisms to maintain the body’s optimal set point.