Blood Glucose Regulation and Diabetes

This lesson covers blood glucose regulation and the causes and consequences of diabetes mellitus as required by the Edexcel A-Level Biology specification (9BI0), Topic 9 -- Control Systems. You need to understand the roles of insulin and glucagon, the cellular mechanisms involved, and the differences between Type 1 and Type 2 diabetes.

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Why is Blood Glucose Regulation Important?

Blood glucose concentration must be maintained within a narrow range (approximately 4-6 mmol/L when fasting, rising after a meal):

Condition	Blood Glucose Level	Consequences
Hyperglycaemia (too high)	>7 mmol/L (fasting)	Increases blood osmolarity → water leaves cells by osmosis → dehydration; long-term damage to blood vessels, nerves, kidneys, retina
Hypoglycaemia (too low)	<3.5 mmol/L	Brain cells cannot function (glucose is their primary energy source) → confusion, seizures, coma, death

Glucose is the primary respiratory substrate for most cells, and the brain relies almost exclusively on glucose for energy. Precise regulation ensures a constant supply to cells while preventing the damaging effects of excess glucose.

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The Pancreas as an Endocrine Gland