Blood glucose control

Biology · Coordination and control. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Cells need a steady supply of glucose for respiration, so the blood glucose concentration must stay close to a set point. Too little and cells, especially brain cells, run short of energy. Too much and water leaves cells by osmosis.

The pancreas detects the concentration and releases two hormones. Insulin is released when blood glucose is too high. It makes the liver take up glucose and convert it to glycogen for storage. Glucagon is released when blood glucose is too low. It makes the liver convert glycogen back to glucose.

In Type 1 diabetes the pancreas does not make enough insulin, so blood glucose stays high and glucose appears in the urine. It is treated with insulin.

Rules to remember

Blood glucose too high → pancreas releases insulin → liver converts glucose to glycogen → blood glucose falls.
Blood glucose too low → pancreas releases glucagon → liver converts glycogen to glucose → blood glucose rises.
Glycogen is stored in the liver and muscles.
Both hormones are made by the pancreas; the liver is the target organ.
Type 1 diabetes signs: increased blood glucose concentration and glucose in the urine.
Type 1 diabetes treatment: administration of insulin, usually by injection.

Common mistake

Glucagon and glycogen are different things. Glucagon is the hormone; glycogen is the storage carbohydrate. Check the spelling before you choose an answer.

Worked example

A student has not eaten for ten hours, but her blood glucose concentration is still close to normal. Explain how.

Her cells keep using glucose for respiration, so the blood glucose concentration starts to fall.
The pancreas detects the fall and releases glucagon into the blood.
Glucagon makes the liver convert stored glycogen into glucose.
The glucose passes into the blood, so the concentration rises back towards the set point.

Answer: Glucagon from the pancreas makes the liver break down glycogen to glucose, which keeps blood glucose near the set point between meals.

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