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Hormonal Coordination in Humans » Controlling Blood Glucose

What you'll learn this session

Study time: 30 minutes

AQA spec: 4.5.3.2

How the pancreas monitors and controls blood glucose concentration
How insulin lowers blood glucose and how glycogen is stored
How to read graphs showing insulin and blood glucose
Higher tier: how glucagon works with insulin in a negative feedback cycle

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Why blood glucose must be controlled

Every cell in your body needs glucose for respiration. The glucose is carried to the cells in your blood. Keeping its level steady is one of the jobs of homeostasis.

The amount of glucose in the blood is called the blood glucose concentration. It goes up after you eat a meal, because glucose from your food is absorbed into the blood. It goes down when your cells use glucose, for example when you exercise. If it is too high or too low, your cells cannot work properly.

Key terms:

Blood glucose concentration: the amount of glucose dissolved in the blood.
Insulin: a hormone made by the pancreas that causes glucose to move from the blood into cells.

The pancreas is in charge

Blood glucose concentration is monitored and controlled by the pancreas. The pancreas is a gland in the endocrine system. It checks the concentration of glucose in the blood all the time. When the concentration changes, the pancreas releases a hormone into the blood.

▲ Glucose too high

This happens after a meal. The pancreas produces the hormone insulin. Insulin lowers the blood glucose concentration.

▼ Glucose too low

This happens when cells have used up glucose. At Higher tier, the pancreas produces the hormone glucagon. Glucagon raises the blood glucose concentration.

How insulin works

If the blood glucose concentration is too high, the pancreas produces insulin. The insulin travels in the blood and causes glucose to move from the blood into the cells. This takes glucose out of the blood, so the blood glucose concentration falls back to normal.

The glucose does not just stay in the cells. In liver cells and muscle cells, the excess glucose is converted to glycogen for storage. Glycogen is a store of glucose that can be used later.

Here is the whole process in order:

You eat a meal, and glucose is absorbed into the blood.
The blood glucose concentration rises above normal.
The pancreas detects this and produces insulin.
Insulin causes glucose to move from the blood into cells.
In liver and muscle cells, excess glucose is converted to glycogen.
The blood glucose concentration falls back to normal.

Common mistakes

Saying that insulin is made in the liver. It is made in the pancreas. Another mistake is saying that glycogen is stored in the blood. Excess glucose is converted to glycogen inside liver cells and muscle cells.

Higher tier only: glucagon and negative feedback

Higher tier only

If the blood glucose concentration is too low, the pancreas produces the hormone glucagon. Glucagon causes glycogen to be converted into glucose, which is released into the blood. This raises the blood glucose concentration back to normal.

Insulin and glucagon work against each other. Together they form a negative feedback cycle: a change in one direction causes a response that brings the level back the other way.

Higher tier only

When glucose is too high, insulin is released and glucose is stored as glycogen, so the level goes down. When glucose is too low, glucagon is released and glycogen is converted to glucose, so the level goes up. Insulin brings a high level down and glucagon brings a low level up, so the blood glucose concentration stays close to its normal level.

Key term (Higher tier only):

Glucagon: a hormone made by the pancreas that causes glycogen to be converted into glucose, which is released into the blood.

Reading graphs of insulin and blood glucose

In the exam you may be given a graph with time along the bottom and blood glucose concentration or insulin up the side. Follow these steps.

Read the axes and the units first.
Describe the pattern: where the line rises, falls or stays level.
Use figures from the graph, for example "rises from 5 to 9 units".
Link the pattern to what is happening in the body: a rise in glucose is followed by a rise in insulin.

Worked example

A person without diabetes drinks a sugary drink at time 0. Their blood glucose rises from 5 units to 9 units in the first 30 minutes, then falls back to 5 units by 120 minutes. Their insulin level rises soon after the glucose rises, and then falls. Explanation: the pancreas detects the rise in glucose and releases insulin. Insulin causes glucose to move into cells and be stored, so the blood glucose falls back to normal. When the glucose is back to normal, less insulin is needed, so the insulin level falls.

Notice that the insulin line follows the glucose line. The rise in glucose causes the rise in insulin, and the insulin then brings the glucose back down. The next lesson, Diabetes, looks at graphs for people whose control does not work properly.

Exam-style question

(a) Name the organ that monitors and controls the blood glucose concentration. [1 mark]

(b) Explain how insulin reduces the blood glucose concentration after a meal. [3 marks]

(d) Higher tier only: Explain how glucagon and insulin work together to control blood glucose. [3 marks]

Model answer

(a) The pancreas (1).

(b) The pancreas produces insulin when the glucose concentration is too high (1). Insulin causes glucose to move from the blood into cells (1). In liver and muscle cells the excess glucose is converted to glycogen for storage (1).

(d) Insulin lowers blood glucose when it is too high (1). Glucagon causes glycogen to be converted to glucose, which raises blood glucose when it is too low (1). They act in a negative feedback cycle, which keeps the blood glucose concentration steady (1).

Exam tip

In a "how" question about insulin, make three points in order: the pancreas releases it, glucose moves into cells, and the excess is stored as glycogen. Each point is a mark.

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