Hormones and blood glucose control – GCSE Combined Science Biology

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Your body has to keep some things steady, such as the amount of glucose in your blood. Hormones help to do this. Hormones are chemical messengers made in glands.

It matters because too much or too little glucose makes you ill. Diabetes is what happens when this control goes wrong. Many people live with it, so it helps to understand it.

By the end you will be able to compare nerves and hormones. You will explain how insulin and glucagon control blood glucose. You will also describe type 1 and type 2 diabetes.

Nerves and hormones

Your body has two main messaging systems. The nervous system sends fast electrical impulses along neurones, which are nerve cells. The effects are quick, short-lived and aimed at one small area.

The endocrine system uses hormones instead. A gland releases a hormone straight into the blood. The blood carries it round the body to its target organ, where it causes a response.

Think of a text message to one friend, compared with a notice sent to the whole school. A reflex is a nervous response. The growth spurt of puberty is a hormonal response.

Glands and hormones

A gland is an organ that makes and releases hormones. The pituitary gland in the brain is the master gland, because its hormones control other glands. The pancreas makes insulin and glucagon. The ovaries and testes make sex hormones.

Adrenaline comes from the adrenal glands when you are frightened or excited. It prepares you for fight or flight. It speeds up the heart and sends more oxygen and glucose to the muscles.

The thyroid makes thyroxine. It controls the metabolic rate, which is how fast the chemical reactions in the body go. It is also important for growth.

Controlling blood glucose

After a meal, glucose from your food enters the blood. The pancreas monitors the level. When it is too high, the pancreas releases insulin.

Insulin makes the cells take up glucose. The liver and muscles also turn the extra glucose into glycogen, which is a store of glucose. So the blood glucose falls.

When the level is too low, the pancreas releases glucagon instead. It makes the liver turn glycogen back into glucose and release it into the blood. So the level rises.

Negative feedback

Insulin and glucagon work as a pair. Together they show negative feedback. A change away from the normal level causes a response that reverses the change.

If glucose is too high, insulin brings it down. If it is too low, glucagon brings it up. The level stays close to normal. Think of a thermostat switching a heater on and off to keep a room steady.

Thyroxine works the same way. If there is too much in the blood, the hormones that tell the thyroid to make it are reduced. Negative feedback is the basis of homeostasis, which means keeping conditions in the body steady.

Diabetes

In type 1 diabetes, the pancreas does not make enough insulin. Blood glucose can rise to a dangerous level. It usually begins in childhood. It is treated with insulin injections, and by controlling diet and the timing of meals.

Insulin is a protein, so it would be digested in the stomach if swallowed. That is why it is injected.

In type 2 diabetes, the body cells no longer respond properly to insulin. It is linked to obesity. It is controlled by diet, exercise and weight loss, and sometimes by medicine or insulin.

Obesity is a major risk factor for type 2 diabetes. Doctors use the body mass index (BMI = mass in kg ÷ height in m squared) and the waist-to-hip ratio to estimate the risk. A high BMI and a high waist-to-hip ratio are both linked to a greater chance of developing type 2 diabetes. A correlation like this does not prove that one causes the other, but there is also evidence for how it happens.

Reading glucose graphs

After a meal, blood glucose rises. In a healthy person, insulin brings it back to normal in a couple of hours. In untreated type 1 diabetes, the level goes much higher and stays high, because there is no insulin.

In a graph question, compare three things. Look at the height of the peak. Look at how long it takes to return to normal. Look at the final level.

Always use numbers from the graph in your answer.

Recap

Hormones are made in glands and carried in the blood. They are slower than nerves but last longer.

High glucose: insulin, and glucose is stored as glycogen. Low glucose: glucagon, and glycogen is broken down.

Type 1: not enough insulin. Type 2: cells do not respond. Insulin is a protein, so it is injected.