⚡ Adrenaline
Made by the adrenal glands, which sit just above the kidneys. It prepares your body for sudden action.
Co-ordination and Response » Adrenaline and Insulin
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 2.94
- Where adrenaline is made and what it does to the body
- Why adrenaline is called the "fight or flight" hormone
- Where insulin is made and how it lowers blood glucose
- What glycogen is and where it is stored
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Unlock This CourseHormones that act fast and hormones that keep things steady
In the lesson Nervous and Hormonal Communication you learned that hormones are chemical messages made in endocrine glands. They travel in the blood and change the activity of their target organs. This lesson looks at two hormones, one that gets your body ready for action and one that keeps your blood glucose under control.
🍬 Insulin
Made by the pancreas, an organ just below the stomach. It lowers the level of glucose in the blood.
Key terms:
- Adrenaline: a hormone made by the adrenal glands that prepares the body for "fight or flight".
- Insulin: a hormone made by the pancreas that lowers the concentration of glucose in the blood.
- Glycogen: a storage carbohydrate made from many glucose molecules joined together. It is stored in the liver and muscles.
Adrenaline: fight or flight
Imagine you are walking home in the dark and a dog suddenly runs at you from behind a wall. Your brain senses danger and your adrenal glands release adrenaline into the blood. Within seconds your body is ready to either stand and fight or run away. This is why adrenaline is called the "fight or flight" hormone.
Adrenaline travels around the body in the blood. Its target organs include the heart, the muscles used for breathing, and the liver. It has these effects:
- Your heart rate increases. The heart pumps faster, so blood carries oxygen and glucose to the muscles more quickly.
- Your breathing rate increases. You take in more oxygen and get rid of carbon dioxide faster.
- More glucose is made available to your muscles. The extra glucose in the blood is used in respiration to release more energy.
All three effects help the muscles to release energy faster. That is exactly what you need to sprint away from a dog or to defend yourself. You also met the effect on heart rate in the lesson Heart Rate and Exercise, so remember that adrenaline is one of the things that can make the heart beat faster.
Fight or flight in one line
Danger or excitement → adrenaline released from the adrenal glands → faster heart rate, faster breathing and more glucose for the muscles → more energy released for action.
The effects of adrenaline wear off once the danger has passed and the hormone has been broken down.
Insulin: lowering blood glucose
When you eat a meal rich in carbohydrate, such as pasta or rice, the carbohydrate is digested to glucose and the glucose moves into the blood. If the level of glucose in the blood stayed high, it would harm the body. Your body needs to keep it within a narrow range.
The pancreas detects the high glucose level and releases insulin into the blood. Insulin travels around the body and reaches its target organs, the liver and the muscles. Insulin makes the liver and muscles change glucose into glycogen. The glycogen is stored in these organs.
Because glucose is being taken out of the blood and turned into glycogen, the concentration of glucose in the blood falls back towards normal.
🍝 Blood glucose is too high
This can happen after eating a carbohydrate-rich meal. The pancreas releases insulin.
📉 Blood glucose falls
Liver and muscles change glucose into glycogen, which is stored. Less glucose is left in the blood.
Insulin in one line
High blood glucose → pancreas releases insulin → liver and muscles change glucose into glycogen → blood glucose falls.
Insulin made in the lab by genetically modified bacteria is covered in the lesson Insulin Production from Bacteria.
Comparing the two hormones
⚡ Adrenaline
- Source: adrenal glands
- Role: prepares the body for fight or flight
- Effects: faster heart rate, faster breathing, more glucose to the muscles
🍬 Insulin
- Source: pancreas
- Role: lowers blood glucose
- Effect: liver and muscles change glucose into glycogen, so blood glucose falls
Worked example
A runner hears the starting gun. Which hormone is released, where does it come from, and what does it do?
The hormone is adrenaline. It comes from the adrenal glands. It makes the heart beat faster and the breathing rate increase, and it makes more glucose available to the muscles, so the muscles can release more energy by respiration for the race.
Common mistakes
- Saying adrenaline is made by the kidneys. The adrenal glands are above the kidneys, but they are separate glands.
- Mixing up glucose and glycogen. Glucose is the sugar in the blood. Glycogen is the stored form kept in the liver and muscles.
- Saying insulin "makes glucose" or "gets rid of glucose". Insulin makes the liver and muscles change glucose into glycogen.
- Writing that adrenaline "gives you energy". It increases heart rate, breathing rate and glucose supply so the muscles can release energy faster.
- Saying the pancreas makes adrenaline, or that the adrenal glands make insulin.
Exam-style question
(a) Name the gland that makes insulin. [1 mark]
(b) Describe how insulin lowers the concentration of glucose in the blood. [2 marks]
(c) A cyclist sees a car pull out suddenly. Explain how adrenaline helps the cyclist to react. [3 marks]
Model answer
(a) The pancreas (1)
(b) Insulin makes the liver and muscles (1) change glucose into glycogen, so there is less glucose in the blood (1)
(c) Adrenaline is released from the adrenal glands (1) and makes the heart rate and breathing rate increase (1), so more oxygen and glucose reach the muscles to release energy for action (1)
Exam tip
When you describe a hormone, give its source, its target and its effect. For insulin, always finish with "so blood glucose falls", and for adrenaline link each effect to more energy for the muscles.