Edexcel IGCSE Biology · Spec 2.94-2.95B
Hormones
The endocrine system, the effects of adrenaline, and how insulin and glucagon control blood glucose.
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Hormones
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Explained
Hormones, and keeping their jobs straight
A hormone is a chemical messenger made by a gland of the endocrine system, carried in the blood to a target organ. That route explains the difference from the nervous system: hormones travel more slowly, reach the whole body, and their effects last longer.
The hormones, and which gland makes each
- Adrenaline, from the adrenal glands: raises heart and breathing rates and redirects blood to the muscles, preparing the body for action.
- Insulin, from the pancreas: released when blood glucose is high, and causes glucose to be taken up by cells and stored as glycogen.
- Glucagon, from the pancreas: released when blood glucose is low, and causes glycogen to be converted back into glucose.
- ADH, from the pituitary gland: increases water reabsorption from the collecting ducts when the blood is too concentrated.
- Testosterone, from the testes: male secondary sexual characteristics and sperm production.
- Oestrogen, from the ovaries: female secondary sexual characteristics, and rebuilds the uterus lining.
- Progesterone, from the ovaries and placenta: maintains the uterus lining and supports pregnancy.
- FSH, from the pituitary gland: stimulates an egg to mature and stimulates oestrogen secretion.
- LH, from the pituitary gland: triggers ovulation.
Controlling blood glucose
Insulin and glucagon work against each other, which is what makes control possible. After a meal, blood glucose rises, the pancreas releases insulin, cells take up glucose and the liver stores the excess as glycogen, so the level falls.
Between meals the level drops, the pancreas releases glucagon, the liver converts glycogen back to glucose, and the level rises. Each correction triggers the opposite response, which is negative feedback.
Glycogen and glucagon are separated by two letters and are completely different things. One is a storage carbohydrate, the other is a hormone. Write them carefully.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Biology describe candidates who understood that the hormones all have roles in the menstrual cycle but confused which role belonged to which, with some suggesting that LH causes eggs to mature.
That is FSH. LH triggers ovulation, which is the release of the egg, not its maturation. The two are easy to swap and the reports show it happening.
On glucose control, responses are credited for identifying people with diabetes as unable to control blood sugar because of a lack of insulin. Saying what the hormone does, not just naming it, is what earns the second mark.
Keeping FSH and LH apart
FSH comes first in the alphabet and first in the cycle: it matures the egg. LH follows and releases it. If you can hold that order, the rest of the cycle falls into place around it.
Spec 2.94-2.95B
What you need to know
- Describe the endocrine system
- Explain adrenaline and blood glucose control
- Recall the other key hormones for Triple
Active recall
Quick check
Answer each question before opening the answer.
What are the effects of adrenaline?
It increases heart rate, breathing rate and blood glucose — preparing the body for 'fight or flight'.
How is blood glucose controlled by the pancreas?
Insulin lowers it (glucose → glycogen in the liver); glucagon raises it (glycogen → glucose).
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