Key Stage 4 science · Biology – Coordination and control

GCSE hormones, contraception and homeostasis explained

Hormones are chemical messengers that coordinate slower, longer-lasting changes in the body, from growth and puberty to blood sugar control. At GCSE, students learn how the endocrine system works, the role of hormones in human reproduction including the menstrual cycle, how hormonal and non-hormonal methods of contraception work, and how negative feedback keeps internal conditions steady. That steadiness is called homeostasis, and it is central to understanding diabetes and temperature control.

Hormones and homeostasis, explained

The endocrine system is made of glands that release hormones directly into the blood. The hormones travel round the body and affect only their target organs. Compared with nerve impulses, the response is slower but lasts longer. The pituitary gland in the brain is often called the master gland because many of its hormones control other glands. Others to know are the thyroid (thyroxine, which sets metabolic rate), the pancreas (insulin and glucagon), the adrenal glands (adrenaline, for the fight or flight response), the ovaries (oestrogen and progesterone) and the testes (testosterone).

Reproductive hormones control puberty and, in females, the menstrual cycle. Over roughly 28 days an egg matures in an ovary and the lining of the uterus thickens. FSH from the pituitary causes an egg to mature and the ovary to release oestrogen. Oestrogen makes the lining grow and triggers a surge of LH, which causes ovulation, the release of the egg, around the middle of the cycle. Progesterone then keeps the lining in place, and if there is no pregnancy, levels of these hormones fall and the lining is shed in a period. Cycle length varies from person to person, and 28 days is a textbook average.

Contraception is taught as part of this topic. Hormonal methods use oestrogen, progesterone or both to stop eggs maturing or being released, or to make it harder for sperm to reach an egg. These include the pill, the implant, the injection and the patch. Non-hormonal methods include condoms and diaphragms, which are barriers, the copper intra-uterine device, sterilisation and abstaining from sex. Only condoms also protect against sexually transmitted infections. Schools teach this factually and alongside wider health education, and students learn how each method works and how they compare.

Homeostasis means keeping conditions inside the body, such as temperature, blood glucose and water content, within narrow limits so that cells and enzymes can work. The mechanism is negative feedback: receptors detect a change, a control centre coordinates the response, effectors reverse the change, and the system returns to its normal level. After a meal, rising blood glucose makes the pancreas release insulin, which causes glucose to move into cells and the liver to store it as glycogen. Between meals, falling glucose triggers glucagon, which converts glycogen back to glucose. In type 1 diabetes the pancreas does not make enough insulin. In type 2 diabetes, body cells stop responding to it properly. Body temperature is controlled by negative feedback too: when you are hot you sweat and the blood vessels near the skin widen to lose heat, and when you are cold you shiver and those vessels narrow. Some courses, often the separate biology GCSE, study temperature control in more detail.

Words your child will hear

Hormone: A chemical messenger made in a gland and carried by the blood to target organs.
Target organ: The organ or tissue that responds to a particular hormone.
Ovulation: The release of a mature egg from an ovary.
Homeostasis: Keeping internal conditions such as temperature and blood glucose within narrow limits.
Negative feedback: A control system in which a change triggers a response that reverses that change.
Insulin and glucagon: Hormones from the pancreas: insulin lowers blood glucose and glucagon raises it.
Glycogen: The storage carbohydrate made from glucose in the liver and muscles.

What the National Curriculum says

The programme of study for Key Stage 4 says:

Students should be taught about principles of hormonal coordination and control in humans
Students should be taught about hormones in human reproduction, hormonal and non-hormonal methods of contraception
Students should be taught about homeostasis

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A model exam answer

Explain how the body controls blood glucose after a meal rich in carbohydrate. (4 marks)

Digestion of the carbohydrate releases glucose, which is absorbed into the blood, so the blood glucose concentration rises above the normal level.
The pancreas detects this rise and responds by releasing the hormone insulin into the blood.
Insulin travels to the liver and muscle cells. It causes the cells to take up glucose from the blood, and the liver converts glucose into glycogen for storage.
As glucose leaves the blood, the concentration falls back to normal. When it is back to normal, the pancreas releases less insulin. This is negative feedback because the response reverses the original change.

Rising blood glucose is detected by the pancreas, which releases insulin. Insulin makes cells take up glucose and the liver store it as glycogen, so the level falls back to normal. This is negative feedback.

Common mistakes and how to help

“Negative” feedback means something bad happens

In everyday speech negative means harmful or critical.

What helps: In biology, negative means the response opposes the change. Like a thermostat switching the heating off when a room is warm enough, it brings the system back to its normal level.

Mixing up insulin and glucagon

Both come from the pancreas, both affect glucose, and the names sound similar.

What helps: Insulin “puts it in”: it takes glucose out of the blood into cells and stores it. Glucagon “gets it out”: it converts glycogen back to glucose, which is released into the blood.

Homeostasis keeps conditions exactly fixed

Textbooks say a level such as 37 °C is “maintained”, which sounds like a single value.

What helps: Conditions vary a little around a set point. Negative feedback keeps them within narrow limits, which is why graphs of body temperature wobble up and down.

The contraceptive pill protects against sexually transmitted infections

People tend to think of contraception as one thing, and the pill is the best-known method.

What helps: Hormonal methods prevent pregnancy, not infection. Only condoms do both. Being clear about the two different purposes avoids a risky muddle.

How to help at home

Spot homeostasis in action. Notice what your body does after a run or in a cold house: going red, sweating, goosebumps, shivering. Ask your teenager to name the receptor, the response and how it reverses the change.
Use a household thermostat. A heating thermostat is a good model of negative feedback, with a set point, a sensor and a heater that switches on and off. Ask where the analogy works and where the body is more complicated.
Sketch the glucose loop. Ask for a diagram of blood glucose rising after a meal and falling after insulin, then the reverse with glucagon. Labelling the two curves and the organs involved is a common exam task.
Be available, not awkward. Puberty, periods and contraception are covered at school as well. Letting your teenager know they can ask you questions, or ask a doctor or nurse, matters more than having perfect answers.