7.1 Hormonal coordination

Why this matters

Homeostasis means keeping internal conditions roughly constant despite changes outside the body. Blood glucose, body temperature and water content are all controlled this way, with the endocrine system as one of two control systems (the nervous system is the other). Hormones are made and released by endocrine glands, travel in blood plasma, and only affect target cells that carry the matching receptor. Nervous signals are fast, short-lasting and travel along neurones; hormonal signals are slower to start but last longer and travel in blood. Most hormonal control in Edexcel 7.1 is built on negative feedback: a change in a variable triggers a response that reverses the change. Insulin and glucagon both come from the pancreas and both act on the liver, but they push glucose in opposite directions. In reproduction, the pituitary releases FSH and LH which act on the ovaries, while the ovaries release oestrogen and progesterone which act on the uterus and feed back on the pituitary. Edexcel also expects you to apply this knowledge to medical situations — using the combined pill (oestrogen + progesterone) to suppress ovulation, and using clomifene to increase FSH and LH and stimulate ovulation in women struggling to conceive. Always anchor your answers in the gland → hormone → target organ → effect chain that Edexcel mark schemes reward.

How to learn this topic

Build on what you already know

• Cell structure and the idea of receptors on cell membranes.
• Circulatory system — blood transports substances around the body.
• Basic idea of homeostasis as keeping internal conditions constant.
• What an enzyme is — useful when discussing glycogen ↔ glucose conversion.

1. Define hormone, endocrine gland and target organ; compare hormonal vs nervous coordination (slower, longer-lasting).
2. Introduce adrenaline from the adrenal glands and trace its fight-or-flight effects (heart rate, blood flow to muscles, blood glucose).
3. Build the blood-glucose negative-feedback loop using insulin and glucagon, with glycogen storage in the liver.
4. Trace the menstrual cycle: FSH from pituitary → oestrogen from follicle → LH surge → ovulation → progesterone.
5. Apply hormonal knowledge to the combined pill (oestrogen + progesterone inhibit FSH → no ovulation).
6. Apply hormonal knowledge to clomifene as a fertility treatment that increases FSH and LH.
7. Practise Edexcel-style 4–6 mark answers using the gland → hormone → target organ → effect chain.

Key terms

hormone

A chemical messenger secreted by an endocrine gland into the bloodstream that acts on a specific target organ. (Edexcel mark schemes want 'chemical' and 'travels in the blood'.)

endocrine gland

A gland that secretes hormones directly into the blood (e.g. pituitary, adrenal, pancreas, ovary).

adrenaline

A hormone released by the adrenal glands during stress that increases heart rate, blood flow to muscles and blood glucose concentration as part of the fight-or-flight response. (Name the adrenal glands AND at least two physical effects.)

insulin

A hormone secreted by the pancreas when blood glucose is too high; causes glucose to be converted to glycogen in the liver. (Edexcel verbatim: 'insulin causes glucose to be converted to glycogen (in liver)'.)

glucagon

A hormone secreted by the pancreas when blood glucose is too low; causes glycogen to be broken down to glucose in the liver. (Spell it 'glucagon' (not glycogen) — these are commonly confused.)

glycogen

The storage form of glucose, kept in the liver; can be broken down back into glucose when blood glucose falls.

pancreas

The gland below the stomach that monitors blood glucose and secretes both insulin and glucagon.

liver

The target organ for insulin and glucagon; site of glycogen storage and breakdown.

negative feedback

A control loop in which a change in a variable triggers a response that reverses the change, restoring the original level.

FSH

Follicle-stimulating hormone, secreted by the pituitary, that stimulates a follicle to mature in the ovary.

LH

Luteinising hormone, secreted by the pituitary; an LH surge triggers ovulation.

oestrogen

A hormone secreted by the follicle in the ovary that thickens the uterus lining; high oestrogen triggers the LH surge.

progesterone

A hormone secreted by the empty follicle after ovulation; maintains the uterus lining; falling progesterone causes menstruation.

combined pill

A hormonal contraceptive containing oestrogen and progesterone that inhibits FSH secretion so follicles do not mature and ovulation does not occur. (Edexcel verbatim: 'contains oestrogen and progesterone | inhibits FSH secretion | follicles do not mature | ovulation does not occur'.)

clomifene

A drug used to treat infertility that increases FSH and LH secretion from the pituitary, causing follicles to mature and ovulation to occur. (Edexcel verbatim: 'clomifene increases FSH secretion | clomifene increases LH secretion | FSH causes follicles to mature | LH triggers ovulation'.)

IVF

In-vitro fertilisation — eggs are extracted, fertilised outside the body, and one or two embryos are transferred to the uterus.

Notes

What the endocrine system is

The endocrine system is a network of glands that secrete chemicals called hormones directly into the bloodstream. The blood carries each hormone to a target organ where it produces a specific effect. Because hormones travel in blood rather than along neurones, hormonal responses are slower in onset but longer lasting than nervous responses. Only cells with the matching receptor respond to a given hormone, which is why a hormone released into the whole bloodstream only acts on certain organs. Edexcel 7.1 focuses on a small set of named hormones — adrenaline, insulin, glucagon, FSH, LH, oestrogen and progesterone — and the glands that secrete them.

Adrenaline and fight or flight

When the body is frightened, stressed or excited, adrenaline is secreted by the adrenal glands (one sitting on top of each kidney). Adrenaline travels in the blood and binds to receptors in several target organs, producing a coordinated 'fight or flight' response:

• it increases heart rate, so blood is pumped more quickly around the body;
• blood flow to the muscles increases, delivering more oxygen and glucose for respiration;
• it increases blood glucose concentration, by causing the liver to release glucose, supplying more fuel to muscles and the brain.

These effects prepare the body to either fight off a threat or run away from it. Adrenaline acts quickly and breaks down quickly — useful for short-term emergencies.

Insulin and glucagon — blood glucose control

Blood glucose concentration is monitored by the pancreas and kept within a narrow range by negative feedback using two hormones, insulin and glucagon.

When blood glucose is too high (e.g. after a sugary meal):

1. Insulin is secreted/released by the pancreas.
2. Insulin causes glucose to be converted to glycogen (in the liver) for storage.
3. Glucose is removed from the blood and blood glucose returns to normal.

When blood glucose is too low (e.g. during exercise or fasting):

1. Glucagon is secreted when blood glucose is too low, by the pancreas.
2. Glucagon causes glycogen to be broken down to glucose (in the liver).
3. The glucose is released into the bloodstream and blood glucose returns to normal.

Both hormones come from the pancreas and both act on the liver, but they push glucose in opposite directions. This is a textbook negative-feedback loop: a change in blood glucose triggers a response that reverses the change.

The menstrual cycle

Four hormones run the menstrual cycle in Edexcel 7.1, two from the pituitary and two from the ovaries.

• FSH (follicle-stimulating hormone) — secreted by the pituitary. FSH secreted by pituitary stimulates a follicle to mature in the ovary and stimulates the ovary to produce oestrogen.
• Oestrogen — secreted by the follicle in the ovary. It thickens the lining of the uterus, ready to receive a fertilised egg. Rising oestrogen also feeds back on the pituitary.
• LH (luteinising hormone) — secreted by the pituitary. High oestrogen triggers an LH surge from the pituitary, and LH triggers ovulation (the mature egg is released from the follicle around day 14).
• Progesterone — secreted by the empty follicle (corpus luteum) after ovulation. It maintains the uterus lining through the second half of the cycle. If no fertilisation happens, progesterone falls and the lining is shed (menstruation).

Hormonal contraception — the combined pill

Hormonal contraceptives prevent pregnancy by interfering with the menstrual cycle. The combined pill contains oestrogen and progesterone. These hormones act on the pituitary to inhibit FSH secretion. Because there is not enough FSH, follicles do not mature in the ovary, and so ovulation does not occur. With no egg released, fertilisation cannot happen.

You should be able to evaluate contraceptive methods on effectiveness, side effects, and whether they protect against sexually transmitted infections. Barrier methods such as condoms physically block sperm and also reduce STI transmission, while hormonal methods only prevent pregnancy.

Hormonal fertility treatment — clomifene and IVF

Some women cannot conceive because they do not ovulate regularly. Clomifene is a drug given to stimulate ovulation:

• clomifene increases FSH secretion by the pituitary;
• clomifene increases LH secretion by the pituitary;
• FSH causes follicles to mature in the ovary;
• LH triggers ovulation.

If clomifene is not enough, IVF (in-vitro fertilisation) can be used. The mother is given FSH and LH to mature several eggs at once; the eggs are collected and fertilised in the lab with the father's sperm; the resulting embryos develop briefly, and one or two are inserted into the mother's uterus. IVF is not always successful, can be emotionally and physically demanding, and may lead to multiple births.

Pulling it together for the exam

Every Edexcel 7.1 answer rewards the same structure: name the gland, name the hormone, name the target organ, describe the effect. For 'fight or flight', that's adrenal glands → adrenaline → heart and muscles → raised heart rate, increased blood flow, higher blood glucose. For blood glucose, that's pancreas → insulin/glucagon → liver → glucose ↔ glycogen. For the menstrual cycle, that's pituitary (FSH, LH) and ovary (oestrogen, progesterone) → uterus and ovary → maturation, ovulation and lining maintenance. For the combined pill, that's pill (oestrogen + progesterone) → pituitary → FSH inhibited → no follicles mature → no ovulation. For clomifene, that's clomifene → pituitary → more FSH and LH → follicles mature and ovulation occurs. Lock these chains in and you'll pick up almost every available mark.

Exam tips

• Always name the gland AND the hormone in any Edexcel 4–6 mark answer (e.g. 'adrenaline released by the adrenal glands', not just 'adrenaline is released').
• For adrenaline, mention all three physical effects when possible: heart rate up, blood flow to muscles up, blood glucose up.
• Spell glycogen and glucagon carefully — they look almost identical but are completely different molecules.
• For the menstrual cycle, remember the source glands: pituitary makes FSH + LH; the follicle in the ovary makes oestrogen; the empty follicle makes progesterone.
• Combined pill answers must include all four points: contains oestrogen + progesterone, inhibits FSH, follicles do not mature, ovulation does not occur.
• Clomifene answers must include all four points: increases FSH, increases LH, follicles mature, LH triggers ovulation. The combined pill and clomifene are opposites — don't muddle them.

Mark-scheme phrasing

Common misconceptions

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Worked example

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Frequently asked questions

Related topics in Edexcel GCSE Biology (1BI0)

• 7.2 Homeostasis