What you'll learn
This revision guide covers the hormonal control of reproduction in humans, a key topic in WJEC GCSE Biology. You'll understand how the endocrine system regulates the menstrual cycle, pregnancy, and fertility treatments. These notes align precisely with WJEC specification requirements and include worked examples mirroring actual exam questions.
Key terms and definitions
Endocrine system — a communication system in the body using hormones transported in blood plasma to target organs
Hormone — a chemical messenger secreted by endocrine glands, transported in the bloodstream to specific target organs where they produce an effect
Menstrual cycle — the recurring monthly process in females involving the thickening of the uterus lining and release of an egg, controlled by hormones
Ovulation — the release of a mature egg from the ovary, occurring approximately day 14 of the menstrual cycle
Follicle Stimulating Hormone (FSH) — hormone produced by the pituitary gland that stimulates egg maturation and oestrogen production
Luteinising Hormone (LH) — hormone from the pituitary gland that triggers ovulation
Oestrogen — hormone produced by the ovaries that stimulates uterus lining repair and inhibits FSH production
Progesterone — hormone produced by the corpus luteum (empty follicle) that maintains the uterus lining during pregnancy
Core concepts
The endocrine system vs the nervous system
The body has two major control systems working together to coordinate responses:
Nervous system characteristics:
- Uses electrical impulses travelling along neurones
- Very rapid responses (milliseconds to seconds)
- Short-lived effects
- Precise, localised responses
- Examples: reflex actions, muscle contraction
Endocrine system characteristics:
- Uses chemical messengers (hormones) in the bloodstream
- Slower responses (seconds to hours)
- Long-lasting effects
- Widespread responses affecting multiple organs
- Examples: growth, metabolism, reproduction
Endocrine glands are ductless — they secrete hormones directly into the bloodstream. The blood carries hormones to all parts of the body, but only target cells with specific receptors respond.
Major endocrine glands you must know:
- Pituitary gland (base of brain) — "master gland" controlling other glands
- Thyroid gland (neck) — controls metabolic rate
- Pancreas (abdomen) — regulates blood glucose
- Adrenal glands (above kidneys) — produce adrenaline for fight-or-flight
- Ovaries (females) — produce oestrogen and progesterone
- Testes (males) — produce testosterone
The menstrual cycle
The menstrual cycle typically lasts 28 days and involves four key hormones working in sequence. Understanding their interactions is essential for GCSE success.
Day 1-5: Menstruation (period)
- Uterus lining breaks down and is shed through the vagina
- Triggered by low progesterone levels from previous cycle
Day 5-14: Follicle phase
- FSH released from pituitary gland
- FSH causes egg maturation in follicle within ovary
- FSH stimulates ovaries to produce oestrogen
- Oestrogen causes uterus lining to thicken and repair
- High oestrogen levels inhibit further FSH production (negative feedback)
- High oestrogen stimulates LH release (positive feedback)
Day 14: Ovulation
- LH surge from pituitary gland
- LH triggers release of mature egg from ovary
- Egg travels down oviduct (fallopian tube)
Day 14-28: Luteal phase
- Empty follicle becomes corpus luteum
- Corpus luteum secretes progesterone (and some oestrogen)
- Progesterone maintains thick uterus lining
- Progesterone inhibits FSH and LH release
- If no pregnancy occurs, corpus luteum breaks down
- Progesterone levels drop, triggering menstruation
- Cycle repeats
Feedback mechanisms:
Negative feedback maintains hormonal balance. High oestrogen inhibits FSH to prevent multiple eggs maturing simultaneously. High progesterone inhibits both FSH and LH to prevent further ovulation during potential pregnancy.
Positive feedback occurs once: high oestrogen triggers the LH surge needed for ovulation.
Hormonal control of pregnancy
When fertilisation occurs, the developing embryo prevents the normal cycle:
- Fertilised egg implants in uterus lining (approximately day 21)
- Embryo produces human chorionic gonadotropin (hCG)
- hCG maintains the corpus luteum
- Corpus luteum continues producing progesterone
- Progesterone maintains uterus lining, preventing menstruation
- Pregnancy tests detect hCG in urine
The placenta develops and takes over progesterone production after the first trimester, maintaining pregnancy until birth.
Contraception methods
Contraception prevents pregnancy through various mechanisms. WJEC requires knowledge of both hormonal and non-hormonal methods.
Hormonal contraception:
Combined pill (oestrogen + progesterone)
- Contains synthetic oestrogen and progesterone
- Inhibits FSH production → prevents egg maturation
- Over 99% effective with perfect use
- Daily tablet taken orally
- Advantages: very effective, regulates periods, reduces period pain
- Disadvantages: must remember daily, side effects (headaches, mood changes), doesn't prevent STIs
Progesterone-only methods
- Mini-pill, injection, implant, hormonal IUS
- Thickens cervical mucus to prevent sperm entry
- Thins uterus lining to prevent implantation
- May prevent ovulation
- Effective alternatives for women who can't take oestrogen
Non-hormonal contraception:
Barrier methods
- Condoms (male/female), diaphragm, cervical cap
- Physically prevent sperm reaching egg
- Condoms also prevent sexually transmitted infections (STIs)
- 82-98% effective depending on correct use
- No side effects, easily accessible
Intrauterine device (IUD/copper coil)
- Small copper device inserted into uterus
- Copper toxic to sperm and prevents implantation
- Over 99% effective
- Lasts 5-10 years
- Hormone-free option
Sterilisation
- Permanent surgical contraception
- Vasectomy (males): sperm ducts cut/sealed
- Tubal ligation (females): oviducts cut/sealed
- Over 99% effective but irreversible
Natural family planning
- Monitoring fertility signs (temperature, cervical mucus)
- Avoiding intercourse during fertile period
- 76-99% effective depending on careful tracking
- No side effects but requires discipline and education
Fertility treatments
Infertility affects approximately 1 in 7 couples in the UK. Hormonal treatments can address certain causes.
Causes of infertility:
- Low sperm count/quality in males
- Failure to ovulate regularly in females
- Blocked oviducts preventing egg transport
- Age-related decline in fertility
Fertility drugs (ovulation stimulation):
Women who don't ovulate regularly can receive:
- FSH injections to stimulate egg maturation
- LH injections to trigger ovulation
- Clomifene tablets to stimulate FSH release
These treatments increase the chance of pregnancy but carry risks:
- Multiple pregnancies (twins, triplets) — higher risk to mother and babies
- Ovarian hyperstimulation syndrome — painful, potentially dangerous
- Emotional and physical stress
- Not always successful
In Vitro Fertilisation (IVF):
IVF involves fertilisation outside the body:
- Woman receives FSH and LH to stimulate multiple egg maturation
- Eggs collected from ovaries under sedation
- Eggs fertilised with sperm in laboratory dish
- Embryos cultured for 2-5 days
- One or two healthy embryos transferred to uterus
- Extra embryos frozen for future attempts
Success rates vary by age:
- Under 35: approximately 32% per cycle
- 35-39: approximately 25% per cycle
- Over 40: approximately 10% per cycle
Ethical considerations:
WJEC may ask you to evaluate fertility treatments:
Arguments supporting IVF:
- Enables infertile couples to have biological children
- Embryo screening can prevent genetic disorders
- Advancing medical knowledge benefits future patients
Arguments against IVF:
- Expensive (£5000+ per cycle in UK private clinics)
- Unused embryos destroyed — some view as potential life
- Multiple births increase health risks
- Emotional stress from repeated failures
- Limited NHS availability creates inequality
Male reproductive hormones
Testosterone is the primary male hormone:
Functions of testosterone:
- Produced in testes from puberty onwards
- Stimulates sperm production
- Develops male secondary sexual characteristics (facial hair, muscle mass, deep voice)
- Maintains sex drive
Control of testosterone:
The pituitary gland releases FSH and LH in males too:
- LH stimulates testosterone production in testes
- FSH (with testosterone) stimulates sperm production
- Negative feedback: high testosterone inhibits LH release
This maintains relatively constant testosterone levels, unlike the cyclical pattern in females.
Worked examples
Example 1: Describe and explain the role of FSH in the menstrual cycle. [4 marks]
Mark scheme answer:
- FSH is produced by the pituitary gland [1]
- FSH causes an egg to mature in the ovary / causes development of follicle [1]
- FSH stimulates the ovary to produce oestrogen [1]
- High oestrogen inhibits further FSH production / negative feedback [1]
Example 2: A woman has irregular menstrual cycles and rarely ovulates. Explain how hormone treatment could help her become pregnant. [3 marks]
Mark scheme answer:
- She could be given FSH (injections/drugs) [1]
- This would stimulate egg maturation/development [1]
- LH could trigger ovulation / release of egg [1]
Example 3: Evaluate the use of hormonal contraceptives compared to barrier methods. [6 marks QWC]
Mark scheme guidance:
Quality of written communication assessed — use correct terminology, logical structure, spelling and grammar.
Model answer demonstrating level 3 (5-6 marks):
Hormonal contraceptives such as the combined pill are highly effective, with over 99% effectiveness when used correctly, compared to condoms at approximately 98%. The pill works by inhibiting FSH production, preventing egg maturation and ovulation. This makes it more reliable than barrier methods which can fail due to incorrect use.
However, hormonal methods require daily commitment and can cause side effects including mood changes and headaches. Barrier methods like condoms have no hormonal side effects and additionally protect against sexually transmitted infections, which hormonal contraceptives cannot do.
The choice depends on individual circumstances. Women wanting the most effective contraception may prefer hormonal methods, while those concerned about STI protection or side effects may choose condoms. Cost and accessibility are also factors, with condoms being cheaper and available without prescription.
Common mistakes and how to avoid them
Confusing FSH and LH functions — Remember FSH = Follicle Stimulating (matures egg), LH = triggers ovulation. FSH comes first in the cycle.
Wrong gland producing hormones — FSH and LH come from the pituitary gland (brain), NOT the ovaries. Oestrogen and progesterone come from the ovaries.
Saying hormones travel through nerves — Hormones travel in blood/bloodstream/blood plasma, never through nerves. This is a key difference from the nervous system.
Mixing up positive and negative feedback — Negative feedback is the normal pattern (high hormone level reduces production). Positive feedback (high oestrogen triggering LH surge) only happens once per cycle.
Incomplete contraception evaluation — When asked to evaluate, you must give advantages AND disadvantages, then reach a conclusion. Don't just list facts.
Vague statements about IVF — Be specific: state that eggs are fertilised outside the body (in vitro = in glass), mention FSH/LH treatment, and know approximate success rates.
Exam technique for "Hormones and Reproduction"
Command word precision — "Describe" requires stating what happens (no explanation needed). "Explain" requires reasons/mechanisms using because/causes/this leads to. "Evaluate" needs both sides plus judgment.
Graph questions — Common exam feature. Identify which hormone peaks at day 14 (LH), which stays high days 14-28 (progesterone), and link patterns to events (ovulation, menstruation). Always quote values from the graph.
Six-mark questions — Structure answers in paragraphs, use scientific terminology precisely, and check spelling of key terms (oestrogen, menstruation, progesterone). These assess quality of written communication.
Mark allocation guides detail — For 3 marks, give 3 distinct points. If a question asks "describe and explain" worth 4 marks, typically 2 marks for description, 2 for explanation.
Quick revision summary
The endocrine system uses hormones transported in blood to coordinate reproduction. Four hormones control the menstrual cycle: FSH stimulates egg maturation and oestrogen production; oestrogen thickens uterus lining and triggers LH release; LH causes ovulation; progesterone maintains the uterus lining. Contraception works hormonally (preventing ovulation/implantation) or mechanically (barriers). Fertility treatments use FSH/LH to stimulate ovulation or IVF for external fertilisation. Know feedback mechanisms, hormone sources (pituitary vs ovaries), and be ready to evaluate treatments considering effectiveness, side effects, and ethical issues.