Hormonal control of the menstrual cycle

What you'll learn

This revision guide covers the hormonal control of the menstrual cycle, a key topic in AQA GCSE Biology. You'll understand how four hormones interact to regulate the monthly cycle in the female reproductive system. This knowledge is essential for exam questions on hormone interactions, feedback mechanisms, and reproductive biology.

Key terms and definitions

Menstrual cycle — the monthly reproductive cycle in females, typically lasting 28 days, controlled by hormones released from the pituitary gland and ovaries

Follicle-stimulating hormone (FSH) — a hormone secreted by the pituitary gland that causes eggs to mature in the ovaries and stimulates oestrogen production

Luteinising hormone (LH) — a hormone released by the pituitary gland that triggers ovulation (release of a mature egg) around day 14 of the cycle

Oestrogen — a hormone produced by the ovaries that causes the uterus lining to thicken and inhibits FSH release while stimulating LH production

Progesterone — a hormone secreted by the empty follicle after ovulation that maintains the thick uterus lining and inhibits both FSH and LH release

Ovulation — the release of a mature egg from the ovary, occurring around day 14 of the menstrual cycle

Uterus lining (endometrium) — the inner layer of the uterus that thickens during the cycle and breaks down during menstruation if fertilisation does not occur

Pituitary gland — a gland located in the brain that produces and releases FSH and LH to control the menstrual cycle

Core concepts

The four key hormones and their sources

The menstrual cycle is controlled by the interaction of four hormones produced in two locations:

Pituitary gland hormones:

• FSH (follicle-stimulating hormone)
• LH (luteinising hormone)

Ovary hormones:

• Oestrogen
• Progesterone

The pituitary gland is located at the base of the brain and acts as the control centre, responding to hormone levels in the blood. The ovaries are the female reproductive organs where eggs mature and which produce oestrogen and progesterone in response to pituitary hormones.

Understanding which gland produces which hormone is crucial for answering exam questions correctly. A common error is confusing the source of these hormones.

The stages of the menstrual cycle

The menstrual cycle is typically 28 days long and consists of distinct stages:

Day 1-5: Menstruation

• The uterus lining breaks down and is shed through the vagina
• This is menstruation (a period)
• Blood and tissue from the uterus lining leave the body
• FSH levels begin to rise

Day 5-14: Follicle development and uterus lining repair

• FSH causes an egg to mature in a follicle in the ovary
• FSH stimulates the ovaries to produce oestrogen
• Oestrogen causes the uterus lining to thicken and repair
• Oestrogen levels rise throughout this phase
• High oestrogen levels inhibit further FSH production
• High oestrogen levels stimulate the pituitary to release LH

Day 14: Ovulation

• A surge in LH triggers the release of a mature egg from the ovary
• The egg travels down the fallopian tube towards the uterus
• This is the point in the cycle when fertilisation is most likely

Day 14-28: Maintenance phase

• The empty follicle develops into a structure called the corpus luteum
• The corpus luteum secretes progesterone
• Progesterone maintains the thick, spongy uterus lining
• Progesterone inhibits the release of both FSH and LH
• This prevents further eggs from maturing
• If fertilisation does not occur, progesterone levels fall
• Low progesterone causes the uterus lining to break down
• The cycle returns to day 1

How FSH controls egg maturation

FSH is released by the pituitary gland at the start of the menstrual cycle. Its primary functions are:

Egg maturation:

• FSH causes an egg to mature inside a follicle in the ovary
• The follicle is a fluid-filled sac that protects and nourishes the developing egg
• Usually only one egg matures per cycle
• As the egg matures, the follicle grows larger

Oestrogen stimulation:

• FSH stimulates the follicle and ovary tissue to produce and secrete oestrogen
• Oestrogen levels rise as the follicle develops
• This creates the hormone interactions that drive the rest of the cycle

FSH levels must be carefully regulated. Too much FSH would cause multiple eggs to mature, while too little would prevent any eggs from developing properly.

How oestrogen prepares the uterus and controls other hormones

Oestrogen is produced by the ovaries in response to FSH. It has multiple important functions:

Uterus lining development:

• Oestrogen causes the uterus lining (endometrium) to thicken
• This creates a spongy, blood-rich tissue
• The thick lining is necessary to support a fertilised egg if pregnancy occurs
• This thickening happens from around day 5 to day 14

Negative feedback on FSH:

• As oestrogen levels rise, they inhibit further FSH production
• This is negative feedback — high levels of one hormone suppress another
• This prevents more eggs from starting to mature
• It ensures typically only one egg matures per cycle

Positive feedback on LH:

• High oestrogen levels stimulate the pituitary gland
• This causes the pituitary to release a surge of LH
• This is positive feedback — high levels of one hormone stimulate release of another
• The LH surge triggers ovulation

Understanding both negative and positive feedback is essential for explaining hormone interactions in exam answers.

How LH triggers ovulation

LH (luteinising hormone) plays a crucial role at the middle of the cycle:

The LH surge:

• Around day 12-13, oestrogen levels peak
• This triggers the pituitary to release a large amount of LH very quickly
• This rapid increase is called the LH surge
• The LH surge occurs around day 14 of a 28-day cycle

Ovulation:

• The surge of LH causes the mature follicle to rupture
• The egg is released from the ovary
• This is ovulation
• The egg enters the fallopian tube
• Fertilisation can occur if sperm are present

After ovulation:

• LH also stimulates the empty follicle to develop into the corpus luteum
• The corpus luteum will then produce progesterone
• This sets up the next phase of the cycle

How progesterone maintains the uterus lining

After ovulation, progesterone becomes the dominant hormone:

Production:

• The empty follicle develops into a structure called the corpus luteum
• The corpus luteum secretes progesterone
• Progesterone levels rise from day 14 onwards

Maintaining the uterus lining:

• Progesterone maintains the thick, spongy uterus lining
• It keeps the lining ready to receive a fertilised egg
• The lining remains thick with good blood supply
• This provides the ideal environment for implantation

Inhibiting FSH and LH:

• High progesterone levels inhibit the release of FSH
• Progesterone also inhibits LH release
• This prevents any more eggs from maturing during this cycle
• This is another example of negative feedback

If fertilisation does not occur:

• The corpus luteum breaks down after about 10-12 days
• Progesterone levels fall rapidly
• Without progesterone, the uterus lining cannot be maintained
• The lining breaks down and menstruation begins
• FSH is no longer inhibited, so levels start to rise
• A new cycle begins

If fertilisation occurs:

• The fertilised egg implants in the uterus lining
• It produces hormones that maintain the corpus luteum
• Progesterone levels remain high
• The uterus lining is maintained throughout pregnancy
• Menstruation does not occur

Summary of hormone interactions

The menstrual cycle demonstrates complex hormone interactions:

Negative feedback loops:

• Oestrogen inhibits FSH (prevents multiple eggs maturing)
• Progesterone inhibits FSH (prevents new eggs maturing)
• Progesterone inhibits LH (prevents ovulation during the maintenance phase)

Positive feedback:

• High oestrogen stimulates LH surge (triggers ovulation at the right time)

Sequential hormone changes:

• FSH → causes oestrogen production
• Oestrogen → triggers LH surge
• LH → causes ovulation and corpus luteum formation
• Corpus luteum → produces progesterone
• Progesterone → maintains uterus lining or drops to start new cycle

This coordinated system ensures eggs mature and are released at the correct times, and that the uterus is prepared for potential pregnancy.

Worked examples

Example 1: Describing hormone changes during the cycle

Question: Describe how hormone levels change during one menstrual cycle. (6 marks)

Mark scheme answer:

At the start of the cycle (day 1-5), FSH levels begin to rise. FSH causes an egg to mature in the ovary and stimulates oestrogen production. Oestrogen levels increase from day 5-14, causing the uterus lining to thicken. High oestrogen levels trigger an LH surge around day 14, which causes ovulation. After ovulation, the empty follicle produces progesterone. Progesterone levels rise from day 14-28 and maintain the thick uterus lining. If fertilisation does not occur, progesterone levels fall, causing the uterus lining to break down and a new cycle to begin.

Examiner tips:

• Mention specific days when possible
• Link each hormone to its function
• Use "causes" to show cause and effect relationships
• Include what happens if fertilisation does not occur

Example 2: Explaining negative feedback

Question: Explain how oestrogen and FSH demonstrate negative feedback in the menstrual cycle. (3 marks)

Mark scheme answer:

FSH stimulates the ovaries to produce oestrogen. As oestrogen levels rise, they inhibit the release of more FSH from the pituitary gland. This prevents multiple eggs from maturing at the same time.

Examiner tips:

• Define what causes oestrogen production first
• Explain that rising oestrogen inhibits FSH
• State the biological advantage/outcome
• The term "negative feedback" means one hormone reduces another

Example 3: Applying knowledge to a graph

Question: The graph shows hormone levels during the menstrual cycle. Identify hormones X and Y and explain your reasoning. (4 marks)

[Graph shows: X peaks around day 14 sharply, Y rises gradually days 1-14 then falls]

Mark scheme answer:

Hormone X is LH because it shows a sharp surge/peak around day 14, which triggers ovulation. Hormone Y is oestrogen because it rises gradually during the first half of the cycle (as the egg matures), peaks just before ovulation, then decreases.

Examiner tips:

• Identify the characteristic shape of each hormone's graph
• LH shows a sharp spike, oestrogen rises then falls
• Progesterone rises after day 14, FSH is highest early in cycle
• Link graph features to biological events

Common mistakes and how to avoid them

• Confusing which gland produces which hormone — Remember: pituitary produces FSH and LH (both end in H for "head gland"); ovaries produce oestrogen and progesterone (both are O-P like "ovary produces")

• Stating that FSH or LH thickens the uterus lining — Only oestrogen and progesterone directly affect the uterus lining; FSH causes egg maturation and oestrogen production; LH triggers ovulation

• Forgetting to mention the corpus luteum — After ovulation, the empty follicle becomes the corpus luteum, which produces progesterone; many students incorrectly say the ovary produces progesterone without mentioning this structure

• Mixing up positive and negative feedback — Negative feedback = one hormone inhibits another (oestrogen inhibits FSH, progesterone inhibits FSH and LH); positive feedback = one hormone stimulates another (high oestrogen triggers LH surge)

• Not linking day numbers to events — Examiners award marks for precision: menstruation days 1-5, ovulation day 14, progesterone dominates days 14-28

• Writing that fertilisation occurs in the uterus — Fertilisation occurs in the fallopian tube (oviduct); the fertilised egg then travels to the uterus for implantation

Exam technique for "Hormonal control of the menstrual cycle"

• "Explain" questions require cause and effect — Use connecting words like "causes," "stimulates," "inhibits," "triggers," and "maintains" to show how hormones interact; stating facts without links loses marks

• "Describe" vs "Explain" questions — Describe = state what happens (oestrogen levels rise); Explain = state what happens AND why (oestrogen levels rise because FSH stimulates the ovaries to produce it)

• Six-mark questions need a logical sequence — Follow the cycle chronologically from day 1, mentioning all four hormones and their effects; use paragraph breaks for clarity between stages

• Graph and diagram questions are common — Practice identifying hormones from their characteristic patterns: FSH peaks early, LH shows sharp spike at day 14, oestrogen rises then falls in first half, progesterone dominates second half

Quick revision summary

The menstrual cycle is controlled by four hormones: FSH and LH from the pituitary gland, and oestrogen and progesterone from the ovaries. FSH causes egg maturation and oestrogen production. Oestrogen thickens the uterus lining and triggers the LH surge. LH causes ovulation around day 14. After ovulation, the corpus luteum produces progesterone, which maintains the uterus lining. If fertilisation does not occur, progesterone levels drop, the lining breaks down, and menstruation begins a new cycle.