By the end of this lesson
- Describe uterine-lining changes during the cycle.
- Explain the roles of oestrogen and progesterone.
- Interpret hormone and lining graphs.
BIG QUESTION
How do changing hormone concentrations prepare the uterus for a possible pregnancy?
The cycle is a coordinated sequence, not a rigid timetable identical in every person.
Menstruation resets the uterine lining
At the start of a cycle, low ovarian hormone concentrations are associated with breakdown and shedding of part of the uterine lining: menstruationThe breakdown and loss of the uterus lining at the start of the menstrual cycle, when no egg has been fertilised..
Cycle length varies among and within individuals; day numbers shown on diagrams are models rather than guarantees.
Oestrogen rebuilds the lining
A developing ovarian follicle releases increasing oestrogenA female sex hormone made mainly by the ovaries that supports female secondary sexual characteristics and rebuilds the uterus lining in the menstrual cycle.. Oestrogen stimulates repair and thickening of the endometrium after menstruation.
Oestrogen also participates in feedback control of pituitary hormones.
Progesterone maintains the lining
After ovulation, the corpus luteum secretes progesteroneA female sex hormone, made by the corpus luteum after ovulation and by the placenta in pregnancy, that maintains a thick uterus lining., maintaining a thick, vascular uterine lining.
If pregnancy does not occur, the corpus luteum degenerates, progesterone falls and menstruation follows. During pregnancy, progesterone remains high, later supported by the placenta.
Hormones and the uterine lining
Read concentration changes alongside tissue response.
| Phase/signal | Hormone pattern | Uterine effect |
|---|---|---|
| Menstruation | Oestrogen and progesterone low. | Part of lining is shed. |
| Follicular phase | Oestrogen rises. | Lining repairs and thickens. |
| After ovulation | Progesterone rises. | Lining is maintained. |
| No pregnancy | Progesterone and oestrogen fall. | Maintenance ends; menstruation begins. |
| Pregnancy | Progesterone remains elevated. | Lining is maintained. |
Language that earns precision
- menstruation
- Shedding of part of the uterine lining with blood and tissue.
- endometrium
- Inner lining of the uterus.
- corpus luteum
- Temporary ovarian structure formed from the follicle after ovulation.
- menstrual cycle
- Recurring ovarian and uterine changes coordinated by hormones.
Common misconceptions
Claim: Menstruation is the release of an egg.
Correction: Ovulation releases an egg; menstruation sheds uterine lining.
Claim: Every cycle lasts exactly 28 days.
Correction: Length and timing vary naturally.
Claim: Progesterone creates the lining from nothing.
Correction: Oestrogen promotes rebuilding; progesterone mainly maintains and develops it after ovulation.
Match the answer to the command word
Describe rise/fall and link it to a named uterine event.
Use “typically” for cycle timing; explain the hormone mechanism.
Recall, apply, then justify
Explain the roles of oestrogen and progesterone in the uterine cycle.
Hint
Rebuild, maintain, then hormone fall.
Suggested marking points
- Oestrogen from the developing follicle stimulates repair/thickening of the uterine lining.
- Progesterone is released by the corpus luteum after ovulation.
- Progesterone maintains the thick uterine lining.
- A fall in ovarian hormones when no pregnancy occurs leads to menstruation.
Explain why menstruation usually does not occur during pregnancy.
Hint
Progesterone and maintenance of the endometrium.
Suggested marking points
- Progesterone concentration remains elevated.
- The uterine lining continues to be maintained.
- The lining is therefore not shed in the normal menstrual pattern.
A graph shows progesterone remaining low after ovulation should have occurred. Predict likely uterine effects.
Planning hint
Corpus luteum → progesterone → lining.
What a strong design includes
- Low progesterone suggests limited corpus-luteum activity or no ovulation.
- The endometrium receives less maintenance signal.
- It may fail to become or remain fully supportive.
- Hormone concentrations may fall earlier than expected.
- Menstruation may occur or timing may be altered.
- Implantation and maintenance of an early pregnancy would be less likely.