16.5 Sex hormones in humans
- Syllabus
- 0610–2026–2027
- Topic
- 16.5
- Level
- —
Learning objectives
16.5.1Roles of testosterone and oestrogen• Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual characteristics during puberty16.5.2Menstrual cycle in terms of changes• Describe the menstrual cycle in terms of changes in the ovaries and in the lining of the uterus16.5.3Sites of production of oestrogen• Describe the sites of production of oestrogen and progesterone in the menstrual cycle and in pregnancy16.5.4Role of hormones in controlling• Explain the role of hormones in controlling the menstrual cycle and pregnancy, limited to FSH, LH, progesterone and oestrogen
Explain sex hormones at puberty
At puberty, sex hormones cause and regulate the development of secondary sexual characteristics—features that distinguish sexually mature bodies but are not the reproductive organs themselves.
| Hormone | Main source | Roles at puberty |
|---|---|---|
| testosterone | testes | promotes male secondary sexual characteristics, including a deeper voice, facial and body hair, and increased muscle development |
| oestrogen | ovaries | promotes female secondary sexual characteristics, including breast development, wider hips and the start and regulation of the menstrual cycle |
Both hormones occur in all sexes at different concentrations. The syllabus focus is their main roles in developing and regulating secondary sexual characteristics.
Describe the menstrual cycle
The menstrual cycle coordinates changes in an ovary with changes in the lining of the uterus, commonly over about 28 days.
| Approximate stage | Ovary | Uterus lining |
|---|---|---|
| days 1–5 | a follicle begins developing | lining is shed: menstruation |
| days 6–13 | egg matures inside the follicle | lining repairs and thickens |
| about day 14 | ovulation releases the egg from the ovary | lining remains thick |
| days 15–28 | remains of the follicle form a structure that supports the cycle | lining is maintained; if pregnancy does not occur it breaks down and the next cycle begins |
Menstruation is shedding of the uterus lining; ovulation is release of an egg from an ovary. They are different events and occur at different times.
Locate oestrogen and progesterone production
| Situation | Oestrogen source | Progesterone source |
|---|---|---|
| menstrual cycle | ovaries | ovaries |
| pregnancy | ovaries and placenta | ovaries and placenta; placenta is the main source later in pregnancy |
The production site changes with reproductive state: the ovaries control the normal cycle, while the placenta becomes an important endocrine organ during pregnancy.
The uterus is a target of oestrogen and progesterone, not their production site. FSH and LH are produced by the pituitary gland, not the ovaries.
Explain hormonal control of the cycle
FSH, LH, oestrogen and progesterone coordinate follicle development, ovulation and the uterus lining through ordered stimulation and inhibition.
| Hormone | Main source | Main role |
|---|---|---|
| FSH | pituitary gland | stimulates development of an ovarian follicle and secretion of oestrogen |
| oestrogen | ovary | repairs and thickens the uterus lining; inhibits FSH and stimulates LH |
| LH | pituitary gland | its mid-cycle surge causes ovulation and supports progesterone secretion |
| progesterone | ovary, and placenta in pregnancy | maintains the uterus lining and inhibits FSH and LH |
Early cycle: FSH → follicle development → rising oestrogen → lining thickens. Mid-cycle: high oestrogen → LH surge → ovulation. After ovulation: progesterone maintains the lining. If progesterone and oestrogen fall, the lining is shed. During pregnancy they remain high, maintaining the lining and suppressing another cycle.
FSH matures a follicle; LH triggers ovulation. Oestrogen mainly rebuilds the lining before ovulation; progesterone mainly maintains it after ovulation and during pregnancy.