CIE iGCSE Biology-16.5 Sex hormones in humans- Study Notes- New Syllabus
CIE iGCSE Biology-16.5 Sex hormones in humans- Study Notes – New syllabus
CIE iGCSE Biology-16.5 Sex hormones in humans- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe the roles of testosterone and oestrogen in the development and regulation of secondary sexual characteristics during puberty
- Describe the menstrual cycle in terms of changes in the ovaries and in the lining of the uterus
Supplement
- Describe the sites of production of oestrogen and progesterone in the menstrual cycle and in pregnancy
- Explain the role of hormones in controlling the menstrual cycle and pregnancy, limited to FSH, LH, progesterone and oestrogen
Roles of Testosterone and Oestrogen in Puberty
Overview:
Puberty is the stage in human development when secondary sexual characteristics begin to appear, under the control of sex hormones:
Testosterone in males and Oestrogen in females.
Testosterone (Male Sex Hormone)
Produced by: Testes
Main Role: Controls development of male secondary sexual characteristics during puberty
| 🔧 Functions |
|---|
| Stimulates sperm production |
| Deepening of the voice |
| Growth of facial, pubic, and body hair |
| Increase in muscle mass and body size |
| Growth of the penis and testes |
Oestrogen (Female Sex Hormone)
Produced by: Ovaries
Main Role: Controls development of female secondary sexual characteristics and regulates menstrual cycle
| 🔧 Functions |
|---|
| Stimulates development of breasts |
| Starts the menstrual cycle |
| Growth of pubic and underarm hair |
| Widening of the hips |
| Development of fat distribution in hips and thighs |
Testosterone = sperm, voice deepens, muscles, hair
Oestrogen = breasts, periods, hips, fat distribution
Both hormones = trigger puberty + regulate reproductive development
The Menstrual Cycle
The menstrual cycle is a monthly process involving hormonal changes, ovulation, and preparation of the uterus for pregnancy.
🔁 Cycle Duration:
Average: 28 days (can vary slightly between individuals)
📆 Phases of the Menstrual Cycle
| Day Range | Changes in Ovaries | Changes in Uterus Lining (Endometrium) |
|---|---|---|
| Day 1–5 | Menstruation: The ovary is at rest. | Uterus lining breaks down and is shed as menstrual blood |
| Day 6–13 | A follicle (egg sac) develops in the ovary. | The lining begins to thicken again in response to oestrogen |
| Day 14 | Ovulation: A mature egg is released from the ovary | Lining is now thick, ready for implantation |
| Day 15–28 | Empty follicle becomes the corpus luteum, which secretes progesterone | Lining remains thick and rich in blood vessels to support a fertilised egg. If no fertilisation, lining breaks down, cycle restarts |
🔄 If Fertilisation Occurs:
The zygote implants into the thick uterine lining
No menstruation occurs
Hormone levels stay high to maintain the lining
🔄 If Fertilisation Does Not Occur:
The corpus luteum breaks down
Hormone levels fall
Uterus lining sheds → menstruation begins
🧠 Hormones Involved:
- Oestrogen: Rebuilds uterine lining and triggers ovulation
- Progesterone: Maintains the thick uterine lining after ovulation
- FSH and LH: Released by the pituitary gland, stimulate egg growth and
Production of Oestrogen and Progesterone
These hormones are essential for regulating the menstrual cycle and maintaining pregnancy.
🩺 During the Menstrual Cycle (Non-pregnant female)
| Hormone | Produced By | Function |
|---|---|---|
| Oestrogen | Growing follicle in the ovary | – Stimulates thickening of uterine lining – Inhibits FSH (to stop more eggs maturing) – Triggers LH surge for ovulation |
| Progesterone | Corpus luteum (remains of follicle after ovulation) | – Maintains thick uterine lining in case of fertilisation – Inhibits FSH and LH to prevent another ovulation |
🤰 During Pregnancy
| Hormone | Produced By | Function |
|---|---|---|
| Oestrogen | Initially: Ovary Later: Placenta | – Helps maintain uterine lining – Stimulates growth of uterus and breast tissue |
| Progesterone | Initially: Corpus luteum Later: Placenta | – Prevents contractions of the uterus – Maintains endometrium and pregnancy – Inhibits menstruation and ovulation |
Hormonal Control of the Menstrual Cycle & Pregnancy
🧪 Hormones Involved:
| Hormone | Full Name | Produced By |
|---|---|---|
| FSH | Follicle-Stimulating Hormone | Pituitary gland (brain) |
| LH | Luteinising Hormone | Pituitary gland (brain) |
| Oestrogen | – | Ovaries (growing follicle) |
| Progesterone | – | Ovaries (corpus luteum → placenta in pregnancy) |
🩺 During the Menstrual Cycle:
| Hormone | Main Functions |
|---|---|
| FSH | – Stimulates maturation of a follicle in the ovary – Stimulates production of oestrogen |
| Oestrogen | – Causes thickening of the uterine lining – Inhibits FSH (stops multiple eggs maturing) – Triggers LH surge |
| LH | – Causes ovulation (release of the egg around day 14) – Stimulates the corpus luteum to produce progesterone |
| Progesterone | – Maintains the thick uterine lining – Inhibits FSH and LH – Drops if no fertilisation → menstruation starts |
🤰 During Pregnancy:
| Hormone | Role in Pregnancy |
|---|---|
| Progesterone | – Maintains uterine lining (no menstruation) – Inhibits uterine contractions – Prevents ovulation during pregnancy |
| Oestrogen | – Stimulates growth of the uterus and breasts – Also contributes to maintaining the endometrium |
After a few weeks, both hormones are mainly produced by the placenta, not the ovary.