Sex hormones in humans
Roles of Sex Hormones in Puberty (Learning Objective 1)
During puberty, sex hormones trigger the development of secondary sexual characteristics. These are physical traits that distinguish males and females but are not directly involved in reproduction. The two main hormones are testosterone (in males) and oestrogen (in females).
| Role: Secondary Sexual Characteristics |
|---|
| Causes development of: deepening of voice, growth of facial/body hair, increased muscle mass, and enlargement of testes/penis. |
| Causes development of: breast development, widening of hips, and growth of pubic/underarm hair. |
Why this matters: Examiners often ask you to identify which hormone causes a specific change. Remember: Testosterone = Male traits; Oestrogen = Female traits. Both hormones also regulate the reproductive system, but their most visible role during puberty is secondary sexual characteristics.
The Menstrual Cycle (Learning Objective 2)
The menstrual cycle is a monthly cycle of changes in the ovaries and the uterus that prepares the female body for pregnancy. It typically lasts 28 days (though it can vary between individuals).
Key Events:
- Ovary: One mature egg is released from an ovary (ovulation) around day 14.
- Uterus Lining: The lining of the uterus thickens with blood vessels to prepare for a fertilized egg.
- Menstruation: If no fertilization occurs, the lining breaks down and is lost as menstrual flow.
Step-by-Step: Hormonal Control of the Menstrual Cycle (Learning Objectives 3 & 4)
To understand how hormones control the cycle, we must look at the feedback loop involving four key hormones: FSH, LH, Oestrogen, and Progesterone. Note: The syllabus limits this explanation to these four hormones.
| Hormone Actions & Effects |
|---|
| FSH (Follicle Stimulating Hormone) is secreted by the pituitary gland. It stimulates the ovaries to produce oestrogen and causes eggs to mature. |
Oestrogen levels rise. This has two effects:
|
| High levels of oestrogen trigger a sudden surge of LH (Luteinising Hormone). This causes the mature egg to be released from the ovary. |
The empty follicle becomes the corpus luteum, which produces progesterone (and some oestrogen).
|
| If no pregnancy occurs, the corpus luteum breaks down. Progesterone levels fall. The uterus lining is lost (menstruation), and FSH production begins again. |
Connection to Pregnancy: If fertilization occurs, the developing embryo produces hormones that keep the corpus luteum alive. The placenta then takes over producing high levels of progesterone and oestrogen to maintain the pregnancy.
⚠︎ Confusing Hormone Functions and Sites
Mistake 1: Confusing FSH and LH roles.
- Incorrect: 'FSH causes ovulation.'
- Correct: LH causes ovulation. FSH stimulates the ovaries to produce oestrogen and mature eggs.
Mistake 2: Incorrect site of progesterone production in pregnancy.
- Incorrect: 'The ovaries produce most progesterone during late pregnancy.'
- Correct: In early pregnancy, the corpus luteum (in the ovary) produces progesterone. However, in late pregnancy, the placenta is the primary site of progesterone production.
Mistake 3: Oestrogen's effect on other hormones.
- Incorrect: 'Oestrogen stimulates LH production.'
- Correct: While oestrogen triggers the initial LH surge, its primary regulatory role in the cycle is to inhibit FSH production via negative feedback.
Describing Graphs and Feedback Loops
WHEN to use this tip: When asked to describe hormone levels from a graph or explain the control mechanism.
Examiner Acceptance: Examiners look for precise language regarding inhibition. Instead of saying 'oestrogen stops FSH,' use 'oestrogen inhibits the secretion of FSH' or 'prevents further FSH production.' This directly addresses the concept of negative feedback.
Example Usage:
Question: Explain how oestrogen controls FSH levels.
Answer: 'High levels of oestrogen inhibit the pituitary gland from secreting FSH. This prevents further maturation of eggs during the cycle.'
WHY this works: It explicitly links the hormone (oestrogen) to its target (pituitary/FSH) and the action (inhibition), which is the core mechanism tested.
Past Paper Style Questions
Q:
Describe two secondary sexual characteristics caused by testosterone in males. [2]
A:
- Deepening of the voice (larynx enlargement).
2. Growth of facial hair (or body hair, increased muscle mass).
Q:
Describe the changes in the uterus lining during the menstrual cycle. [2]
A:
- The lining thickens and becomes rich in blood vessels (around day 14).
2. If no fertilization occurs, the lining breaks down/is lost (menstruation).
Q:
Identify the hormone that causes ovulation. [1]
A:
LH (Luteinising Hormone).
Q:
Explain the role of progesterone in maintaining pregnancy. [2]
A:
- It maintains the thickness of the uterus lining.
2. It prevents menstruation (or prevents the release of further eggs/FSH).