Sex hormones in humans

1. Overview

Sex hormones are chemical messengers produced by the endocrine glands that coordinate the development of the reproductive system and regulate human fertility. These hormones trigger the physical changes seen during puberty and control the monthly menstrual cycle in females, ensuring the body is prepared for potential pregnancy.

Key Definitions

• Hormone: A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.
• Puberty: The stage of life during which adolescents reach sexual maturity and become capable of reproduction.
• Secondary Sexual Characteristics: Physical features that appear during puberty which distinguish the two sexes but are not directly part of the reproductive system.
• Ovulation: The release of a mature egg (ovum) from an ovary into the oviduct.
• Menstruation: The monthly shedding of the lining of the uterus (endometrium) through the vagina if fertilization has not occurred.

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Core Content

Roles of Testosterone and Oestrogen in Puberty

During puberty, the pituitary gland stimulates the gonads (testes and ovaries) to release sex hormones.

Testosterone (produced in the testes):

• Primary role: Stimulates the production of sperm.
• Secondary characteristics:
  • Growth of facial and body hair.
  • Deepening of the voice (growth of the larynx).
  • Increased muscle mass and bone density.
  • Growth of the penis and testes.

Oestrogen (produced in the ovaries):

• Primary role: Regulates the menstrual cycle and triggers egg maturation.
• Secondary characteristics:
  • Development of breasts.
  • Widening of the hips (to prepare for childbirth).
  • Growth of pubic and underarm hair.
  • Beginning of the menstrual cycle (periods).

The Menstrual Cycle (Changes in Ovaries and Uterus)

The cycle lasts approximately 28 days and involves two main locations of change:

1. In the Uterus (The Lining):

   • Days 1–5: Menstruation occurs; the thickened uterine lining breaks down and is lost from the body.
   • Days 6–13: The lining begins to thicken again (repair phase) to prepare for a possible embryo.
   • Days 14–28: The lining is maintained. If no egg is fertilized, the lining breaks down at Day 28, and the cycle repeats.

2. In the Ovaries (The Egg):

   • Days 1–13: An egg follicle develops and matures inside the ovary.
   • Day 14 (Ovulation): The mature egg is released from the ovary into the oviduct.
   • Days 15–28: The empty follicle turns into a structure called the corpus luteum.

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Extended Content (Extended Curriculum Only)

Sites of Production

• Menstrual Cycle: Oestrogen and Progesterone are primarily produced by the ovaries (specifically the follicle and the corpus luteum).
• Pregnancy: Initially, the corpus luteum produces these hormones. Later, the placenta takes over the production of progesterone and oestrogen to maintain the pregnancy.

Hormonal Control of the Menstrual Cycle

The cycle is controlled by a complex feedback loop involving four hormones:

1. FSH (Follicle Stimulating Hormone):
   • Produced by: Pituitary Gland.
   • Function: Stimulates the growth of a follicle in the ovary and stimulates the ovary to produce oestrogen.
2. Oestrogen:
   • Produced by: Ovaries.
   • Function: Causes the uterine lining to thicken/repair. It inhibits (stops) FSH and stimulates the pituitary to release LH.
3. LH (Luteinising Hormone):
   • Produced by: Pituitary Gland.
   • Function: A "surge" in LH triggers ovulation at Day 14 and stimulates the empty follicle to become the corpus luteum.
4. Progesterone:
   • Produced by: Corpus Luteum (and later the placenta).
   • Function: Maintains the thick lining of the uterus. It inhibits the release of LH and FSH (to prevent further eggs from maturing).

Hormones in Pregnancy

If fertilization occurs, the corpus luteum does not break down.

• Progesterone levels remain high: This keeps the uterine lining intact so the embryo can remain implanted.
• Oestrogen levels remain high: This prevents the pituitary gland from releasing FSH, ensuring no new eggs are matured during pregnancy.

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Key Equations

• There are no mathematical equations for this topic. However, students should be able to calculate the date of ovulation if given the start date of a cycle (usually Day 14).

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Common Mistakes to Avoid

• ❌ Wrong: Oestrogen causes the lining to be maintained.
• ✓ Right: Oestrogen repairs/thickens the lining; Progesterone maintains it.
• ❌ Wrong: FSH and LH are produced in the ovaries.
• ✓ Right: FSH and LH are produced in the Pituitary Gland (in the brain).
• ❌ Wrong: Testosterone is only found in males and oestrogen only in females.
• ✓ Right: Both sexes produce both hormones, but they are present in much higher concentrations in the respective biological sex.

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Exam Tips

• Interpreting Graphs: You will often be asked to identify hormones on a graph showing their levels over 28 days. Remember: FSH peaks early, Oestrogen peaks just before Day 14, LH peaks sharply at Day 14, and Progesterone peaks during the second half of the cycle (the luteal phase).
• Command Words: If asked to "Describe," state what happens (e.g., "the lining thickens"). If asked to "Explain," state how/why it happens (e.g., "Oestrogen is released which causes the lining to thicken").
• Link Structure to Function: When discussing the placenta in the Supplement section, mention its role in hormone production is vital because it ensures the lining is not shed, which would result in a miscarriage.
• Real-world Context: These hormones are often the focus of questions regarding the "contraceptive pill" (which uses progesterone/oestrogen to inhibit FSH and prevent ovulation).

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Exam-Style Questions

Practice these original exam-style questions to test your understanding. Each question mirrors the style, structure, and mark allocation of real Cambridge 0610 Theory papers.

Exam-Style Question 1 — Short Answer [6 marks]

Question:

(a) State two secondary sexual characteristics that develop in females during puberty. [2]

(b) Explain the role of oestrogen in the development of one of the secondary sexual characteristics you stated in (a). [2]

(c) State the primary source of oestrogen production in females during puberty. [1]

(d) State one function of oestrogen in the menstrual cycle other than development of secondary sexual characteristics. [1]

Worked Solution:

(a)

1. Development of breasts. This identifies one secondary sexual characteristic.
2. Widening of hips. This identifies a second secondary sexual characteristic.

How to earn full marks:

• Stating that breasts develop earns 1 mark.
• Stating that hips widen earns 1 mark. Accept other correct examples such as growth of pubic hair, start of menstruation.

(b)

1. Oestrogen stimulates the growth of mammary glands and deposition of fat tissue in the breasts. This links oestrogen with the specific development.
2. This causes the breasts to enlarge and become more prominent. This describes the effect on the breasts.

How to earn full marks:

• Stating that oestrogen stimulates the growth of mammary glands and deposition of fat earns 1 mark.
• Stating that this causes the breasts to enlarge earns 1 mark.

(c)

1. Ovaries This correctly identifies the source of oestrogen.

How to earn full marks:

• Stating ovaries earns 1 mark.

(d)

1. Thickening of the uterus lining. This identifies a function of oestrogen in the menstrual cycle.

How to earn full marks:

• Stating that oestrogen causes thickening of the uterus lining earns 1 mark. Accept other correct examples such as stimulates the release of LH.

Common Pitfall: Students sometimes confuse primary and secondary sexual characteristics. Remember that primary sexual characteristics are those present at birth and directly involved in reproduction, while secondary sexual characteristics develop during puberty.

Exam-Style Question 2 — Extended Response [8 marks]

Question:

(a) Describe the changes that occur in the uterus lining during the menstrual cycle. [4]

(b) Explain the role of FSH and LH in controlling the menstrual cycle. [4]

Worked Solution:

(a)

1. The uterus lining (endometrium) thickens. This describes the initial change.
2. This thickening is due to increased blood supply and growth of cells. This explains the mechanism of thickening.
3. If fertilization does not occur, the lining breaks down. This describes what happens later in the cycle if no fertilisation.
4. The broken-down lining, along with blood, is shed (menstruation). This describes menstruation.

How to earn full marks:

• Stating that the uterus lining thickens earns 1 mark.
• Stating that this thickening is due to increased blood supply and growth of cells earns 1 mark.
• Stating that if fertilization does not occur, the lining breaks down earns 1 mark.
• Stating that the broken-down lining is shed (menstruation) earns 1 mark.

(b)

1. FSH stimulates the development of follicles in the ovary. This describes the role of FSH.
2. These follicles produce oestrogen. This links follicle development to oestrogen production.
3. Oestrogen stimulates the release of LH. This describes the role of oestrogen in LH release.
4. LH triggers ovulation (release of egg from the follicle). This describes the role of LH.

How to earn full marks:

• Stating that FSH stimulates the development of follicles earns 1 mark.
• Stating that these follicles produce oestrogen earns 1 mark.
• Stating that oestrogen stimulates the release of LH earns 1 mark.
• Stating that LH triggers ovulation earns 1 mark.

Common Pitfall: It's easy to mix up the roles of FSH and LH. Remember that FSH primarily stimulates follicle development, while LH triggers ovulation. Think of "F" for follicle and "L" for luteinizing (leading to ovulation).

Exam-Style Question 3 — Extended Response [9 marks]

Question:

A woman has been pregnant for 3 months.

(a) State the name of the hormone that maintains the uterus lining during the first few weeks of pregnancy. [1]

(b) State the source of this hormone during the first few weeks of pregnancy. [1]

(c) Describe how the source of this hormone changes as the pregnancy progresses. [3]

(d) Explain the roles of the placenta in maintaining the pregnancy. [4]

Worked Solution:

(a)

1. Progesterone Correctly identifies the hormone

How to earn full marks:

• Stating progesterone earns 1 mark.

(b)

1. Corpus luteum Correctly identifies the source

How to earn full marks:

• Stating the corpus luteum earns 1 mark.

(c)

1. Initially, the corpus luteum produces progesterone. This describes the initial source.
2. As the pregnancy progresses, the placenta takes over progesterone production. This states the change in source.
3. The corpus luteum eventually degenerates. This describes the fate of the initial progesterone source.

How to earn full marks:

• Stating that the corpus luteum initially produces progesterone earns 1 mark.
• Stating that the placenta takes over progesterone production earns 1 mark.
• Stating that the corpus luteum eventually degenerates earns 1 mark.

(d)

1. The placenta produces progesterone and oestrogen, which maintain the uterus lining. This describes hormonal support.
2. The placenta allows the exchange of nutrients and oxygen from the mother's blood to the fetal blood. This describes nutrient transfer.
3. It allows the removal of waste products (e.g., carbon dioxide) from the fetal blood to the mother's blood. This describes waste removal.
4. The placenta acts as a barrier to some harmful substances (e.g., some pathogens), protecting the fetus. This describes the barrier function.

How to earn full marks:

• Stating that the placenta produces progesterone and oestrogen, which maintain the uterus lining earns 1 mark.
• Stating that the placenta allows the exchange of nutrients and oxygen from the mother's blood to the fetal blood earns 1 mark.
• Stating that it allows the removal of waste products from the fetal blood to the mother's blood earns 1 mark.
• Stating that the placenta acts as a barrier to some harmful substances earns 1 mark.

Common Pitfall: Remember that the placenta has multiple roles beyond just hormone production. It's crucial for nutrient and waste exchange between the mother and fetus, and it also provides a protective barrier.

Exam-Style Question 4 — Short Answer [5 marks]

Question:

(a) Define the term hormone. [2]

(b) State two differences between the effects of testosterone and oestrogen on secondary sexual characteristics. [3]

Worked Solution:

(a)

1. A hormone is a chemical substance. This identifies the hormone as a chemical.
2. Produced by a gland and transported in the blood. This describes the production and transport of hormones.

How to earn full marks:

• Stating that a hormone is a chemical substance earns 1 mark.
• Stating that it is produced by a gland and transported in the blood earns 1 mark.

(b)

1. Testosterone promotes the growth of facial hair, while oestrogen does not. This states one difference.
2. Oestrogen causes breast development, while testosterone does not. This states a second difference.
3. Testosterone increases muscle mass, while oestrogen has a lesser effect on muscle mass. This states a third difference.

How to earn full marks:

• Stating that testosterone promotes the growth of facial hair, while oestrogen does not earns 1 mark.
• Stating that oestrogen causes breast development, while testosterone does not earns 1 mark.
• Stating that testosterone increases muscle mass, while oestrogen has a lesser effect on muscle mass earns 1 mark.

Common Pitfall: When comparing the effects of testosterone and oestrogen, be specific about the secondary sexual characteristics. Avoid vague statements; instead, mention specific examples like facial hair, breast development, or voice deepening.