Hormones in Human Reproduction

This section explains the hormones used in human reproduction, the process puberty and the menstrual cycle.

Puberty

Puberty is the stage of development when a child's body matures into an adult capable of reproduction. It is controlled by hormones released by the endocrine system.

• In males, testosterone (produced by the testes) stimulates sperm production and the development of secondary sexual characteristics, such as increased muscle growth, body hair, and a deeper voice.
• In females, oestrogen (produced by the ovaries) triggers the development of breasts, the start of the menstrual cycle, and other secondary sexual characteristics such as wider hips and body hair.

The Menstrual Cycle

The menstrual cycle is a recurring process in females that prepares the body for pregnancy. It lasts around 28 days and involves several hormonal changes:

Day 1-5: Menstruation – The uterus lining breaks down and is shed as a period.

Day 6-14: Uterus Lining Rebuilds – Oestrogen causes the uterus lining to thicken in preparation for a fertilised egg.

Day 14: Ovulation – A mature egg is released from the ovary, triggered by a surge in luteinising hormone (LH).

Day 15-28: Uterus Lining Maintained – Progesterone maintains the thickened uterus lining. If no fertilisation occurs, progesterone levels fall, leading to menstruation and the cycle repeating.

Negative Feedback in the Menstrual Cycle

Hormonal control of the menstrual cycle operates through a negative feedback system involving four key hormones:

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Follicle-Stimulating Hormone (FSH):

• Released by the pituitary gland.
• Stimulates the growth and maturation of an egg in the ovary.
• Stimulates oestrogen production.

Oestrogen:

• Produced by the ovaries.
• Causes the uterus lining to thicken.
• Inhibits FSH (to prevent multiple eggs from developing).
• Stimulates the release of LH.

Luteinising Hormone (LH):

• Released by the pituitary gland.
• Triggers ovulation (release of the egg).
• Stimulates the empty follicle to produce progesterone.

Progesterone:

• Produced by the empty follicle after ovulation.
• Maintains the uterus lining.
• Inhibits FSH and LH to prevent further egg release.
• When progesterone levels fall, menstruation occurs, and FSH is released to restart the cycle.

The regulation of the menstrual cycle through negative feedback ensures that hormone levels remain balanced and that the cycle proceeds efficiently. Understanding these hormonal interactions is crucial in Biology and for the study of fertility treatments and contraception.