Oestrogen is the main female reproductive hormone produced in the ovary.

The idea

Oestrogen is a steroid hormone and the principal female reproductive hormone. It is secreted by the ovaries, specifically by the developing follicle and the corpus luteum after ovulation. As a hormone, it travels in the bloodstream to target cells with complementary receptors, so it can act on distant tissues. Its roles include promoting female secondary sexual characteristics at puberty, such as breast development and widening of the hips, and regulating the menstrual cycle by stimulating thickening of the uterus lining and influencing the release of other hormones. For example, rising oestrogen concentrations in the first half of the cycle help trigger a surge in luteinising hormone that leads to ovulation. Understanding its ovarian source and main female role is essential before studying cycle control.

What earns the marks

• States that oestrogen is a hormone, so it is a chemical messenger carried in the blood plasma to target cells.
• Identifies the ovary as the main site of oestrogen production in females.
• Names the ovary as the organ containing the follicles and corpus luteum that secrete oestrogen.
• Describes at least one reproductive role, such as promoting female secondary sexual characteristics at puberty.
• Explains that oestrogen helps regulate the menstrual cycle, including thickening of the uterus lining.
• Links oestrogen to the control of other reproductive hormones, such as its role in triggering the luteinising hormone surge before ovulation.

Common mistakes and how to put them right

• Saying oestrogen is produced by the uterus.

  Put it right by naming the ovary as the main production site.

• Confusing oestrogen with progesterone and assigning all cycle-maintenance roles to oestrogen.

  Put it right by stating that progesterone is the main hormone maintaining the uterus lining after ovulation.

• Describing oestrogen as a male hormone or as produced by the testes.

  Put it right by stating that testosterone is the main male reproductive hormone and oestrogen is the main female reproductive hormone.

Exam tips

• Use the phrase main female reproductive hormone when defining oestrogen, because the specification distinguishes main roles from other hormones.
• When asked where it is produced, write ovary rather than reproductive system, as the organ is the precise answer.
• Link oestrogen to a named effect, such as uterus lining thickening or female secondary sexual characteristics, to show understanding rather than recall of a single word.