IGCSE Biology 0610: Menstrual Cycle Hormones - FSH, LH, Oestrogen and Progesterone

A student researching human fertility reads the following description of one part of the menstrual cycle.

"Rising levels of one hormone cause an egg cell to mature inside a follicle in an ovary. A sharp rise in a second hormone then triggers the follicle to release the egg cell (ovulation). After ovulation, the remains of the follicle develop into a structure that produces a third hormone, which maintains the thickened lining of the uterus. If the egg cell is not fertilised, the level of this third hormone falls, and the lining of the uterus breaks down."

(a) Name hormone 1, hormone 2 and hormone 3 described above. [3]

(b) Name the structure in the ovary that develops from the remains of the follicle after ovulation. [1]

(c) Explain what happens to the level of hormone 3 if the egg cell is fertilised and implantation occurs, and explain why this change is necessary for the pregnancy to continue. [3]

(d) State two secondary sexual characteristics that develop in females during puberty as a result of rising oestrogen levels. [2]

Part (a): Naming the three hormones

The description follows the sequence of events in the menstrual cycle controlled by hormones:

Hormone 1, which causes the egg cell to mature inside a follicle, is FSH (follicle-stimulating hormone).
Hormone 2, whose sharp rise triggers ovulation, is LH (luteinising hormone).
Hormone 3, produced after ovulation and responsible for maintaining the uterus lining, is progesterone.

Part (b): The structure that produces hormone 3

After the follicle releases its egg cell, its remains develop into the corpus luteum. This structure produces progesterone (and some oestrogen), which maintains the thickened lining of the uterus during the second half of the cycle.

Part (c): Progesterone levels after fertilisation

If the egg cell is fertilised and the resulting embryo implants in the uterus lining, the level of progesterone stays high, rather than falling.

This is necessary because progesterone is what maintains the thickened, blood-supplied lining of the uterus. If progesterone levels fell as they normally do towards the end of an unfertilised cycle, the lining would break down and be shed. Exactly as happens during menstruation. Since the embryo is implanted in this lining, a fall in progesterone at this stage would cause the lining (and the embryo within it) to be lost. Keeping progesterone levels high therefore keeps the lining intact, allowing the pregnancy to continue.

Part (d): Oestrogen and puberty

Beyond its role in the menstrual cycle, oestrogen also drives the development of secondary sexual characteristics in females during puberty. Rising oestrogen levels bring about several distinct changes, each earning its own mark: for example, the development of the breasts is one characteristic, and the widening of the hips is a separate, independently earnable characteristic (the start of menstrual cycles is another acceptable alternative). Two different, clearly distinguishable characteristics are needed to gain both marks.

Final answers

(a) Hormone 1 = FSH; hormone 2 = LH; hormone 3 = progesterone.
(b) The corpus luteum.
(c) Progesterone stays high (does not fall), maintaining the uterus lining so the implanted embryo is not lost.
(d) Two secondary sexual characteristics such as breast development and widening of the hips, developing due to rising oestrogen.