3.9 The menstrual cycle 3.9 Understand the roles of oestrogen and progesterone in the menstrual cycle

The menstrual cycle lasts about 28 days 1 egg is released into the oviduct every month. Before the egg is release the lining of the uterus becomes thick and spongy. This is to prepare itself for the fertilised egg. If the egg is not fertilised, it is dead by the time it reaches the uterus. It doesn’t sink into the spongy wall, instead it continues onwards, down through the vagina. This is called menstruation (a period). ▫It usually lasts for about 5 days.

The menstrual cycle It is controlled by hormones. First a follicle develops inside an ovary. The developing follicle secretes oestrogen. ▫Oestrogen makes the lining of the uterus grow thick and spongy. When the follicle is fully developed, ovulation takes place.

The follicle stops secreting oestrogen. It becomes a corpus luteum. The corpus luteum starts to secrete another hormone called progesterone. ▫Progesterone keeps the uterus lining thick and spongy and well supplied with blood, in case the egg is fertilised. When progesterone stops being produced, the uterus lining breaks down. (the period) The cycle begins again.

Draw and annotate the diagram on page 80. Answer the questions in section 3.9 of the workbook.