The menstrual cycle lasts approximately 28 days. It has 4 main stages which are:
- Bleeding due to break down of endometrium
- Build-up of endometrium
- Ovulation
- Maintenance of endometrium
The cycle is controlled by hormones and negative feedback. These hormones include Follicle Stimulating Hormone (FSH), Luteinising Hormone (LH), oestrogen and progesterone. Here are their jobs.
FSH – is secreted by the pituitary gland to stimulate a follicle to mature and start the production of oestrogen
Oestrogen – Inhibits the secretion of FSH and builds up the endometrium (uterus lining). Stimulates an LH surge
LH – Stimulates ovulation and remnants of follicles to turn into a corpus luteum
Progesterone – is secreted by the corpus luteum and maintains the endometrium. It inhibits further production of LH and FSH but when levels are low (not pregnant), oestrogen levels will also drop so FSH is produced again. The cycle repeats.
You will be asked about these hormones in I/GCSE Biology
- An example of negative feedback is that when FSH is secreted, oestrogen is made but when oestrogen is high, FSH stops being secreted.
Reference; https://www.forthwithlife.co.uk/wp-content/uploads/sites/8/2021/03/hormone-graph-1024x718.png
Drafted by Catrina (Biology)