Normal Menstrual Cycle
Follicular Phase
- This is the first half of the cycle and begins with menstruation.16
- The hypothalamus stimulates the pituitary gland to release follicle stimulating hormone (FSH) and leutinizing hormone (LH) which act on the ovary causing maturation of a follicle.17
- Oestrogen levels rise stimulating the endometrium to proliferate and thicken and also causing an LH surge which triggers ovulation.16,17
Luteal Phase
- This is the second half of the cycle and begins with ovulation.
- The ruptured follicle evolves into the corpus luteum and secretes progesterone.16,17
- If the egg is not fertilised, the corpus luteum involutes after 14 days causing a drop in progesterone which triggers sloughing of the endometrium. This is evident as menstrual bleeding.17
- The first day of the menstrual period marks day one of the next menstrual cycle.16