The Menstrual Cycle • Like puberty, the menstrual cycle is regulated by hormones: LH, FSH, oestrogen and progesterone. • The purpose of the menstrual cycle is to prepare the body for reproduction. • The menstrual cycle can be divided into a series of phases and the length of each phase varies between women and from cycle to cycle.
Menstrual Phase Days 1 - 5 • The menstrual phase begins after oestrogen and progesterone levels drop at the end of the previous cycle. • This causes the blood vessels in the endometrium to constrict, cutting off the supply of blood. • As a result, the outer endometrial layer dies and begins to deteriorate.
Menstrual Phase Days 1 - 5 • The sloughing off of tissue is gradual and a total of 35-50 ml of blood and tissue is lost.
Proliferative Phase Days 6 - 13 • This phase is stimulated and sustained by the oestrogen produced by the developing follicle in the ovary. • Rising oestrogen levels cause the endometrium to grow a new blood lining.
Ovulation Day 14 • High oestrogen levels cause the pituitary to produce a surge of LH. • High LH levels stimulates ovulation (the bursting of the follicle releasing the ovum from the ovary). • The ovum is then swept up into the fallopian tube.
Secretory Phase Day 15 - 28 • The follicle that released the ovum into the fallopian tube continues to grow and divide for a while. • After ovulation, the follicle transforms into the corpus luteum. • The corpus luteum will produce progesterone in addition to oestrogen for the next 2 weeks.
Secretory Phase Day 15 - 28 • The presence of oestrogen and progesterone cause the uterine arteries to lengthen and the blood lining to thicken. • Near the end of the two weeks the corpus luteum deteriorates and hormone levels drop. • The cycle then starts all over.
Developing Follicle Young Follicles Graafian Follicle Oocyte Mature Corpus Luteum Follicle at Ovulation Ovum
Developing follicle produces oestrogen. FSH from pituitary causes an egg to start ripening. High oestrogen causes pituitary to make LH. Corpus Luteum stops hormone production. High LH causes follicle ovulation. Corpus Luteum produces oestrogen and progesterone.