Describe how hormones from the ovary and pituitary gland interact to control the human menstrual cycle.
Hormones produced by the ovary include progeserone and oestrogen while the pituitary gland produces luteinizing hormones (LH) and follicle stimulating hormone (FSH) which interact as shown to control events of the menstrual cycle.
During the early menstrual phase, levels of oestrogen and progesterone fall. This induces the pituitary gland to secrete FSH and LH.
Increased levels of FSH stimulate one or more Graafian follicles to start growing. It also stimulates follicle cells to secrete oestrogen. The levels of oestrogen in blood increase gradually for a few days and reaches the peak on the 12th day of the cycle. High oestrongen concentration inhibits FSH secretion which induces increased production of LH within 12hrs.
The high LH causes ovulation with subsequent formation of corpus luteum.
During the post ovulatory phase, corpus luteum secretes progesterone. Progesterone acts on the uterine wall to promote cellular proliferation in preparation for implantation and also maintains corpus luteum.
High levels of progesterone and oestrogen inhibit the secretion of LH and FSH.
If fertilization occurs, the corpus luteum degenerates. Progesterone level reduces markedly and the uterine wall is shed in menstruation. This initiates events of the next cycle (i.e this is day 1 of the next cycle).
