Describe the Sequence of the Ovarian Cycle. How Do Hormones Regulate the Cycle?
If pregnancy implantation does not occur, the lining is sloughed off. After about five days, estrogen levels rise and the menstrual cycle enters the proliferative phase. The endometrium begins to regrow, replacing the blood vessels and glands that deteriorated during the end of the last cycle.
These include breast development, flaring of the hips, and a shorter period necessary for bone maturation. Progesterone assists in endometrial re-growth and inhibition of FSH and LH release. In females, FSH stimulates development of egg cells, called ova, which develop in structures called follicles. Follicle cells produce the hormone inhibin, which inhibits FSH production. LH also plays a role in the development of ova, induction of ovulation, and stimulation of estradiol and progesterone production by the ovaries. Estradiol and progesterone are steroid hormones that prepare the body for pregnancy. Estradiol produces secondary sex characteristics in females, while both estradiol and progesterone regulate the menstrual cycle.
Then follicular growth resumes and a new ovarian cycle begins (Grudzinskas, J.G., 1995).
Concentrating on information derived from studies in women and in rhesus and marmoset monkeys, this paper examines some of the hormonal mechanisms underlying the primate ovarian cycle with particular reference to the factors controlling preovulatory follicular development during the follicular phase.
Adashi, E.Y. Ovulation: Evolving Scientific and Clinical Concepts. New York: Springer Verlag, 2000.
Grudzinskas, J.G., and J. Yovich, eds. Gametes: The Oocyte. Cambridge: Cambridge University Press, 1995.
Heffner, Linda G. Human Reproduction at a Glance. Oxford: Blackwell Science, 2001.