Reproductive Anatomy of Female

Oogenesis

Ovulation and Formation of Zygote

Estradiol and progesterone during estrous cycle of female rat

Menstrual Cycle

During the follicular phase of the ovulatory cycle, FSH and low levels of LH stimulate the development of one or a few (depending on the species) ovarian follicles. Relatively low levels of estrogen secreted by the developing follicles have a negative feedback action on the hypothalamic-pituitary axis. This feedback action helps to regulate the amount of hypothalamic GnRH and pituitary FSH and LH secretion, so that the ovaries do not become ‘overstimulated’ and produce too many mature follicles. (Inhibin---a peptide hormone---is also secreted by ovarian folicles; inhibin inhibits FSH secretion.) As the follicle becomes fully mature it secretes much larger amounts of estrogen. When the blood estrogen level becomes high, this triggers release of a very large burst of LH (and some FSH) from the pituitary---resulting of ovulation of the mature follicle(s). The sudden increase in LH also stimulates secretion of progesterone from the mature follicles. In many species, the sequence of increased estrogen followed by increased progesterone is the endocrine signal that triggers female sex behavior. Females of species like rats and hamsters do not exhibit sex behavior except when exposed to this sequence of steroid hormones, which generally only occurs shortly prior to ovulation.

Sexual behavior in rats

Surge and pulse centers of the hypothalamus

The hypothalamus contains several discrete clusters of nerve cell bodies (soma). Each cluster is called a nucleus and each has specific functions. The ventromedial nucleus (plural “nuclei”, since each of these nuclei are bilateral---one on each side of the brain) is particularly important in the endocrine regulation of female sex behavior.