Page 858 - Atlas of Histology with Functional Correlations

In response to both follicle-stimulating hormone (FSH) and LH, the cells of

the corpus lutein secrete estrogen and large amounts of progesterone. High
levels of both hormones further stimulate the development of the uterus and
mammary glands in anticipation of the implantation of a fertilized egg and
pregnancy.

Rising levels of estrogen and progesterone produced by the corpus

luteum eventually inhibit further release of FSH and LH, by its action on the
neurons in the hypothalamus and gonadotrophs in the adenohypophysis. This
effect prevents further ovulation.

If the ovulated secondary oocyte is not fertilized, the corpus luteum

continues to secrete its hormones for about another 12 days and then begins
to regress. After its regression, it is called the corpus luteum of
menstruation, eventually becoming a connective tissue scar corpus
albicans. With decreased functions of the corpus luteum, estrogen and
progesterone levels decline, affecting the blood vessels in the endometrium

of the uterus and inducing the shedding of the stratum functionalis of the
endometrium in the menstrual flow.

As the corpus luteum ceases function, the inhibitory effects of estrogen,
progesterone, and inhibin on the hypothalamus and pituitary gland cells are

removed. As a result, FSH is again released from the adenohypophysis,
initiating a new ovarian cycle of follicular development and maturation.

Corpus Luteum and Pregnancy

If fertilization of the oocyte and implantation of the embryo occurs, the
corpus luteum increases in size and becomes the corpus luteum of

pregnancy. The hormone human chorionic gonadotropin (hCG), secreted
by the trophoblast cells of the developing placenta in the implanting embryo,
continues to stimulate luteal functions of the corpus luteum and prevents its
regression. The influence of hCG is similar to that by LH from the pituitary

gland and extends its function of progesterone secretion. As a result, the
corpus luteum of pregnancy persists for several months. As the pregnancy
progresses, however, the function of the corpus luteum diminishes and is
taken over by the placenta after about 6 weeks of pregnancy. During

pregnancy, the placenta functions as a temporary endocrine organ and
continues to secrete sufficient amounts of estrogen and progesterone to
maintain the pregnancy until parturition.

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