Page 284 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Release of Female Sex Hormones
The gonadotropic hormones FSH and LH are tors). Even if the hypothalamus is undamaged,
released from the anterior lobe of the pituitary gonadotropin release can be impaired by dam-
gland in a pulsative manner (every 60 to age to the pituitary (hemorrhage, ischemia, in-
90 min for 1 min) after pulsatile stimulation flammation, trauma), by displacement of go-
by GnRH from the hypothalamus at the same nadotropin-producing cells by tumors, or by
frequency (→ A2; see also p. 272). FSH and LH inhibition due to a raised concentration of sex
are essential for the maturing of the follicles hormones (ovulation inhibitors, anabolic sub-
and for the temporal coordination of the pro- stances with androgen action, tumors, adreno-
duction of female sex hormones. In the female genital syndrome; → p. 264).
organism FSH promotes the maturation of the If androgen production is raised, the release
follicles and estrogen production in the granu- of FSH is inhibited and follicle maturation is
losa cells of the follicles (→ A2). The estrogens thus interrupted. Polycystic ovaries are formed.
(estrone, estradiol, estriol) at first stimulate Some of the androgens are transformed into
the further release of gonadotropins (positive estrogens which, via stimulation of LH release,
feedback) until the maturation of a follicle promote further formation of ovarian andro-
leads to ovulation and corpus luteum forma- gens.
Hormones logs), formed by the corpus luteum under the gonadotropin release to be due to raised pro-
tion. Progestogens (progesterone and ana-
It is relatively common for a reduction in
lactin secretion, for example, as a result of the
influence of LH, and the estrogens (after ovula-
prolactin or a prolactin-producing pituitary
(→ A3). The concentration of gonadotropins
9 tion) inhibit further release of gonadotropins absence of inhibition of pituitary secretion of
falls again, as does, after some delay, that of tumor (→ p. 260). Gonadotropin release can
the estrogens and progestogens (→ A4). As a be inhibited by dopaminergic drugs that cause
rule this cycle takes 28 days, although the in- a rise in prolactin secretion. Lastly, gonadotro-
terval between menstruation and ovulation pin release can be inhibited by damage to the
varies greatly. The granulosa cells also form in- pituitary through head trauma, abnormal an-
hibin and activin, while the theka cells form lage or maturation, radiation, tumors, degen-
the androgens androstenedione and testoste- erative or inflammatory disease, or defective
rone. Activin promotes gonadotropin release, biosynthesis.
while inhibin suppresses it (see p. 272 for the The formation of estrogens and/or proges-
effect of testosterone). Prolactin produced in togens can be impaired by ovarian insufficiency
the anterior pituitary inhibits the pulsatile re- caused by an abnormal development (→
lease of gonadotropins. It also decreases the p. 278) or by damage (e.g., radiation, chemo-
ovary’s responsiveness to gonadotropins. therapeutic agents). Inadequate follicular mat-
An excess of female sex hormones is usually uration or transformation in the corpus lu-
due to an exogenous supply (contraceptive teum (corpus luteum insufficiency) can cause
pills). In addition, some tumors produce sex the deficiency. Lack of estrogen can also be
hormones. due to an enzyme defect. In the resistant ovary
A lack of estrogens and progestogens is fre- syndrome the ovaries are refractory to the ac-
quently the result of a decreased GnRH release tion of gonadotropins. This may be caused by
in severe psychological or physical stress (e.g., defective receptors or inactivating antibodies.
malnutrition, serious systemic disease, high- The result is a lack of estrogens despite an in-
performance sport). GnRH release can also be creased release of gonadotropins.
reduced through the influence of the neuro-
transmitters norepinephrine, dopamine, sero-
tonin, and endorphins (→ A1).
However, it is not only reduced, but also
persistently high concentrations of GnRH (or its
274 analogs) that decrease the release of gonado-
tropins (down-regulation of the GnRH recep-
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
All rights reserved. Usage subject to terms and conditions of license.