Hormones & Signal Transduction 5 Sections28 LessonsLifetime
Sex Hormones
Sex Hormones
The Sex hormones are secreted by the gonads in response to pituitary gonadotropins (LH and FSH)
These are:
- Estrogen
- Progesterone and
- Testosterone
Ovarian Hormones
Ovarian hormones are C18 estrogens, C19 androgens and C21 progesterone.
These are produced by the ovarian follicles.
The Follicular thecal cells produce C19 androgens.
These C19 androgens are then converted to C18 estrogens by granulosa cells, by aromatization of ring A and loss of C19 methyl group.
Estradiol is the most important estrogen.
It is then converted to estrone by liver.
It is further hydroxylated to estriol, which is inactive.
Estradiol is bound to plasma SHBG (Sex Hormone Binding Globulin).
Estradiol (E2) is the predominant sex hormone present in females; But, it is also present in males, at lower levels..
Estradiol has not only a critical impact on reproductive and sexual functioning, but also affects other organs including the bones.
Estradiol enters cells freely and interacts with a cytoplasmic target cell receptor;
Then it enters the nucleus of the target cell, and regulates gene transcription.
Estradiol binds with equal affinity to both estrogen receptors ER-alpha & ER-beta.
Selective Estrogen Receptor Modulators (SERMs) preferentially act on one of these receptors.
Regulation of Ovarian Hormones
FSH influences follicles to ripen, which produces estrogen.
Estrogen level gradually increases in the second week of the menstrual cycle.
Estrogen level is maximum 24 hours before the LH peak.
High doses of estrogen can suppress the LH release and, therefore effective as contraceptive.
Under the influence of Estrogen, uterine endometrium proliferates. Glands in endometrium are hypertrophied.
Ducts in mammary glands are proliferated and progesterone receptors are synthesized.
LH level peaks 16 hours before the ovulation.
The LH surge induces the ovulation.
The corpus luteum then starts secreting progesterone.
Under the influence of progesterone, endometrium enters the secretory phase, and prepares for implantation of the fertilized ovum.
LH is required for maintenance of corpus luteum.
If implantation occurs (day 22–24), the LH function is taken over by the hCG, produced by the cytotrophoblast cells of the early embryo.
The hCG can be detected 5–7 days after. missing a period.
If implantation does not occur, hormone levels are decreased and the secretory glands of the endometrium are denuded.
Clomiphene citrate competes with estrogen for receptors in hypothalamus, thus removing the feedback inhibition.
So GnRH level is increased, with consequent high levels of LH and FSH, which may produce follicular stimulation and ovulation.
Clomiphene is therefore used to produce ovulation in infertile females.
Testicular Hormones
Testosterone is the major hormone in the males.
The Leydig cells (interstitial cells), secrete the androgens, under the influence of LH (also called ICSH – interstitial cell stimulating hormone).
The androgens exert feedback effect on LH secretion, through inhibition of GnRH.
Thus, in patients with hypogonadism, LH level is high.
FSH binds to Sertoli cells (basement membrane cells of seminiferous tubules) and promotes the synthesis of Androgen Binding Protein (ABP).
Thus high concentration of androgen is made available locally in the seminiferous tubules, at the site of spermatogenesis
In patients with azoospermia, the FSH level is very high, due to lack of negative feedback.
Androgens stimulate spermatogenesis, produce hypertrophy of prostate, seminal vesicles, muscles, bones and kidney cells.
Testosterone is anabolic.
Dihydrotestosterone (DHT) is the cause for the benign prostate hypertrophy, that affects more than 75% of men over the age of 60 years
The enzyme 5-alpha-reductase is needed to convert testosterone to DHT
Finasteride can inhibit 5-alpha-reductase, and hence it is used as a treatment for prostate hypertrophy.
Summary
