Reproductive Physiology - NCLEX-PN

In an adult male, luteinizing hormone triggers the production of testosterone by the Leydig (interstitial) cells in the testes. Testosterone is converted to DHT (dihydrotestosterone) by the enzyme 5-alpha reductase. Sperm production and maturation is triggered by follicle-stimulating hormone (FSH) rather than LH in adult males.

The most prevalent and biologically active estrogen in an adult female is estradiol (E2). Estrone and estriol are less active forms of estrogen, and progesterone is not a form of estrogen, but rather a distinct progestogen reproductive hormone.

After menopause, the most predominant form of circulating estrogen is estrone (E1). Estradiol is more prevalent in pre-menopausal women who are not pregnant, while estriol and estetrol are both only elevated during pregnancy.

The only form of estrogen that is exclusively present in pregnant women is estetrol (E4).

The conversion of androgens into estrogen is performed by aromatase, also known as estrogen synthetase or estrogen synthase. 5-alpha-reductase is responsible for the conversion of testosterone to dihydrotestosterone. Amylase is a salivary enzyme that breaks down starches during mastication, and protease is a digestive enzyme that aids in the breakdown of proteins.

All of the hormones listed, and testosterone, are androgens except 2-hydroxyestrone, which is a metabolite of estrone (a form of estrogen).

Androstenedione is produced by the ovaries, the testes, and the adrenal cortex. The adrenal medulla primarily secretes epinephrine and norepinephrine.

Dehydroepiandrosterone (DHEA), an endogenous steroid hormone that is a precursor for both estrogen and testosterone, is synthesized from pregnenolone in the gonads, the adrenal glands, and the brain.

Normal DHEA levels in an adult female under the age of fifty range from . DHEA levels are higher in younger women and decline as women approach menopause.

The normal DHEA levels in an adult male under the age of fifty can range from . They are highest in early adulthood and decline with age.

The most abundant circulating steroid hormone in the human body is Dehydroepiandrosterone (DHEA). DHEA is a precursor to several important sex hormones including testosterone and estrogen. It also functions as a neuroactive steroid.

The hormone that is secreted by the corpus luteum in order to prepare the endometrium for implantation of a fertilized ovum is progesterone. Progesterone prevents the constriction of blood vessels to the endometrium, which in turn prevents the shedding of the endometrial lining (menses). It also alters the endometrium, converting it to it's secretory phase in preparation for implantation.

Progesterone serves many functions in pregnancy. It prepares the endometrial lining for implantation of the embryo, it increases the contractility of the uterus, it inhibits lactation during pregnancy, and it is thought to reduce maternal immune response to the developing fetus. Breast enlargement and maturation in preparation for lactation is facilitated by estrogen, rather than progesterone.

Testis-determining factor, also known as sex-determining region Y (SRY) protein**,** is a sex-determining gene found exclusively on the Y-chromosome in humans. It's transcription triggers the development of male sexual characteristics in the developing fetus.

Leydig cells, located in the testes adjacent to the seminiferous tubules, secrete testosterone in response to lutenizing hormone (LH). Sertoli cells are also adjacent to the seminiferous tubules. They play a role in stimulating spermatogenesis in spermatogenic cells. Wolffian cells are a part of the fetal male reproductive tract and do not produce testosterone.

The Wolffian ducts are fetal urogenital structures that develop into the seminal vesicles, the vas deferens, and the epididymis. They also form parts of the bladder wall.

The Sertoli cells of the testes are responsible for the secretion of many substances, including anti-Müllerian hormone, androgen binding protein, glial cell line-derived neurotrophic factor, and estradiol.

In polycystic ovarian syndrome (PCOS), luteinizing hormone (LH) levels are elevated, while follicle-stimulating hormone (FSH) levels are often low. Because FSH aromatizes androgens to estrogen, low FSH will cause androgens to increase. Low levels of FSH and high androgens keep the follicle from maturing & prevent ovulation. Hypogonadism is significantly more rare, and while extreme stress and poor nutrition may inhibit ovulation, in the United States PCOS is the leading cause of anovulation (failure to release an ovule from the ovary).

Normal FSH values for a menstruating adult female are . A FSH of would be considered normal in a premenarchal female, while normal FSH after menopause can range from .