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These two hormones work alongside luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to regulate the female menstrual cycle. The two primary sex organs in the female reproductive system are the ovaries and the uterus. We can apply our knowledge of male sex hormones to the new strategies being developed for "male birth control". The diagram below depicts how male sex hormones are regulated by endocrine control. At the onset of puberty in males, the hypothalamus starts secreting Gonadotropin releasing hormone (GnRH) which acts on the pituitary gland to release FSH and LH. FSH and LH affect reproductive structures to cause the formation of sperm and the preparation of eggs for release and possible fertilization. Reproductive endocrinologists undergo extensive medical training, first in a four-year residency in obstetrics and gynecology, then in a three-year fellowship in reproductive endocrinology. Doctors may use fertility drugs, surgery, or assisted reproductive techniques (ART) in their therapy. A reproductive endocrinologist is a physician who treats a variety of hormonal disorders related to reproduction and infertility in both men and women. Estrogen is involved in calcium metabolism and, without it, blood levels of calcium decrease. The endometrium begins to degenerate as the progesterone levels drop, initiating the next menstrual cycle. The level of estrogen produced by the corpus luteum increases to a steady level for the next few days. Slowly rising levels of FSH and LH cause the growth of follicles on the surface of the ovary. The proliferative phase is named after the growth, or proliferation of the endometrium during this phase, which is caused by increasing concentrations of estrogen. LH also plays a role in the development of ova, induction of ovulation, and stimulation of estrogen and progesterone production by the ovaries. Follicle cells produce the hormone inhibin, which inhibits FSH production. The Sertoli cells also produce the hormone inhibin, which is released into the blood when the sperm count is too high. LH also enters the testes and stimulates the interstitial cells of Leydig to make and release testosterone into the testes and the blood. At the onset of puberty, the hypothalamus causes the release of FSH and LH into the male system for the first time. Estrogens are plasma protein bound to albumin and/or sex hormone-binding globulin in the circulation. Hence, both granulosa and theca cells are essential for the production of estrogen in the ovaries.citation needed This compound crosses the basal membrane into the surrounding granulosa cells, where it is converted either immediately into estrone, or into testosterone and then estradiol in an additional step. Androstenedione is a substance of weak androgenic activity which serves predominantly as a precursor for more potent androgens such as testosterone as well as estrogen. These secondary sources of estrogens are especially important in postmenopausal women.The pathway of estrogen biosynthesis in extragonadal tissues is different. This reaction engages penile reflexes (such as erection and ejaculation) that aid in sperm competition when more than one male is present in mating encounters, allowing for more production of successful sperm and a higher chance of reproduction. Therefore, these mammals may provide a model for studying clinical populations among humans with sexual arousal deficits such as hypoactive sexual desire disorder. Testosterone treatment for reasons other than possible improvement of sexual dysfunction may not be recommended. It is unclear if the use of testosterone for low levels due to aging is beneficial or harmful. Decline of testosterone production with age has led to interest in androgen replacement therapy. In androgen-deficient men with concomitant autoimmune thyroiditis, substitution therapy with testosterone leads to a decrease in thyroid autoantibody titres and an increase in thyroid's secretory capacity (SPINA-GT). These are an honest signal of health, and may assist females in sexual selection for species that use lek mating, such as the roach Rutilus rutilus. Another of Fisher's ideas is the sexy son hypothesis, whereby females will desire to have sons that possess the characteristic that they find sexually attractive in order to maximize the number of grandchildren they produce. The primary sex organs are different from the secondary sex organs because at maturity they are directly related to the production gametes, which are haploid male or female germ cells, and their uniting with one another during sexual reproduction to form a zygote. Although adrenarche happens alongside increases in sex hormones during puberty, adrenal glands may also produce androgens that impact pubic hair. This triggers your child’s gonads to begin releasing sex hormones — either estrogen or testosterone. Men taking testosterone replacement must be carefully monitored for prostate cancer. There are times when low testosterone is not such a bad thing. For example, problem with function of pituitary gland or adrenal glands may lead to reduced testosterone production. As surprising as it may be, women can also be bothered by symptoms of testosterone deficiency. For example, a man with osteoporosis and low testosterone can increase bone strength and reduce his fracture risk with testosterone replacement. Some men who have a testosterone deficiency have symptoms or conditions related to their low testosterone that will improve when they take testosterone replacement. The testes produces less testosterone, there are fewer signals from the pituitary telling the testes to make testosterone. The amount of testosterone synthesized is regulated by the hypothalamic–pituitary–testicular axis (Figure 2). Testosterone is also synthesized in far smaller total quantities in women by the adrenal glands, thecal cells of the ovaries, and, during pregnancy, by the placenta. In the final and rate limiting step, the C17 keto group androstenedione is reduced by 17β-hydroxysteroid dehydrogenase to yield testosterone. The first step in the biosynthesis involves the oxidative cleavage of the side-chain of cholesterol by cholesterol side-chain cleavage enzyme (P450scc, CYP11A1), a mitochondrial cytochrome P450 oxidase with the loss of six carbon atoms to give pregnenolone. In addition, the amount of testosterone produced by existing Leydig cells is under the control of LH, which regulates the expression of 17β-hydroxysteroid dehydrogenase. The number of Leydig cells in turn is regulated by luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In the bones, estradiol accelerates ossification of cartilage into bone, leading to closure of the epiphyses and conclusion of growth.
