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Reproductive Hormones Overview - Anatomy & Physiology (view source)
Revision as of 14:01, 25 August 2011
, 14:01, 25 August 2011→Testosterone (T)
Progesterone is a steroid hormone that is produced by the corpus luteum and the placenta. In males the target tissues are the accessory sex glands, the tunica dartos (scrotum), the seminiferous tubules and skeletal muscles. In females the target tissues are the uterine endometrium, the mammary gland, the myometrium and the hypothalamus. Progesterone results in increased endometrial secretions and inhibits the release of GnRH in females. It also inhibits female reproductive behaviour as well as acting to maintain a pregnancy. Progesterone has no primary action in the male.
Progesterone is a steroid hormone that is produced by the corpus luteum and the placenta. In males the target tissues are the accessory sex glands, the tunica dartos (scrotum), the seminiferous tubules and skeletal muscles. In females the target tissues are the uterine endometrium, the mammary gland, the myometrium and the hypothalamus. Progesterone results in increased endometrial secretions and inhibits the release of GnRH in females. It also inhibits female reproductive behaviour as well as acting to maintain a pregnancy. Progesterone has no primary action in the male.
===Testosterone (T)===
===Testosterone (T)===
Testosterone is a steroid hormone that is produced in the leydig cells within the testes and also via theca interna cells within follicles. In males the target tissue for testosterone are the anterior pituitary gland, specifically the gonadotroph cells. In females the target tissues are the brain, skeletal muscle and granulosa cells. This is because testosterone acts as a substrate for estradiol. The synthesis of testosterone rather than estradiol can lead to abnormal masculinisation in females. In males the primary action of testosterone is anabolic growth, spermatogenesis promotion and promotion of secretion from the accessory sex glands.
The male sex hormone is called testosterone and this hormone is required for [[Spermatogenesis_and_Spermiation_-_Anatomy_%26_Physiology|spermatogenesis]]. Testosterone is a steroid hormone that is produced in the leydig cells within the testes. A relatively high concentration of testosterone is maintained within the testicular tissue and testosterone is circulated around the body by diffusion of the hormone from the spermatic cord into the testicular veins and arteries. The primary action of testosterone is anabolic growth, spermatogenesis promotion and promotion of secretion from the accessory sex glands.
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Male sex hormones are regulated by negative feedback systems that operate at various levels within the male sex hormone system. The starting point for the production of testosterone (and therefore the production of spermatozoa)is the hypothalamus. The hypothalamus contains neuroendocrine cells that are capable of secreting a substance called '''Gonadotropin-releasing hormone''' or GnRH. GnRH stimulates cells in the anterior pituitary, via the "portal system" to secrete two intermediate hormones within the male sex hormone cycle; '''Luteinizing hormone''' (LH) and '''Follicle-Stimulating Hormone''' (FSH).
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The secretion of GnRH is pulsatile and can vary greatly throughout the day and/or year, and therefore the secretion of LH and FSH are also pulsatile (although the plasma concentration of FSH does not fluctuate as much as LH due to the effect of Inhibin, see below). The activity of GnRH neuroendocrine cells is determined by spontaneous rhythms and by sensory impulses. Cycles such as seasonal sexual activity are controlled by this pulsatile system. In male animals there are generally 4 to 12 GnRH pulses per day.
===Inhibin===
===Inhibin===
Inhibin is a type of glycoprotein that is synthesised within the granulosa cells in females and in sertoli cells in the male. In both males and females the target organ for inhibin is the anterior pituitary, specifically the gonadotroph cells. In the male inhibin inhibits FSH secretion whilst in females it stimulates FSH secretion.
Inhibin is a type of glycoprotein that is synthesised within the granulosa cells in females and in sertoli cells in the male. In both males and females the target organ for inhibin is the anterior pituitary, specifically the gonadotroph cells. In the male inhibin inhibits FSH secretion whilst in females it stimulates FSH secretion.