Difference between revisions of "Sex Hormones"
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| − | + | ==Introduction== | |
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| + | ==Male Sex Hormones== | ||
| + | The male sex hormone is called '''Testosterone''' and this hormone is required for [[Spermatogenesis_and_Spermiation_-_Anatomy_%26_Physiology|spermatogenesis]]. 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. | ||
| + | ===Hormone Production=== | ||
| + | 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. | ||
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| + | FSH causes Sertoli cells to produce estradiol and the peptide hormone Inhibin. LH acts on Leydig cells causing them to produce testosterone. Testosterone and estradiol form part of the negative feedback loop on GnRH secretion by the hypothalamus. Inhibin is part of a further negative feedback system, acting on the anterior pituitary to inhibit the secretion of FSH. | ||
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| + | Leydig cells produce testosterone using cholesterol as a base molecule. Leydig cells contain various enzymes such as 18-hydroxylase that facilitate the production of steroid hormones. In some species such as pigs, the testes also produce '''androstenone''' which acts as a pheromone and is secreted via the saliva, often producing a copulatory position from sows in oestrous. Androstenone is also responsible for bore taint. | ||
| + | ===Regulation of Male Sex Hormones=== | ||
| + | ===Effects of Male Sex Hormones=== | ||
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| + | ==Female Sex Hormones== | ||
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| + | [[Category:Reproductive System - Anatomy & Physiology]] | ||
| + | [[Category:To Do - A&P]] | ||
Revision as of 15:36, 13 July 2011
Introduction
Male Sex Hormones
The male sex hormone is called Testosterone and this hormone is required for spermatogenesis. 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.
Hormone Production
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).
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.
FSH causes Sertoli cells to produce estradiol and the peptide hormone Inhibin. LH acts on Leydig cells causing them to produce testosterone. Testosterone and estradiol form part of the negative feedback loop on GnRH secretion by the hypothalamus. Inhibin is part of a further negative feedback system, acting on the anterior pituitary to inhibit the secretion of FSH.
Leydig cells produce testosterone using cholesterol as a base molecule. Leydig cells contain various enzymes such as 18-hydroxylase that facilitate the production of steroid hormones. In some species such as pigs, the testes also produce androstenone which acts as a pheromone and is secreted via the saliva, often producing a copulatory position from sows in oestrous. Androstenone is also responsible for bore taint.