The Male Reproductive System - 1 Hypothalamus-Pituitary-Gonad Axis

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The Male Reproductive System - 1 Hypothalamus-Pituitary-Gonad Axis Jennifer Carbrey Ph.D. Department of Cell Biology Sexual Differentiation Primordial germ cells in male & female generated in embryogenesis. Chromosomal sex determinants are XX and XY. Expression of the SRY gene on chromosome Y results in testes (male). Presence of testes vs ovaries determines gonadal sex. Gonads are the source of hormone which determines external and internal genitalia (phenotypic sex). The SRY gene is necessary for maleness but not sufficient. The testosterone receptor gene on the X chromosome is also required. Common Axis In males & females, GnRH secretion is pulsatile. Local secretion of testosterone is needed for development of ovum (female) and of sperm (male). Inhibin B decreases FSH secretion. Sex hormones regulate GnRH, LH and FSH. image by Uwe Gille (modified), http://commons.wikimedia.org/wiki/File:Hypothalamus-Hypophysis-Testicle-Hormone-Axis_%28engl.%29.svg, Creative Commons Attribution-Share Alike 3.0 Unported license Maturation of the H-P-Gonad Axis At puberty, adult pattern of GnRH secretion is attained. Male = 24 hr cycle. Female = 28 day cycle. Maturation requires kisspeptin and GRP54 activity in hypothalamic neurons secreting GnRH. Key Concepts Differentiation of germ cells as well as synthesis and secretion of sex hormones are common functions of the ovaries and testes. Reproduction in both males and females is controlled by pulsatile secretion of GnRH from the hypothalamus which controls FSH and LH secretion from the pituitary. FSH and LH govern germ cell maturation and sex steroid hormone production in both males and females. Sex steroid hormones regulate FSH and LH by negative feedback (through kisspeptin neurons), are required for fertility and secondary sexual physical characteristics. .

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