inner va jna FIGURE 1213B AND C right and most of the wolffian system

Inner va jna figure 1213b and c right and most of the

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inner va- jna (FIGURE 12.13B AND C, right), and most of the wolffian system degenerates, n males, hormones secreted by the testes orchestrate the converse outcome: the •olffian ducts develop into epididymis, vas deferens, and seminal vesicles (FIGURE 12.13B AND C, left), while the mullerian ducts shrink to mere remnants. Two testicular secretions drive masculinization: testosterone, which promotes the . lopment of the wolffian system, and anti-miillerian hormone (AMH), which causes regression of the mullerian system. In the absence of testes and their secretions, he genital tract develops in a feminine pattern, as the wolffian ducts regress and the ntillerian ducts develop into components of the female internal reproductive tract. Testosterone also masculinizes other, non-wolffian-derived structures such as e fetal genitalia. Local conversion of testosterone into a more potent androgen, dlhydrotestosterone (DHT), accomplished by the enzyme 5a-reductase in the jenital skin, induces the bipotential genitals to form a scrotum and penis (see Figure 2.13). We'll see later that without local conversion into DHT, testosterone is able D masculinize the genitalia only partially. If androgens are absent altogether, the ital tissues grow into the female labia and clitoris. In general, unless the indifferent gonad becomes a testis and begins secreting hormones, an immature mammal develops as a female in most respects. As noted earlier, immature ovaries produce few hormones. So the sex chromosomes deter- mine the sex of the gonad, and differential exposure to gonadal hormones controls subsequent sexual differentiation of the rest of the body-(FIGURE 12.14A). Later in fe, hormones and experience act in concert to guide further sexual differentiation and the development of gender identity (FIGURE 12.14B). anti-miillerian hormone (AMH) A protein hormone secreted by the fetal testis that inhibits mullerian duct development. dihydrotestosterone (DHT) The So-reduced metabolite of testosterone; a potent androgen that is principally responsible for the masculinization of the external genitalia in mammalian sexual differentiation. 5<x-reductase An enzyme that converts testosterone into dihydrotestos- terone (DHT). GENETIC SEX Gene expression XY chromosomes SRY expressed XX chromosomes No SRY expressed V V IONADALSEX Hormone secretion Anti-miillerian hormone (AMH) and testosterone (T) AMH 'HENOTYPfC SEX Internal AMH causes mullerian ducts to regress. Testosterone induces wolffian ducts to form epididymis, vas deferens, and seminal vesicles, ^ and other tissues to form prostate and bulbourethral gland. Ovaries produce no AMH, no T In absence of AMH, mullerian ducts form oviducts, uterus, and inner vagina. In absence of testosterone, wolffian ducts regress, and no prostate or bulbo- urethral gland forms.
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