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Lecture_15_Comparative Anatomy_The Urogenital System

O in female mammals the mesonephric duct wolffian duct

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Unformatted text preview: duct and is flushed out of the uterus during the next menstruation. Testis Overview • Each mammalian testis also consists of an outer tunica albuginea, which encloses the seminiferous tubules that produce sperm. • Within the walls of the seminiferous tubules, stem cells multiply and grow into sperm that eventually are released into the lumen. • The coiled seminiferous tubules straighten, forming tubuli recti just before they join the rete testis. The rete testis joins the epididymis, where sperm are temporarily stored, via the efferent ductules. • Upon ejaculation, sperm travel along the vas deferens (ductus deferens) into the urethra. Along the way, three accessory sex glands (the seminal vesicle, prostate, and bulbourethral (Cowper’s) gland) add their secretions as sperm move from the testes to the urethra. The fluid and sperm it contains constitute seminal fluid, or semen. o Embryonic Development  Gonads and Gametes • The paired gonads arise from the genital ridge, initially thickening in the splanchnic mesoderm to which adjacent mesenchyme cells contribute. At this point, this germ cell containing gonad shows neither male nor female characteristics and is therefore called an indifferent gonad. • Interestingly, the germ cells do not arise in the genital ridge or adjacent mesoderm; in fact, they do not arise from the embryo at all. Germ cells arise from the extraembryonic endoderm! o In females, germ cells establish residence in the cortex. o In males, arriving germ cells establish residence in the medulla, which develops into the seminiferous tubule.  Reproductive Tracts • Parts of the embryonic urinary system are salvaged by or shared with the genital system. o In female mammals, the mesonephric duct (wolffian duct) drains the embryonic mesonephros, but it regresses later in development when the metanephros and its ureter become the kidney of the adult. However, a parallel Mullerian duct arises next to the embryonic mesonephric duct before it regresses. The Mulle...
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