Sam Mesiano, Ervin E. Jones
The male reproductive system consists of two essential elements: the gonads (in this case the testes) and the complex array of glands and ducts that constitute the sex accessory organs (Fig. 54-1A, B).
FIGURE 54-1 Anatomy of the male internal genitalia and accessory sex organs. A, The two major elements of the male sexual anatomy are the gonads (i.e., testes) and the sex accessories (i.e., epididymis, vas deferens, seminal vesicles, ejaculatory duct, prostate, bulbourethral or Cowper's glands, urethra, and penis). Note that the urethra can be subdivided into the prostatic urethra, the bulbous urethra, and the penile urethra. B, The vas deferens expands into an ampulla before coursing across the rear of the urinary bladder and merging with the outflow from the seminal vesicle. The merger forms the ejaculatory duct. The left and right ejaculatory ducts penetrate the prostate gland and open into the prostatic urethra. C, The spermatozoa form in the seminiferous tubules and then flow into the rete testis and from there into the efferent ductules, the epididymis, and the vas deferens. E, The seminiferous tubule is an epithelium formed by Sertoli cells, with interspersed germ cells. The most immature germ cells (the spermatogonia) are near the periphery of the tubule, whereas the mature germ cells (the spermatozoa) are near the lumen of the tubule. The Leydig cells are interstitial cells that lie between the tubules.
The testes are responsible for the production of gametes, the haploid cells—spermatozoa, plural of spermatozoon—necessary for sexual reproduction and for the synthesis and secretion of hormones, including the principal male sex hormone, testosterone. These hormones are necessary for functional conditioning of the sex organs, the male secondary sexual characteristics, feedback control of gonadotropin secretion, and modulation of sexual behavior.
The testes (see Fig. 54-1C) are composed mainly of seminiferous tubules (see Fig. 54-1D, E) and interstitial cells of Leydig, located in the spaces between the tubules. A seminiferous tubule is an epithelium made up of Sertoli cells (see Fig. 54-1E) and is also the site of spermatogenesis—the production of the haploid spermatozoa from the diploid germ cells. The seminiferous epithelium rests on a basement membrane, itself supported by a thin lamina propria externa.
The male sex accessory organs include the paired epididymides, the vas deferens, the seminal vesicles, the ejaculatory ducts, the prostate, the bulbourethral glands (Cowper's glands), the urethra, and the penis. The primary role of the male sex accessory glands and ducts is to store and transport spermatozoa to the exterior, and thus enable spermatozoa to reach and fertilize female gametes.