101. Differentiation of The Male Genital Tracts and Auxiliary Glands

  1. Introduction: development of the male urogenital system is caused by action of androgenic fetal hormones produced by the fetal testes. They take effect at the end of month 2 as seen by regression of the paramesonephric (m?llerian) structures and differentiation of the mesonephric (wolffian) structures
  2. Development of upper portion of male genital tract: after regression of the mesonephric (wolffian) body, the inguinal ligament inserts at the inferior pole of the testis (above) and in the inguinal region (below), forming the so-called gubernaculum testis. The diaphragmatic ligament disappears
    1. BOTH PARAMESONEPHRIC DUCTS regress completely, in the male, by week 11
      1. The appendix testis persists at the superior pole of each testis, and the utriculus prostaticus (prostate utricle) persists from the early joining of the paramesonephric stays at the back of the urogenital sinus between the mesonephric ducts
    2. THE 2 MESONEPHRIC (WOLFFIAN) DUCTS persist and develop as follows
      1. Their most cranial portion forms the appendix of the epididymis
      2. The segment of the mesonephric duct opposite the testis forms the epididymis or ductus epididymidis, with its cranial end connected to the vasa efferentia
        1. Below the cranial end, the epididymis is highly convoluted and descends along the testis, still receiving mesonephric tubules (ducts of Haller) which do not connect to the rete testis. Below, isolated mesonephric tubules form the paradidymis
      3. Below the testis, the mesonephric ducts acquire a thick investment of smooth muscle and form the ductus deferens
        1. As each ductus deferens joins the posterior side of the urogenital sinus, 2 lateral outgrowths form the seminal gland or vesicle
      4. The ductus deferens finally becomes the ejaculatory duct, that duct portion between the seminal vesicle duct and the urethra
      5. The ejaculatory ducts open on the posterior wall of the urogenital sinus on an elevation, called the verumontanum or seminal colliculus
        1. The seminal colliculus, a small elevation in the prostatic urethra, is the remnant of the m?llerian tubercle and is homologous to the hymen
        2. The prostatic utricle, seen between the ejaculatory duct openings, opens on the colliculus in the prostatic urethra and is probably homologous to the vagina
  3. Development of the lower portion of the male genital tract: the urogenital sinus caudal to the union of the mesonephric ducts consists of a vertical pelvic segment and a horizontal phallic segment in the genital tubercle. The latter, after resorption of the urogenital membrane, opens to the exterior. The 2 segments undergo reorganization, from month 3, related to secretion of androgenic hormones
    1. THE PELVIC SEGMENT: epithelial (entodermal) buds begin to detach themselves from the posterior aspect of the urogenital sinus, on both sides of the verumontanum, during month 3. They penetrate the adjacent mesenchyme and form the glandular epithelium of the prostate gland, which usually is well differentiated at 4 months
      1. The prostate eventually encloses the ejaculatory ducts and the prostatic utricle and completely surrounds the prostatic urethral area of the urogenital sinus
        1. The prostatic urethra thus is composed of a cephalic half, between the bladder and verumontanum, which belongs to the urinary region of the urogenital sinus; and a caudal half, between the verumontanum and the cranial part of the pelvic segment of the urogenital sinus
      2. The remaining pelvic segment forms the membranous urethra. The latter is continuous with the phallic segment of the urethra (described under the external organs)
        1. The pea-sized bulbourethral (Cowper's) glands develop from paired entodermal outgrowths from the membranous urethr Adjacent mesenchyme contributes both smooth muscle fibers and stroma

differentiation of the male genital tracts and auxiliary glands: image #1