Male Internal Organs of Reproduction Anatomy
The organs of reproduction in the male comprise the paired testes, epididymides, ductus (vasa) deferentia, seminal vesicles, ejaculatory ducts and bulbourethral glands, as well as the prostate and penis. The superficial organs (the external genitalia) include the penis (p. 245) and the testes and epididymides within the scrotum (pp 149–151).
The reproductive organs described here are those that lie within the pelvis, namely the prostate, the seminal vesicles, the intrapelvic parts of the ductus deferentia (Fig. 5.22) and the ejaculatory ducts.
The prostate is an approximately spherical organ lying immediately below the bladder (Fig. 5.23). The flattened superior surface (base) is applied to the neck of the bladder and is pierced by the urethra, which descends through the gland and emerges near the blunt apex. The part of the prostate behind the urethra and above and between the ejaculatory ducts (see below) is sometimes described as the median lobe (Fig. 5.24).
Anteriorly, the prostate is anchored by the puboprostatic ligaments (Fig. 5.19) to the inferior border of the pubic symphysis. Inferior to the organ lies the intermediate urethra (Fig. 5.23) surrounded by the external urethral sphincter, and posteriorly are the rectovesical septum and the ampulla of the rectum. On each side of the prostate is the medial border of levator ani.
The gland often enlarges with advancing age (benign prostatic hypertrophy) and is a site of malignant change (prostatic carcinoma), which may metastasize to the vertebral column (p. 397). Both conditions may obstruct the prostatic part of the urethra. The gland is palpable on rectal examination and may be biopsied through the rectal wall.
Each seminal vesicle is a sacculated gland approximately 3 cm long, lying lateral to the ampulla of the ductus deferens (Figs 5.24 & 5.25). The seminal vesicles lie in front of the rectum and rectovesical pouch of peritoneum (Fig. 5.23) and extend up the posterior wall of the bladder as far as the terminal parts of the ureters (Fig. 5.25).
Ductus (vas) deferens
Each ductus (vas) deferens begins at the tail of the epididymis in the scrotum, ascends within the spermatic cord and traverses the inguinal canal (pp 146–148). After emerging from the deep inguinal ring, the ductus runs along the lateral pelvic wall, covered by peritoneum, and passes medial to the superior vesical vessels and obturator nerve and vessels. The ductus then crosses above the ureter (Figs 5.22 & 5.23) and turns downwards and medially, posterior to the bladder (Fig. 5.23). The terminal part of the ductus is dilated to form the ampulla, which lies medial to the seminal vesicle. The ampulla is related posteriorly to the peritoneum of the rectovesical pouch and to the rectovesical septum and rectum.
The bulbourethral glands (Fig. 5.21) lie adjacent to the intermediate urethra and are described on p. 227.
The duct of each seminal vesicle joins the ampulla of the corresponding ductus deferens to form the ejaculatory duct (Fig. 5.24). The right and left ducts pierce the prostate and run downwards, forwards and medially through its substance to open into the prostatic urethra at slit-like orifices on the summit of the seminal colliculus.
The artery to the ductus deferens is usually a small vessel that arises from the superior vesical artery and accompanies the ductus as far as the epididymis. The ampulla of the ductus, the seminal vesicle and prostate are supplied by the inferior vesical artery. From the internal reproductive organs, blood passes into the venous plexus (Fig. 5.21) surrounding the prostate to drain into the internal iliac veins.
Semen contains spermatozoa from the testes and secretions from the ampullae of the ductus, the seminal vesicles and prostate. Under the control of the sympathetic nervous system, contraction of smooth muscle in the ductus, seminal vesicles and prostate propels secretions into the prostatic urethra. Semen is then expelled from the urethra by contractions of the bulbospongiosus muscles, which compress the bulb of the penis (p. 245). Reflux of semen into the bladder is prevented by contraction of the smooth muscle in the wall of the bladder neck, the preprostatic sphincter.