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.
Bulbourethral gland
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.
Ejaculation
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.
