Male Internal Genital Organs
The male internal genital organs include the testes, epididymides (singular = epididymis), ductus deferentes (singular = ductus deferens), seminal glands, ejaculatory ducts, prostate, and bulbo-urethral glands (Fig. 3.34). The testes and epididymides (described in Chapter 2) are considered internal genital organs on the basis of their developmental position and homology with the internal female ovaries. However, because of their external position postnatally and because in dissection they are encountered during the dissection of the inguinal region of the anterior abdominal wall, they were considered with the abdomen in Chapter 2.
Figure 3.34.Hemisected male pelvis and perineum (right half).
The genital organs are demonstrated: testis, epididymis, ductus deferens, ejaculatory duct, and penis, with the accessory glandular structures (seminal gland, prostate, and bulbo-urethral gland). The spermatic cord connects the testis to the abdominal cavity, and the testis lies externally in a musculocutaneous pouch, the scrotum.
The ductus deferens (vas deferens) is the continuation of the duct of the epididymis. The ductus deferens:
- Has relatively thick muscular walls and a minute lumen, giving it a cord-like firmness.
- Begins in the tail of the epididymis, at the inferior pole of the testis (Fig. 2.21).
- Ascends posterior to the testis, medial to the epididymis.
- Is the primary component of the spermatic cord.
- Penetrates the anterior abdominal wall via the inguinal canal.
- Crosses over the external iliac vessels and enters the pelvis.
- Passes along the lateral wall of the pelvis, where it lies external to the parietal peritoneum.
- Ends by joining the duct of the seminal gland to form the ejaculatory duct.
During the pelvic part of its course, the ductus deferens maintains direct contact with the peritoneum; no other structure intervenes between them. The ductus crosses superior to the ureter near the posterolateral angle of the urinary bladder, running between the ureter and the peritoneum of the ureteric fold to reach the fundus of the bladder. The relationship of the ductus deferens to the ureter in the male is similar, although of lesser clinical importance, to that of the uterine artery to the ureter in the female. The developmental basis of this relationship is shown in Figure 3.35. Posterior to the bladder, the ductus deferens at first lies superior to the seminal gland, then descends medial to the ureter and the gland. Here the ductus deferens enlarges to form the ampulla of the ductus deferens before its termination (Fig. 3.36).
Figure 3.35.Structures crossing male ureter in abdomen and pelvis.
During development, as the testis descends inferiorly and laterally from its original position (medial to the site of the kidneys on the posterior abdominal wall) to and then through the inguinal canal, the ureter is crossed by testicular vessels in the abdomen and by the ductus deferens in the pelvis. This relationship is retained throughout life.
Figure 3.36.Posterior aspect of male pelvic viscera and posterior dissection of prostate.
A.The posterior pelvic wall, rectum, and rectovesical septum have been removed. The umbilical ligaments, like the urinary bladder, are embedded in extraperitoneal or subperitoneal fascia (mostly removed in this dissection). B.The ejaculatory ducts are formed by the merger of the duct of the seminal gland and the ductus deferens. The vestigial prostatic utricle, usually seen as an invagination in an anterior view, appears in this posterior dissection as an evagination lying between the ejaculatory ducts.
Arterial Supply and Venous Drainage of Ductus Deferens
The tiny artery to the ductus deferens usually arises from a superior (sometimes inferior) vesical artery (Figs. 3.16 and 3.34), and terminates by anastomosing with the testicular artery, posterior to the testis. Veins from most of the ductus drain into the testicular vein, including the distal pampiniform plexus. Its terminal portion drains into the vesicular/prostatic venous plexus.
Each seminal gland (vesicle) is an elongated structure (approximately 5 cm long but sometimes much shorter) that lies between the fundus of the bladder and the rectum (Figs. 3.34 and 3.36). The seminal glands are obliquely placed superior to the prostate and do not store sperms (as the term “vesicle” implies). They secrete a thick alkaline fluid with fructose (an energy source for sperms), and a coagulating agent that mixes with the sperms as they pass into the ejaculatory ducts and urethra.
The superior ends of the seminal glands are covered with peritoneum and lie posterior to the ureters, where the peritoneum of the rectovesical pouch separates them from the rectum. The inferior ends of the seminal glands are closely related to the rectum and are separated from it only by the rectovesical septum (Fig. 3.34). The duct of the seminal gland joins the ductus deferens to form the ejaculatory duct.
Arterial Supply and Venous Drainage of Seminal Glands
The arteries to the seminal glands derive from the inferior vesical and middle rectal arteries (see Figs. 3.16 and 3.37; Table 3.4). The veins accompany the arteries and have similar names (Fig. 3.19C).
Figure 3.37.Pelvic part of ureters, urinary bladder, seminal glands, terminal parts of ductus deferens, and prostate.
The left seminal gland and ampulla of the ductus deferens are dissected free and sliced open. Part of the prostate is also cut away to expose the ejaculatory duct. The perineal membrane lies between the external genitalia and the deep part of the perineum (anterior recess of ischio-anal fossa). It is pierced by the urethra, ducts of the bulbo-urethral glands, dorsal and deep arteries of the penis, cavernous nerves, and the dorsal nerve of the penis.
The ejaculatory ducts are slender tubes that arise by the union of the ducts of the seminal glands with the ductus deferentes (Figs. 3.34, 3.36, and 3.37). The ejaculatory ducts (approximately 2.5 cm long) arise near the neck of the bladder, and run close together as they pass antero-inferiorly through the posterior part of the prostate and along the sides of the prostatic utricle. The ejaculatory ducts converge to open on the seminal colliculus by tiny, slit-like apertures on, or just within, the opening of the prostatic utricle (Fig. 3.30). Although the ejaculatory ducts traverse the glandular prostate, prostatic secretions do not join the seminal fluid until the ejaculatory ducts have terminated in the prostatic urethra.
Arterial Supply and Venous Drainage of Ejaculatory Ducts
The arteries to the ductus deferens, usually branches of the superior (but frequently inferior) vesical arteries, supply the ejaculatory ducts (Figs. 3.37). The veins join the prostatic and vesical venous plexuses (Fig. 3.19C).
The prostate (approximately 3 cm long, 4 cm wide, and 2 cm in antero-posterior (AP) depth) is the largest accessory gland of the male reproductive system (Figs. 3.34, 3.36, and 3.37). The firm, walnut-size prostate surrounds the prostatic urethra. The glandular part makes up approximately two thirds of the prostate; the other third is fibromuscular.
The fibrous capsule of the prostate is dense and neurovascular, incorporating the prostatic plexuses of veins and nerves. All this is surrounded by the visceral layer of the pelvic fascia, forming a fibrous prostatic sheath that is thin anteriorly, continuous anterolaterally with the puboprostatic ligaments, and dense posteriorly where it blends with the rectovesical septum. The prostate has
- A base closely related to the neck of the bladder.
- An apex that is in contact with fascia on the superior aspect of the urethral sphincter and deep perineal muscles.
- A muscular anterior surface, featuring mostly transversely oriented muscle fibers forming a vertical, trough-like hemisphincter (rhabdosphincter), which is part of the urethral sphincter. The anterior surface is separated from the pubic symphysis by retroperitoneal fat in the retropubic space.
- A posterior surface that is related to the ampulla of the rectum.
- Inferolateral surfaces that are related to the levator ani.
Although not clearly distinct anatomically, the following lobes of the prostate are traditionally described (Fig. 3.38A):
- The isthmus of the prostate (commissure of prostate; historically, the anterior “lobe”) lies anterior to the urethra. It is fibromuscular, the muscle fibers representing a superior continuation of the external urethral sphincter muscle to the neck of the bladder, and contains little, if any, glandular tissue.
- Right and left lobes of the prostate, separated anteriorly by the isthmus and posteriorly by a central, shallow longitudinal furrow, may each be subdivided for descriptive purposes into four indistinct lobules defined by their relationship to the urethra and ejaculatory ducts, and—although less apparent—by the arrangement of the ducts and connective tissue:
- an inferoposterior (lower posterior) lobule that lies posterior to the urethra and inferior to the ejaculatory ducts. This lobule constitutes the aspect of the prostate palpable by digital rectal examination.
- an inferolateral (lower lateral) lobule directly lateral to the urethra, forming the major part of the right or left lobe.
- a superomedial lobule, deep to the inferoposterior lobule, surrounding the ipsilateral ejaculatory duct.
- an anteromedial lobule, deep to the inferolateral lobule, directly lateral to the proximal prostatic urethra.
Figure 3.38.Lobules and zones of prostate demonstrated by anatomical section and ultrasonographic imaging.
A.Poorly demarcated lobules demonstrated in anatomic sections. B.The ultrasound (US) transducer was inserted into the rectum to scan the anteriorly located prostate. The ducts of the glands in the peripheral zone open into the prostatic sinuses, whereas the ducts of the glands in the central (internal) zone open into the prostatic sinuses and the seminal colliculus.
An embryonic middle (median) lobe gives rise to (3) and (4) above. This region tends to undergo hormone-induced hypertrophy in advanced age, forming a middle lobule that lies between the urethra and the ejaculatory ducts and is closely related to the neck of the bladder. Enlargement of the middle lobule is believed to be at least partially responsible for the formation of the uvula that may project into the internal urethral orifice (Fig. 3.30).
Some clinicians, especially urologists and sonographers, divide the prostate into peripheral and central (internal) zones (Fig. 3.38B). The central zone is comparable to the middle lobe.
The prostatic ducts (20–30) open chiefly into the prostatic sinuses that lie on either side of the seminal colliculus on the posterior wall of the prostatic urethra (Fig. 3.37). Prostatic fluid, a thin, milky fluid, provides approximately 20% of the volume of semen (a mixture of secretions produced by the testes, seminal glands, prostate, and bulbo-urethral glands that provides the vehicle by which sperms are transported) and plays a role in activating the sperms.
Arterial Supply and Venous Drainage of Prostate
The prostatic arteries are mainly branches of the internal iliac artery (see Table 3.4; Figs. 3.17A and 3.37), especially the inferior vesical arteries, but also the internal pudendal and middle rectal arteries. The veins join to form a plexus around the sides and base of the prostate (Figs. 3.19C and 3.37). This prostatic venous plexus, between the fibrous capsule of the prostate and the prostatic sheath, drains into the internal iliac veins. The prostatic venous plexus is continuous superiorly with the vesical venous plexus and communicates posteriorly with the internal vertebral venous plexus.
The two pea-size bulbo-urethral glands (Cowper glands) lie posterolateral to the intermediate part of the urethra, largely embedded within the external urethral sphincter (Figs. 3.30B, 3.34, 3.36, and 3.37). The ducts of the bulbo-urethral glands pass through the perineal membrane with the intermediate urethra, and open through minute apertures into the proximal part of the spongy urethra in the bulb of the penis. Their mucus-like secretion enters the urethra during sexual arousal.
Innervation of Internal Genital Organs of Male Pelvis
The ductus deferens, seminal glands, ejaculatory ducts, and prostate are richly innervated by sympathetic nerve fibers. Presynaptic sympathetic fibers originate from cell bodies in the intermediolateral cell column of the T12–L2 (or L3) spinal cord segments. They traverse the paravertebral ganglia of the sympathetic trunks to become components of lumbar (abdominopelvic) splanchnic nerves and the hypogastric and pelvic plexuses (see Fig. 3.29).
Presynaptic parasympathetic fibers from S2 and S3 spinal cord segments traverse pelvic splanchnic nerves, which also join the inferior hypogastric/pelvic plexuses. Synapses with postsynaptic sympathetic and parasympathetic neurons occur within the plexuses, en route to or near the pelvic viscera. As part of an orgasm, the sympathetic system stimulates contraction of the internal urethral sphincter to prevent retrograde ejaculation. Simultaneously, it stimulates rapid peristaltic-like contractions of the ductus deferens, and the combined contraction of and secretion from the seminal glands and prostate that provide the vehicle (semen), and the expulsive force to discharge the sperms during ejaculation. The function of the parasympathetic innervation of the internal genital organs is unclear. However, parasympathetic fibers traversing the prostatic nerve plexus form the cavernous nerves that pass to the erectile bodies of the penis, which are responsible for producing penile erection.
Male Internal Genital Organs
The common method of sterilizing males is a deferentectomy, popularly called a vasectomy. During this procedure, part of the ductus deferens is ligated and/or excised through an incision in the superior part of the scrotum (Fig. B3.11). Hence, the subsequent ejaculated fluid from the seminal glands, prostate, and bulbo-urethral glands contains no sperms. The unexpelled sperms degenerate in the epididymis and the proximal part of the ductus deferens.
Reversal of a deferentectomy is successful in favorable cases (patients < 30 years of age and < 7 years postoperation) in most instances. The ends of the sectioned ductus deferentes are reattached under an operating microscope.
Abscesses in Seminal Glands
Localized collections of pus (abscesses) in the seminal glands may rupture, allowing pus to enter the peritoneal cavity. Seminal glands can be palpated during a rectal examination, especially if enlarged or full. They are palpated most easily when the bladder is moderately full. They can also be massaged to release their secretions for microscopic examination to detect gonococci (organisms that cause gonorrhea), for example.
Hypertrophy of Prostate
The prostate is of considerable medical interest because enlargement or benign hypertrophy of the prostate (BHP) is common after middle age, affecting virtually every male who lives long enough. An enlarged prostate projects into the urinary bladder and impedes urination by distorting the prostatic urethra. The middle lobule usually enlarges the most and obstructs the internal urethral orifice. The more the person strains, the more the valve-like prostatic mass occludes the urethra.
BHP is a common cause of urethral obstruction, leading to nocturia (need to void during the night), dysuria (difficulty and/or pain during urination), and urgency (sudden desire to void). BHP also increases the risk of bladder infections (cystitis) as well as kidney damage.
The prostate is examined for enlargement and tumors (focal masses or asymmetry) by digital rectal examination (Fig. B3.12). The palpability of the prostate depends on the fullness of the bladder. A full bladder offers resistance, holding the gland in place and making it more readily palpable. The malignant prostate feels hard and often irregular. In advanced stages, cancer cells metastasize both via lymphatic routes (initially to the internal iliac and sacral lymph nodes and later to distant nodes), and via venous routes (by way of the internal vertebral venous plexus, to the vertebrae and brain).
Because of the close relationship of the prostate to the prostatic urethra, obstructions may be relieved endoscopically. The instrument is inserted transurethrally through the external urethral orifice and spongy urethra into the prostatic urethra. All or part of the prostate, or just the hypertrophied part, is removed (transurethral resection of the prostate; TURP). In more serious cases, the entire prostate is removed along with the seminal glands, ejaculatory ducts, and terminal parts of the deferent ducts (radical prostatectomy).
TURP and improved open operative techniques attempt to preserve the nerves and blood vessels associated with the capsule of the prostate that pass to and from the penis, increasing the possibility for patients to retain sexual function after surgery, as well as restoring normal urinary control.
The Bottom Line
Male Internal Genital Organs
Ductus deferens: The cord-like ductus deferens is the primary component of the spermatic cord, conducting sperms from the epididymis to the ejaculatory duct.
- The distal portion of the ductus is superficial within the scrotum (and, therefore, easily accessible for deferentectomy or vasectomy) before it penetrates the anterior abdominal wall via the inguinal canal.
- The pelvic portion of the ductus lies immediately external to the peritoneum, with its terminal portion enlarging externally as its lumen becomes tortuous internally, forming the ampulla of the ductus deferens.
Seminal glands, ejaculatory ducts, and prostate: Obliquely placed seminal glands converge at the base of the bladder, where each of their ducts merges with the ipsilateral ductus deferens to form an ejaculatory duct.
- The two ejaculatory ducts immediately enter the posterior aspect of the prostate, running closely parallel through the gland to open on the seminal colliculus.
- Prostatic ducts open into prostatic sinuses, adjacent to the seminal colliculus. Thus, the major glandular secretions and sperms are delivered to the prostatic urethra.
- The seminal glands and prostate produce by far the greatest portion of the seminal fluid, indispensable for transport and delivery of sperms.
- These internal genital organs, located within the anterior male pelvis, receive blood from the inferior vesicle and middle rectal arteries, which drain into the continuous prostatic/vesicle venous plexus.
- Sympathetic fibers from lumbar levels stimulate the contraction and secretion resulting in ejaculation.
- The function of parasympathetic fibers from S2–S4 to the internal genital organs is unclear, but those traversing the prostatic nerve plexus to form the cavernous nerves produce erection.