Male Reproductive Organ Anatomy
- Author: Zachary W A Klaassen, MD; Chief Editor: Thomas R Gest, PhD more...
The male reproductive system is a network of external and internal organs that function to produce, support, transport, and deliver viable sperm for reproduction. Prenatally, the male sex organs are formed under the influence of testosterone secreted from the fetal testes; by puberty, the secondary sex organs further develop and become functional. Sperm is produced in the testes and is transported through the epididymis, ductus deferens, ejaculatory duct, and urethra. Concomitantly, the seminal vesicles, prostate gland, and bulbourethral gland produce seminal fluid that accompany and nourish the sperm as it is emitted from the penis during ejaculation and throughout the fertilization process (see image below).
The scrotum is a fibromuscular pouch divided by a median septum (raphe) forming 2 compartments, each of which contains a testis, epididymis and part of the spermatic cord. Layers of the scrotum consist of skin, dartos muscle, external spermatic fascia, cremasteric fascia and internal spermatic fascia, which is in close contact with the parietal layer of the tunica vaginalis.
The skin and dartos layers of the scrotum are supplied by the perineal branch of the internal pudendal artery in addition to the external pudendal branches of the femoral artery. The layers deep to the dartos muscle are supplied by the cremasteric branch of the inferior epigastric artery. The veins of the scrotum accompany the arteries, eventually draining into the external pudendal vein and subsequently the greater saphenous vein. Lymphatic drainage of the skin of the scrotum is by the external pudendal vessels to the medial superficial inguinal lymph nodes.
The scrotum has a rich sensory nerve supply that includes the genital branch of the genitofemoral nerve (anterior and lateral scrotal surfaces), the ilioinguinal nerve (anterior scrotal surface), posterior scrotal branches of the perineal nerve (posterior scrotal surface), and the perineal branch of the posterior femoral cutaneous nerve (inferior scrotal surface).
The testes are the primary male reproductive organ and are responsible for testosterone and sperm production. Each testis is 4-5-cm long, 2-3-cm wide, weighs 10-14 g and is suspended in the scrotum by the dartos muscle and spermatic cord. Each testis is covered by the tunica vaginalis testis, tunica albuginea, and tunica vasculosa. The tunica vaginalis testis is the lower portion of the processus vaginalis and is reflected from the testes on the inner surface of the scrotum, thus forming the visceral and parietal layers. Beneath the visceral layer of the tunica vaginalis is the tunica albuginea, which forms a dense covering for the testes.
Internal to the tunica albuginea is the tunica vasculosa, containing a plexus of blood vessels and connective tissue. Bilateral testicular arteries originating from the aorta, just inferior to the renal arteries, provide arterial supply to the testes. The testicular arteries enter the scrotum in the spermatic cord via the inguinal canal and split into two branches at the posterosuperior border of the testis.
Additionally, the testes receive blood from the cremasteric branch of the inferior epigastric artery and the artery to the ductus deferens. The pampiniform plexus drains both the testis and epididymis before coalescing to form the testicular vein, usually above the spermatic cord formation at the deep inguinal ring. Lymphatic drainage via the testicular vessels passes into the abdomen, ending in the lateral aortic and pre-aortic nodes. The tenth and eleventh thoracic spinal nerves supply the testes via the renal and aortic autonomic plexuses.
The epididymis is a C-shaped structure lying intimately along the posterior border of each testis and includes an enlarged head, a body and a tail. The tunica vaginalis covers the epididymis except at the posterior border. Vasculature and innervation of the epididymis is the same as for the testes (see the image below).
Ductus (vas) deferens
The ductus (vas) deferens is the continuation of the epididymis; it is 30-45-cm long and conveys sperm to the ejaculatory ducts.[1, 2] The convoluted portion of the ductus deferens becomes straighter (diameter, 2-3-mm) as it travels posterior to the testis and medial to the epididymis. Subsequently, the ductus ascends on the posterior aspect of the spermatic cord until it reaches the deep inguinal ring, where it participates in the formation of the spermatic cord and loops over the inferior epigastric artery.
At this point, the ductus travels along the lateral pelvic wall, medial to the distal ureter, along the posterior wall of the bladder until it reaches the seminal vesicles dorsal to the prostate. Each ductus deferens has an artery usually derived from the superior vesical artery (artery to the ductus), with venous drainage to the pelvic venous plexus. Lymphatic drainage of the ductus deferens is to the external and internal iliac nodes and innervation is mainly sympathetic from the pelvic plexus.
The spermatic cord extends from the deep inguinal ring, through the inguinal canal to the testis. The layers of the spermatic cord include (from outward to inward): external spermatic fascia (derived from the deep fascia of the external abdominal oblique muscle), cremasteric fascia (derived from the internal oblique muscle), and internal spermatic fascia (derived from the transversalis fascia). The structures that form the spermatic cord include: (i) the ductus deferens and associated vasculature and nerves (posterior wall of the cord), (ii) the testicular artery, (iii) the pampiniform plexus, ultimately forming the testicular vein, and (iv) the genital branch of the genitofemoral nerve.
The ejaculatory ducts are 2-cm in length and derived from the union of the seminal vesicle and the ampulla of the vas deferens. Each duct starts at the base of the prostate and terminates at the seminal colliculus (verumontanum). The vasculature, innervation, and lymphatics of the ejaculatory ducts are the same as for the ductus deferens.
The 2 seminal vesicles are located between the bladder and the rectum and measure approximately 5 cm in length. The anterior surface is in contact with the posterior wall of the bladder and the posterior surface is in contact with rectovesical (Denonvilliers) fascia. The ampulla of the ductus deferens lies medial to the seminal vesicles and the prostatic venous plexus lies laterally. Arterial blood supply to the seminal vesicles includes branches from the inferior vesical and middle rectal arteries, while venous and lymphatic drainage accompanies these arteries. The inferior division of the hypogastric plexus provides innervation to the seminal vesicles.
The bilateral bulbourethral glands are 2 cm in diameter and lie lateral to the membranous urethra and are enclosed by the external urethral sphincter. The excretory duct of the gland penetrates the perineal membrane and opens within the bulbar urethra. Vasculature, lymphatic drainage, and innervation are generally the same as for the seminal vesicles.
The prostate gland is an ovoid structure encompassing the proximal portion of the urethra and is approximately 2.5-3.0-cm by 4.0-4.5-cm, normally weighing 20-25 g. The base of the prostate is in contact with the bladder, the apex is superior to the perineal membrane, the anterior border is in contact with the vesicoprostatic plexus, the posterior border is separated from the anterior surface of the rectum by the rectovesical (Denonvilliers) fascia and the lateral border is in contact with the levator ani and the prostatic venous plexus. Fibers of the external urethral sphincter surround the prostate (see the image below).
The arterial supply to the prostate gland is derived from the inferior vesical artery and branches of the middle rectal artery. Venous drainage of the prostate forms the prostatic plexus, which eventually drains into the internal iliac vein and lymphatic drainage flows to the internal iliac nodes. Innervation is derived from the inferior portion of the hypogastric plexus, primarily to the connective tissue surrounding the gland.
The urethra stretches from the bladder to the tip of the glans penis, serving as a passage for urine and semen. The prostatic urethra extends vertically from the bladder neck, through the prostate before becoming the membranous urethra and before penetrating the perineal membrane. Of note, the prostatic urethra contains the orifice of the ejaculatory ducts. As the membranous urethra enters the deep perineal space, the urethra is surrounded by fibers of the external urethral sphincter, eventually entering the bulb of the corpus spongiosum, providing the orifice for the bulbourethral glands and subsequently becoming the penile urethra. When the urethra reaches the glans penis the diameter diminishes to that of the external ostium, the least dilatable portion of the urethral canal.
The penis is made up of an attached root and a pendulous body. The root consists of two crura and the bulb—3 bodies of erectile tissue attached to the pubic arch (crura) and perineal membrane (bulb).
Near the border of the pubic sypmphysis the bilateral crura continue as the corpora cavernosa throughout the body of the penis. The bulb lies between the two crura, narrows anteriorly and continues as the corpus spongiosum. The body of the penis contains the bilateral corpora cavernosa and the median corpus spongiosum. During penile erection, all 3 erectile bodies become engorged with blood. The corpora cavernosa are enveloped in a thick fibrous tunica albuginea, which is comprised of a longitudinal running superficial fibers and a deep layer of circular oriented fibers. The corpus spongiosum is penetrated by the urethra as it traverses the body of the penis (see the images below).
The superficial penile fascia includes loose connective tissue intertwined with dartos muscle fibers. The deep penile fascia, or Buck’s fascia, is a tough fascial layer that encompasses both corpora cavernosa and the corporus spongiosum. The skin of the penis is thin. The corona of the penis is where the skin folds to become the prepuce (foreskin), enveloping the glans penis (see the image below).
The vasculature of the penis is extensive. The perineal artery (a branch of the internal pudendal artery) together with the posterior scrotal artery and the inferior rectal artery supply tissues from the bulb of the penis to the anus. The artery of the bulb of the penis, from the internal pudendal, penetrates the penile bulb and subsequently supplies the corpus spongiosum. The deep artery of the penis is one of two terminal branches of the internal pudendal artery; it enters the crus of the penis and continues through the length of the bilateral corpus cavernosum. The other terminal branch of the internal pudendal artery is the dorsal artery of the penis running along the dorsal surface of the penis supplying the penile skin and the glans penis (see the image below).
The venous drainage of the penis includes the veins draining the corpora cavernosa, which subsequently drains into the circumflex veins. These veins receive venous blood from the corpus spongiosum on the ventral aspect of the penis and wrap around the penis to drain into the deep dorsal vein. The superficial dorsal vein drains the penile skin and prepuce before draining via the superficial external pudendal vein into the external pudendal veins. The deep dorsal vein further drains blood from the glans penis and corpora cavernosa before joining the prostatic venous plexus. The lymphatic drainage of the penis encompasses three locations: the superficial inguinal nodes (penile skin), deep inguinal and external iliac nodes (glans penis), and internal iliac nodes (erectile tissue and urethra; see image below).
Sensory innervation to the penile skin is through the dorsal nerve of the penis, one of the terminal branches of the pudendal nerve. Autonomic innervation includes both sympathetic and parasympathetic aspects to the corpora cavernosum via the cavernous nerves. The sympathetic fibers originate at the level of T11-T12 and the parasympathetic fibers originate from the pelvic plexus at S2-S4.
The testes are divided into approximately 400 segments called lobules each of which
is occupied by 2-4 seminiferous tubules, which are responsible for producing spermatozoa. Each testis has 600-1200 seminiferous tubules with a total length of 280-400-m. At the mediastinum testis, on the posterior border of the testis, the seminiferous tubules empty spermatozoa into the tubuli recti and rete testis, eventually coalescing to form 6-8 efferent ductules. The efferent ductules drain spermatozoa into the epididymis (see image below).
The seminiferous tubule epithelium consists of proliferating spermatogenic cells and the sustentacular Sertoli cells. Spermatogenic cells are at various stages of spermatogenesis and Sertoli cells are columnar cells that extend from the basement membrane to the lumen of the seminiferous tubule. Interstitial cells in the testis, including the Leydig cells, constitutes 20-30% of the tissue in the gland and are found in between seminiferous tubules. The washed out cytoplasm of the Leydig cells is due a high lipid content in the form of cholesterol for synthesis of testosterone.
The main component of the epididymis is a tightly packed, tortuous duct approximately 6-m long and 400-µm in diameter. The head consists of the most dense pack coils of efferent ductules, which are lined with ciliated columnar epithelium for transport of spermatozoa through the epididymis.
Ductus (vas) deferens
The ductus deferens is composed of pseudostratified columnar epithelium including columnar cells and basal cells. The underlying lamina propria is dense with elastic fibers and the wall of the ductus contains three thick smooth muscle layers. The outermost layer of adventitia is rich in blood vessels and nerves.
The seminal vesicles are tubulosaccular glands consisting of connective tissue and secretory epithelium projecting into the lumen of the gland. The epithelium is pseudostratified with basal and columnar cells, while the wall of the vesicle is consistent with a thick wall of smooth muscle that contracts during ejaculation.
The prostate is traditionally divided into three concentric zones: (i) peripheral, (ii) central and (iii) transitional. The peripheral zone constitutes 70% of the prostate and contains the tubuloalveolar glands of the organ, the central zone constitutes 25% and contains submucosal glands and the transitional zone constitutes 5% of the prostate. The tubuloalveolar glands are embedded in a fibrous stroma and open through branching ducts in the prostatic urethra. The secretory nature of the epithelium is evident as it consists of pseudostratified epithelium containing basal and secretory cells.
The prostatic urethra is lined by transitional epithelium, the membranous urethra is lined by stratified columnar epithelium and the penile urethra is initially stratified columnar epithelium and becomes stratified squamous epithelium at the fossa navicularis.
The erectile bodies of the penis are composed of fibroelastic connective tissue, smooth muscle and a network of vascular sinuses lined with endothelium. The sinuses are continuous with the arteries that supply them and the veins that drain them.
In the relaxed state (non-contracted dartos and cremasteric muscles), the scrotum is smooth and pendulous. However, when the dartos and cremasteric muscles contract secondary to cold or emotional stimuli, the scrotum becomes smaller, rounder and more wrinkled.
Although the shape of the testis varies little, the variation in size may be considerable. Contributing factors may include overall body habitus and race; however, certain conditions (ie. Fragile X syndrome) are associated with larger (macro-orchidism) and smaller (micro-orchidism -Klinefelter syndrome) testicles.
The 2 most common natural variations for the epididymis are the size and the rigidity with which the structure is attached to the testicle.
The seminal vesicles show considerable variation in size, most notably when the vesicle is in the full or empty state.
In the flaccid state, the penis varies in length from 8-12 cm and in width from 3-4.5 cm. Factors influencing size may include race and physiological differences. For example, when the temperature is cold, contraction of the dartos muscle causes the penis to decrease in size. In the erectile state, the penis varies in length from 12-18 cm and in width from 4-5 cm.
A developmental defect may occur that allows the tunica vaginalis to retain direct communication with the peritoneum and the possibility of subsequent bowel herniation. A congenital inguinal hernia can be differentiated from an acquired inguinal hernia by the intraoperative finding of bowel in contact with the testis. Bifid scrotum occurs when the two halves of the scrotum are separated by a cleft due to failed fusion of the paired genital swellings and is commonly associated with severe degrees of hypospadias or ambiguous genitalia.
Anorchidism is a rare condition consisting of bilateral absence of the testis. Monorchidism is the presence of one testis and polyorchidism is the presence of a supernumerary testis.
Cryptorchidism (undescended testes) is one of the most frequent anomalies of the congenital organs and may occur in up to 1 of 500 male births, as well as unilaterally or bilaterally. Undescended testis are usually small, atrophic and often non-functional. Arrested migration may occur at any point during testis descent. Abdominal cryptorchidism occurs when the testis arrest superior to the inguinal canal, inguinal cryptorchidism occurs within the inguinal canal and subinguinal cryptorchidism occurs between the superficial inguinal ring and the scrotum.
Patients with undescended testis are at increased risk of testicular malignancy, most commonly testicular seminoma. The incidence of a testicular tumor in the general population is 1 in 100,000 and in men with a cryptorchid testis is 1 in 2550, resulting in an overall relative risk of greater than 40.
Ductus (vas) deferens
The ductus deferens may be congenitally absent, a condition known as vasal aplasia. This condition has been linked to cystic fibrosis, resulting in azoospermia even though the process of spermatogenesis is often normal.
A short spermatic cord occurs when the growth of the spermatic cord does not keep pace with the rest of the body’s growth. In these instances, the testis may be higher in the scrotum often referred to as an ascending or retractile testis.
Ejaculatory duct obstruction is a rare condition and may lead to azoospermia or oligozoospermia. Potential causes of this condition are congenital cysts such as paramesonephric (Mullerian) cysts.
The seminal vesicles may be absent or atrophic. These conditions are often associated with malformations such as bladder exstrophy, cloacal abnormalities, or ambiguous genitalia.
The prostate may show variation in form usually determined by rectal examination. The posterior surface of the prostate has a midline sulcus that may be wider, narrower, deeper or shallower than normal, or be absent altogether. Serous malformations of the prostate are often associated with epispadias, hypospadias, or bladder exstrophy.
Absence of the urethra may be a true absence or may be associated with absence of the penis. Urethra atresia and duplicity may occur. Accessory urethral canals occur when an accessory channel lies dorsal or ventral to the true urethra. A bifid urethra forms when accessory channels originate from the true urethra and form an additional meatus at the glans penis. Paraurethral ducts are blind pits that open on the glans penis and are usually a few millimeters in depth, but may connect back to the true urethra.
Posterior urethral valves are one of the most serious anomalies associated with the neonatal period, often leading to decreased renal function and incontinence and occurring in 1 in 8,000 to 25,000 live births. Young’s classification Type 1 make up 95% of posterior urethral obstruction, where there is a ridge on the floor of the urethra, continuous with the seminal colliculus. Anterior urethral valves are rarer than posterior urethral valves and often occur in the form of a diverticulum of the urethra. These valves form when there is a defect in the corpus spongiosum, leading to a thin-walled urethra that balloons during urination and subsequent obstruction.
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A hydrocele (communicating) is a collection of peritoneal fluid that accumulates between the layers of the tunica vaginalis when the processus vaginalis fails to obliterate between the deep inguinal ring and the superior border of the scrotum. Most communicating hydroceles are smaller in the morning and increase in size throughout the day when the individual is in the upright position. Diagnosis is based on physical examination and transillumination of the hydrocele sac.
Fournier’s gangrene is a form of necrotizing fasciitis affecting the scrotum and often extending to the perineum, penis and abdominal wall. Patients with diabetes mellitus, local trauma, periurethral extravasation of urine and perianal infection are predisposed to Fournier’s gangrene. The initial diagnosis can be made based on a swollen, erythematous and tender infection of the scrotum and the most common pathogens are facultative organisms, anaerobes and group-A streptococcus.
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Testicular torsion may occur if the testis twists on the suspending spermatic cord. This is a surgical emergency, as the blood supply needs to be restored to the testis within six hours of symptom onset in order decrease the risk of testis infarction. The testis should subsequently be sutured to the scrotal wall (orchiopexy) to prevent recurrence, in addition to orchiopexy of the contralateral testis.
Most acute presentations of scrotal pain and swelling can be attributed to epididymitis, testicular torsion, or torsion of a testicular appendage. In many cases, torsion of a testicular appendage, although a benign condition, may present identically to testicular torsion, a true urologic emergency. Ultrasound may be used to aid in diagnosis, however a normal clinical exam of a non-tender testis in the presence of a paratesticular nodule at the superior pole may be more diagnostic for appendical torsion. Classically, a blue-dot appearance (Blue Dot sign) may be seen in the area of the injury, however this is only present in 20% of cases.
Varicocele is a common condition characterized by enlargement and thickening of the pampiniform plexus in the spermatic cord. Varicocele is most commonly causes by defective venous valves but also may be due more serious causes such as testicular vein compression secondary to an abdominal tumor. Symptoms of varicocele include a dull, aching pain in the scrotum, testicular heaviness, testicular atrophy and visible and palpable veins in the scrotum commonly referred to as feeling like “a bag of worms.”
Epididymitis is inflammation of the epididymis. It may be due to infectious process, commonly in men ages 19-35. In this age group, the antibiotic treatment should be initiated for N gonorrhea and C trachomatis. In young children and men over 65 years of age, E coli is the most common pathogen. Furthermore, other pathogens include Ureaplasma, M tuberculosis, and the drug amiodarone, commonly used for cardiac rate control.
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Benign prostatic hyperplasia
Urethral stricture disease refers to anterior urethral disease leading to scarring of the penile urethra and secondary reduction of the urethral lumen. Any process that leads to injury of the urethral epithelium can be an etiological factor for urethral stricture. The most common cause is urethral trauma, usually saddle trauma; however, iatrogenic trauma, namely multiple transurethral endoscopic examinations of the upper urinary system does occur.
Inflammatory strictures secondary to gonorrhea were historically the most common cause of urethral stricture, however they still do take place. Other infectious causes of urethral stricture include Chlamydia and Ureaplasma urealyticum. Treatment of urethral stricture disease is arduous as stricturere formation is common. The most common treatment modalities include internal urethrotomy (transurethral incision of the stricture), laser ablation and open stricture excision and urethral anastomosis.
Injury to the anterior urethra (bulbous urethra, penile urethra, fossa navicularis) is most commonly due to blunt trauma, penetrating injuries and instrumentation, and injury to the posterior urethra (prostatic and membranous urethra) is most commonly associated with pelvic fractures. Urinary extravasation may result from urinary trauma. If the deep fascia (Buck’s fascia) of the penis is not ruptured, urine extravasation is usually limited to the penis, however if the fascial plane is breached, urine may extravasate to the penis, scrotum, perineum and abdominal wall.
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