# Lecture 3: Male Reproductive System ## Unit 1.5: Human Gross Anatomy III - Pelvis and Head/Neck --- ## Learning Objectives By the end of this lecture, students will be able to: 1. Describe the anatomy of the testes, epididymis, and spermatic cord 2. Trace the course of the vas deferens and ejaculatory ducts 3. Describe the anatomy of the seminal vesicles and prostate gland 4. Describe the structure of the penis and urethra 5. Explain the blood supply, innervation, and lymphatic drainage of male reproductive organs 6. Correlate anatomical features with clinical conditions --- ## Overview of the Male Reproductive System The male reproductive system comprises the gonads (testes), a system of excretory ducts (epididymis, vas deferens, ejaculatory ducts), accessory glands that contribute to semen (seminal vesicles, prostate, bulbourethral glands), and the external genitalia (penis and scrotum). This system serves the dual functions of spermatogenesis (the continuous production of male gametes) and hormone production (testosterone synthesis by Leydig cells), while the ductal system and accessory glands store, nourish, and transport sperm and produce the fluid components of semen. Panel A: Sagittal section through male pelvis showing testis in scrotum with epididymis attached posteriorly. Panel B: Vas deferens as thick-walled tube ascending through inguinal canal and curving over ureter behind bladder. Panel C: Seminal vesicle joining vas deferens to form ejaculatory duct entering posterior prostate at bladder neck. Panel D: Penis with three erectile bodies and urethra, with bladder and rectum providing anatomical context. --- ## The Scrotum The scrotum is a cutaneous sac suspended below the pubic symphysis, containing and protecting the testes while maintaining them at a temperature slightly below core body temperature—essential for normal spermatogenesis. A median raphe externally and a septum internally divide the scrotum into right and left compartments, each containing a testis with its associated epididymis and the lower portion of the spermatic cord. The scrotal wall consists of multiple layers, each derived from corresponding layers of the anterior abdominal wall through which the testis descended during development. From superficial to deep, these include the thin, rugated skin; the dartos fascia and muscle, a continuation of superficial fascia containing smooth muscle that contracts in response to cold or sexual stimulation; the external spermatic fascia, derived from the external oblique aponeurosis; the cremasteric muscle and fascia, derived from the internal oblique muscle and providing the cremasteric reflex (elevation of the testis in response to stroking the inner thigh); the internal spermatic fascia, derived from the transversalis fascia; and the parietal layer of the tunica vaginalis, a serous membrane derived from the processus vaginalis. Blood supply to the scrotal skin comes anteriorly from the external pudendal arteries (branches of the femoral artery) and posteriorly from the scrotal branches of the internal pudendal artery. Innervation follows a similar pattern: the anterior scrotum receives sensation from the ilioinguinal nerve and genital branch of the genitofemoral nerve, while the posterior scrotum is supplied by posterior scrotal nerves from the pudendal nerve and the perineal branch of the posterior femoral cutaneous nerve. Lymphatic drainage from the scrotal skin flows to the superficial inguinal lymph nodes—distinct from the para-aortic drainage of the testis itself. Panel A: Cross-section of scrotal wall showing thin wrinkled skin with sparse hair follicles and pink dartos fascia containing smooth muscle. Panel B: External spermatic fascia as thin white layer with cremasteric muscle showing red striated fibers beneath. Panel C: Internal spermatic fascia and parietal tunica vaginalis lining the scrotal cavity containing testis and epididymis. Panel D: Median septum dividing right and left compartments with inset showing embryological derivation from abdominal wall layers. --- ## The Testis The testes are paired oval organs measuring approximately 4 by 3 by 2.5 centimeters, located within the scrotum with the left testis typically hanging slightly lower than the right. Each testis is oriented with its long axis nearly vertical and the epididymis attached to its posterolateral surface. Three fibrous coverings invest the testis. The tunica vaginalis, a serous membrane derived from the processus vaginalis, has parietal and visceral layers that create a potential space allowing the testis to move smoothly within the scrotum; fluid accumulation in this space constitutes a hydrocele. The tunica albuginea is a dense fibrous capsule that gives the testis its characteristic firm consistency; posteriorly, it thickens to form the mediastinum testis, through which vessels and ducts enter and exit. The tunica vasculosa is a vascular layer immediately beneath the albuginea. Internally, fibrous septa extending from the mediastinum testis divide the organ into 200-300 lobules, each containing one to four highly convoluted seminiferous tubules where spermatogenesis occurs. The seminiferous tubules converge at the mediastinum, becoming straight tubules that connect to an anastomosing network called the rete testis, which in turn drains through 10-15 efferent ductules that pierce the tunica albuginea to enter the head of the epididymis. Two principal cell types populate the testis beyond the developing germ cells. Sertoli cells within the seminiferous tubules support and nourish developing sperm, form the blood-testis barrier, and secrete inhibin. Leydig cells (interstitial cells) in the connective tissue between tubules produce testosterone in response to luteinizing hormone. Panel A: Cross-section of testis with thick white tunica albuginea capsule and posterior mediastinum testis thickening. Panel B: Fibrous septa radiating from mediastinum dividing parenchyma into lobules with coiled pink seminiferous tubules. Panel C: Enlarged inset showing Sertoli cells spanning basement membrane to lumen with developing germ cells and interstitial Leydig cell clusters. Panel D: Rete testis as network of channels at mediastinum connecting to efferent ductules exiting toward epididymis. --- ## The Epididymis The epididymis is a comma-shaped organ applied to the posterolateral surface of the testis, consisting of a single, highly coiled duct approximately 6 meters long when uncoiled. It serves as the site of sperm maturation (during which sperm acquire motility and fertilizing capacity) and storage, and represents the beginning of the excretory duct system. Anatomically, the epididymis comprises three regions. The head (caput) caps the superior pole of the testis and receives the efferent ductules draining the rete testis. The body (corpus) extends along the posterior border of the testis as the duct becomes progressively more coiled. The tail (cauda) at the inferior pole serves as the main storage site for mature sperm and continues as the vas deferens. Blood supply to the epididymis derives from two sources: the testicular artery provides the superior epididymal branch to the head, while the artery to the vas deferens supplies the inferior epididymal branch to the tail. This dual supply has clinical significance—the artery to the vas deferens can maintain testicular viability if the testicular artery is compromised. Panel A: Posterolateral view of epididymis with head forming cap over testis superior pole and efferent ductules entering as fine channels. Panel B: Epididymal body extending along posterior testis border as tightly coiled structure. Panel C: Tail at inferior pole continuing as thick-walled vas deferens ascending toward inguinal canal with arterial supply illustrated. Panel D: Inset showing single highly coiled epididymal duct stretched to demonstrate its 6-meter true length. --- ## The Spermatic Cord The spermatic cord is the neurovascular stalk suspending the testis in the scrotum, extending from the deep inguinal ring through the inguinal canal to emerge at the superficial inguinal ring and descend to the posterior aspect of the testis. Its structure reflects the passage of testicular vessels and ducts through the abdominal wall during development. The contents of the spermatic cord include the vas deferens, positioned posteriorly as the most palpable structure (feeling like a firm "whipcord"); the testicular artery, originating from the abdominal aorta at L2; the artery to the vas deferens from the inferior vesical artery; the cremasteric artery from the inferior epigastric artery; the pampiniform plexus of veins, which coalesce to form the testicular vein; the genital branch of the genitofemoral nerve (motor to the cremaster muscle); sympathetic nerve fibers accompanying the vessels; lymphatic vessels draining to the para-aortic nodes; and the remnant of the processus vaginalis (usually obliterated). Three fascial coverings envelop the cord, from outer to inner: external spermatic fascia (from external oblique), cremasteric muscle and fascia (from internal oblique), and internal spermatic fascia (from transversalis fascia). Panel A: Transverse section of spermatic cord with three concentric fascial layers - external spermatic, cremasteric with muscle fibers, and internal spermatic. Panel B: Vas deferens as thick-walled tube posteriorly with red testicular artery and blue pampiniform plexus surrounding it. Panel C: Small nerve fibers and thin-walled lymphatic vessels within the cord structure. Panel D: Longitudinal diagram showing cord course from deep inguinal ring through canal to scrotum. --- ## The Vas Deferens The vas deferens (ductus deferens) is a thick-walled muscular tube approximately 45 centimeters long that transports sperm from the epididymis to the ejaculatory duct. Its prominent muscular wall, comprising three layers of smooth muscle, enables powerful peristaltic contractions during ejaculation. The course of the vas deferens demonstrates important anatomical relationships. From its origin at the tail of the epididymis, it ascends along the posterior border of the testis within the spermatic cord, passes through the inguinal canal, and at the deep inguinal ring separates from the other cord structures by hooking around the lateral side of the inferior epigastric artery. It then crosses the external iliac vessels, descends along the lateral pelvic wall on the medial aspect of the obturator nerve and vessels, crosses the ureter posteriorly ("water under the bridge"—the vas passes over the ureter), and passes between the bladder base and the seminal vesicle. The terminal portion dilates as the ampulla before joining the duct of the seminal vesicle to form the ejaculatory duct. The vas deferens receives blood from the artery to the vas deferens, which arises from the superior or inferior vesical artery. This anastomoses with the testicular artery and can maintain testicular viability if the testicular artery is ligated. Panel A: Vas deferens ascending from epididymal tail through inguinal canal within spermatic cord with inset showing hook around inferior epigastric artery. Panel B: Vas crossing external iliac vessels and descending along pelvic sidewall. Panel C: Vas crossing over ureter ("water under the bridge") and passing medial to seminal vesicle to dilate as ampulla. Panel D: Junction of vas ampulla with seminal vesicle duct forming ejaculatory duct entering prostate with bladder landmarks. --- ## The Seminal Vesicles The seminal vesicles are paired, elongated glandular structures situated between the bladder fundus anteriorly and the rectum posteriorly, lateral to the ampullae of the vasa deferentia. Each seminal vesicle measures approximately 5 centimeters in length but consists of a single coiled tube that would extend to 15 centimeters if unraveled. These accessory glands produce 60-70% of the seminal fluid volume, contributing a viscous, alkaline secretion rich in fructose (the primary energy source for sperm), prostaglandins, and clotting factors (including semenogelin, which causes initial coagulation of ejaculated semen). The duct of each seminal vesicle joins the ampulla of the ipsilateral vas deferens to form the ejaculatory duct. The seminal vesicles receive blood from branches of the inferior vesical and middle rectal arteries. Their posterior relationship to the rectum allows palpation during digital rectal examination, though they are normally not distinctly felt unless enlarged. Panel A: Posterior view of bladder base with bladder reflected superiorly revealing elongated lobulated seminal vesicles flanking midline. Panel B: Vasa deferentia running between seminal vesicles with each duct joining vas ampulla to form ejaculatory duct. Panel C: Ejaculatory ducts entering posterior prostate with inset showing coiled seminal vesicle structure and secretory products. Panel D: Rectum positioned posteriorly demonstrating relationship for digital rectal examination. --- ## The Ejaculatory Ducts and Prostate ### Ejaculatory Ducts The ejaculatory ducts, approximately 2 centimeters long, form by the union of each vas deferens with its corresponding seminal vesicle duct. They pass through the posterior aspect of the prostate gland to open into the prostatic urethra on the seminal colliculus (verumontanum), a midline ridge on the posterior urethral wall. Obstruction of these ducts can cause infertility with azoospermia. ### Prostate Gland The prostate is a walnut-sized gland (approximately 3 × 4 × 2 cm) that surrounds the prostatic urethra at the bladder neck. Its base (superior aspect) is attached to the bladder neck, while its apex (inferior aspect) rests on the external urethral sphincter. The posterior surface lies against the anterior rectal wall, allowing examination through digital rectal examination. The McNeal zonal classification divides the prostate into zones with distinct clinical significance. The peripheral zone, comprising approximately 70% of glandular tissue, occupies the posterior and lateral aspects and represents the most common site of prostate cancer origin. The central zone, approximately 25% of glandular tissue, surrounds the ejaculatory ducts. The transition zone, only 5% initially, surrounds the proximal urethra and is the site of benign prostatic hyperplasia (BPH). The anterior fibromuscular stroma contains no glandular tissue. The prostate contributes approximately 20-30% of seminal fluid volume as a thin, milky secretion containing prostate-specific antigen (PSA), citric acid, and zinc. The prostatic urethra traverses the gland and features the urethral crest with the seminal colliculus, where the ejaculatory ducts and prostatic utricle open. Blood supply derives primarily from the inferior vesical artery, with contributions from the middle rectal artery. Venous drainage flows through the prostatic venous plexus, which communicates with Batson's vertebral venous plexus—a significant route for metastatic spread of prostate cancer to the spine. Lymphatic drainage goes primarily to internal iliac nodes. Panel A: Sagittal section of prostate surrounding prostatic urethra below bladder with ejaculatory ducts entering posteriorly and urethral crest and colliculus labeled. Panel B: Transverse section showing McNeal zones - blue peripheral zone posterolaterally, green central zone around ejaculatory ducts, yellow transition zone around urethra. Panel C: Clinical annotations indicating peripheral zone as cancer site (palpable on DRE) and transition zone as BPH site causing obstruction. Panel D: Vascular diagram showing prostatic venous plexus communicating with vertebral veins. --- ## The Bulbourethral Glands The bulbourethral glands (Cowper's glands) are paired pea-sized structures located within the deep perineal space, posterolateral to the membranous urethra. Their ducts, approximately 2.5 centimeters long, pierce the perineal membrane and open into the proximal spongy (bulbar) urethra. These glands produce a clear, viscous pre-ejaculatory fluid that lubricates the urethra and neutralizes residual acidity from urine, preparing an optimal environment for sperm passage. The secretion appears during sexual arousal before ejaculation. Panel A: Coronal section through membranous urethra showing paired bulbourethral glands as small oval structures posterolateral to urethra. Panel B: Glands embedded in external urethral sphincter musculature within deep perineal space. Panel C: Ducts traced forward piercing perineal membrane and opening into bulbar spongy urethra with bulb of penis below. Panel D: Enlarged inset showing glandular structure secreting clear mucoid pre-ejaculatory fluid. --- ## The Penis The penis comprises a root (fixed in the perineum) and a body (shaft, freely pendulous). Functionally, it serves as the male copulatory organ and the conduit for both urination and ejaculation. ### Root of the Penis The root lies in the superficial perineal space and consists of three components attached to the perineal membrane and ischiopubic rami. The two crura attach to the ischiopubic rami and are covered by the ischiocavernosus muscles; they converge anteriorly to form the corpora cavernosa. The bulb attaches to the perineal membrane in the midline and is covered by the bulbospongiosus muscle; it continues as the corpus spongiosum. ### Erectile Bodies The shaft contains three cylindrical masses of erectile tissue. The paired corpora cavernosa, positioned dorsally, form the main erectile bodies, surrounded by the thick tunica albuginea. During erection, blood fills the cavernosal sinusoids, and the tunica albuginea compresses draining veins against the rigid surrounding tissue, maintaining tumescence. The single corpus spongiosum lies ventrally, surrounding the spongy urethra. Its thinner tunica albuginea permits less rigidity, keeping the urethra patent during ejaculation. The corpus spongiosum expands distally to form the glans penis, with its sensitive mucocutaneous junction at the corona. ### Coverings From deep to superficial, the penile coverings include Buck's (deep) fascia, which encloses all three erectile bodies and the dorsal neurovascular bundle, and the loose superficial fascia (continuous with dartos and Colles' fascia), which allows the skin to move freely over the underlying structures. The skin extends over the glans as the prepuce (foreskin), which may be removed by circumcision. ### Blood Supply Arterial supply derives entirely from the internal pudendal artery through three terminal branches: the deep artery of the penis (central artery), which runs through each corpus cavernosum supplying the erectile tissue; the dorsal artery of the penis, which runs beneath Buck's fascia to supply the glans and skin; and the artery of the bulb, which supplies the bulb and corpus spongiosum. Venous drainage occurs through superficial and deep systems—the superficial dorsal vein drains to the external pudendal veins, while the deep dorsal vein passes beneath the pubic symphysis to the prostatic plexus. ### Innervation Sensory innervation to the glans and shaft comes from the dorsal nerve of the penis (branch of pudendal nerve, S2-S4). Autonomic innervation controls erection and ejaculation: parasympathetic fibers from pelvic splanchnic nerves (S2-S4) cause erection through arterial dilation and sinusoidal relaxation (point and shoot: "parasympathetic points"), while sympathetic fibers from the hypogastric nerves (T11-L2) control ejaculation. Panel A: Perineal view of penile root showing crura attached to ischiopubic rami with ischiocavernosus and bulb on perineal membrane with bulbospongiosus. Panel B: Cross-section of shaft with paired corpora cavernosa dorsally containing deep arteries and tunica albuginea, and ventral corpus spongiosum with urethra. Panel C: Dorsal neurovascular bundle between Buck's fascia and tunica albuginea with longitudinal view showing crura-to-corpora and bulb-to-spongiosum transitions. Panel D: Arterial supply traced from internal pudendal artery to its three terminal branches supplying erectile tissue. --- ## The Male Urethra The male urethra, approximately 20 centimeters long, conducts both urine and semen from the bladder and ejaculatory ducts to the external environment. It comprises three anatomically distinct segments with differing characteristics and clinical significance. The prostatic urethra (approximately 3 cm) passes through the prostate gland as the widest and most distensible segment. Its posterior wall features the urethral crest, a longitudinal ridge bearing the seminal colliculus—an elevation where the ejaculatory ducts open laterally and the blind prostatic utricle (a vestigial remnant of the müllerian ducts) opens in the midline. Prostatic ducts open on either side of the urethral crest. The membranous urethra (approximately 1 cm) traverses the external urethral sphincter (sphincter urethrae) and deep perineal space. This is the narrowest, least distensible, and most vulnerable segment—a common site of traumatic injury, particularly with pelvic fractures that disrupt the membranous urethra at its attachment to the perineal membrane. The spongy urethra (approximately 15-16 cm) passes through the corpus spongiosum from the bulb to the external urethral meatus at the glans. The bulbourethral gland ducts open into the proximal bulbar segment. The intrabulbar portion has a slight dilation, while the penile portion maintains a relatively uniform caliber. The navicular fossa is a terminal dilation within the glans. The external urethral meatus, the narrowest fixed point, is a vertical slit. The urethra has two curvatures: a fixed curvature at the pubic symphysis and a mobile curvature at the penopubic junction that can be straightened by elevating the penis to facilitate catheterization. Panel A: Sagittal section showing prostatic urethra in blue as widest segment within prostate with urethral crest and seminal colliculus. Panel B: Membranous urethra in red as narrow segment surrounded by external sphincter. Panel C: Spongy urethra in yellow as longest segment within corpus spongiosum showing bulbourethral duct openings and navicular fossa. Panel D: Two urethral curvatures indicated with fixed curve at pubic symphysis and mobile curve straightening during catheterization with cross-sectional diameter comparisons. --- ## Blood Supply and Lymphatic Drainage Summary Understanding the vascular supply and lymphatic drainage of male reproductive structures has important clinical implications, particularly for surgery and cancer staging. The testis receives arterial blood from the testicular artery (from the abdominal aorta at L2) with supplementation from the artery to the vas deferens and cremasteric artery. Venous drainage flows through the pampiniform plexus, which coalesces into the testicular vein—the right draining to the IVC, the left to the left renal vein. This asymmetry explains why varicoceles occur predominantly on the left side. Lymphatic drainage from the testis follows the testicular vessels retroperitoneally to para-aortic (lumbar) lymph nodes—not to inguinal nodes. This reflects the embryological origin of the testis in the posterior abdominal wall. In contrast, scrotal skin drains to superficial inguinal nodes. This distinction is clinically important: testicular cancer metastasizes to para-aortic nodes, while scrotal skin cancer spreads to inguinal nodes. The prostate receives blood from the inferior vesical artery, with venous drainage through the prostatic plexus that communicates with Batson's vertebral venous plexus, providing a direct route for prostate cancer metastasis to the vertebral column. Lymphatic drainage goes to internal iliac nodes. Penile skin drains to superficial inguinal nodes, while the glans drains to deep inguinal and then external iliac nodes. Panel A: Testis lymphatics ascending with testicular vessels to para-aortic nodes at L1-L2 level highlighted for cancer staging. Panel B: Scrotal skin drainage to superficial inguinal nodes distinct from testicular drainage. Panel C: Prostate drainage to internal iliac nodes with venous communication to vertebral plexus for metastatic spread. Panel D: Penile skin drainage to superficial inguinal nodes and glans to deep inguinal nodes with color-coded pathways. --- ## Clinical Correlations ### Varicocele A varicocele represents dilation of the pampiniform plexus, appearing as a "bag of worms" in the scrotum. It occurs predominantly on the left (approximately 90%) because the left testicular vein drains at a right angle into the left renal vein (higher resistance), whereas the right testicular vein drains obliquely into the IVC. Varicoceles may impair fertility through elevated testicular temperature. ### Testicular Torsion Testicular torsion occurs when the testis rotates on the spermatic cord, occluding venous and then arterial blood supply. The "bell-clapper" deformity, in which a horizontal testicular lie results from high attachment of the tunica vaginalis, predisposes to torsion. This condition presents with sudden severe scrotal pain and represents a surgical emergency—detorsion and orchidopexy must be performed within 4-6 hours to salvage the testis. ### Benign Prostatic Hyperplasia BPH develops in the transition zone surrounding the urethra, causing progressive urethral compression with age. Symptoms include hesitancy, weak stream, frequency, nocturia, and incomplete emptying. Unlike prostate cancer, BPH does not arise from the peripheral zone and is therefore often not palpable on digital rectal examination. ### Prostate Cancer Prostate cancer typically arises in the peripheral zone and may be detected as a nodule on digital rectal examination or through elevated PSA. Metastatic spread characteristically involves the vertebral column via Batson's plexus. The neurovascular bundles, running posterolateral to the prostate, carry the cavernosal nerves responsible for erectile function—damage during radical prostatectomy can cause erectile dysfunction. ### Hypospadias Hypospadias results from incomplete fusion of the urethral folds during development, positioning the urethral opening on the ventral surface of the penis. Severity ranges from glanular (most common, meatus on ventral glans) to penoscrotal or perineal (meatus at the base of penis or perineum). Surgical correction is typically performed in infancy. Panel A: Varicocele showing dilated tortuous pampiniform plexus veins with drainage anatomy explaining left-sided predominance. Panel B: Testicular torsion with twisted spermatic cord and resulting venous congestion requiring emergency detorsion. Panel C: BPH showing transition zone hyperplasia compressing urethra versus prostate cancer nodule in peripheral zone palpable on DRE. Panel D: Hypospadias spectrum from glanular to perineal with normal meatal position for comparison. --- ## Summary The testes, residing in the scrotum in a layered covering derived from the abdominal wall, produce sperm in seminiferous tubules and testosterone in Leydig cells. Sperm mature in the epididymis and travel through the vas deferens (which crosses the ureter as "water under the bridge") to the ejaculatory duct. The seminal vesicles contribute fructose-rich fluid (60-70% of semen volume), while the prostate adds secretions containing PSA. The prostate's peripheral zone is the common site of cancer, while the transition zone gives rise to BPH. The penis contains paired corpora cavernosa (main erectile tissue) and a single corpus spongiosum (surrounding the urethra, forming the glans). The male urethra has three parts: prostatic (widest), membranous (narrowest, most vulnerable), and spongy (longest). Testicular lymphatics drain to para-aortic nodes (not inguinal), reflecting retroperitoneal embryological origin, with important implications for cancer staging. --- ## Key Terms **Pampiniform plexus**: The network of veins draining the testis that surrounds the testicular artery in the spermatic cord, functioning as a countercurrent heat exchanger and coalescing to form the testicular vein. **Tunica vaginalis**: The serous membrane derived from the processus vaginalis that covers the testis, with parietal and visceral layers creating a potential space (hydrocele forms when fluid accumulates here). **Vas deferens**: The thick-walled muscular duct (approximately 45 cm) that transports sperm from the epididymis, crossing the ureter to reach the prostate where it joins the seminal vesicle duct to form the ejaculatory duct. **Seminal colliculus (verumontanum)**: The midline elevation on the posterior wall of the prostatic urethra where the ejaculatory ducts and prostatic utricle open. **Corpus cavernosum**: The paired dorsal erectile bodies of the penis, arising from the crura and comprising the main erectile tissue with thick tunica albuginea. **Prostatic urethra**: The proximal segment of the male urethra (approximately 3 cm) passing through the prostate, receiving the ejaculatory ducts and prostatic secretions; the widest and most distensible portion. --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*