The identical embryologic anlage produce female or male external genetalia depending the level of testosterone. Lack of the SRY gene (typically found on the Y chromosome) leads to development of ovaries, with subsequent maturation of female sex organs. Conversely, the presence of this gene leads to testicular development, with masculinization of the reproductive tract. The scrotum and penis are cognates of the labia majora and clitoris, respectively. Ambiguous genitalia occur when development and maturation occurs with a mixed genetic substrate or hormonal environment.
The male reproductive organs are the testes, epididymis, vas deferens, seminal vesicles, prostate, and penis. The testes arise intraabdominally and descend through the inguinal canal into the scrotum, usually by birth. The scrotal location is more conducive to spermatogenesis being slightly cooler than body temperature. Leutenizing hormone causes testicular Leydig cells to produce testosterone. Spermatogenesis in the seminiferous tubules requires follicle-stimulating hormone and paracrine testosterone production. Sperm are collected in the epididymis and travel up the vas deferens to the level of the prostate and seminal vesicles in the spermatic cord. The spermatic cord also contains the testicular artery and vein and the lymphatics. Ejaculate contains sperm, prostatic, and seminal vesicle secretions.
At puberty, the mons pubes becomes covered with hair that extends onto the skin of the abdomen to form the male escutcheon, which describes an upright triangle with the apex near the umbilicus.
The shaft of the penis is formed by three columns of erectile tissue, the two dorsolateral corpora cavernosa and the ventral smaller corpus spongiosum containing the urethra (Fig. 12–1). Fibrous tissue binds the three columns into a cylinder. The tip of the penis is an obtuse cone of erectile tissue, the glans penis, containing the urethral meatus. The glans has a corona at its junction with the shaft. A flap of skin, the prepuce or foreskin, covers the glans. The frenulum is a fold of the prepuce that extends ventrally into the ventral notch in the glans. Penile erection and ejaculation are complex physiologic and hemodynamic processes that can be disrupted by vascular disease, drugs, injury to nerves, endocrine abnormalities, and anxiety. The male reproductive system is designed to produce and store sperm cells, which can be deposited at the entrance to the female cervix with forceful ejaculation of the sperm and spermatic fluids via the erect, penetrating penis. Successful reproduction is dependent upon the coordinated functioning of this system.
Structure of the Penis. A. The shaft in its ventrolateral aspect, with Integument removed. B. A sagittal section of the shaft with integument included. C. A cross-section of the shaft.
This pouch is formed by a layer of thin, rugous skin overlying the tightly adherent dartos tunic consisting of muscle and fascia (Fig. 12–2C). The sac hangs from the root of the penis. The scrotal skin is bisected by a median raphe. Internally, the two halves of the pouch are separated by a septal fold of dartos tunic. Each half contains a testis with its epididymis and spermatic cord. The scrotal contents slide easily in a fascial cleft between the scrotal wall and the covering of the testis and cords. The skin of the scrotum is deeply pigmented and contains large, sebaceous follicles that have a tendency to form cysts. The dartos muscle tone determines scrotal size, with exposure to cold shrinking the sac and heat enlarging the pouch. In advanced age, the dartos muscle becomes relatively atonic. The action of the dartos muscles is independent of contractions of the cremasteric muscles that elevate the testes. The arterial, venous and lymphatic drainage of the scrotal contents arises intraabdominally and reaches its scrotal location via the inguinal canal and spermatic cord. Lymphatics from the scrotal contents drain to the pelvic lymph nodes. The scrotal vascular and lymphatic supply is in continuity with the perineum and its lymphatics drain to the inguinal lymph nodes.
Anatomy of the scrotal wall and epididymis. A. Cavities of the tunica vaginalis are opened anteriorly to show testis and cord. B. Parts of the epididymis and cord. C. Layers of the scrotum.
Testis, Epididymis, Vas Deferens, and Spermatic Cord
Toward the end of fetal development, the testis begins its descent from the abdomen to the scrotum. The peritoneum covering the testis becomes the processus vaginalis, and the gubernaculum leads the testis into its scrotal position. Normally, the spermatic cord portion of the peritoneal pouch is obliterated, leaving a cavity surrounding the testis and epididymis, except for their posterior aspect (Fig. 12–2A). This serous membrane is the tunica vaginalis. Abnormal persistence of this peritoneal connection leads to congenital hernias or funicular hydroceles. The testis is a smooth, solid ovoid, compressed laterally, and roughly 4 cm × 2 cm. The spermatic cord suspends the testis in the scrotum with the long axis nearly vertical. The head of the epididymis caps the upper pole of the testis. The body of the epididymis forms an elongated inverted cone attached vertically to the posterior surface of the testis. The apex of the cone, or tail of the epididymis, approaches the lower pole of the testis (Fig. 12–2B). The epididymis is continuous with the vas deferens, which joins other vessels to form the spermatic cord. The spermatic cord consists of the vas deferens, arteries, veins, nerves, and lymphatic vessels, all held together by the spermatic fascia. From the testis, the cord extends upward, entering the external inguinal ring and coursing through the inguinal canal to the ...