Chapter 74: Male Reproductive System Anatomy

The comprehensive framework of the male reproductive system involves the gonads (testes), the spermatic cord, the external genitalia, and the accessory sex glands, all regulating reproductive function, sexual behavior, and physical development. The testes, measuring between 15 and 25 ml in average volume for adults, are situated within the scrotum and maintained at a temperature 3–4 °C below core body temperature through the scrotal skin characteristics and the counter-current heat exchange facilitated by the pampiniform plexus. The testis is protected by three layers: the inner vascular layer, the dense fibrous tunica albuginea, and the outer tunica vaginalis, which is a continuation of the fetal processus vaginalis; failure of the processus vaginalis to obliterate can result in hydroceles or indirect inguinal hernias. The primary function of the testes is spermatogenesis, which occurs within the highly coiled seminiferous tubules that constitute up to 80% of the total testicular volume. Within the seminiferous tubules, Sertoli cells (nurse cells) organize the stratification of sperm development, forming tight junctions that create a critical blood–testis barrier, separating basal spermatogonia from maturing spermatocytes and spermatids in the adluminal compartment. Interstitial endocrine cells (Leydig cells), located outside the tubules, produce and secrete testosterone, responding to pituitary gonadotropins. After approximately 64 days, structurally mature but non-motile spermatozoa pass from the tubules into the rete testis and then into the efferent ductules and the epididymis. The epididymis is essential for absorbing about 90% of testicular fluid and enabling the acquisition of mature motility patterns by the sperm. Sperm transport continues through the ductus deferens, a long, highly muscular tube innervated by sympathetic fibers from the inferior hypogastric plexus. The accessory sex glands, including the seminal glands (contributing at least two-thirds of the ejaculate volume and rich in fructose) and the bulbo-urethral glands (providing lubrication), release their secretions into the prostatic urethra via the ejaculatory ducts. The external genitalia include the penis, composed of the paired corpora cavernosa and the corpus spongiosum containing the spongy urethra. Penile erection is a neurovascular process initiated by parasympathetic relaxation of corporal smooth muscle, leading to rapid blood influx via the helicine arteries and engorgement of the cavernous spaces. This tumescence transitions to rigidity when the resulting pressure compresses emissary veins against the tunica albuginea, a mechanism termed veno-occlusion. Ejaculation is a two-part process—emission (sympathetic control) followed by expulsion (autonomic and somatic control, involving bulbospongiosus contraction and urinary bladder neck closure). Important clinical considerations include cryptorchidism (undescended testes), a condition where early orchidopexy is recommended to maximize the potential for spermatogenesis, though it does not mitigate the associated testicular cancer risk.