OVERVIEW OF MALE REPRODUCTIVE PHYSIOLOGY
The same embryologic anlage produces female or male external genitalia depending on the level of testosterone. The SRY gene (typically found on the Y chromosome) leads to testicular development, with masculinization of the reproductive tract. When this gene is absent, ovaries develop with subsequent maturation of female sex organs. The scrotum and penis are cognates of the labia majora and clitoris, respectively. Ambiguous genitalia are the result of development and maturation 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 intra-abdominally and descend through the inguinal canal into the scrotum, usually by birth. Being slightly cooler than body temperature, scrotal location is more conducive to spermatogenesis. Luteinizing hormone causes testicular Leydig cells to produce testosterone. Spermatogenesis in the seminiferous tubules requires follicle-stimulating hormone (FSH) and paracrine Sertoli cell. Sperm collected in the epididymis travels up the vas deferens within the spermatic cord to the prostate and seminal vesicles. The spermatic cord also contains the testicular artery and vein and the lymphatics. Ejaculate contains sperm suspended in prostatic and seminal vesicle secretions.
MALE REPRODUCTIVE SYSTEM ANATOMY
At puberty, the mons pubes develops hair that extends onto the abdomen forming the triangular male escutcheon, with its superior apex near the umbilicus.
The male reproductive system is designed to produce and store sperm cells that are to be deposited on the female cervix by forceful ejaculation of the sperm and spermatic fluids via the erect penetrating penis. The shaft of the penis contains three columns of erectile tissue, the two dorsolateral corpora cavernosa and the smaller ventral corpus spongiosum containing the urethra (Fig. 12-1). The three columns form a cylinder bound by fibrous tissue. Surrounding the urethral meatus at the tip of the penis is an obtuse cone of erectile tissue, the glans penis. 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 extending into the ventral notch of the glans. Penile erection and ejaculation are complex physiologic processes which can be disrupted by vascular disease, drugs, nerve injury, endocrine abnormalities, and anxiety. 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.
The scrotum is a sac of thin, rugous skin overlying the tightly adherent dartos muscle and fascia that form the dartos tunic (Fig. 12-2C). ...