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, ...