Conditions of the penis and urethra

Abstract The formation of the external genitalia of the male is a complex developmental process. The SRY region on the Y chromosome causes the undifferentiated gonads to differentiate and produce testosterone (Leydig cells) and anti-Müllerian hormone (Sertoli cells). It starts in the fourth gestational week with the appearance of the genital tubercle. The genital tubercle elongates, while the urogenital sinus gives rise to the urethral plate (which tubularizes) and the labioscrotal folds fuse to form the scrotum, all under the influence of testosterone produced by the testes, which has been converted to dihydrotestosterone by the action of 5-alpha reductase. This chapter covers the embryology of the penis and urethra. Many of the common conditions that affect the prepuce (foreskin), buried penis, hypospadias, and urethral conditions are congenital abnormalities where normal development has not occurred.