Growth and functional maturation of the male reproductive organs occurs throughout childhood and adolescence with peak activity during puberty. This chapter will describe the pattern of this growth and maturation. The various stages of normal male puberty are described in Chapter 533 and testicular as well as scrotal masses are described in Chapter 78.
External genitalia develop from a genital tubercle, which forms ventral to the cloaca. Early development is androgen independent and instead depends on transgenic pathways including sonic hedgehog. Once the genital tubercle is sexually dimorphic, further masculinization is dependent on androgen exposure. Elongation of the genital tubercle leads to the formation of a phallus, and closure of the urethral folds forms a penile urethra. The scrotum is formed by fusion of the labioscrotal swellings.
In infancy the average length and girth of the penis are 3.5 and 4.4 cm respectively. While penile growth continues through childhood, a spurt in this growth is seen during stage 3 of the sexual maturity rating (SMR) system. The penis starts to increase in length prior to an increase in girth. During puberty, the scrotum enlarges, its skin darkens, and it develops rugae. Most external genital growth is complete within 5 years of entering SMR stage 2.
EPIDIDYMIS, VAS DEFERENS, SEMINAL VESICLES, AND PROSTATE GLAND
The epididymis, vas deferens, and seminal vesicles develop from the wolffian duct under the influence of androgens. The epididymis has three regions: a caput, which is responsible for fluid resorption and secretion of glycopeptides; a corpus, where maturation of the sperm occurs; and a cauda, where sperm is stored. Its development follows a biphasic pattern with initial growth between 2 and 4 months of fetal life, followed by regression during infancy and then definitive development during childhood and puberty. When mature, it has a stretched length of 3 meters with the globular caput lying on the superior pole of the testis and the narrow cauda on its inferior pole.
The vas deferens starts where the cauda epididymis straightens out and, when fully grown, has a length of about 35 cm. Besides serving as a conduit to the ejaculatory duct, its complex epithelium has secretory and absorptive functions that contribute to the semen.
In the fetus, the seminal vesicle develops as a hook-like duct with side ducts from the distal wolffian duct. During puberty, the gland has increasing amounts of connective tissue and smooth muscle and its interior starts to appear septate. Its weight increases by a factor of 10. Functionally, the ampulla of the vas deferens, the seminal vesicle, and the ejaculatory duct can be considered a unit whose roles include secretion, resorption, and spermatophagy.
The prostate gland starts to develop at around 12 weeks of gestation. During childhood, there is progressive decline in the amount of smooth muscle ...