Learning Objective
Understand the hormonal changes in males throughout life, including fetal development, childhood, puberty, adulthood, and aging, and their impact on reproductive function.
Fetal Life
The development of male and female internal and external structures depends on the fetal hormonal environment. Initially, both Wolffian and Müllerian ducts are present in all fetuses. Without hormonal input (normal female fetus), female internal and external structures develop (Müllerian ducts persist, Wolffian ducts regress).
Normal male development requires three hormones: testosterone, dihydrotestosterone, and Müllerian inhibiting factor (MIF).
- hCG + LH → Leydig cells → testosterone → Wolffian ducts
- 5-α-reductase: testosterone → dihydrotestosterone → urogenital sinus & genital organs
- Sertoli cells → MIF → prevents female internal structures
Clinical relevance: Absence of MIF in males can lead to the persistence of Müllerian ducts, resulting in internal female structures alongside male organs.
Wolffian ducts differentiate into male internal structures: epididymis, vas deferens, and seminal vesicles. In the absence of testosterone, these regress.
Dihydrotestosterone induces differentiation of the urogenital sinus and genital tubercle into the scrotum, penis, and prostate gland. Without it, female external structures develop.
Activity
Childhood
After birth, LH and testosterone levels drop and remain low until puberty. The mechanism for this prolonged quiescence is not fully understood. LH secretion remains low despite low testosterone.
Puberty
At puberty, the amplitude of LH pulses increases, particularly during sleep. Elevated LH stimulates Leydig cells to produce testosterone, initiating secondary sexual characteristics and spermatogenesis.
Adulthood
During adulthood, LH secretion directly drives testosterone production. The levels of these hormones generally parallel each other, maintaining normal reproductive function.
Aging Adult
With aging, testosterone and inhibin secretion decline. Men in their seventies produce approximately 60–70% of the testosterone levels of men in their twenties.
Activity
Clinical relevance:
Unlike women, men do not experience a sudden drop in testosterone at a specific age. The reduced negative feedback increases LH and FSH secretion.
