The journey from embryo to fully developed reproductive system is a marvel of biology. It all starts with genetic sex, determined at fertilization, which sets off a cascade of events leading to the development of gonads, genitalia, and secondary sexual characteristics.

Puberty marks the final stage of reproductive system development, triggered by hormonal changes. These hormones kickstart the maturation of reproductive organs and the emergence of adult sexual characteristics, preparing the body for potential reproduction.

Development of the Male and Female Reproductive Systems

Sexual differentiation in embryos

• Genetic sex determined at fertilization by presence or absence of Y chromosome
  • XY chromosomes typically develop into males
  • XX chromosomes typically develop into females
• Gonadal sex determined by development of gonads into testes or ovaries
  • SRY gene on Y chromosome initiates testicular development
  • Absence of SRY gene allows gonads to develop into ovaries
• Phenotypic sex refers to internal and external genitalia and secondary sexual characteristics
  • Testosterone secreted by testes leads to development of male genitalia and characteristics (penis, scrotum)
  • Absence of testosterone allows for development of female genitalia and characteristics (clitoris, labia)
• Sexual dimorphism emerges as a result of these differentiation processes

Origins of reproductive organs

• Undifferentiated structures in early embryonic development
  • Genital ridge thickening of intermediate mesoderm gives rise to gonads
  • Wolffian ducts (mesonephric ducts) develop into male reproductive structures (epididymis, vas deferens)
  • Müllerian ducts (paramesonephric ducts) develop into female reproductive structures (fallopian tubes, uterus)
• Male reproductive organ development
  • Testes develop from genital ridge under influence of SRY gene
  • Epididymis, vas deferens, and seminal vesicles develop from Wolffian ducts
  • Prostate gland and bulbourethral glands develop from urogenital sinus
  • Penis and scrotum develop from genital tubercle and labioscrotal folds
• Female reproductive organ development
  • Ovaries develop from genital ridge in absence of SRY gene
  • Fallopian tubes, uterus, and upper portion of vagina develop from Müllerian ducts
  • Lower portion of vagina develops from urogenital sinus
  • Clitoris and labia develop from genital tubercle and labioscrotal folds
• Primordial germ cells migrate to the developing gonads and contribute to gametogenesis

Gonadal Development and Function

• Gonadal differentiation occurs early in fetal development
• Testes and ovaries develop specialized structures for hormone production (steroidogenesis) and gamete formation
• Gametogenesis begins during fetal development and continues throughout reproductive life

Hormonal changes during puberty

• Puberty triggered by activation of hypothalamic-pituitary-gonadal (HPG) axis
  • Gonadotropin-releasing hormone (GnRH) secreted by hypothalamus
  • GnRH stimulates anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
  • FSH and LH stimulate gonads to produce sex hormones (testosterone in males, estrogen in females)
• Male puberty
  • Increased testosterone production leads to:
    1. Growth of testes, penis, and prostate gland
    2. Deepening of voice due to laryngeal enlargement
    3. Growth of facial, body, and pubic hair
    4. Increased muscle mass and bone density
    5. Initiation of spermatogenesis
• Female puberty
  • Increased estrogen production leads to:
    1. Development of breasts and widening of hips
    2. Growth of pubic and axillary hair
    3. Maturation of ovaries and initiation of ovulation
    4. Onset of menstrual cycles
• Both sexes experience growth spurt during puberty due to increased production of growth hormone and insulin-like growth factor-1 (IGF-1)