Development of the Reproductive Systems
- Differentiation of female and male genitalia begins around 7 to 8 weeks of embryonic development, when the gonads of genetically male embryos begin to secrete male sex hormones, primarily testosterone. Until that time, the primitive reproductive organs of males and females are homologous (the same).
- The structure and function of both male and female reproductive systems depend on interactions among the central nervous system (hypothalamus), the endocrine system (anterior pituitary), the gonads (ovaries, testes), and the hypothalamic-pituitary-gonadal (H-P-G) axis. A set of complex neurologic and hormonal interactions accelerate at puberty and lead to sexual maturation and reproductive capability.
- Extrahypothalamic factors cause the hypothalamus to secrete gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete gonadotropin follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that stimulate the gonads (ovaries and testes) to secrete female or male sec hormones. Paracrine hormones (inhibin, active, and follistatin) influence the positive and negative feedback loops that occur along the H-P-G axis.
- Production of primitive female gametes (ova) occurs solely during fetal life. From puberty to menopause, one female gamete matures per menstrual cycle. Production of the male gametes (sperm) begins at puberty; after that, millions are produced daily, usually for life.