Chapter 34: Structure and Function of the Reproductive Systems

Sexual differentiation in utero occurs through genetic regulation involving the SRY gene and sex hormone signaling, with testosterone and Müllerian inhibitory hormone directing male development while female development proceeds when these hormones are absent. The onset of puberty activates the hypothalamic-pituitary-gonadal axis, triggering gonadotropin release and increased sex hormone production that drives reproductive maturation, secondary sexual characteristics, and adult sexual function. In females, estrogen and progesterone regulate the menstrual cycle through distinct phases: the follicular phase involves follicle growth and endometrial proliferation culminating in an LH surge that triggers ovulation, the luteal phase maintains the corpus luteum to produce progesterone for endometrial secretion, and the menstrual phase involves endometrial shedding if pregnancy does not occur. The female reproductive organs include the ovaries as endocrine and exocrine glands, the uterus as the site of embryonic implantation and fetal development, the fallopian tubes for gamete transport, and the vagina as the passage for intercourse and childbirth. Breast tissue develops and functions under hormonal control from estrogen, progesterone, prolactin, and oxytocin, with milk production and delivery occurring postpartum. The male reproductive system comprises the testes as the site of spermatogenesis supported by Sertoli cells and Leydig cells, the epididymis for sperm maturation and storage, the vas deferens and accessory glands that contribute to semen formation, and the penis as the organ of copulation and urination. Ejaculation involves coordinated neural and vascular mechanisms to deliver semen through the urethra. The chapter concludes by addressing reproductive aging: menopause in women involves follicle depletion and declining ovarian hormone production leading to vasomotor symptoms, vaginal atrophy, bone loss, and cardiovascular changes, while andropause in men represents a more gradual testosterone decline affecting sexual function, muscle mass, and testicular volume.