Chapter 56: Fertilization, Pregnancy, and Lactation

Following fertilization, the chapter explores early embryonic development and the establishment of pregnancy, including blastocyst formation, implantation into the uterine endometrium, and the formation of extraembryonic tissues such as the placenta and amniotic sac. The placental structure and function are examined as central to maternal-fetal exchange, including mechanisms of nutrient transport, gas exchange, and waste removal across the placental barrier. The chapter details hormonal changes during pregnancy, emphasizing the roles of human chorionic gonadotropin in maintaining the corpus luteum, progesterone in sustaining the endometrium and suppressing uterine contractions, and estrogen in preparing maternal tissues for delivery. Maternal physiological adaptations are discussed, including cardiovascular changes such as increased blood volume and cardiac output, respiratory adjustments to meet fetal oxygen demands, and metabolic modifications supporting fetal growth. The chapter then transitions to the physiology of labor and delivery, examining the role of oxytocin in uterine contraction, prostaglandin involvement in cervical dilation, and the mechanical processes of parturition. Finally, the chapter addresses lactation, including mammary gland development during pregnancy driven by prolactin and placental hormones, the initiation of milk secretion following delivery, and the composition and nutritional significance of human milk for neonatal development and immune function.