Overview
Physiologic Transition at Birth
Major physiologic changes occurring at birth: Cardiovascular transition: In utero: Blood bypasses lungs (non functional) via: Ductus venosus (umbilical vein → inferior vena cava...
Major physiologic changes occurring at birth:Cardiovascular transition: - In utero: Blood bypasses lungs (non-functional) via: - Ductus venosus (umbilical vein → inferior vena cava, bypassing liver) - Foramen ovale (right atrium → left atrium, bypasses lungs) - Ductus arteriosus (pulmonary artery → aorta, bypasses lungs) - At birth: 1. First breath → lungs expand → pulmonary vascular resistance (PVR) decreases 2. Clamping umbilical cord → systemic vascular resistance (SVR) increases 3. Increased LA pressure → foramen ovale closes functionally 4. Rising PO2 → ductus arteriosus constricts (within 10–15 hours, permanently closes 2–3 weeks) 5. Ductus venosus closes (fibrous closure: 1–2 weeks → ligamentum venosum) Respiratory transition: - Fetal lung fluid cleared by: chest compression (vaginal delivery), lymphatic absorption, pulmonary circulation - First breath initiated by: hypoxia, hypercapnia, cold stimulus (temperature change), sensory stimulation - Surfactant: essential for alveolar stability; deficient in prematurity → RDS Thermoregulation: - Newborns cannot shiver to generate heat - Brown adipose tissue (BAT): unique to newborns; non-shivering thermogenesis via uncoupling protein - Heat loss mechanisms: evaporation (wet skin), conduction (cold surface), convection (air currents), radiation...