Adaptation for life: a review of neonatal physiology

The neonatal period (first 28 days of life or 44 weeks postconceptual age) contains the most dramatic and rapid physiological changes seen in humans. They vary from the immediate changes seen in the respiratory and cardiovascular systems to the slower progression seen in the hepatic, haematological and renal systems. These adaptations support life during the development from intrauterine physiology to adult physiology. This article describes neonatal physiological changes in a system-based approach, including slower changes that may extend beyond the neonatal period.