Neonatal physiology Flashcards
What does the foetal circulation receive?
Oxygenated, purified, detoxified blood via the placental/ maternal circulation in the umbilical vein
How is blood reoxygenated and returned?
Umbilical arteries
What is different about liver and lung circulation in fetus?
partially bypassed by anatomic shunts as function of these organs is taken by mother’s circulation
Specifically how does oxygenated blood from umbilical vein travel in liver?
50% pass through and into IVC- 50% bypasses liver and goes straight into ductus venosus (links hepatic, portal and umbilical circulations)
Other role of IVC in directing fetal blood flow
Returns deoxygenated blood from lower body- mixed O blood into right atrium ( 2 streams, mostly straight into LA via foramen ovale)
Where does blood go from LA
Partially O blood > LV, supplies the fetal head- returns at right atrium, mainly into RV and pulmonary trunk ( majority into D. aorta via ductus arteriosus)
How does circulation and shunts change in the newborn?
shunts close, umbilical as and vs clamped off- rise in peripheral resistance in systemic circulation, ^ BP
What happens to foramen ovale and ductus arteriousus?
close over and fibrose shortly after birth- problems if not closed over, as although no effect on oxygenation, it increases work of heart (cardiac failure)
Respiratory adjustments at birth
Lungs must function immediately to prevent anoxia- initial breath requires huge insp. intrapleural pressure to overcome surface tension of alveolar fluid (quickly drops)
Active expiration in baby vs passive in foetus
Needed to overcome increased resistance from airway fluid- twice the adult ventilation when accounting for body size. Resp distress syndrome in preterms, surfactant deficiency increasing work of breathing
weight gain and nutrition
initial weight drop from fluid loss, potenital difficulty feeding from mother: vit d, calcium and iron needed so maternal supplementation often indicated
Temperature
2x metabolic rate of adult (more heat generated), fluctuation in core temperature due to immaturity of TR systems
High SA/V ratio so lose heat quicker- countered by brown fat (uncouples ADP phosphorylation, extra heat gen)
Liver function
poorly formed at birth, ^ plasma bilirubin and neonatal jaundice.
Falls within months. Glycogen storage and manufacture compromised, necessitates frequent feeding.
P. proteins, inc clotting factors low, inc risk of bleeding
Immunity
Active acquired poor in newborn, relies on mothers IgG’s from placenta. IgA in colostrum,
Passive immunity declines, taken over as exposure to pathogens occurs.
Immunisation programmes start around 2-3m when infant has capable acquired immunity.
