Fetal Physiology

Question 1

describe what is happening to the fetus in utero (in terms of nutrition & growth) that is important for survival after birth.

Answer 1

• 30-40% of their calories for growth
• drop in body weight first few days (due to change from high ECF, high water content –> solid, fat, higher ICF. This cont from 5m GA –> 1yr old)

Question 2

describe what is happening to the fetus in utero (in terms of O2 transport) that is important for survival after birth.

Answer 2

• Foetal oxygen decreases during contraction of the uterus
• HbF (α chain) has greater affinity to O2, causing a left shift on the Hb saturation curve (foetal Hb can preferentially take up more O2 from maternal circulation)
- switch from HbF –> HbA in first 6m

Question 3

describe what is happening to the fetus in utero (in terms of circulation) that is important for survival after birth.

Answer 3

1. fetus receives O2 blood from placenta via umbilical vein (UV) –> liver –> 2/3 bypasses via ductus venosus (DV)
2. O2 blood enters RA –> shunted via foramen ovale to LA –> head, neck; deoxyg blood returning to RA from rest of body, some of it enters RV –> pulm artery –> shunted via Ductus arteriosus to descending aorta to lower limbs –> returns to Umbilical artery (placenta) to be re-oxygenated
3. AFTER BIRTH: clamping of cord means low-resistance system of placenta is removed + baby’s lung expands (decrease pulm resistance) –> increasing circulating blood volume + increased blood flow to lungs
4. decreased resistance pulm system means less blood shunted via DA –> 02 of blood + decreased shunting means this valve can close
5. higher blood flow through pulm system –> higher filling & stroke vol of L heart –> higher P in L ventricle –> stop shunting of blood RA > LA via FO, thus also closes

Question 4

describe what is happening to the fetus in utero (in terms of the lungs) that is important for survival after birth.

Answer 4

• foetal lung liquid produced in the lung
• this is switched off by Adrenaline surge at birth. Removed by lymphatics, pulm vasc, squeezing head through canal at birth
• breathing via small diaphragmatic contractions
• asphyixa = gasp of air –> potetially resulting in swallow of amniotic fluid / mesoconium
• Breathing stimuli: cooling, chemical (pH, O2, CO2), pain/sound etc.
• Surfactant need to reduce surface tension lung, prevent airway collapse –> produced around 34wks via cortisol –> thus prem babies need steroids –> no surfactant = Resp DIstress Syndrome (HMB)

Question 5

describe what is happening to the fetus in utero (in terms of the gut & kidney) that is important for survival after birth.

Answer 5

GUT

• fetus swallows amniotic fluid around wk 22wks + –> produce dilute urine
• mesoconium produced times of stress

KIDNEY

• dilute urine produced by kidneys –> amniotic fluid
• no kidneys / poorly functioning –> oligohydramnios
• glycosuria (GDM) –> polyuria –> polyhydramnios