Fetal And Newborn Physiology Flashcards
Umbilical vein oxygen saturation
Where does blood flow from the umbilical vein
80%
Half through liver after merging with portal vein
Half through ductus venosus into ivc.
Oxygen Saturation of fetal ivc after joining of ductus venosus
Oxygen saturation of fetal svc
65%
25%
Flow from ivc and svc through the heart
Most ivc blood directed from RA through foramen ovale to LA and LV then pumped into systemic circulation
Most svc blood directed from RA to RV and pulmonary artery. Most of this then passes through ductus arteriosus into aorta
How much of fetal blood passes through the pulmonary circulation? Why?
10% due to very high PVR and patent ductus arteriosus
Oxygen saturation of blood supplying brain in fetus
What about supplying lower body
65% (same as ivc)
55% - mix of ivc blood now in aorta and svc blood through ductus arteriosus
Where do the blood vessels return to the placenta in the fetus? What proportion of fetal cardiac output is to the placenta?
From the internal iliacs
60%
How does fetal circulation change at birth?
Rapid fall in PVR
Blood flows from RV through the lungs
Clamping of the cord results in increased SVR
As a result reversal of flow through ductus arteriosus (aorta to pulmonary artery)
Higher pressure on left closes foramen ovale
Oxygenated blood and reduced prostoglandin E2 causes closure of ductus arteriosus
Ductus venousus closes possibly due to lack of blood flow
When does the ductus arteriosus close and obliterate
Effect of prematurity?
Closes at 24hrs
Obliterates by 3 weeks
Opens longer in prematurity
Drug that closes ductus arteriosus
Drug that keeps it open
Closes - indomethacin
Opens - prostaglandin E2
Effect on fetal cirucation of hypoxia
Very musclar pulmonary vessels
Vasoconstriction to hypoxia with increased PRV
Increased rv pressure
Reversal of shunt through foramen ovale
Difference between newborn and adult heart
Results in?
Poorly organised myofibril
Increased connective tissue
Limited contractility and compliance
Flat starling curve
Responds poorly to both low and high preload
Significantly higher heart rate and lower Bp
Incomplete sympathetic innervation to heart and vessels
Less BP drop in spinal, less response to vasopressors
Why does the developing fetus make breathing movements
Develop muscles
What happens to fluid in fetal lungs as term approaches?
Catecholamines and T3 stimulate reabsorption
Passage down birth canal stimulates further final absorption
When does surfactant production begin?
What stimulates it
26 weeks gestation
Cortisol
What are the differences between a newborn and adult lung
Lack of alveoli
Increased compliance of chest wall
Very compressible chest wall
Horizontal ribs
Less slow twitch muscle - rapid fatigue
