Session 9: Fetal Physiology Flashcards
Progesterones effect on ventilation in pregnancy.
Causes hyperventilation leading to the mother developing a physiological respiratory alkalosis.
Respiratory alkalosis in the mother would lead to increased pH and also increased maternal affinity for O2.
This is not favourable for giving up to the foetus. How is this resolved?
There is an increase in production of maternal 2,3-BPG to shift the dissociation curve back to the right to promote release of oxygen to the foetus.
Why is progesterone-driven hyperventilation then important for giving up oxygen to the foetus?
It leads to a lower conc. of CO2 in the maternal blood. This means that the gradient allows gas exchange of CO2 from foetus to mother and ultimately lowers CO2 conc. in the foetus. This makes haemoglobin giving up CO2 and having higher affinity for O2.
What is the haemoglobin in the foetus?
HbF 2 alpha and 2 gamma
Why is HbF in foetal circulation?
Has greater oxygen affinity because it does not bind 2,3-BPG as maternal Hb does.
Explain the double Bohr effect.
1 - As CO2 passes into intervillous blood the pH will decrease. This is in the maternal circulation leading to a decreased affinity for O2 in the mother.
2 - The foetus will give up CO2 leading to an increased pH in the foetus resulting in increased affinity for O2.
What is the Haldane effect?
Maternal Hb gives up O2 promoting binding to CO2.
Foetal Hb gives up CO2 promoting binding to O2.
What’s a possible foetal response to hypoxia?
Bradycardia via vagal stimulation.
This is done to reduced the O2 demand on the heart.
What is harmful about bradycardia in the foetus?
A part of fetal distress and can lead to intrauterine growth restriction.
Give a common cause of chronic hypoxaemia in foetus.
Smoking which can lead to intrauterine growth restriction.
Shunts in foetal circulation.
Ductus venosus (to bypass the liver)
Foramen ovale (to bypass the lungs and straight into LA)
Ductus arteriosus (to bypass the lung but still get some blood into the RV and then into aorta instead of lungs)
What hormones are key to foetal growth?
Insulin-like growth factors IGF-1 and IGF-2.
What type of growth happens to cells in the first trimester?
Hyperplasia
What type of growth happens to cells in the second trimester?
Hyperplasia and hypertrophy
What type of growth happens to cells in the third trimester?
Mainly hypertrophy
What type of growth restriction can maternal malnutrition cause?
Symmetrical growth restriction.
Asymmetrical growth restriction.
What is symmetrical growth restriction?
All parts of the fetus are small
What is asymmetrical growth restriction?
Called head sparing with growth restriction on the abdomen that will be smaller than head.
Purpose of the amniotic fluid?
Mechanical protection and also contains substances that are critical for lung development.
How does the volume of the amniotic fluid relate to the size of the foetus?
The volume is proportional to the size of the fetus.
How is amniotic fluid clinically relevant in utero?
It contains foetal cells so amniocentesis can be done which where you aspirate amniotic fluid for analysis.
Explain amniocentesis and its clinical relevance.
Aspiration of amniotic fluid.
This is important in foetal karyotyping for e.g. a definitive diagnosis for Down’s syndrome.
It is however invasive and carries a risk of miscarriage.
Give a clinical sign of fetal distress related to meconium.
Meconium staining
Explain what meconium staining is.
When meconium is prematurely released from the GI tract.
This can cause the fetus to inhale the meconium that has been released into the amniotic fluids.
This can lead to meconium aspiration
When does amniotic fluid production start?
At around 9 weeks.
(It is basically a production of urine)
Give two ways of how recycling of amniotic fluid is done.
Inhalation of amniotic fluid by the foetus to practice for breathing. This is also important for the production of surfactant.
Swallowing amniotic fluid so it enters the GI-tract of the foetus. Debris from the GI tract accumulate as the meconium.
Composition of amniotic fluid.
Water
Electrolytes
Common substances from urine
Foetal skin
Explain why there might be jaundice of a newborn.
There is sometimes a delay in a newborn’s ability to conjugate and excrete bilirubin.
However if this jaundice appears within 24 hours of partum then it can be indicative of a more serious pathology.
State more examples of hormones necessary for foetal growth.
IGF-I
IGF-II
Insulin
Leptin (placental prod)
EGF
TGFalpha
How is bilirubin metabolise in utero?
By the placenta as the fetus can’t conjugate bilirubin.
What is the crista dividens?
A crest found on the free border of septum secundum.
This leads the formation of two streams of blood flow. One that goes to LA (majority) and then a minor proportion going to the RV.
Fetal response to hypoxia
Increasing conc. of HbF
Redistribution of flow to heart and brain
Bradycardia to reduce O2 demand via vagal stimulation. (compared to in adults where tachycardia would ensue).
Growth restriction
Behavioural changes
