15 Fetal Physiology Flashcards
The uterine arteries bathe the chorionic villi in maternal blood via the umbilical veins and arteries. Which of these carries oxygenated blood?
Outline how the fetus receives enough oxygen despite the increase in maternal blood pH which would shift the oxygen dissociation curve to the left (increase maternal affinity for oxygen).
Increase in 2,3-BPG produced
Oxygen dissociation curve shifts right
Promote release to fetus
Fetal blood has lower partial pressure of oxygen
How does fetal haemoglobin differ from normal haemoglobin? When is fetal haemoglobin predominant (ie which week)?
Fetal haemoglbin doesn’t bind to 2,3-BPG - so greater affinity for O2
Predominant: from week 12
2 alpha and 2 gamma subunits
Explain what the Bohr effect is and how this speeds up oxygen transfer from the mother to the fetus
-
Double bohr effect
- CO2 passes into intervillous blood- pH decrease- decreased affinity for O2 in mother
- Fetus giving up CO2- increased pH- increase affinity for oxygen
Explain how CO2 is able to transfer from the fetus to the mother.
Proggesterone induced Hyperventilation
Lower conc of CO2 in maternal blood- gradient allows gas exchange
What is the haldane effect?
- Maternal Hb gives up oxygen- accepts increasing amounts of CO2
- Fetal Hb gives up more CO2 as oxygen accepted
What is fetal distress? Explain how it can occur and give a specific cause of it.
Compromise of the fetus due to inadequate oxygen or nutrient supply
Fetal response to hypoxia
Vagal stimulation–> BRADYCARDIA
Specific cause:
Smoking- chronic hypoxaemia- intrauterine growth restriction
Describe the 3 shunts that occur in the cardiovascular system of the fetus:
Why is it important that the majority of the blood in fetal circulation bypasses the liver?
- Live is proportionately very large- could potentially consume whole fetal circulation
- To maintain high level of oxygen arriving to brain and rest of body
What happens to the foramen ovale at birth?
In fetus: pressure in right atrium higher than left- blood shunts
At birth: pressure reverses- foramen ovale shunts
Which of the following processes is predominant in each of the trimesters: Hyperplasia or Hypertrophy
Differentiate between symmetrical and asymmetrical growth restriction. What can cause growth restriction of the fetus?
Cause: maternal malnutrition
What are the functions of amniotic fluid? What is it composed of?
- Lung development substances
- Mechanical protection
Composition:
- Electrolytes
- Creatinine
- Urea
- Bile pigments
- Renin
- Glucose
- Hormones
- Fetal cells
- Lanugo
- Vernix caseosa
How does the volume of amniotic fluid relate to the size of the fetus?
Size of fetus= directly proportional to volume of amniotic fluid
What is amniocentesis and what can it test for?
WHAT?
Apiration of amniotic fluid- contains fetal cells
TESTs?
Fetal karyotyping
Eg Down’s syndrome
Does amniocentesis carry a risk?
Yes= invasive and carries risk of miscarriage
What is meconium?
Earliest stool of infant
Debris from the GI tract- accumulates as meconium
Meconium staining is a clinical sign of fetal distress. Outline how this occurs.
Premature meconium release from GI tract
Fetus can potentially inhale it (meconium aspiration)
How is amniotic fluid produced? When does it start to be produced?
Essentially= fetal urine- starts at around 9 weeks
How is amniotic fluid recycled?
- Inhaling- fetus inhales fluid- helps lung development esp surfactant
- Swallowing- enters fetal GI tract
What is amniotic fluid composed of?
Water, electrolytes, fetal skin (lost in pregnancy)
Why do some babies get physiologically jaundice (less than 24hrs) ?
Delay in newborns ability to conjugate and excrete bilirubin
In utero clearance of fetal bilirubin= handled by placenta
What is the approximate pO2 of fetal blood?
4kPa
Useful diagram showing shunts:
List some of the hormones requird for fetal growth:
Apprximately how much amniotic fluid is there at 8 weeks and at 38 weeks gestation?
10ml- 8 weeks
1L- 38 weeks
Outline how amniotic fluid is recycled in the fetus:
