9.1 Fetal Physiology Flashcards
What type of blood is carries in the umbilical vein?
Oxygenated blood
What type of blood is carried in the umbilical arteries?
Deoxygenated
What adaptations are present to increase fetal partial pressure of O2?
Fetal haemoglobin variant
Fetal haematocrit is increased over that in the adult
Increased maternal production of 2,3 DPG
Double Bohr effect
What stimulated the increased maternal production of 2,3 DPG
Secondary to physiological respiratory alkalosis of pregnancy
When is HbF the predominant form of haemoglobin in the foetus?
At week 12
When does the foetus begin producing HbA?
Slowly produced from week 12
What is the subunits of HbF?
2 alpha subunits and 2 gamma units
Why does HbF have a higher affinity for oxygen than HbA?
As HbF doesn’t bing 2,3-DPG as effectively as HbA.
Therefore binds O2 at a higher affinity as doesn’t dissociate O2 as easily as HbA
What is the function of the double Bohr affect?
To speed up the process of O2 transfer at the placenta
What is the double Bohr affect?
- Decreased maternal Hb affinity for O2 - CO2 passes into intervillous blood vessels in the placenta. Causes decrease in pH. Bohr affect, O2 released
- Increased fetal Hb affinity for O2 - CO2 lost from umbilical arteries, causing pH to rise. Bohr affect. Increased affinity of fetal Hb for O2
How is the concentration gradient of CO2 between maternal and fetal blood maintained?
Progesterone driven hyperventilation causes mother to blow off CO2. Lowers pCO2 in maternal blood to maintain a concentration gradient where there is less pCO2 in the maternal blood
What is the double haldane effect seen in pregnancy?
- As maternal Hb releases O2 at the placenta, it can accept increasing amounts of CO2
- As foetus Hb releases CO2 at the placenta, it can accept O2.
This helps maintain the CO2 concentration gradient between maternal and foetal blood.
Why must foetal blood be oxygenated at the placenta?
As fetal lungs are non-functional
Where in the heart does oxygenated blood from the umbilical vein drain into?
RV
What are the fetal circulatory shunts?
Ductus venosus
Foramen ovale
Ductus arteriosus
Why does blood by pass liver?
As liver would consume much of the nutrients and oxygen that have just been gained from diffusion at the placenta. Important that this nutrients is available for other developing structures
What is the function of the ductus venosus?
Connects the umbilical vein to the IVC and then into the right atrium
Shunts the blood around the liver to maintain/preserve the pO2 and nutrient saturation for developing structures such as the brain.
What is the function of the foramen ovale?
Allows blood flow between right and left atrium
Right atrial pressure is greater than that in the left atrium
Forces leaves of FO apart and blood flows into LA and then into the aorta
What is the crista dividens?
A crest on the free border of the septum secundum
What is the function of the crista dividens?
Creates 2 streams of blood flow
Majority flows into the LA to be pumped around body
Majority goes into RV to ensure muscular development of the RV. Mixes with blood from the SVC (deoxygenated)
Describe the blood supply entering the left atrium in the foetus
- Small amount of pulmonary venous return - deoxygenated blood from development of the lungs
- Oxygenated blood through the foramen ovale.
What is the oxygen saturation of blood in the LA of foetus?
60%
Which structures get the largest amount of nutrients in the foetus?
Heart and lungs
What is the function of the ductus arteriosus?
By-passes developing pulmonary circulation
Shunts blood from RV and PT to aorta
Joins aorta distal to the supply
to the head (and heart), minimising drop in O2 saturation
How dos the foetus respond to hypoxia?
Adaptations to manage transient decreases in oxygenation
HbF and increased haematocrit
Redistribution of flow to protect supply to heart and brain (reducing supply to GIT, kidneys, limbs)
Fetal heart rate SLOWS in response to hypoxia to reduce O 2 demand
Fetal chemoreceptors detecting decreased pO2 or increased pCO2- Vagal stimulation leading to bradycardia in foetus
How does chronic hypoxaemia affect the foetus?
Growth restriction Behavioural changes (impacts development)
Where are most of the fetal hormones produced?
In the fetal liver
What is hypoxemia?
Insufficient oxygenation of the blood
What hormones are necessary for fetal growth?
- Insulin
- IGFI and IGFII
- IGF II nutrient independent, dominant in first trimester
- IGF1 nutrient dependent, dominates in T2 and T3
- Leptin (Placental production)
- Plus EGF, TGFa
What can malnutrition in pregnancy effect fetus?
Asymmetrical or symmetrical growth restriction
Nutritional and hormonal status during fetal life can influence health in later life.
Describe how cellular growth varies during fetal development?
0 - 20 weeks = hyperplasia
20 - 28 weeks = hyperplasia and hypertrophy
28 weeks to term = hypertrophy
What is the function of amniotic fluid?
Protection
Development of lungs
How does volume of amniotic fluid vary?
Increases throughout pregnancy
- 10ml at 8 weeks
- 1L at 38 weeks
What produces the amniotic fluid?
Fetal urine predominantly
Fetal lungs
Fetal GI tract
How is amniotic fluid recycled?
Placenta and fetal membranes (intramembranous pathway)
Swallowed (absorption of water and electrolytes)
What is the composition of amniotic fluid?
98% water
Plus electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones and fetal cells, lanugo and vernix caseosa
What is lanugo?
Fine hair that covers babies
What is the meconium?
Babies first stool after delivery. Debris of the amniotic fluid that accumulated in gut and intestinal secretions including bile. Green colour
Meconium can be passed prematurely in the amniotic fluid before birth. What is this a sign of?
Fetal distress.
What is amniocentesis?
Sampling of the amniotic fluid using a syringe through the abdomen guided by ultrasound. Allows collection of fetal cells that can be used for diagnostic testing. Often used for fetal karyotyping to indicate inherited disorders.
What can be used for diagnostic testing of fetus?
Amniotic fluid
Sample of chorionic villi (greater risk)
Why is physiological jaundice common in new born?
During gestation clearance of fetal bilirubin is handled efficiently by the placenta
Fetus cannot conjugate bilirubin
Immaturity of liver and intestinal processes for metabolism, conjugation and excretion
