Flashcards in Repro 9.1 fetal physiology. Deck (37):
Where does materno-foetal exchange occur?
At the placenta, at the tips of the chorionic villi.
What is the function of the umbillical vein?
To carry oxygenated blood from the placenta to the fetus
What is the function of the umbillical artery?
To carry de-oxygenated blood from the fetus to the placenta
How do the maternal and fetal pO2 levels differ?
The maternal pO2 is much greater than the fetal pO2.
The maternal pO2 increases marginally during pregnancy, but the fetus' pO2 i much lower in general.
What is the approximate pO2 of the fetus compared to maternal pO2?
What factors increase fetal O2 content?
-fetal haemaglobin variant
-higher concentration of haemaglobin.
Give some features of fetal haemaglobin which help to increase O2 content of the fetus:
-Contains 2 alpha and 2 gamma subunits
-has a higher affinity for oxygen than adult haemaglobin
-doesn't bind 2,3 DPG as effectively as adult haemaglobin, which normally leads to decreased O2 affinity, therefore affinity is not affected.
Explain the double bohr effect seen during pregnancy:
-CO2 passes from the fetus to the mother.
-fetal blood becomes less acidic due to loss of CO2, this shifts the ODC to the left, promoting O2 uptake.
-maternal blood becomes more acidic due to increased CO2 content, leading to a shift of the ODC to the right, and promoting loss of O2.
(Basically on one side youre wanting to give O2 up, and on the other side you're wanting to accept it.)
How is the maternal CO2 level compared to the fetal CO2 level and how is this maintained?
Maternal pCO2 is lower than the fetal pCO2.
Progesterone dives hyperventilation, which increases exhalation of CO2, so maternal blood CO2 remains low.
Describe the double Haldane effect:
As Hb gives up O2, it can accept CO2 more readily.
So as maternal Hb is giving up O2, it is accepting the CO2 from the fetus,
likewise as the fetus is giving up CO2, it can accept O2 from the mother.
There is no change in the local maternal concentration of CO2 because it is going from fetal blood to being bound to Hb.
What shunts are seen in the fetus?
What is the function of the ductus venosus?
Shunts blood from the umbilical vein to the IVC, bypassing the liver.
If this didn't exist, the liver, which is very metabolic, would use a large amount of the O2 in the blood, so there wouldn't be enough left for development of the fetus.
What is the adult remenant of the ductus venosus?
ligamentum venosum, which runs within the ligamentu teres of the liver.
What is the function of the foreamen ovale?
Conducts blood from the RA (which has high pressure) to the LA (lower pressure) to avoid most of the blood travelling to the lungs, which are delicate so would become damaged, and are non functioning.
Why doesn't the foreamen ovale persist once born?
Baby takes first breath, which increases the pressure in the left side of the heart, which pushes the leaves of the shunt closed.
Does all the blood bypass the lungs?
No, a small amount of blood must travel through the RV, the pulmonary artery to the lungs, to aid their development.
What are the functions of the LA during fetal life?
Accepts the blood which has shunted through the foreamen ovale.
Also gets a small amount of pulmonary venous return from the lungs, which is deoxygenated (no breathing occuring during gestation) which gets pumped to the LV and to the aorta.
Which organs get the largest proportion of O2 in the fetus?
Which anatomical feature supports this?
-Ductus arteriosus joins the aorta after branches for the brain and heart have happened. Blood returning through the ductus arteriosus is deoxygenated, so by making branches to the heart and brain before this, the pO2 isn't affected by the deoxygenated return.
What is the function of the Ductus arteriosus?
Shunts blood from the pulmonary trunk and the right ventricle to the aorta.
This shunt happens after the branches supplying the head and heart are made, to reduce the effect of the addition of de-oxygenated blood.
What is the fetal response to transient drops in pO2?
detected by th chemoreceptors
leads to stimulation of vagal activity
reduction in heart rate (to reduce O2 demands)
Also get redistribution of flow to prioritise the heart and brain, reducing blood flow to the GIT, kidneys and limbs)
What are the effects of chronic hypoxaemia on the fetus?
Can lead to growth restrictions
behavioral changes such as reduced movement, impaired development.
What hormones are necessary for fetal growth?
-Insulin like growth factors:
--- IGF I-nutrient dependant, dominates in timesters 2, 3
--- IGF II- nutrient independant, dominates in trimester 1
What can be the effects of malnutrition on fetal growth?
-Can lead to symetrical or asymetrical growth restriction
-Can lead to changes for health in later life although not well understood, (epigenetics, barker hypothesis)
What are the dominant cellular growth mechanisms in the different trimesters in pregnancy?
1st trimester- hyperplasia
2nd trimester- hyperplasia and hypertrophy
3rd trimester- hypertrophy
What is the function of amniotic fluid?
Mainly protection for the fetus
-contributes to lung development
What is the volume of amniotic fluid at:
8 weeks- around 10ml
38 weeks- around 1 litre
What happens to the volume of amniotic fluid after 38 weeks and why?
It's volume depletes, the placenta has a built in time scale of 38 weeks, after which its function diminishes.
How does amniotic fluid help with development of the lungs?
Whilst in the amniotic fluid, the fetus does some 'practice breaths' in which amniotic is inhaled into the lungs and aids the development.
What is the composition of amniotic fluid?
electrolytes, creatinine, urea, glucose, bile pigments, lanugo, vernix caseosa
What is the function of lanugo?
It's a fine hair coverring which covers the fetus.
What is the function of vernix caseosa?
Waterproofs the fetus' skin to help protect it.
How is amniotic fluid produced and recycled?
produced through the kidneys and urination,
recylced via lung movements, swallowing, and the placental and fetal membranes.
What is meconium?
The debris of the amniotic fluid as it passes through the GI tract. Shouldnt be released until after birth.
What are some complications of meconium being passed before birth?
-due to practice breathing it can lead to respiratory distress
-the presence of the meconium into the amniotic fluid can cause distress of the child.
-the amniotic fluid will become tinged yellow/green.
What is amniocentesis?
Sampling of the amniotic fluid using a probe that is ultrasound guided.
allows collection of fetal cells which can be used for genetic testing.
Safer than chorionic villus sampling which carries a higher mortality rate.
How is billirubin metabolism conducted in the fetus and why?
via the placenta,
The fetus has no way of excreting billirubin, so it doesnt conjugate it which allows it to be transfered to the placenta and to the mothers circulation.