Foetal Physiology Flashcards
Explain why the umbilical vein carries oxygenated blood but is still called a vein. (2)
Because it is returning blood to the heart of the foetus, it’s just that this blood has come directly from the placenta rather than the having travelled around the body.
Explain why 2,3-BPG needs to be increased in pregnancy. (6)
Progesterone causes hyperventilation, which causes respiratory alkalosis and a raise in pH. This would move the curve to the left to increase the mothers affinity to oxygen.
However, this would mean that the foetus would get no oxygen, so maternal 2,3-BPG is increased to move the curve back to the right and reduce the maternal affinity for oxygen.
Explain the differences between foetal and maternal haemoglobin. (3)
HbF is made from two alpha and two gamma subunits, meaning it has a greater affinity for oxygen because it cannot bind 2,3-BPG. This means that the foetus can still get oxygen even in the relatively hypoxic environment.
Explain the double Bohr effect. (5)
Mother - as CO2 passes into the intervillous blood, the pH will decrease, causing a decreased affinity for oxygen here, meaning more oxygen will diffuse across the boundary into foetal blood.
Foetus - because the foetus is giving up its CO2 to the intervillous blood, the pH there increases, causing it’s affinity for oxygen to increase, so it can bind all of the oxygen moving from the maternal blood.
Explain why smoking can cause foetal distress or growth restriction. (4)
The foetal response to hypoxia is bradycardia to try to reduce the oxygen demand of the heart. This is called foetal distress. Smoking can cause chronic hypoxia, which short term can cause distress and long term can cause growth restrictions.
Explain the Haldane effect. (3)
Mother - as maternal blood gives up more O2, it has more room available to accept CO2.
Foetus - the foetal Hb gives up more CO2 as oxygen is accepted.
Describe the different stages of cellular development of a foetus. (3)
Weeks 0-20: hyperplasia of cells
Weeks 20-28: mix of hyperplasia and hypertrophy.
Weeks 28-term: mainly hypertrophy.
Describe the possible effects on the foetus of maternal malnutrition. (2)
Symmetrical growth restriction: all of the foetus is small.
Asymmetrical growth restriction: ‘head sparing’ - only the body is restricted.
Describe amniotic fluid:
Purpose (2)
Production (1)
Recycling (3)
Mechanical protection and contains substances vital for lung development.
Produced from foetal urine from the metanephros.
Recycling occurs as the foetus ‘inhales’ the amniotic fluid to help lung and surfactant development. Swallowing of the fluid helps clear the GI tract, and is excreted after delivery as meconium.
Describe physiological jaundice. (3)
The normal jaundice that occurs over 24 hours after birth as there is a delay in the ability to conjugate and excrete bilirubin. Pathological if before 24 hours.
