Describe how gas exchange is influenced across the placenta near the term of pregnancy.

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College Answer

For a good answer candidates were expected to account how the placenta allows for effective
diffusion to occur. Good answers incorporated the parameters within the Fick equation (eg.
area of placental gas exchange, pressure of gas in maternal sinuses (PO2 = 50 mmHg),
pressure of gas in umbilical vein (PO2 = 30 mmHg ). Also expected was an explanation of
the role of foetal haemoglobin, the double Bohr and double Haldane effects. These were
commonly omitted.
Syllabus – O12d
Reference: Power and Kam p354