Physiology

Question 1

How do changes in oxygen concentration differently affect the pulmonary arterioles and the systemic arterioles?

Answer 1

Increased oxygen concentration causes pulmonary arterioles to dilate, but systemic arterioles to constrict
Decreased oxygen concentration causes pulmonary arterioles to constrict, but systemic arterioles to dilate

Question 2

How do the lungs achieve V/Q matching?

Answer 2

Increased perfusion results in increased concentration of CO2 in the alveoli - this causes bronchorelaxation, decreased airway resistance and increased ventilation to match perfusion
Increased ventilation leads to increased concentration of oxygen in alveoli - this causes vasodilation of pulmonary arteries to increase perfusion, matching the increased ventilation.

Question 3

What four factors influence the rate of gas exchange across alveolar membrane?

Answer 3

1. Partial pressure gradient of O2 and CO2
2. Diffusion coefficient of O2 and CO2
3. Surface area of alveolar membrane
4. Thickness of alveolar membrane

Question 4

What would a large difference between alveolar PO2 (PAO2) and arterial PO2 (PaO2) suggest?

Answer 4

Problem with gas exchange in the lungs or a right to left shunt in the heart.

Question 5

What is apneusis and what prevents it?

Answer 5

apneusis is prolonged inspiratory gasps with short expiration - prevented by the pneumotaxic centre which is stimulated when the dorsal respiratory neurones fire - firing inhibits inspiration, preventing apneusis.