Final answer:
In the absence of any shunt, alveolar blood flow depends on the pressure difference between the alveoli and blood vessels. The partial pressure of oxygen in alveolar air is about 104 mm Hg, while the partial pressure of oxygenated blood in pulmonary veins is about 100 mm Hg.
Step-by-step explanation:
In the absence of any shunt, alveolar blood flow relies on the pressure difference between the alveoli and the blood vessels. The partial pressure of oxygen in alveolar air is about 104 mm Hg, while the partial pressure of oxygenated blood in pulmonary veins is about 100 mm Hg. When ventilation is sufficient, oxygen enters the alveoli at a high rate, maintaining a high partial pressure of oxygen in the alveoli. This allows for efficient diffusion of oxygen across the respiratory membrane into the bloodstream.
However, in cases of insufficient ventilation, the partial pressure of oxygen in the alveoli drops, affecting gas exchange. To compensate, the body redirects blood flow to well-ventilated alveoli by constricting pulmonary arterioles serving dysfunctional alveoli and dilating arterioles serving well-ventilated alveoli. This redistribution of blood flow ensures that alveoli with sufficient ventilation receive adequate blood supply for gas exchange.