<prompt> If PaeryPalveolusPvein, under normal circumstances, which zone of the lung is being described?Zone IZone IIZone IIIZone IV  <response>: Zone I no blood flow Palv PaPvein Zone II intermittent blood flow, i.e., during systole - Pa, capPalvPvein, Zone III continuous blood flow PaPveinPalv These zones get created due to the interplay between alveolar pressure and the pressure in the pulmonary vessels. - In the recumbent posture, entire lung has zone III type of blood flow as hea would not have to pump blood against gravity to any region of the lung. 