Gas Exchange

Reference: Guyton 14th; P- 515

Davidson 24th

Respiratory gases pass through the alveolar capillary membrane by passive diffusion.

Zones 1, 2, and 3 of Pulmonary Blood Flow
The capillaries in the alveolar walls are distended by the blood pressure inside them but simultaneously are compressed by the alveolar air pressure on their outsides. Therefore, whenever the lung alveolar air pressure becomes greater than the capillary blood pressure, the capillaries close, and there is no blood flow.
Under different normal and pathological lung conditions, one may find any one of three possible zones (patterns) of pulmonary blood flow, as follows:

Zone 1: No blood flow during all portions of the cardiac cycle because the local alveolar capillary pressure in that area of the lung never rises higher than the alveolar air pressure during any part of the cardiac cycle
Zone 2: Intermittent blood flow only during the peaks of pulmonary arterial pressure because the systolic pressure is then greater than the alveolar air pressure, but the diastolic pressure is less than the alveolar air pressure
Zone 3: Continuous blood flow because the alveolar capillary pressure are remains greater than alveolar air pressure during the entire cardiac cycle

Normally, the lungs have only zones 2 and 3 blood flow-zone 2 (intermittent flow) in the apices and zone 3 (continuous flow) in all the lower areas.

কোন ব্যাখ্যা যোগ হয় নি।

কোন ব্যাখ্যা যোগ হয় নি।

Davidson 24th

The ultimate goal of respiration is to maintain proper concentrations of O2, CO2 & H+

[Ganong 24th p-643]

Reference: Guyton 14th; P- 533

Reference: Guyton 14th; P- 526

Reference: Guyton 14th; P- 528

Guyton 13 th page 522

Va/Q is infinity : No perfusion but ventilation remains normal.
Causes:
1. Embolism
2. Emphysema
3.Bronchiectasis

Reference: Guyton 14th; P- 513

Explanation: