PATHOLOGY

Detailed explanation-1: -The air in the lungs has a higher concentration of oxygen than that of oxygen-depleted blood and a lower concentration of carbon dioxide. This concentration gradient allows for gas exchange during respiration. Partial pressure is a measure of the concentration of the individual components in a mixture of gases.

Detailed explanation-2: -Since carbon dioxide is expired, the partial pressure of carbon dioxide within the lungs should be greater than that of the expired air. Therefore during expiration, the carbon dioxide concentration in the alveolar air is greater than that in the expired air.

Detailed explanation-3: -A low alveolar oxygen tension increases pulmonary vascular resistance (hypoxic pulmonary vasoconstriction), and a high alveolar oxygen tension decreases pulmonary vascular resistance.