Question

Compared to the atmospheric air, the alveolar air has
(a) More ${ pO }_{ 2 }$ and less { pCO }_{ 2 }
(b) Less ${ pO }_{ 2 }$ and more { pCO }_{ 2 }
(c) More ${ pO }_{ 2 }$ and more { pCO }_{ 2 }
(d) Less ${ pO }_{ 2 }$and less { pCO }_{ 2 }

Answer 1

Hint: There are a continuous Oxygen and Carbon dioxide exchange going on between the lungs and the atmospheric air, oxygen is inhaled into the alveoli from the atmosphere because of the lesser oxygen content in the alveoli, and carbon dioxide is exhaled due to increased accumulation of carbon dioxide in the lungs.

Complete step by step answer:
The partial pressure of alveolar oxygen is lower than the atmospheric partial pressure of oxygen for the following two reasons. The air which enters the lungs is already humidified by the respiratory tract and thus the partial pressure of water vapor (47 mmHg) reduces the oxygen partial pressure to about 150 mmHg. The residual difference is a result of continuous oxygen uptake by the pulmonary capillaries and the continual diffusion of ${ CO }_{ 2 }$ out of the capillaries into the alveoli.
The rate of total body consumption of oxygen and ${ CO }_{ 2 }$ production has a huge impact on the partial pressure of these gases in the alveoli.
When the ratio of carbon dioxide production to alveolar ventilation increases above normal values – greater than 45mmHg the condition is called Hypoventilation and if it is associated with pH less than 7.35 it is termed as respiratory acidosis.
Similarly, when the ratio decreases to less than 35mm of hg, the condition is termed Hyperventilation, and if it is associated with pH greater than 7.45 it is called respiratory alkalosis.
So, the correct answer is ‘less ${ pO }_{ 2 }$ and more ${ pCO }_{ 2 }$’

Note: The alveoli consist of thin-walled parenchyma cells which are just about one wall thick, they represent tiny bubbles floating in the lung parenchyma. The alveoli are the tiny air sacs where the actual exchange of atmospheric air occurs between pulmonary capillaries and the alveolar air.