Which of these correctly ranks the normal pressure values in the atmosphere (atm), alveoli (alv), and intrapleural space (ip) when a person is resting at functional residual capacity (FRC) ?

Patm = Palv> Pip

Patm>Palv> Pip

Patm < Palv < Pip

Patm = Palv = Pip

Patm = Palv < Píp

Correct answer is A

Explanation

This is because whenever the alveolar is at rest, it's pressure = 0 since it is measured in relation to the atmospheric P, therefore, Patm = Palv

However, When the intrapleural P at rest, it's pressure Pip < 0 i. e Negative

because of the competing forces on the intrapleural cavity

Patm = Palv>pip

Explanation:

The functional residual capacity is the volume of air that is in the lungs after an expiration. After an expiration there is still air in our lungs but as the atmosphere pressure (Patm) and the alveoli pressure (Palv) are balanced no air goes in or out, in order to expulse more air a forced expiration is needed where the Palv increases and the Patm decreases. The pressure in the intrapleural space (Pip) is always negative, it will be higher than the alveoli pressure if there is a problem such as water or air in the intrapleural space.