Question

multiple choice question
what effect does contraction of the diaphragm have on intra - alveolar pressure?
o increases intra - alveolar pressure
o decreases intra - alveolar pressure

Explanation:

When the diaphragm contracts, it moves downward. This increases the volume of the thoracic cavity. According to Boyle's law ($PV = k$, where $P$ is pressure, $V$ is volume, and $k$ is a constant), when volume ($V$) increases, pressure ($P$) decreases (assuming temperature is constant). Since the alveoli are within the thoracic cavity, an increase in thoracic cavity volume (due to diaphragm contraction) leads to a decrease in intra - alveolar pressure. This pressure difference (lower intra - alveolar pressure compared to atmospheric pressure) causes air to flow into the lungs (inspiration).

Answer:

decreases intra - alveolar pressure