In quiet breathing, what occurs to alveolar pressure as inspiration takes place?

• A. Increases
• B. Decreases
• C. Remains constant
• D. Fluctuates

Answer: (B)

During quiet breathing, as inspiration occurs, the diaphragm and intercostal muscles contract, leading to an expansion of the thoracic cavity. This increase in volume results in a decrease in alveolar pressure. According to the principles of gas laws, as the volume of the thoracic cavity increases, the pressure within that cavity (and therefore in the alveoli) decreases, allowing air to flow into the lungs. This is essential for ventilation, as air moves from an area of higher pressure (the atmosphere) to an area of lower pressure (the alveoli). Thus, the decrease in alveolar pressure is a key mechanism that facilitates the intake of air during the inspiratory phase of quiet breathing.