Contraction of diaphragm

Options

A. Increases intra-alveolar pressure resulting in exhalation
B. Decreases intra-alveolar pressure resulting in exhalation
C. Increases intra-alveolar pressure resulting in inhalation
D. Decreases intra-alveolar pressure resulting in inhalation

Answer

### Step-by-Step Solution:

1. **Understanding Diaphragm Function**: The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. Its primary role is in the process of breathing.

2. **Diaphragm Contraction**: When the diaphragm contracts, it moves downward. This contraction occurs during the process of inhalation.

3. **Effect on Thoracic Cavity Volume**: As the diaphragm contracts and moves downward, the volume of the thoracic cavity increases.

4. **Impact on Intra-Alveolar Pressure**: According to Boyle's Law, when the volume of a container increases, the pressure within that container decreases. Therefore, as the thoracic cavity volume increases due to diaphragm contraction, the intra-alveolar pressure (the pressure within the alveoli of the lungs) decreases.

5. **Air Flow into the Lungs**: The decrease in intra-alveolar pressure creates a pressure gradient between the atmosphere and the alveoli. This gradient causes air to flow into the lungs from the outside environment.

6. **Conclusion**: Based on the above points, the contraction of the diaphragm decreases intra-alveolar pressure, resulting in inhalation. Therefore, the correct answer to the question is option D: "decreases intra-alveolar pressure resulting in inhalation."