When the diaphragm and external intercostal muscles contract: choose one• none of these conditions would occur• intrapleural pressure decreases• intrapulmonary pressure increasesO expiration occurs• volume of the lungs decreases

The correct answer is: intrapleural pressure decreases.

Here's the step by step explanation:

1. The diaphragm and external intercostal muscles are the primary muscles involved in breathing.

2. When these muscles contract, the size of the chest cavity increases.

3. An increase in the size of the chest cavity causes a decrease in the pressure inside the chest cavity (intrapleural pressure).

4. This decrease in pressure allows air to flow into the lungs, causing inhalation.

So, when the diaphragm and external intercostal muscles contract, the intrapleural pressure decreases.

Intrapleural pressure decreases.

The correct answer is "intrapleural pressure decreases".

Step 1: Understand the question. The question is asking what happens when the diaphragm and external intercostal muscles contract.

Step 2: Know the function of the diaphragm and external intercostal muscles. The diaphragm and external intercostal muscles are involved in the process of breathing. When they contract, they help to expand the chest cavity.

Step 3: Understand the effects of the contraction of these muscles. When the diaphragm and external intercostal muscles contract, the chest cavity expands. This expansion decreases the pressure inside the chest cavity, specifically the intrapleural pressure.

Step 4: Choose the correct answer. Therefore, when the diaphragm and external intercostal muscles contract, the intrapleural pressure decreases.