Which of the following is the correct order of the protective meningeal layers of the brain from inside to outside?.

The correct answer is: c. Air flows into the lungs.

Choice A: A pneumothorax forms, collapsing the lungs.

A pneumothorax occurs when air enters the pleural space, the area between the lung and the chest wall, causing the lung to collapse. This condition is typically caused by trauma or a spontaneous rupture of a lung bleb, not by a drop in lung pressure below atmospheric pressure. When the pressure in the lungs drops below atmospheric pressure, it facilitates the inflow of air into the lungs, not the collapse of the lungs.

Choice B: The bronchioles constrict, causing respiratory distress.

Bronchiolar constriction, or bronchoconstriction, is a narrowing of the airways in the lungs due to the tightening of surrounding smooth muscle. This can cause respiratory distress and is commonly seen in conditions like asthma. However, this is not directly related to the pressure changes in the lungs relative to atmospheric pressure. The primary effect of a drop in lung pressure below atmospheric pressure is the inflow of air, not bronchoconstriction.

Choice C: Air flows into the lungs.

When the pressure in the lungs drops below atmospheric pressure, a pressure gradient is created that allows air to flow into the lungs. This process is known as inspiration or inhalation. The diaphragm and intercostal muscles contract to increase the volume of the thoracic cavity, thereby decreasing the pressure within the lungs relative to the outside atmosphere, causing air to rush in.

Choice D: Air flows out of the lungs.

Air flows out of the lungs, or expiration, occurs when the pressure inside the lungs exceeds atmospheric pressure. This happens when the diaphragm and intercostal muscles relax, decreasing the volume of the thoracic cavity and increasing the pressure within the lungs. This is the opposite of what happens when lung pressure drops below atmospheric pressure.

Choice A rationale:

Vasodilation increases the diameter of blood vessels, which decreases resistance and thus decreases pressure. However, the increased diameter allows for increased blood flow, not decreased.

Choice B rationale:

Vasodilation decreases pressure due to the increased diameter of the blood vessels, and it increases flow because of the reduced resistance to blood flow.

Choice C rationale:

Vasodilation does not increase pressure; it decreases it.

Choice D rationale:

While vasodilation decreases pressure, it does not decrease flow; it increases it.