Which blood vessels connect the two sides of the vascular system?.

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:

Sinusoids are a type of capillary found in some organs, such as the liver, bone marrow, and spleen. They are not vessels that carry blood away from the heart.

Choice B rationale:

Veins are blood vessels that carry blood from the body back into the heart.

Choice C rationale:

Capillaries are delicate blood vessels that deliver blood, nutrients and oxygen to cells throughout the body. They do not carry blood away from the heart.

Choice D rationale:

Arteries are blood vessels that carry oxygenated blood away from the heart to the body.