Gases move freely across the walls of the bronchioles into the capillaries that surround them.

Bronchioles

The small airway passages in the lungs that extend from the bronchi and lead to the air sacs (alveoli).

Capillaries

The smallest blood vessels in the body, responsible for the exchange of various substances between the blood and surrounding tissues.

Gases

States of matter consisting of particles that have neither a defined volume nor shape, expanding to fill their container.