What are alveoli?

Alveoli are tiny sacs of lung tissue specialized for gas exchange, playing a crucial role in the respiratory system. They provide a large surface area where oxygen from inhaled air can diffuse into the blood, while carbon dioxide from the blood can move into the alveoli to be exhaled. This efficient exchange occurs due to the thin walls of the alveoli and their extensive network of capillaries, allowing for rapid transfer of gases. Their structure supports optimal gas exchange, making them essential for breathing and overall respiratory function.

In contrast, the other choices do not accurately describe alveoli. Tissues that produce vocal sounds involve the vocal cords, while muscles that help in breathing refer to the diaphragm and intercostal muscles, which assist with inhalation and exhalation. Additionally, parts of the trachea are involved in directing airflow but do not participate in gas exchange like alveoli do. Therefore, the correct choice rightly identifies the unique and vital function of alveoli within the lungs.