What buffering system in the blood helps maintain pH by converting carbon dioxide into bicarbonate?

A. Supporting the alveoli: Alveoli are supported by elastic fibers in the lung parenchyma, not by smooth muscle. Their primary function is gas exchange, and structural support is provided by connective tissue, not the muscular walls of bronchioles.

B. Facilitating gas exchange: Gas exchange occurs across the alveolar-capillary membrane, not within the bronchioles. While bronchioles conduct air to the alveoli, smooth muscle does not directly participate in oxygen or carbon dioxide diffusion.

C. Altering diameter and resistance of airflow: Smooth muscle in the walls of bronchioles contracts or relaxes to regulate airway diameter, directly affecting airflow resistance. Bronchoconstriction decreases airflow, while bronchodilation increases airflow, allowing the respiratory system to respond to physiological demands, such as exercise or allergic reactions.

D. Preventing the collapse of airways: Cartilage, present in larger bronchi, provides structural rigidity to prevent airway collapse. Bronchioles lack cartilage; smooth muscle helps regulate airflow but does not fully prevent collapse under negative pressure.

E. Producing mucus for the mucociliary escalator: Mucus is secreted by goblet cells and submucosal glands, not by smooth muscle. The smooth muscle primarily regulates airway caliber rather than producing secretions.

A. Digesting food: The glottis is part of the larynx and is not involved in digestion. Its structure—including the vestibular (false) folds, vocal (true) folds, and the rima glottidis (space between)—plays no role in mechanical or chemical breakdown of food, which occurs in the oral cavity, stomach, and intestines.

B. Filtering air: While the upper respiratory tract contributes to filtering air, the glottis itself does not filter particles. Filtration is primarily carried out by nasal hairs, mucus, and cilia in the upper airway; the glottis functions as a passageway for air and a regulator of airflow into the trachea, not as a filter.

C. Circulating blood: The glottis has no role in the circulatory system. Blood circulation is managed by the heart and vascular system, whereas the glottis is a respiratory and phonatory structure, serving entirely different physiological functions.

D. Producing sound and breathing: The glottis is essential for phonation and respiration. Air passing through the space between the vocal folds produces sound, while the vestibular folds help protect the airway. The glottis also regulates airflow during inhalation and exhalation, making it integral to both breathing and voice production.