Clara cell

Clara cells are a type of secretory cell found in the bronchioles of the lungs. They are located in the terminal bronchioles, which are the last purely air-conducting airways before the gas-exchanging alveoli begin. Clara cells replace goblet cells in these smaller airways and are responsible for secreting a fluid that helps to protect the lung tissue. This fluid is part of the mucociliary escalator, a mechanism that clears inhaled particles from the airways.1

The lungs contain approximately 300 million pulmonary alveoli, which are tiny air spaces where the exchange of carbon dioxide and oxygen occurs between the blood and the air. The walls of the alveoli are very thin and lined with flat cells, and they are surrounded by capillaries. This structure, along with a large internal surface area, facilitates efficient gas exchange through diffusion.2