The lungs are an organ made up of different types of tissues that work together to facilitate gas exchange. Squamous epithelium lines the alveoli and is thin and flat, allowing for efficient gas exchange between air and blood. Goblet cells in the lungs secrete mucus that traps dirt and bacteria inhaled through the air. Ciliated epithelium contains cilia that beat in rhythm to move the mucus and trapped particles up the trachea where they are swallowed and destroyed in the stomach, preventing lung infections. Damage from cigarette smoke can impair the cilia's ability to clear mucus, leading to coughing and increased susceptibility to lung infections in smokers.

1. The lungs

6. Squamous epithelium

8. Goblet cells