The human lungs are essential respiratory organs situated in the thoracic cavity, protected by the rib cage and surrounded by the pleura, a double-layered membrane. They are divided into lobes, with the right lung having three and the left lung two, accommodating the heart. Air enters through the nose or mouth, passing through the nasal and oral cavities, pharynx, larynx, trachea, bronchi, and bronchioles, finally reaching the alveoli, where gas exchange occurs.

 

During inhalation, the diaphragm and intercostal muscles contract, expanding the thoracic cavity and drawing air in, while exhalation involves relaxation of these muscles and expulsion of air. In the alveoli, oxygen diffuses into the capillaries and carbon dioxide diffuses out to be exhaled. Breathing is regulated by the brainstem's respiratory center, responding to changes in blood levels of gases and pH.

 

The lungs also have protective mechanisms, including cilia, mucus, the cough reflex, and immune cells like alveolar macrophages. Various conditions, such as asthma, COPD, pneumonia, lung cancer, and pulmonary fibrosis, can impair lung function, highlighting the importance of understanding lung operation for maintaining respiratory health.