- The lungs are a pair of spongy, air-filled organs located within the thoracic cavity, on either side of the heart, and are the primary organs of the respiratory system. Their chief function is to facilitate the exchange of gases, specifically the intake of oxygen (O₂) and the removal of carbon dioxide (CO₂), a process essential for cellular respiration and metabolic function throughout the body.
- Protected by the rib cage and separated from the abdominal cavity by the diaphragm, the lungs operate in close coordination with the cardiovascular system to maintain homeostasis.
- Anatomically, the lungs are divided into lobes—three in the right lung (superior, middle, and inferior) and two in the left lung (superior and inferior), with the left lung slightly smaller to accommodate the position of the heart. Each lung is enclosed in a double-layered pleural membrane: the visceral pleura, which adheres to the lung surface, and the parietal pleura, which lines the chest wall. The space between them, the pleural cavity, contains a thin film of fluid that reduces friction during breathing and creates surface tension that aids lung expansion.
- Air enters the body through the nose or mouth, passes through the pharynx, larynx, and trachea, and enters the lungs via the bronchi. These bronchi further divide into smaller bronchioles, ending in microscopic air sacs called alveoli. Each lung contains approximately 300 million alveoli, providing a vast surface area (around 70 square meters in adults) for efficient gas exchange. The walls of the alveoli are extremely thin and surrounded by a dense network of capillaries. Oxygen diffuses across the alveolar membrane into the blood, where it binds to hemoglobin in red blood cells, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.
- The act of breathing, or pulmonary ventilation, is primarily driven by the diaphragm and intercostal muscles. When the diaphragm contracts and moves downward, the thoracic cavity enlarges, reducing pressure inside the lungs and allowing air to flow in (inhalation). When the diaphragm relaxes, the cavity decreases in volume, increasing pressure and pushing air out (exhalation). This rhythmic movement ensures a constant exchange of gases that supports metabolic activity in every tissue.
- The lungs also play important secondary roles beyond gas exchange. They help regulate blood pH by controlling CO₂ levels, filter small blood clots and air bubbles, and serve as a reservoir for blood. Specialized cells within the respiratory tract, including goblet cells and ciliated epithelial cells, contribute to innate immunity by producing mucus and sweeping out inhaled particles and pathogens. Alveolar macrophages further patrol the lungs to engulf and digest harmful debris or microbes.
- Various diseases can impair lung function, including asthma, chronic obstructive pulmonary disease (COPD), pneumonia, pulmonary fibrosis, and lung cancer. Environmental factors such as smoking, air pollution, and occupational exposure to dust or chemicals can contribute significantly to respiratory disease. Advances in medical imaging, pulmonary function tests, and therapies—including bronchodilators, corticosteroids, oxygen therapy, and even lung transplantation—have improved the diagnosis and treatment of many pulmonary conditions.
