Lungs

The lungs are a pair of soft, spongy, cone-shaped organs that fill most of the chest (thoracic) cavity, one on each side of the heart. They are the central organs of the respiratory system, where oxygen from inhaled air enters the blood and carbon dioxide is removed.

Gross Structure and Location

Each lung sits within its own pleural cavity, wrapped in a thin double-layered membrane called the pleura, with a slippery fluid between the layers that lets the lungs glide as they expand and recoil. The right lung is slightly larger and divided into three lobes (upper, middle, lower); the left lung has two lobes (upper and lower) and a notch called the cardiac notch that accommodates the heart. Air, blood vessels, and nerves enter and exit at the hilum on the inner surface of each lung. The lungs rest on the dome-shaped diaphragm below and reach up just above the first rib.

Key Functions

The lungs' primary job is gas exchange. Inhaled air travels down the trachea and bronchi into ever-smaller airways, ending in roughly 300 million tiny air sacs called alveoli, which are surrounded by capillaries. Oxygen passes from the alveoli into the blood, while carbon dioxide passes out to be exhaled. The lungs also help regulate blood pH, filter small clots, and contribute to immune defense by trapping and clearing inhaled particles and microbes with mucus and tiny hair-like cilia.

Clinical Relevance

Because the lungs are exposed to everything we breathe, they are vulnerable to a wide range of disorders. Asthma and chronic obstructive pulmonary disease (COPD) narrow the airways and limit airflow. Pneumonia is an infection that fills alveoli with fluid, reducing gas exchange. Lung cancer often begins in the lining of the airways and is strongly linked to smoking. A collapsed lung (pneumothorax) occurs when air enters the pleural space. Pulmonary embolism, a clot blocking lung blood vessels, can be life-threatening. Doctors assess lung function with spirometry, chest X-rays, and CT scans.

This page is educational and not a substitute for professional medical advice.