The lungs are the primary organs of the respiratory system in air-breathing vertebrates, responsible for gas exchange , adding oxygen to and removing carbon dioxide from the blood. Located in the chest cavity, each lung is protected by the pleura , a thin membrane, and connects to the trachea via the main bronchus. The right lung has three lobes, while the left has two, further divided into lobules containing bronchioles and alveoli. Alveoli are minute air sacs where oxygen and carbon dioxide exchange occurs with blood capillaries. The lungs facilitate the absorption and excretion of certain substances and also synthesize and degrade molecules like pulmonary surfactant.

Where are the lungs located in the human body?

The lungs, the primary organs for gas exchange in humans, are located in the thorax, safeguarded by the bony and muscular thoracic cage. The thoracic cage is formed by the 12 thoracic vertebrae, the 24 ribs, and the sternum. The lungs occupy most of the intrathoracic space, separated by the mediastinum, which houses the heart, major blood vessels, trachea, esophagus, and thymus gland. The right lung has three lobes, while the left lung, smaller due to the heart's position, has two. The lung bases rest on the diaphragm, with their apexes extending above the first rib. The lungs connect medially to the mediastinum at the hilum, where airways, vessels, and nerves enter or exit. The thoracic cavities and lung surfaces are lined by serous membranes that facilitate smooth movement during breathing.

What is the main function of the lungs?

The lungs' main function is to facilitate gas exchange, adding oxygen to the blood and removing carbon dioxide. This process occurs in the pulmonary alveoli , small air spaces in the lungs, where oxygen enters the blood and carbon dioxide leaves. The lungs' structure provides a large internal surface area for efficient gas exchange between the alveoli and pulmonary capillaries. The movement of oxygen and carbon dioxide between the air and blood is achieved through diffusion, driven by differences in partial pressures.

What are the parts that make up the inside of a lung?

The lungs are located in the thorax and are protected by the thoracic cage. The lungs facilitate a continuous flow of oxygen to the body's tissues and remove carbon dioxide. Key components include: * Lower airway system The lower airway system consists of the larynx, the trachea, the stem bronchi, and the intrapulmonary bronchi, the bronchioles, and the alveolar ducts. * Pulmonary segments The lung lobes consist of smaller units known as pulmonary segments. The right lung has 10 segments, while the left lung has eight to 10 segments. * Bronchi The bronchi are large airway passages that diverge from the trachea and connect to the lungs. The bronchi warm, moisten, and clean inspired air and distribute it to the gas-exchanging zone of the lung. * Pulmonary alveoli The pulmonary alveoli are air spaces in the lungs where carbon dioxide leaves the blood, and oxygen enters it. * Pleura The pleura is the membrane lining the thoracic cavity (parietal pleura) and covering the lungs (visceral pleura). * Vascular systems The lung has two vascular systems: the pulmonary system and the bronchial system. * Lymphatic vessels Lymph is drained from the lung through two interconnected sets of lymphatic vessels: the superficial, subpleural lymphatic network and the deep lymphatic system.

How do lungs help bring oxygen into the body and remove carbon dioxide?

The lungs facilitate the exchange of oxygen and carbon dioxide through the coordinated processes of ventilation and diffusion. During inhalation, air enters the lungs, and oxygen diffuses from the alveoli into the blood. Simultaneously, carbon dioxide moves from the blood into the alveoli. This occurs because the partial pressure of carbon dioxide in the blood is higher than in the alveoli, driving the diffusion process. The structure of the lungs , with their vast network of alveoli, creates a large surface area that enhances gas exchange. The blood carries oxygen to the body's tissues and returns carbon dioxide to the lungs for exhalation.

What are alveoli, and why are they important in lung function?

The pulmonary alveoli are tiny air spaces in the lungs where gas exchange occurs. Inhaled air travels through the bronchi and flows into approximately 300,000,000 alveoli at the ends of the bronchioles. These alveoli form clusters called alveolar sacs. The walls of the alveoli are lined with thin, flat cells (Type I) and contain capillaries where oxygen enters the blood and carbon dioxide leaves. This gas exchange is made efficient by the large surface area (50–100 square meters) and thin walls of the alveoli. Type II cells in the alveolar walls secrete surfactant, which lowers alveolar surface tension, preventing collapse. Alveolar macrophages engulf foreign particles, keeping the lungs clean.

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Images, Videos & Interactives

A swimmer wearing goggles and a swim cap turns their head to breathe while swimming in open water, emphasizing the act of breathing during exercise.

Medical image showing a detailed view of healthy human lungs, highlighting the trachea, bronchi, and branching bronchioles within the chest.

Fibrotic tissue isolated from the lung of a mouse.

Quick Facts

Key People:: William Stokes

Related Topics:: bronchus; intrapulmonic pressure; deflation; inflation; lobe

On the Web:: National Center for Biotechnology Information - Physiology, Lung (Oct. 16, 2026)

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Top Questions

What are lungs?
The lungs are the primary organs of the respiratory system in air-breathing vertebrates, responsible for gas exchange, adding oxygen to and removing carbon dioxide from the blood.

Located in the chest cavity, each lung is protected by the pleura, a thin membrane, and connects to the trachea via the main bronchus. The right lung has three lobes, while the left has two, further divided into lobules containing bronchioles and alveoli. Alveoli are minute air sacs where oxygen and carbon dioxide exchange occurs with blood capillaries. The lungs facilitate the absorption and excretion of certain substances and also synthesize and degrade molecules like pulmonary surfactant.
4 Britannica Sources
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Where are the lungs located in the human body?
The lungs, the primary organs for gas exchange in humans, are located in the thorax, safeguarded by the bony and muscular thoracic cage. The thoracic cage is formed by the 12 thoracic vertebrae, the 24 ribs, and the sternum.

The lungs occupy most of the intrathoracic space, separated by the mediastinum, which houses the heart, major blood vessels, trachea, esophagus, and thymus gland. The right lung has three lobes, while the left lung, smaller due to the heart's position, has two.

The lung bases rest on the diaphragm, with their apexes extending above the first rib. The lungs connect medially to the mediastinum at the hilum, where airways, vessels, and nerves enter or exit. The thoracic cavities and lung surfaces are lined by serous membranes that facilitate smooth movement during breathing.
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1. human skeleton: The rib cage
2. human respiratory system: Gross anatomy
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What is the main function of the lungs?
The lungs' main function is to facilitate gas exchange, adding oxygen to the blood and removing carbon dioxide. This process occurs in the pulmonary alveoli, small air spaces in the lungs, where oxygen enters the blood and carbon dioxide leaves. The lungs' structure provides a large internal surface area for efficient gas exchange between the alveoli and pulmonary capillaries. The movement of oxygen and carbon dioxide between the air and blood is achieved through diffusion, driven by differences in partial pressures.
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What are the parts that make up the inside of a lung?
The lungs are located in the thorax and are protected by the thoracic cage. The lungs facilitate a continuous flow of oxygen to the body's tissues and remove carbon dioxide.

Key components include:
* Lower airway system The lower airway system consists of the larynx, the trachea, the stem bronchi, and the intrapulmonary bronchi, the bronchioles, and the alveolar ducts.
* Pulmonary segments The lung lobes consist of smaller units known as pulmonary segments. The right lung has 10 segments, while the left lung has eight to 10 segments.
* Bronchi The bronchi are large airway passages that diverge from the trachea and connect to the lungs. The bronchi warm, moisten, and clean inspired air and distribute it to the gas-exchanging zone of the lung.
* Pulmonary alveoli The pulmonary alveoli are air spaces in the lungs where carbon dioxide leaves the blood, and oxygen enters it.
* Pleura The pleura is the membrane lining the thoracic cavity (parietal pleura) and covering the lungs (visceral pleura).
* Vascular systems The lung has two vascular systems: the pulmonary system and the bronchial system.
* Lymphatic vessels Lymph is drained from the lung through two interconnected sets of lymphatic vessels: the superficial, subpleural lymphatic network and the deep lymphatic system.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do lungs help bring oxygen into the body and remove carbon dioxide?
The lungs facilitate the exchange of oxygen and carbon dioxide through the coordinated processes of ventilation and diffusion.

During inhalation, air enters the lungs, and oxygen diffuses from the alveoli into the blood. Simultaneously, carbon dioxide moves from the blood into the alveoli. This occurs because the partial pressure of carbon dioxide in the blood is higher than in the alveoli, driving the diffusion process. The structure of the lungs, with their vast network of alveoli, creates a large surface area that enhances gas exchange. The blood carries oxygen to the body's tissues and returns carbon dioxide to the lungs for exhalation.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are alveoli, and why are they important in lung function?
The pulmonary alveoli are tiny air spaces in the lungs where gas exchange occurs. Inhaled air travels through the bronchi and flows into approximately 300,000,000 alveoli at the ends of the bronchioles.

These alveoli form clusters called alveolar sacs. The walls of the alveoli are lined with thin, flat cells (Type I) and contain capillaries where oxygen enters the blood and carbon dioxide leaves. This gas exchange is made efficient by the large surface area (50–100 square meters) and thin walls of the alveoli. Type II cells in the alveolar walls secrete surfactant, which lowers alveolar surface tension, preventing collapse. Alveolar macrophages engulf foreign particles, keeping the lungs clean.
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lung, in air-breathing vertebrates, either of the two large organs of respiration located in the chest cavity and responsible for adding oxygen to and removing carbon dioxide from the blood. In humans each lung is encased in a thin membranous sac called the pleura, and each is connected with the trachea (windpipe) by its main bronchus (large air passageway) and with the heart by the pulmonary arteries. The lungs are soft, light, spongy, elastic organs that normally, after birth, always contain some air. If healthy, they will float in water and crackle when squeezed; diseased lungs sink.

In the inner side of each lung, about two-thirds of the distance from its base to its apex, is the hilum, the point at which the bronchi, pulmonary arteries and veins, lymphatic vessels, and nerves enter the lung. The main bronchus subdivides many times after entering the lung; the resulting system of tubules resembles an inverted tree. The diameters of the bronchi diminish eventually to less than 1 mm (0.04 inch). The branches 3 mm and less in diameter are known as bronchioles, which lead to minute air sacs called alveoli (see pulmonary alveolus), where the actual gas molecules of oxygen and carbon dioxide are exchanged between the respiratory spaces and the blood capillaries.

Each lung is divided into lobes separated from one another by a tissue fissure. The right lung has three major lobes; the left lung, which is slightly smaller because of the asymmetrical placement of the heart, has two lobes. Internally, each lobe further subdivides into hundreds of lobules. Each lobule contains a bronchiole and affiliated branches, a thin wall, and clusters of alveoli.

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In addition to respiratory activities, the lungs perform other bodily functions. Through them, water, alcohol, and pharmacologic agents can be absorbed and excreted. Normally, almost a quart of water is exhaled daily; anesthetic gases such as ether and nitrous oxide can be absorbed and removed by the lungs. The lung is also a true metabolic organ. It is involved in the synthesis, storage, transformation, and degradation of a variety of substances, including pulmonary surfactant, fibrin, and other functionally diverse molecules (i.e., histamine, angiotensin, and prostaglandins).

A person not engaged in vigorous physical activity uses only about one-twentieth of the total available gaseous-exchange surface of the lung. Pressure inside the lungs is equal to that of the surrounding atmosphere. The lungs always remain somewhat inflated because of a partial vacuum between the membrane covering the lung and that which lines the chest. Air is drawn into the lungs when the diaphragm (the muscular portion between the abdomen and the chest) and the intercostal muscles contract, expanding the chest cavity and lowering the pressure between the lungs and chest wall as well as within the lungs. This drop in pressure inside the lungs draws air in from the atmosphere.

The lungs are frequently involved in infections and injuries. Some infections can destroy vast areas of a lung, rendering it useless. Inflammation from toxic substances, such as tobacco smoke, asbestos, and environmental dusts, can also produce significant damage to the lung. Healed lung tissue becomes a fibrous scar unable to perform respiratory duties. There is no functional evidence that lung tissue, once destroyed, can be regenerated.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Meg Matthias.

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