The most important function of the lungs is to take oxygen from the environment and transfer it to the bloodstream. Lung functions tests can show how well the lungs carry out this task.
This article looks at the form and function of the lungs, diseases that affect them, and how to maintain healthy lungs.
Fast facts on the lungs
- The left and right lungs are different sizes.
- The lungs play a part in many functions, including regulating the acidity of the body.
- Smoking tobacco is the biggest cause of lung-related complaints.
- Preventive and lifestyle measures can help keep the lungs healthy.
The organs require help from surrounding structures in the body in order to breathe properly. To
As the diaphragm relaxes and returns to its resting position, the lung volume decreases because the pressure inside the chest cavity goes up, and the lungs expel the air. The lungs are like bellows — as they expand, they suck in air for oxygen. As they compress, the exchanged carbon dioxide waste is pushed back out during exhalation.
When air enters the nose or mouth, it travels down the
From there, similar to branches on a tree, the pipe-like bronchi split again into smaller bronchi and then even smaller bronchioles. This ever-decreasing pipework eventually terminates in the alveoli, which are tiny air sacs. Here, gas exchange occurs.
The lungs reside in the chest, behind the rib cage on either side of the heart. They are roughly conical in shape with a rounded point at their apex and a flatter base where they meet the diaphragm.
Although they are a pair, the lungs are
Two membranes, known as the pulmonary pleurae, surround the lungs. The inner layer directly lines the outer surface of the lungs, and the outer layer attaches to the inner wall of the rib cage. The space between the two membranes contains pleural fluid, which helps the pleura stay moist and reduces friction between the membranes when breathing.
Click on the BodyMap above to interact with a 3D model of the lungs.
Some examples of lung function tests include:
- Spirometry: This test measures how much and how quickly people can move air in and out of their lungs.
- Plethysmography: Also known as a lung volume test, this measures the amount of air individuals can hold in the lungs and how much air remains after breathing out.
- Gas diffusion test: This test can measure gases, such as oxygen, moving from the lungs to the bloodstream.
- Exercise stress test: This test typically involves a bike or treadmill to investigate how exercise affects lung function.
A doctor may also suggest some imaging scans to help diagnose, screen, and monitor lung function.
After the lungs, the body takes oxygen out of the bloodstream to its other tissues as it travels around the circulatory system. The blood that has given up its oxygen in exchange for carbon dioxide from the tissues then passes through the heart and travels to the lungs to reach the capillaries surrounding the alveoli.
The alveoli now contain a new supply of oxygen that a person has inhaled. This oxygen passes across a membrane, called the alveolar-capillary membrane, into the bloodstream. At the same time, the carbon dioxide that has collected in the bloodstream during its travels around the body enters the alveoli. From there, a person’s body breathes it back out into the atmosphere during exhalation.
Put simply, as the oxygen goes in, carbon dioxide comes out — an example of a gas exchange process.
Special cells in the alveoli produce a compound known as pulmonary surfactant. It comprises lipids, proteins, and carbohydrates. Surfactant features both hydrophilic and hydrophobic regions — water attracts hydrophilic regions but repels hydrophobic regions.
Pulmonary surfactant has several vital functions, including allowing for better breathing efficiency and preventing the alveoli from collapsing on themselves. Each alveolus is similar to a plastic bag that is wet inside. If there were no surfactant, the bag would collapse in on itself and the internal sides would stick together. Surfactant prevents this from happening to the alveoli.
Pulmonary surfactant carries out its role by reducing the amount of surface tension. By doing this, it reduces the effort necessary to inflate the alveoli.
Respiration is the best-known role of the lungs, but they carry out other important functions, including:
- Balancing pH: Too much carbon dioxide can cause the body to become acidic. If the lungs detect a rise in acidity, they increase the ventilation rate to expel more of the unwanted gas, which helps
- Protecting the body: The lungs help protect the body from harmful substances. For example, they can secrete
immunoglobulin A, which can prevent infection. Additionally, the lungs can use mucociliary clearance. This involves mucus trapping pathogens and dust particles, after which small hair-like projections, known as cilia, move these particles upward so the body can either cough them out or swallow and destroy them using the digestive system.
- Speech: Without airflow, a person would be unable to speak.
Inflammatory lung diseases
This group includes:
- cystic fibrosis
- acute respiratory distress syndrome
- chronic obstructive pulmonary disease (COPD), including emphysema and chronic bronchitis
COPD usually results from the damage that tobacco smoking causes to the lungs.
Asthma involves an obstructive narrowing and swelling of the airways and the production of excess mucus. This triggers shortness of breath and wheezing. Triggers can
- tobacco and wood smoke
- dust mites
- air pollution
- cockroach allergens
- some foods
Restrictive lung diseases
This means that the airway is restricted, so the amount of air a person can take in is reduced, and breathing in becomes harder. It can occur due to:
- the lungs becoming stiff
- airways filling with phlegm
- a problem with the chest wall or breathing muscles, for example, as with idiopathic pulmonary fibrosis
- a curvature of the spine
Respiratory tract infections
Infections can occur at any point in the respiratory tract. Some examples include:
- Upper respiratory tract infection (URTI): The most frequent URTI is the common cold. Others include laryngitis, pharyngitis, and tonsillitis.
- Lower respiratory tract infection (LRTI): The most common type is bacterial infection, especially bacterial pneumonia. Other causes of LRTI include viruses and fungi.
Complications can develop from these types of infections, including lung abscesses and the spread of infection to the pleural cavity.
Lung cancer is when cells in the lungs divide uncontrollably. This can cause tumors to grow, which can reduce a person’s ability to breathe. Evidence suggests lung cancer is the
Smoking is the
Pleural cavity diseases
The pleural cavity is the gap between the inner and outer pleural membranes that encase the outside of the lungs.
Pleural effusion describes a build-up of fluid in the pleural cavity. It always results from other conditions, such as cancer, congestive heart failure, or liver cirrhosis. A collapsed lung, also known as pneumothorax, occurs when air gets into the space between the chest wall and the lung, called the pleural space. This can compress the lungs, and when severe, it causes them to collapse like a balloon.
Pulmonary vascular disease
Pulmonary vascular diseases affect the vessels that carry blood through the lungs. Examples can include:
- Pulmonary artery embolism: A blood clot forms elsewhere in the body and travels in the bloodstream to the heart and then to the lungs, where it becomes lodged. This can result in sudden death. More rarely, an embolism can consist of fat, amniotic fluid, or air.
- Pulmonary arterial hypertension: Increased pressure can build up in the pulmonary arteries. Sometimes, the reasons for this are unclear.
- Pulmonary edema: This occurs when fluid leaks from capillaries into the air spaces within the alveoli. It most often happens due to congestive heart failure.
Some ways of keeping the lungs healthy include:
- Not smoking: Smoking tobacco, including secondhand smoke, can lead to lung cancer and COPD, including chronic bronchitis and emphysema. Over time, it causes a narrowing of the airways, lung inflammation, and tissue damage.
- Prevent infection: Ways to prevent the spread of respiratory infections include washing hands, avoiding crowds in flu season, and asking your health provider about influenza and pneumonia vaccinations.
- Exercise: Aerobic exercise improves lung capacity, and staying fit can ward off other diseases that might affect the lungs.
- Check-ups: Regular health checks, even when feeling well, can detect problems in the early stages, when it is easier to treat them.
- Avoiding pollutant exposure: Garden or home chemicals may damage the lungs. With this in mind, wear a mask if using strong chemicals. Additionally, radon is a naturally occurring chemical that has associations with 21,000 lung cancer deaths a year in the U.S. Around 2,900 of these people have never smoked.
- Control moisture: Keep indoor humidity down to an acceptable level by using exhaust fans and vents. A person should also aim to keep moist surfaces clean and dry wherever possible and keep the home ventilated with external fresh air.