Lungs

Figure A shows the location of the respiratory structures in the body. Figure B is an enlarged image of airways, alveoli, and the capillaries. Figure C shows the location of gas exchange between the capillaries and alveoli. Source: NHLBI.

The lungs are part of the body's respiratory system. The lungs bring air into the body and help get rid of waste products such as carbon dioxide.

Description

The lungs are organs in the chest that allow the body to take in oxygen from the air. They also help remove carbon dioxide (a waste gas that can be toxic) from the body.

The lungs' intake of oxygen and removal of carbon dioxide is called gas exchange. Gas exchange is part of breathing, which is a vital function of life.

The lungs lie on either side of the breastbone and fill the chest. The left lung is slightly smaller than the right lung to allow room for the heart.

The lungs are divided into five main sections called lobes (three in the right lung, and two in the left lung). The left lung comprises a superior lobe and an inferior lobe, separated by the major (oblique) fissure. In the right lung, the superior lobe is further subdivided by the minor (horizontal) fissure, yielding a small middle lobe. In the treatment of lung disease, one of these lobes is sometimes removed in an operation called a lobectomy. A person who has had a lobectomy can still breathe well using the rest of the lung.

Air is conveyed into the lungs through the trachea|trachea (windpipe). The trachea bifurcates into left and right primary (mainstem) bronchus at the level of the T4/T5 intervertebral disk. Within the lungs, the bronchi further ramify into secondary (lobar) bronchi. Each secondary bronchus leads into one of the lobes of a lung and is named for the lobe it enters (for example, left superior lobar bronchus). Each lobar bronchus branches into multiple tertiary (segmental) bronchi, each serving a bronchopulmonary segment. Ultimately segmental bronchi ramify into thousands of smaller, thinner tubes called bronchioles. These tubes end in bunches of tiny round air sacs called alveoli.

Each of these air sacs is covered in a mesh of tiny blood vessels called capillaries. The capillaries connect to a network of arteries and veins that move blood through the body.

Role of the Lungs in the Body

All body tissues need oxygen to function. The lungs bring this oxygen into the blood, and remove the byproducts, which are exhaled back into the air.

Other organs and tissues also help make breathing possible. These organs and tissues make up the respiratory system. They function together to help control breathing. The main parts of this system are the airways, the lungs and their blood vessels, and the muscles that enable breathing.

How the Lungs Work

The lungs work with the other parts of the respiratory system. The airways are pipes that carry oxygen-rich air to the lungs and allow carbon dioxide to leave the lungs. The lungs and their blood vessels deliver oxygen to the body and remove carbon dioxide. Muscles in the upper part of the body aid in breathing. These muscles include the diaphragm, intercostal muscles, abdominal muscles, and muscles in the neck and collarbone area.

When a person breathes in, the diaphragm and the muscles between the ribs contract to increase the space inside the chest, so the lungs have room to expand. As the lungs expand, air is sucked in through the nose or mouth. The air travels down the windpipe and into the lungs' air sacs.

In the air sacs, oxygen moves from the air into the blood in the lungs. At the same time, carbon dioxide moves from the blood in the lungs into the air sacs. Surrounding blood vessels carry the oxygen-rich air to the rest of the body.

When a breath is released, the diaphragm and rib muscles relax to make the size of the chest cavity smaller. As this happens, air rich in carbon dioxide is forced out of the lungs and windpipe, and then out of the nose or mouth.

Video: Air Exchange

Diseases of the Lungs

Many steps are involved in breathing. If injury, disease, or other factors affect any of the steps, a person can have trouble breathing.

For example, the fine hairs (cilia) that line the upper airways may not trap all of the germs that are inhaled. These germs can cause an infection in the bronchi (bronchitis) or deep in the lungs (pneumonia). These infections cause a buildup of mucus and/or fluid that narrows the airways and hinders airflow in and out of the lungs.

People who have asthma may find that inhaling certain substances to which they are sensitive can trigger the airways to narrow. This makes it hard for air to flow into and out of the lungs.

Breathing in cigarette smoke or air pollutants for many years can damage the airways and the air sacs. This can lead to a condition called COPD (chronic obstructive pulmonary disease). COPD prevents proper airflow in and out of the lungs and can hinder gas exchange in the air sacs.

An important step to breathing is the movement of the diaphragm and other muscles in the chest, neck, and abdomen. This movement allows inhalation and exhalation. Nerves that run from the brain to these muscles control their movement. Damage to these nerves in the upper spinal cord can cause breathing to stop, unless a machine is used (a ventilator or a respirator).

A steady flow of blood in the small blood vessels that surround the air sacs is vital for gas exchange. Long periods of inactivity or surgery can cause a blood clot in an artery in the lung. This is called a pulmonary embolism. This reduces or stops the flow of blood in the small blood vessels and interferes with gas exchange.

Below are several diseases of the lungs:

• Acute respiratory distress syndrome
• Asthma
• Bronchiectasis
• Bronchopulmonary dysplasia
• Cancer. Some examples of cancer affecting the lung are the following:
  • Malignant Mesothelioma
  • Non-small cell lung cancer
  • Small cell lung cancer
• Chronic Obstructive Pulmonary Disease
• Cystic fibrosis
• Histoplasmosis
• Pleural effusion
• Pneumonia
• Pneumothorax (Collapsed Lung)
• Pulmonary arterial hypertension
• Pulmonary embolism
• Tuberculosis

Symptoms

Symptoms of lung disease include the following:

• Cough
• Pleurisy (a sharp pain in the chest when taking a deep breath)
• Shortness of breath

Related conditions

Several conditions can affect lung function:

• Alpha-1 antitrypsin deficiency
• Marfan syndrome
• Sarcoidosis
• Sjögren Syndrome|Sjögren syndrome
• Tetralogy of Fallot
• Wegener's granulomatosis

Procedures

Many procedures have been developed to diagnose and treat diseases of the lungs:

• Bronchoscopy
• Lung function tests
• Thoracentesis

Surgery

Surgeries on the lungs are designed to remove diseased tissue. A lobectomy is used to remove a lobe and lung transplants are used to replace a whole lung.

Radiographic studies

• Chest CT
• Chest MRI
• Chest x-ray
• Ventilation-perfusion scan (V/Q Scan)

History

How lungs were named

The word lung comes from Middle English lunge and Old English lungen. It is related to Old High German lungun (lung) and līhti (light in weight). The term has been in use since before the 12th century.^[1]

Research

According to the Centers for Disease Control and Prevention (CDC), chronic lung disease is the fourth leading cause of death in the United States.^[2]

References

1. ↑ Merriam-Webster Online. Lungs.
2. ↑ Centers for Disease Control and Prevention. National Center for Health Statistics Web site. Health E-stats.

External Links

American Lung Association

National Heart, Lung, and Blood Institute