Anatomy Lung

The lungs are the primary organs of the respiratory system. The main function of the human respiratory system is to transport oxygen from the atmosphere into the blood, and to expel carbon dioxide from the body. Healthy levels of oxygen are absolutely crucial for the human body, as oxygen gives our cells energy and helps them regenerate.

The Anatomy of the Lung

Each lung is divided into lobes. The right lung, which has three lobes, is slightly larger than the left, which has two. The lungs are housed in the chest cavity, or thoracic cavity, and covered by a protective membrane called the pleura. The diaphragm, the primary muscle involved in respiration, separates the lungs from the abdominal cavity.

The pulmonary arteries carry de-oxygenated blood from the right ventricle of the heart to the lungs. The pulmonary veins, on the other hand, carry oxygenated blood from the lungs to the heart, so it can be pumped to the rest of the body.

Anatomy of the Lungs - The Human Lung

How the Lungs Work

The lungs expand upon inhalation, or inspiration, and fill with air. They then return to their resting volume and push air out upon exhalation, or expiration. These two movements make up the process of breathing, or respiration.

The respiratory system contains several structures. When you breathe, the lungs facilitate this process:

  1. Air comes in through the mouth and/or nose, and travels down through the trachea, or “windpipe.” This air travels down the trachea into two bronchi, one leading to each lung. The bronchi then subdivide into smaller tubes called bronchioles. The air finally fills the alveoli, which are the small air sacs at the ends of the bronchioles.
  2. In the alveoli, the lungs facilitate the exchange of oxygen and carbon dioxide to and from the blood. Adult lungs have hundreds of alveoli, which increase the lungs’ surface area and speed this process. Oxygen travels across the membranes of the alveoli and into the blood in the tiny capillaries surrounding them.
  3. Oxygen molecules bind to hemoglobin in the blood and are carried throughout the body. This oxygenated blood can then be pumped to the body by the heart.
  4. The blood also carries the waste product carbon dioxide back to the lungs, where it is transferred into the alveoli in the lungs to be expelled through exhalation.

Smoking can damage the alveoli and make breathing labor intensive, resulting in emphysema or lung cancer.

Types of Respiration

Two types of respiration exist:

  • Quiet respiration happens when the body is at rest. During quiet respiration, the diaphragm contracts and pulls down, lowering the pressure in the lungs and causing air to enter the lungs through the mouth and nose to equalize the pressure. When the diaphragm relaxes, it moves back up, pushing air back out of the lungs. The lungs and chest walls also return to their resting positions. This also reduces the size of the chest cavity and helps to push air out of the lungs.
  • Active respiration occurs when the body is active and requires higher levels of oxygen to the blood than when resting. During active respiration, the muscles around the ribs raise and push out the ribs and sternum, which increases thoracic volume, helping the lungs take in more air. During exhalation, the intercostals force the ribs to contract, and the abdominal muscles contract, forcing the diaphragm to rise. Both these movements make the thoracic cavity contract, and help push air out of the lungs.

The Lungs’ Protections

Several lung parts and functions act as protective mechanisms to keep out irritants and foreign particles. The hairs and mucus in the nose prevent foreign particles from entering the respiratory system.

The breathing tubes in the lungs secrete mucus, which also helps protect the lungs from foreign particles. This mucus is naturally pushed up toward the epiglottis, where is passed into the esophagus and swallowed. Coughing up any of this mucus is usually an indication of a respiratory infection, or a condition such as bronchitis or chronic obstructive pulmonary disease (COPD). Irritants can also cause bronchospasm, in which the muscles around the bronchial tubes constrict in order to keep out irritants. Asthma involves inflammation and constriction of the bronchial tubes, and is often triggered by environmental irritants. Bronchial constriction causes breathing difficulties.

About Breathing Difficulties

Damage to any part of the respiratory pathway can also cause breathing difficulties. Understanding human lung anatomy and physiology makes clear how the different lung parts are affected in disease.

In people with bronchitis, the bronchial tubes become inflamed and irritated. They produce mucus, resulting in a cough. Bronchitis can be acute, with a sudden onset and quick recovery, or chronic, and last much longer.

Chronic obstructive pulmonary disease (COPD) involves symptoms of both chronic bronchitis and emphysema. Blockage in the bronchioles and alveoli make it difficult to exhale. This traps air in the lungs and in turn makes proper inhalation difficult.

Interstitial lung disease, including pulmonary fibrosis, causes a buildup of scar tissue in the lungs and reduces lung function. Any of these conditions affect not only the lungs, but the entire body, as the healthy respiration is required to supply oxygen to the body and its organs.


American Thoracic Society. (n.d.). Anatomy and function of the normal lung. Retrieved February 17, 2009, from the American Thoracic Society Web site:

Johns Hopkins School of Medicine. (1995). Muscles of respiration. Retrieved February 17, 2009, from Johns Hopkins School of Medicine Web site:

Mayo Clinic. (n.d.). COPD. Retrieved February 17, 2009, from the Mayo Clinic Web site:

Mayo Clinic. (n.d.). Emphysema. Retrieved February 17, 2009, from the Mayo Clinic Web site:

Mayo Clinic. (n.d.). Pulmonary fibrosis. Retrieved Retrieved February 17, 2009, from the Mayo Clinic Web site:

U.S. National Cancer Institute. (n.d.). Anatomy of the lung. Retrieved February 17, 2009, from The U.S. National Cancer Institute’s Surveillance, Epidemiology and End Results Web site: