Lung Anatomy

  • Medical Author:
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

How is air moved into and out of the lungs during respiration?

Respiration is divided into two components, inhalation and exhalation.

Inhalation is active, because it requires muscle contraction. The major muscle of respiration is a sheet-like dome shaped muscle called the diaphragm that is located below the lungs. The diaphragm separates the chest and abdominal cavities. As the diaphragm contracts, it flattens out, moving toward the abdominal cavity. This action causes an increase in the size of the chest cavity, thus creating a vacuum. Air is then sucked in through the mouth or nose. When physical activity increases dramatically, or with some lung conditions, other muscles like those of the neck and those between the ribs also assist in the increase in size of the chest cavity. These muscles are referred to as accessory muscles of respiration.

Exhalation is passive because it does not require muscle contraction. During this phase, the expanded lung acts like a stretched rubber band and simply contracts to its resting position. This contraction forces air out of the lungs and through the mouth.

How does gas exchange occur?

As energy is utilized by cells, one of the waste products is the gas carbon dioxide. Oxygen-enriched red blood cells release oxygen to the cells of the body and then pick up the waste carbon dioxide. This oxygen- deprived, dark blue blood is then delivered to the blood vessels of the lungs. Carbon dioxide is released by the red cells, easily passes through the capillary wall into the space in the air sac of the adjacent alveoli, and is then eliminated with each breath out of the mouth (exhalation). Oxygen present in the air sac easily passes into the capillaries and into the red blood cells. The capillary network carrying this oxygen-rich, bright red blood flows to larger vessels and eventually empties into the left side of the heart where it is pumped to all the tissues of the body. Thus, the cycle or circle of blood is complete; hence, the name circulation.

Medically Reviewed by a Doctor on 3/14/2016

Subscribe to MedicineNet's Allergy and Asthma Newsletter


Health Solutions From Our Sponsors