Lung Anatomy: How the Lungs Work
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.
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.
Human lung anatomy definition and facts
- The lungs exchange oxygen and carbon dioxide between the air we breathe and the blood.
- The tracheobronchial tree is the passage way from the mouth to the interior of the lung.
- Gas exchange occurs in the alveoli deep in the lungs.
- Breathing air in (inhalation) requires muscular effort.
- Air is warmed, humidified, and cleaned by the nose and lungs.
What are the lungs?
What is carbon dioxide poisoning? What are the symptoms?
The cells in the body constantly need a new supply of oxygen to produce energy. With lack of oxygen, cellular function is impaired and damage or cell death may occur. As energy is utilized, waste products are created, one of which is the gas carbon dioxide. Eliminating carbon dioxide from the body is just as important as breathing in oxygen from the air. If carbon dioxide builds up in the blood it will lead to headaches, drowsiness, coma, and eventually even death.
What is the structure of the respiratory system?
Air enters the body via the nose (preferably) or the mouth. The air enters the main windpipe, called the trachea, and continues en route to each lung via either the right or left bronchus (plural=bronchi). The lungs are separated into sections called lobes, two on the left and three on the right. The air passages continue to divide into ever smaller tubes, which finally connect with tiny air sacs called alveoli. This gradually branching array of tubes is referred to as the tracheobronchial "tree" because of the remarkable similarity to the branching pattern of a tree.
The other half of the respiratory system involves blood circulation. Venous blood from the body is returned to the right side of the heart and then pumped out via the pulmonary artery. This artery splits in two for the left and right lungs and then continues to branch much like the tracheobronchial tree. These vessels branch into a fine network of very tiny tubes called capillaries. The capillaries are situated adjacent to the alveoli and are so small that only one red blood cell at a time can pass through their openings. It is during this passage that gases are exchanged between the blood and the air in the nearby alveoli. After passing the alveoli, capillaries then join together to begin forming the pulmonary veins, which carry the blood back to the left side of the heart.
Inhalation and exhalation
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.
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