The lungs provide oxygen for energy production in the body, and are part of the respiratory system. Air enters through the mouth and is absorbed into alveoli, which have a large surface area. The diaphragm controls breathing, and the lungs also filter blood and protect the heart.
The lungs supply our body with the oxygen it needs to generate energy in the form of adenosine triphosphate (ATP). ATP is the body’s energy currency and is required for all energy-consuming cellular processes. Over the course of a lifetime, a person can use their lungs to breathe more than a billion times. Animals breathe in oxygen and breathe out carbon dioxide, the opposite of plant respiration.
The lungs are the central component of the respiratory system, which is used for breathing. Fresh air enters through the mouth, down the windpipe (windpipe), into the lungs through cartilaginous pathways called bronchi and bronchioles, where it is absorbed into tiny air sacs called alveoli. The alveoli are approximately 0.05 mm in diameter, but swell to 0.1 mm during inhalation. By comparison, a typical cell is about 0.01 mm in size.
The entire inhalation process is guided by the diaphragm, a large muscle under the lungs. When the diaphragm is at rest, the lungs open wide, taking in oxygen. When the diaphragm contracts, the lungs are compressed, forcing out carbon dioxide. This process repeats itself continuously, even while we sleep.
The alveoli exist in a finely branched structure, starting with the great trachea and continuing down to the individual air sacs. Because of this branching structure, they have a very large combined area, approximately 750 – 1,000 square feet (70 – 90 square meters). This is similar in area to a football field, although the lungs themselves are only as big as a pair of steaks.
A network of capillaries – thin blood vessels – covers the alveoli. Oxygen from the alveoli diffuses into the bloodstream, which then travels to the heart, where it’s pumped throughout the body. Oxygenated blood has a bright red color, while deoxygenated blood has a bluish tint.
Lungs aren’t just for breathing. They also play a role in filtering the blood and shielding the heart, which is almost surrounded by it.
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