Lungs Design And Purpose (cont.)
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. 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. 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.
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
cell, 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 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.
Next: What are other important events during the breathing cycle? »
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