Slide 1
A meeting between air and blood
Alveoli are tiny air sacs in the lungs. Their thin boundaries bring inhaled air close to blood in surrounding capillaries.
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Air reaches them through branching airways. Moving air down this tree is ventilation; transferring gases across the air-blood boundary is gas exchange. One process can be impaired even when the other still occurs.
Slide 2
A muscle changes the space
When the diaphragm contracts, it moves downward and enlarges the chest cavity. The resulting pressure change draws air into the lungs.
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The lungs do not pull themselves open with muscle. During quiet breathing, relaxation and elastic recoil usually drive expiration; harder breathing recruits additional muscles.
Slide 3
Two gases cross in opposite directions
Oxygen enters the blood from alveolar air, while carbon dioxide leaves the blood. Breathing renews the air available for this exchange.
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Red cells carry much of the incoming oxygen attached to hemoglobin. The protein greatly increases the amount transported beyond what could dissolve in blood fluid alone.
Slide 4
The journey continues in tissues
The heart carries oxygenated blood onward to the body. Cells use oxygen in metabolism and produce carbon dioxide that blood brings back.
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Gas transfer at the lungs depends on air reaching the exchange surface and blood reaching its capillaries. A functioning airway alone does not guarantee adequate delivery to the rest of the body.
Slide 5
Breathing responds to demand
The nervous system adjusts breathing as conditions change. Sensors help detect chemical signals that reflect the body’s need for gas exchange.
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Control involves the brainstem, signals from the body and the muscles that execute each breath. Injury to a control pathway can therefore affect breathing even without a primary injury to the lung tissue.
Sources
- What Breathing Does for the Body
NHLBI, NIH
- How Your Body Controls Breathing
NHLBI, NIH