We've learned before about how air comes in to the lungs and all the way down to the blood-air barrier where the oxygen goes into the blood.
On one side of the barrier are the alveoli holding the oxygen, and the other side has the capillaries which hold the blood that is ready to take in oxygen.
Capillaries are very tiny small tubes. They bring the blood right to the blood air barrier and then carry it off to the heart.
(from: wikipedia - capillary)
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