Capillary walls are only one layer of cells thick. Passage of oxygen into and out of the capillaries is controlled most by which process?.

The channels through which blood is distributed to all body tissues are called blood vessels. These vessels make up two closed systems of tubes. They start and end at the heart.

One of these systems is the pulmonary vessel. It transports blood from right ventricle to the lungs, and then back to the left atrium.

Arteries, veins, and capillaries are the three types of blood vessels. These vessels hold a special role in circulation process of the body.

Arteries: they carry oxygenated blood from the heart to the other tissues.
Veins: they carry deoxygenated blood form body tissues to the heart and lungs.
Capillaries: they are what makes the passage between these blood vessels.

Therefore, passage of oxygen in and out of the capillaries is mostly controlled by the process of collection of waste materials.

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