Blood Vessels and Circulation

Section 1Arteries, veins, and capillaries

Arteries carry blood away from the heart under high pressure. Veins carry blood back to the heart under lower pressure and often have valves. Capillaries are tiny vessels with thin walls for exchange of substances.

Section 2Oxygenated and deoxygenated blood

Oxygenated blood has picked up oxygen, usually from the lungs. Deoxygenated blood has delivered oxygen to body cells and contains less oxygen. The terms are about oxygen level, not whether the blood is clean or dirty.

Section 3Pathway through the body

Deoxygenated blood returns from the body to the right side of the heart, then goes to the lungs. Oxygenated blood returns from the lungs to the left side of the heart, then is pumped to the body. This pathway keeps blood moving in the correct direction.

Section 4Exchange at capillaries

Capillaries are only one cell thick, so substances can move between blood and body cells quickly. Oxygen and glucose move from blood to cells. Carbon dioxide and other wastes move from cells into blood.