circulation of oxygen

The circulation of oxygen is the whole point of having a heart and blood vessels: getting fresh oxygen from the lungs to every living cell. Every tissue runs on oxygen the way an engine runs on fuel, and the cardiovascular system is the delivery network that never stops refuelling.

Oxygen is carried mostly bound to hemoglobin inside red blood cells. Blood loads up with oxygen in the lungs, the left heart pumps it out through the arteries, and in the capillaries oxygen diffuses into the surrounding tissue. The amount delivered depends on three things multiplied together: how much blood the heart pumps, how much hemoglobin is present, and how fully that hemoglobin is loaded with oxygen.

When delivery falls short of what tissues need — from a blocked artery, a failing pump, severe anemia or low blood oxygen — cells switch to less efficient backup metabolism and, if starved long enough, are injured or die. This oxygen supply-and-demand mismatch is the common thread behind heart attacks, angina and shock.