Despite their small size and easy permeability, capillaries are quite strong.
They are protected from the full force of the heartbeat by the muscles of the arteries which lead to them.
You have probably heard the old story about how every pound of fat adds thus-and-such many capillaries that your heart must work to perfuse. That's true -- but most of the time, the vast majority of the capillaries in the body are not receiving appreciable blood flow. Fat receives very little blood flow despite its many capillaries. Most of the increased cardiovascular burden of obesity results from the extra weight that must be carried.
This is a lucky shot of a capillary that shows it at considerable length as it runs through the brain.
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Kansas City University of Medicine and Biosciences