Capillaries

blood vessels · circulation · microscopic · human body

Incredibly tiny tubes. Capillaries are only 5 to 10 micrometers wide, which means about 10 of them lined up would equal the width of a human hair. You absolutely need a microscope to see them.

Thinner than thin. Capillaries have walls made of just a single layer of flat cells, making them so delicate that oxygen and other important stuff can slip right through. This paper-thin design is exactly what makes them perfect for their job.

The exchange happens here. Capillaries are where the real magic occurs: your blood drops off oxygen and picks up carbon dioxide from your cells, and also exchanges water, glucose (sugar), and other waste products. They're like the marketplace where your cells get what they need and hand off their trash.

Part of a bigger system. Capillaries connect the smallest arteries (arterioles) to the smallest veins (venules), creating a bridge between your heart's delivery system and your body's drainage system. There are also special lymph capillaries that collect fluid from around your cells.