Day 2: The Heart of the Matter

Anatomy of the Circulatory System

The circulatory system is made up of miles and miles of blood vessels, branching from the large superhighways of the major arteries and veins that come off the heart, to smaller highways that supply individual organs. Blood only travels in one direction along these vessels and so makes a circular trip through the body. Vessels carrying blood away from the heart are called arteries; vessels carrying blood to the heart are called veins.

Inside organs, the vessels continue to branch into smaller and smaller vessels. The smallest of these vessels are called capillaries. Just as many apartment buildings have back roads or alleys connecting them to main roads, the capillaries provide individual cells access to the bloodstream. The capillary walls are so thin that nutrients can easily pass from the blood to adjacent cells. Likewise, products manufactured by the cell can also pass through the capillary wall and travel to other parts of the body where they are needed. The cell's waste products can also pass from the cell into the capillaries and travel to the lungs, skin, kidneys, and other organs, that specialize in removing waste, to be expelled.

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