Circulatory System Vocabulary

Vessels• Hollow tubes within

your body that transport blood throughout your body. Some are large; others are small. But they all serve the same purpose: to carry blood to your body’s cells.

Plasma• A yellow-colored

liquid that makes up more than half of your blood. It helps to transport materials in and out of cells, and make things flow smoothly through your vessels.

Red Blood Cells• Cells in your blood

that carry oxygen to your cells and carbon dioxide away from your cells. They contain a protein called hemoglobin that grabs on to these gases.

Hemoglobin• A protein in a red

blood cell that allows it to carry oxygen. It carries it much like you carry a back pack—on your back, but not inside you.

Atrium and Ventricle• You have two atriums

on both sides of your heart. They are the top chambers where blood first enters your heart. They then pump blood into your ventricles. Your ventricles are the lower chambers and they pump blood into back to your body.

Veins• The vessels in your

circulatory system that transport blood back to your heart. They are labeled blue because blood that is in your veins has lost its oxygen and gained carbon dioxide.

Valve• The pink flap inside

this vein prevents blood from flowing backwards. It is vital to your body that blood moves in one direction through your circulatory system.

Arteries• The thick, muscular

vessels in your circulatory system that carry oxygen-rich blood to the cells in your body. They carry blood away from your heart. Remember “artery—away”. They are colored red to show they contain oxygen-rich blood.

Capillaries• Thin vessels that

transport blood from your arteries to cells to drop off oxygen. From the cells, blood travels into the veins and will go to the lungs to drop off carbon dioxide. Cells are very thin, and oxygen and other nutrients can travel across their thin walls.

Circulation• The circular path in

which blood travels through the human body. Notice how blood leaves the heart and heads towards a part of your body. Eventually, it will return to your lungs and your heart, and start the cycle again.