What prevents blood from flowing back into the atria when the ventricles contract?

• semilunar valves

• sinoatrial node

• atrioventricular node

• tricuspid and bicuspid valves

When blood leaves this chamber of the heart, it heads out to the body (not the lungs)

• left atrium

• right atrium

• left ventricle

• right ventricle

One of the body's largest blood vessels that transports blood from the body region below the diaphragm to the heart

• superior vena cava

• inferior vena cava

• pulmonary trunk

• pulmonary veins

When this chamber contracts, it pushes blood through the tricuspid valve

• right atria

• right ventricle

• left atria

• left ventricle

This initiates the action potential that causes the heart to beat

• Inferior vena cava

• Atrioventricular node (AV node)

• Superior vena cava

• Sinoatrial node (SA node)

When blood leaves this chamber of the heart, it heads to the lungs

• right atrium

• right ventricle

• left atrium

• left ventricle

This blood vessel splits in two and sends oxygen-poor blood away from the heart and to the lungs

• aorta

• pulmonary veins

• superior vena cava

• pulmonary trunk

This chamber of the heart receives oxygenated blood from the lungs

• right atrium

• right ventricle

• left atrium

• left ventricle

These are the smallest blood vessels with the thinnest walls in order to maximize diffusion of nutrients in and out of the interstitial fluid

• arteries

• veins

• capillaries

• aorta

Which best explains why capillary walls are so thin?

• because they do not need to pump blood

• because they are found only in the smallest organs and tissues

• because they maximize diffusion of nutrients

• because blood only travels through them slowly