Away and back

The idea

Arteries carry blood away from the heart and have thick, elastic walls as the blood is under high pressure; veins bring blood back to the heart, need no thick walls, and have valves that keep blood flowing one way.

Two kinds of pipes

Blood moves in tubes called blood vessels. Some carry blood away from the heart, others bring it back.

Which kind do you think needs the thicker, stretchy wall?

• The ones carrying blood away from the heart
• The ones bringing blood back
• Neither

Artery or vein?

Sort each feature: artery or vein?

Built for the job

Arteries carry blood away from the heart to various organs. Blood leaves the heart under high pressure, so the arteries have thick, elastic walls. Veins collect blood from the organs and bring it back to the heart. The blood in them is no longer under pressure, so they do not need thick walls. Instead they have valves that keep the blood flowing one way.

Arteries carry blood away from the heart and have thick, elastic walls as the blood is under high pressure; veins bring blood back to the heart, need no thick walls, and have valves that keep blood flowing one way.

Notes

Arteries: blood away from the heart, thick elastic walls (high pressure). Veins: blood back to the heart, no thick walls, valves for one-way flow.

Check yourself

Why do arteries have thick, elastic walls?

What do the valves in veins do?

Which vessels bring blood back to the heart?

Why do veins not need thick walls?

• They have valves. Valves are in veins; they keep the blood flowing in one direction.
• They bring blood back to the heart. Arteries carry blood away from the heart; veins bring it back.
• The blood emerges from the heart under high pressure — correct. Yes!
• They ensure that blood flows in only one direction — correct. Yes!
• They make the walls thick. Veins do not need thick walls; the valves keep the blood moving one way.
• They pump the blood forward. The valves keep blood from going the wrong way; the heart pumps the blood.
• Arteries. Arteries carry blood away from the heart.
• Veins — correct. Yes!
• Valves. Valves are flaps in veins and the heart, not vessels.
• They carry blood away from the heart. Veins collect blood from organs and bring it back to the heart.
• The blood in them is under very high pressure. The blood in arteries, not veins, is under high pressure.
• The blood in them is no longer under pressure — correct. Yes!