Thick walls and one-way doors

The idea

Ventricles have thicker muscular walls than atria because they pump blood into various organs, and valves prevent blood from flowing backwards when the atria or ventricles contract.

Who works harder?

The upper chambers of the heart receive blood. The lower chambers send blood out to the rest of the body.

Which chambers do you think need the stronger muscle?

• The lower chambers
• The upper chambers
• Both need exactly the same

Walls and valves

Press Next step.

Strong pumps, one-way doors

The atria mostly receive blood, so their walls are thin. The ventricles must push blood out to different organs, so their muscular walls are thicker. Valves are like doors that open one way. They make sure that blood does not flow backwards when the atria or the ventricles contract.

Ventricles have thicker muscular walls than atria because they pump blood into various organs, and valves prevent blood from flowing backwards when the atria or ventricles contract.

Notes

Ventricles have thicker muscular walls than atria since they pump blood into various organs; valves stop blood flowing backwards when atria or ventricles contract.

Check yourself

Which chambers of the heart have thicker muscular walls?

Why do the ventricles have thicker muscular walls?

What do the valves of the heart do?

When do the valves prevent blood from flowing backwards?

• The atria. The atria have thinner walls than the ventricles.
• All chambers have walls of equal thickness. The ventricles have thicker muscular walls than the atria.
• The ventricles — correct. Yes!
• They have to pump blood into various organs — correct. Yes!
• They only collect blood from the body. Collecting blood is the work of the atria; the ventricles pump it out.
• They hold the valves of the lungs. The reason given in the book is that ventricles pump blood into various organs.
• They add oxygen to the blood. Oxygen enters the blood in the lungs.
• They prevent blood from flowing backwards — correct. Yes!
• They make the walls thicker. The valves are doors that keep blood moving one way; they do not change the walls.
• Only when the heart is not working. Valves ensure that blood does not flow backwards when the atria or ventricles contract.
• When blood is in the lungs. The valves of the heart act when the atria or ventricles contract.
• When the atria or ventricles contract — correct. Yes!