B209 - Circulatory System

Which of the following is the main organ of the circulatory system?

• Lungs

• Liver

• Heart

• Stomach

Blood vessels carry ___ blood throughout the body.

Reorder the following blood vessels in the order that blood passes through them as it leaves the heart.

• Veins

• Arteries

• Capillaries

Answer explanation

Which type of blood vessel has the thickest walls?

Answer explanation

Arteries have the thickest walls because they need to withstand the high pressure caused by the heart.

The heart needs high pressure to make sure that blood can reach all over your body, even at the ends of your toes and fingers.

Which blood vessels have the largest lumen (the hollow part in the centre)?

Answer explanation

Veins have the largest lumens so they can maximise transport of blood back to the heart. They don't need thick walls since the blood is at a low pressure.

Which of the following blood vessels has the thinnest walls?

• Artery

• Vein

• Capillary

Answer explanation

Capillaries have walls which are only one cell thick. This makes it easier for oxygen to diffuse into them, and for carbon dioxide to diffuse out of them.

Which of the following blood vessels surround the alveoli in the lungs?

• Artery

• Vein

• Capillary

Answer explanation

Capillaries have walls which are only one cell thick. This makes it easier for oxygen to diffuse into them, and for carbon dioxide to diffuse out of them.

What type of blood vessel has valves?

• Artery

• Vein

• Capillary

Answer explanation

Veins have valves because the blood moves forwards at low pressure. The valves help to stop the blood from flowing backwards away from the heart.

Match the following blood vessels to their function.

• Vein

• Facilitates diffusion of oxygen in the lungs.

• Capillary

• Transports deoxygenated blood towards the heart.

• Artery

• Transports oxygenated blood away from the heart.

Answer explanation

Match the following part of the respiratory system with its function.

• Arteries

• Allows exchange of materials between blood and body cells.

• Veins

• Site of gas exchange.

• Alveoli

• Carries oxygen-rich blood away from heart.

• Heart

• Carries oxygen-poor blood back to heart.

• Capillaries

• Pumps blood around the body