Section 6 - Blood Vessels

Question 1

Where do arteries carry blood?

Answer 1

Away from the heart

Question 2

What do arteries subdivide into?

Answer 2

Smaller vessels called arterioles

Question 3

What do arterioles subdivide into?

Answer 3

Microscopic vessels called capillaries

Question 4

What do capillaries join up to form?

Answer 4

Veins

Question 5

Where do veins carry blood?

Answer 5

To the heart

Question 6

Describe the structure of arteries

Answer 6

• Arteries have a thick wall compared to the diameter of the lumen.
• There’s an outer layer of fibrous tissue, then a thick layer of elastic tissue and smooth muscle, then a very thin inner layer of folded endothelial tissue.

Question 7

Describe what happens to the arteries when the ventricles contract

Answer 7

When the ventricles contract, blood enters the arteries at high pressure. This stretches the folded endothelium and elastic walls.

Question 8

Describe what happens to the arteries when the ventricles relax

Answer 8

When the ventricles relax, it’s the elastic recoil of the artery wall (when the wall shrinks back to its original size) that keeps the blood pressure up. Important organs, like the kidneys, wouldn’t be able to function if the blood pressure dropped too far between heartbeats.

Question 9

Describe the differences of arterioles with arteries (2)

Answer 9

• Arterioles are narrower than arteries
• Arterioles have a higher proportion of smooth muscle fibres and a lower proportion of elastic tissue

Question 10

What can arterioles control?

Answer 10

The diameter of their lumen, hence the amount of blood flowing to a particular organ

Question 11

How do arterioles reduce the diameter of the lumen?

Answer 11

Their circular muscle fibres contract

Question 12

Describe the structure of capillaries (2)

Answer 12

• Capillary walls consist of a single layer of endothelial cells (cells that line the blood vessels)
• Some capillaries have tiny gaps between the endothelial cells

Question 13

How are capillaries suited to their job?

Answer 13

The very thin walls and gaps between the cells allow water and substances like glucose and oxygen to diffuse quickly from the blood into the cells. Waste products, such as carbon dioxide and urea, diffuse from the cells into the blood.

Question 14

Does blood flow through capillaries slow or fast?

Answer 14

Slow

Question 15

Why does the blood flow slow in capillaries?

Answer 15

It allows more time for diffusion to occur

Question 16

Describe the structure of veins (3)

Answer 16

• A vein has a large lumen and a relatively thin wall containing some elastic tissue and smooth muscle.
• Veins also have valves that prevent the blood flowing backwards.

Question 17

How do leg muscles allow the blood in veins to return to the heart?

Answer 17

When the leg muscles contract they bulge and press on the walls of the veins, pushing the blood up the veins. When the muscles relax, the valves close. This action helps the blood return to the heart.