3B The Circulatory System

Question 1

Why do multicellular organisms, like mammals, need a circulatory system?

Answer 1

These organisms have a low surface area to volume ratio. So they need a specialised mass transport system to carry raw materials from specialised exchange organs to their body cells.

Question 2

Name the 5 types of blood vessels.

Answer 2

Arteries, arterioles, capillaries, venules, veins.

Question 3

Name the four main blood vessels entering and leaving the heart.

Answer 3

Pulmonary artery, pulmonary vein, aorta, vena cava.

Question 4

Which blood vessel carries deoxygenated blood from the heart to the lungs?

Answer 4

Pulmonary artery.

Question 5

Which blood vessel carries oxygenated blood from the lungs to the heart?

Answer 5

Pulmonary vein.

Question 6

Which blood vessel carries oxygenated blood from the heart to the rest of the body?

Answer 6

Aorta.

Question 7

Which blood vessel carries deoxygenated blood from the rest of the body to the heart?

Answer 7

Vena cava.

Question 8

What does blood carry around the body?

Answer 8

Respiratory gases, products of digestion, metabolic wastes and hormones.

Question 9

Which blood vessels supply the heart?

Answer 9

The left and right coronary arteries.

Question 10

Describe the two circuits in the body that blood travels through.

Answer 10

One circuit takes blood from the heart to the lungs, then back to the heart.
The other loop takes blood around the rest of the body.

Question 11

In which blood vessel is blood pressure the lowest?

Answer 11

The vena cava. Blood flows from a higher pressure to a lower pressure.

Question 12

Which blood vessels connect the kidneys to the circulatory system?

Answer 12

The renal vein and renal artery.

Question 13

Describe the gross structure of arteries.

Answer 13

Their walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, to maintain the high pressure.
The inner lining (endothelium) is folded, allowing the artery to stretch to also maintain high blood pressure.

Question 14

Describe the gross structure of arterioles.

Answer 14

Arterioles form a network throughout the body. Blood is directed to different areas of demand by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow blood flow.

Question 15

Describe the gross structure of veins.

Answer 15

Veins have a wider lumen with very little elastic or muscle tissue. They contain valves to stop the low pressure blood flowing backwards. Blood flow through veins is helped by the contraction of the body muscles surrounding them.

Question 16

Describe the gross structure of capillaries.

Answer 16

They are the smallest of blood vessels and have walls one cell thick. They connect arterioles to venules. They allow exchange of substances between cells and the circulatory system.

Question 17

How are capillaries adapted for efficient exchange?

Answer 17

They are found very close to cells in exchange tissues and have very thin walls so there is a short diffusion pathway. There are a large number of them to increase surface area for exchange.

Question 18

What are capillary beds?

Answer 18

Networks of capillaries in tissue.

Question 19

Where is tissue fluid found and what is it made up of?

Answer 19

It surrounds cells in tissues. It’s made of small molecules that leave the blood e.g. small proteins, oxygen, water and nutrients. It doesn’t contain large proteins or red blood cells, as they cannot fit through the capillary walls.

Question 20

In a capillary bed, how do substances move out of capillaries into the tissue fluid?

Answer 20

By pressure filtration.

Question 21

Describe the process of pressure filtration.

Answer 21

1. At the start of the capillary bed by the arterioles, the hydrostatic pressure inside the capillaries is higher than that in the tissue fluid.
2. This pressure forces fluid out of the capillaries into the spaces around cells.
3. At the venule end, when a lot of fluid has left, the hydrostatic pressure in the capillaries decreases.
4. Due to fluid loss and an increasing concentration of plasma proteins in the capillaries, the water potential in the venule end is lower than that of the tissue fluid.
5. Some water reenters the capillaries by osmosis.

Question 22

What happens to excess tissue fluid?

Answer 22

Excess tissue fluid is drained into the lymphatic system, which transports it from the tissues and eventually back into the circulatory system.