The Circulatory System

Question 1

What is the circulatory system?

Answer 1

A specialised transport system to carry raw materials from specialised exchange organs to their body cells

Question 2

What is the circulatory system made up from?

Answer 2

The heart and blood vessels

Question 3

What does the heart do?

Answer 3

The heart pumps blood through blood vessels (arteries, arterioles, veins and capillaries) to reach different parts of the body

Question 4

What does blood do?

Answer 4

Blood transports respiratory gases, products of digestion, metabolic wastes and hormones around the body

Question 5

What are the two circuits of the circulatory system?

Answer 5

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

Question 6

What vessels supply the heart with blood?

Answer 6

The left and right coronary arteries

Question 7

What do arteries do?

Answer 7

Arteries carry blood from the heart to the rest of the body

Question 8

What is the structure of the arteries?

Answer 8

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

Question 9

Do arteries carry oxygenated or deoxygenated blood?

Answer 9

All arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs

Question 10

What are arterioles?

Answer 10

Arteries divide into smaller vessels called arterioles. These form a network in the body. Blood is directed to different areas of demand in the body by muscles inside the arterioles, which contract to constrict blood flow or relax to allow full blood flow

Question 11

What do veins do?

Answer 11

Veins take blood back to the heart under low pressure

Question 12

What is the structure of veins?

Answer 12

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

Question 13

Do veins carry oxygenated or deoxygenated blood?

Answer 13

All veins carry deoxygenated blood, except for the pulmonary veins which carry oxygenated blood to the heart from the lungs

Question 14

What are capillaries?

Answer 14

Arterioles branch into capillaries, which are the smallest of the blood vessels. Substances are exchanged between cells and capillaries, so they’re adapted for efficient diffusion

Question 15

How are capillaries adapted for efficient diffusion?

Answer 15

1. They’re always found near cells in exchange systems
2. Their walls are only one cell thick, which shortens the diffusion pathway
3. There are a large number of capillaries, to increase surface area for exchange

Question 16

What are networks of capillaries in tissues called?

Answer 16

Capillary beds

Question 17

What is tissue fluid?

Answer 17

Tissue fluid is the fluid that surrounds cells in tissues

Question 18

What is tissue fluid made from?

Answer 18

Small molecules that leave the blood plasma

Question 19

What do cells take in from and release into the tissue fluid?

Answer 19

Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it.

Question 20

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

Answer 20

Pressure filtration

Question 21

Explain pressure filtration

Answer 21

1. At the start of the capillary bed, nearest the arteries, the hydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid
2. This difference in hydrostatic pressure means an overall outward pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid
3. As fluid leaves, the hydrostatic pressure reduces in the capillaries - so the hydrostatic pressure is much lower at the venule end of the capillary bed
4. Due to the fluid loss, and an increasing concentration of plasma proteins, the water potential at the venule end of the capillary bed is lower than the water potential of the tissue fluid
5. This means that some water re-enters the capillaries from the tissue fluid at the venule end by osmosis

Question 22

At the end of pressure filtration, what happens to any excess tissue fluid?

Answer 22

Excess tissue fluid is drained into the lymphatic system, which transports this excess fluid from the tissues and puts it back into the circulatory system