6. The Cardiovascular System

Question 1

Who was Galen? What did he believe about blood? When did beliefs about blood finally change? Who brought about this change?

Answer 1

• an ancient Greek philosopher (and doctor)
• believed: blood is produced in the liver, pumped out by the heart and consumed in the other organs of the body
• 17th century
• William Harvey

Question 2

What did William Harvey do to get his beliefs about blood to be accepted?

Answer 2

had to overcome widespread opposition because Galen’s theories were so well established:

• published his results
• toured Europe to demonstrate experiments that overturned previous theories and provided evidence for his theory

Question 3

What did William Harvey demonstrate regarding blood?

Answer 3

1. that blood flow through vessels is unidirectional with valves to prevent backflow
2. also that the rate of flow through major vessels is far too high for blood to be consumed in the body after being pumped out by the heart.
3. heart pumps blood out in the arteries and that it returns in veins

Question 4

What did William Harvey predict? Why couldn’t he prove it?

Answer 4

• the presence of numerous fine vessels, too small to be seen with contemporary equipment, that linked arteries to veins in the tissues of the body
• he published his theory in 1628, microscopes were invented in 1660

Question 5

What did the microscope reveal to be happening regarding the journey of blood?

Answer 5

flowed from arteries to veins through capillaries (as Harvey predicted)

Question 6

What sort of circulation do humans have? What does this mean?

Answer 6

double circulation - there are separate circulations for the lungs (pulmonary circulation) and for the other organs of the body (systemic circulation)

Question 7

Sketch and label the double circulation system. (p74)

Answer 7

-

Question 8

What sort of pump is the heart? What do the two sides pump?

Answer 8

• double pump
• right: pumps deoxygenated blood to the lungs via pulmonary artery
• • oxygenated blood returns to the left side of the heart in the pulmonary vein
• left: pumps oxygenated blood to all parts of the body (apart from the lungs) via the aorta
• • deoxygenated blood is carried back to the right side of the heart in the vena cava

Question 9

What are blood vessels?

Answer 9

tubes that carry blood

Question 10

How many main types of blood vessel are there? Name them.

Answer 10

3:

• arteries
• capillaries
• veins

Question 11

What is the role of arteries in the circulation system?

Answer 11

• convey blood pumped out at high pressure by the ventricles of the heart
• carry the blood to tissues of the body

Question 12

What is the role of veins in the circulation system?

Answer 12

• carry blood through tissues

- have permeable walls that allow exchange of materials between the cells of the tissue and the blood in the capillary

Question 13

What is the role of veins in the circulation system?

Answer 13

• collect blood at low pressure from the tissues of the body and return it to the atria of the heart

Question 14

Draw and label a capillary. Explain how the features make it well suited to its role. (p74)

Answer 14

• wall consists of a single layer of thin cells so the distance for diffusion in or out is small
• pores between cells in the wall allow some of the plasma to leak out and form tissue fluid. Phagocytes can also squeeze out
• very narrow lumen - only about 10um across so that capillaries fit into small spaces. Many small capillaries have a larger surface area than fewer wider ones would

Question 15

Draw and label an artery. Explain how the features make it well suited to its role. (p74)

Answer 15

• tough outer coat
• thick wall to withstand the high pressure
• narrow lumen to help maintain the high pressures
• thick layer containing elastic fibres that maintain high pressure between pumping cycles and muscle that contracts or relaxes to adjust the diameter of the lumen

Question 16

Draw and label a vein. Explain how the features make it well suited to its role. (p74)

Answer 16

• thin layer of tissue with few or no elastic fibres or muscle as blood flow is not pulsatile
• wide lumen is needed to accommodate the low pressure, slow flowing blood. Valves are present at intervals in veins to prevent back-flow
• thin walls allow the vein to be pressed flat by adjacent muscles, helping to move the blood
• outer coat is thin as there is no danger of veins bursting

Question 17

What 4 categories should you talk about when comparing how capillaries, arteries and veins are adapted for their particular role?

Answer 17

• size of lumen
• thickness of wall (of vessel)
• pressure of blood (inside vessel)
• elastic fibres (thick, thin, none)