Overview of the Cardiovascular System

Question 1

What is the main function of the CVS?

Answer 1

TRANSPORT

Question 2

Give examples of the following in the CVS:

1. Transport from the external to internal environment
2. Transport from cell to cell
3. Transport of materials leaving the body

Answer 2

1. Oxygen, nutrients and water to all cells
2. wastes e.g. gut to liver, immune cells and antibodies, hormones to target cells
3. metabolic waste, heat and CO2 from all cells

Question 3

Describe the most simplistic arrangement of the CVS

Answer 3

Systemic Circulation
Venous system
Right atrium –> Right ventricle –> Pulmonary artery
Pulmonary Circulation
Pulmonary vein –> Left atrium –> Left ventricle –> Aorta
Systemic Circulation

Question 4

Describe the relationship between the left and right side of the heart and the vascular beds using the words parallel and in series

Answer 4

The R and L sides of the heart are in series with each other
Vascular beds are in parallel arrangement

Question 5

What is the significance of the R and L heart being in series with each other?

Answer 5

output of the RV into pulmonary circulation and then left atrium equals the output of the LV into the systemic circulation

Question 6

In what circumstance would the output of the RV not equal to output of the LV?

Answer 6

If blood is being lost or pooling somewhere

Question 7

What is the standard unit of pressure in the CVS?

What is its conversion?

Answer 7

mmHg

1kPa = 7.5mmHg

Question 8

What is the significance of the vascular beds being arranged in parallel?

Answer 8

All beds get blood with same level of oxygenation

Prevent changes in blood flow in one organ affecting flow in other organs.

Question 9

List the following pressures in the heart as compared to atmospheric pressure:

• IVC and SVC –> right atrium
• Pulmonary artery –> lungs
• Aorta –> systemic circulation

Answer 9

• 0mmHg
• 25mmHg
• 90mmHg

Question 10

What is cardiac output?
How is it calculated?
What is a normal cardiac output?
What is the significance of the cardiac output of the left and right heart?

Answer 10

volume of blood pumped out of the ventricle per minute
CO = stroke volume x heart rate
5L per minute = 70ml x 70bpm
They are equal

Question 11

How is pulse pressure calculated?

What does it indicate?

Answer 11

Pulse pressure = SP - DP
If pulse pressure is high, they have a bounding pulse
If pulse pressure is low, they have a weak pulse
This tells you nothing about absolute pressure i.e. they could have extremely high blood pressure with a weak pulse (low pulse pressure)

Question 12

Why is the midpoint of systolic and diastolic pressure not the mean aortic pressure?
How is the mean aortic pressure calculated?

Answer 12

Not the midpoint because diastole is 60% of the cardiac cycle
Mean ABP = (SP-DP)/3 +DP

Question 13

What maintains the pressure during diastole?

Answer 13

The elastic recoil of the tissues

Question 14

Describe the changes in pressure across systemic vasculature? Why is this?

Answer 14

Pressure drops as you move through the system

–> there must therefore be resistance to flow

Question 15

As you move through the systemic circulation when is the biggest drop in pressure and why?

Answer 15

Into arterioles. These are sometimes called resistance vessels.

Question 16

What to things determine pressure in the arterial system?

Which law is this analogous to?

Answer 16

1. Resistance to blood flow
2. Blood volume in the arterial system
   Ohms law V = IR
   Pressure = flow x resistance
   ABP = CO x total peripheral resistance

Question 17

What is the total peripheral resistance?

Answer 17

the resistance to flow offered by all systemic vasculature excluding pulmonary

Question 18

How do arterioles control blood flow to organs?

What is this controlled by?

Answer 18

Vasoconstriction or vasodilation changed resistance and therefore controls flow
Resistance is controlled by sympathetic nerves and local factors e.g. adenosine, histamine, O2, CO2…

Question 19

Describe briefly the following…

1. arteries
2. small arteries and arterioles
3. capillaries
4. venules
5. veins

Answer 19

1. carry blood at high pressure, thick muscular walls, elastic layers, relatively narrow lumen, high pressure conduits
2. carry blood at modest pressure, thick muscular walls, muscle under influence of local factors and ANS, function of control flow to tissues
3. carry blood at low pressure, single endothelial cell wall, maximise exchange between blood and tissue
4. low pressure, resemble capillaries, low pressure conduits
5. carry blood at very low pressure, thin walls, muscle under control of ANS, wide lumen accommodates large volumes, reservoirs used to adjust ventricular filling

Question 20

What is the approximate mean pressure in each of the following?

1. arteries
2. small arteries and arterioles
3. capillaries
4. venules
5. veins

Answer 20

1. 90mmHg
2. 50mmHg
3. 35mmHg
4. 15mmHg
5. 10mmHg

Question 21

What % of body weight does total blood volume account for?

Therefore what is the normal blood volume for a 70kg male?

Answer 21

approx 7%

5l

Question 22

Venous return = Cardiac output

Any imbalance between VR and CO lead to a coordinated response so that ABP is maintained. Give 2 examples

Answer 22

E.g. standing. Your venous return decreases, coordinated response to maintain blood pressure
Exercise Increase CO, therefore need to increase VR

Question 23

What kind of feedback maintains ABP?

Answer 23

negative feedback control