Flow Through Tubes

Question 1

How is blood flow around the cardiovascular system driven?

Answer 1

It is driven by the pressure gradient.

Question 2

What determines flow for a given change in pressure?

Answer 2

The resistance which includes the nature of the fluid and the vessel.

Question 3

Define flow.

Answer 3

This is the volume of fluid passing a particular point in the vessel per unit time

Question 4

What is velocity in relation to the CVS?

Answer 4

This is the rate of flow of fluid through the vessel.

Question 5

In the CVS, what is constant, velocity or flow?

Answer 5

Flow is constant. Velocity changes as the radius of the tube changes.

Question 6

What is the relationship between velocity and cross sectional area of the tube?

Answer 6

Inversely proportional.

Question 7

Within the whole system, which vessels have the fastest velocity?

Answer 7

The capillaries me because collectively they have the largest total cross sectional area.

Question 8

Describe laminar flow.

Answer 8

This is where there is a gradient of velocity from the outside inwards, so the fluid moving fastest is in the centre of the vessel.

Question 9

When can turbulent flow occur?

Answer 9

If mean velocity increases too much then this can cause turbulent flow where the velocity gradient breaks down. The fluid tumbles over each other and this leads to an increase in flow resistance.

Question 10

What two factors does mean velocity and therefore flow depend on?

Answer 10

The radius of the tube and the viscosity of the fluid.

Question 11

Explain how viscosity affects blood flow.

Answer 11

In laminar flow, the layers of fluid are sliding over each other and this leads to a decreased average velocity when viscosity is higher and there is more resistance to this sliding.

Question 12

What affect does increasing the radius have on the mean flow?

Answer 12

It increases it because there is an increased velocity due to the gradient between the layers of laminar flow remaining the same but there being more layers present.

Question 13

Name four factors of a tube which can increase flow.

Answer 13

Increase radius, increase pressure difference, decrease viscosity and decrease length.

Question 14

Name two causes of hyper viscosity syndrome.

Answer 14

Abnormally high plasma proteins, abnormally high red or white blood cells.

Question 15

Why do functional cardiac murmurs occur in severe anaemias?

Answer 15

In severe anaemia there is high blood flow velocity to deliver sufficient oxygen and also reduced plasma proteins and therefore low viscosity which leads to turbulent flow.

Question 16

What equation links flow, resistance and pressure?

Answer 16

Pressure = flow X resistance.

Question 17

How does the effective resistance change for vessels in series and in parallel?

Answer 17

In series, resistance is increased and for vessels in parallel resistance is decreased.

Question 18

In what vessels in the circulatory system is there a large pressure drop?

Answer 18

In the arterioles as these are high resistance vessels.

Question 19

If arteriolar resistance remains constant, what happens to blood pressure with increased cardiac output?

Answer 19

It increases.

Question 20

Why arterial pressure high?

Answer 20

Due to the high resistance of the arterioles.

Question 21

Name three factors which can cause turbulent flow.

Answer 21

Low viscosity of fluid, high flow velocity, irregular vessel.

Question 22

What sound can be heard when there is turbulent flow?

Answer 22

A bruit

Question 23

In what situation in the heart will we hear a bruit?

Answer 23

If there is stenosed cardiac valves.

Question 24

Name four common arteries where atherosclerotic plaque leads to a bruit being heard.

Answer 24

Femoral artery, hepatic artery, renal artery and carotid artery.

Question 25

What is transmural pressure?

Answer 25

This is the pressure between the inside of a vessel and the outside which determines how much the walls stretch and how much the vessel distends.

Question 26

What is capacitance?

Answer 26

This is the ability of a blood vessel to store blood and occurs when in flow is faster than out flow.

Question 27

In distensible vessels, when is it easiest for blood to flow?

Answer 27

When the pressure is higher as this causes the vessel to distend.

Question 28

What is compliance?

Answer 28

This is the ability of a vessel to distend and increase volume due to an increased pressure.

Question 29

How can we calculate cardiac output?

Answer 29

Cardiac output = heart rate X stroke volume

Question 30

What features does the arterial tree posses and why is this important?

Answer 30

It is high pressure, low resistance, low compliance vessel. This means that CO is driven into the high resistance arterioles.

Question 31

What is total peripheral resistance?

Answer 31

This is the sum of the arteriolar resistance.

Question 32

What happens in the arteries during diastole to ensure smooth flow?

Answer 32

Elastic recoil.

Question 33

When is the energy for elastic recoil of the arteries stored?

Answer 33

Mechanical energy is stored during systole and then this. Is dissipated over diastole.

Question 34

What can reduced arterial compliance lead to?

Answer 34

Hypertension.

Question 35

How can we calculate pulse pressure?

Answer 35

This is the difference between the systolic and diastolic pressures.

Question 36

Why is it important that there is a significant pressure gradient decrease of the blood before it reaches the capillaries?

Answer 36

This means that efficient substrate exchange can occur.

Question 37

Name two things which control blood flow into capillary beds.

Answer 37

Arterioles and pre capillary sphincters

Question 38

Why is vasomotor tone of the arterioles important to the tissues?

Answer 38

This controls the blood flow into the capillaries and ensures that supply meets the metabolic demands of the tissues.

Question 39

How is vasomotor tone controlled?

Answer 39

By the sympathetic nervous system. Noradrenaline acts on a1 adrenoceptors to cause vasoconstriction and also acts on B2 to cause vasodilation.

Question 40

When does vasodilation occur?

Answer 40

In high metabolic tissues, there are many local vasodilatory including H+,K+, Co2, adenosine and lactate which all have a vasodilatory effect.

Question 41

What is vasodilatation?

Answer 41

This is when there is a reduction or offset of a signal which is causing vasoconstriction.

Question 42

What is hyperemia?

Answer 42

This occurs when we exercise and is when there is increased blood flow. This will return back to normal after we finish exercising.

Question 43

Name three factors which can affect vasomotor tone.

Answer 43

Hormonal, myogenic and endothelial

Question 44

What are autacoids?

Answer 44

These are released from arteriolar endothelium and cause +/- in vasomotor tone.

Question 45

State two ways in which veins differ from the arterial system.

Answer 45

Veins have low resistance and very high capacitance.

Question 46

How is venous pressure determined?

Answer 46

This is the amount of blood contained within the veins

Question 47

What factors can affect venous pressure?

Answer 47

Cardiac output, body metabolic demand and back pressure.

Question 48

What is the range of values that central Venous pressure can take?

Answer 48

Central venous pressure varies between -10mmHg and 10mmHg.

Question 49

How do you calculate mean arterial blood pressure?

Answer 49

Diastolic blood pressure + 1/3 of pulse pressure.

Question 50

Define auto regulation.

Answer 50

This is the intrinsic ability of an organ to maintain constant blood flow to its self.

Question 51

Define venous return.

Answer 51

This is the rate of blood flow back to the heart.