Haemodynamics

Question 1

Haemodynamics

Answer 1

Physical laws governing pressure/flow relationships in blood vessels

Question 2

Why do they standard principles of fluid mechanics not technically apply to blood

Answer 2

Blood is a non newtonian fluid; red and white cells, platelets and lipids are suspended in a solution of proteins

Question 3

Formula for flow of blood

Answer 3

Pressure gradient between arteries and veins (created by pumping) / Resistance of blood vessels against blood flow

Question 4

What separates the vascular lumen from the media

Answer 4

Intima (endothelium)

Question 5

In which layer of the vessel is smooth muscle contained

Answer 5

Tunica Media

Question 6

Biggest artery

Answer 6

Aorta

Question 7

Discuss elasticity of arteries as they get smaller (from aorta to arterioles/capillaries)

Answer 7

Elasticity decreases, with no elasticity at all at the capillaries

Question 8

Compare elasticity & SM of capillaries, venules, veins and vena cava

Answer 8

No elasticity or smooth muscle in capillaries & venules, but there is some in veins and even more in the vena cava (not much still)

Question 9

Biggest Vein

Answer 9

Vena Cava

Question 10

Compare the individual vessel diameters

Answer 10

Aorta > Arteries > Arterioles > Capillaries

Question 11

Compare total Cross Sectional Areas (CSA) of vessels

Answer 11

Aorta < Arteries < Arterioles < Capillaries

BECAUSE THERE ARE SO MANY CAPILLARIES

Question 12

Velocity of blood formula

Answer 12

Question 13

Look at this graaph

Question 14

4 Determinants of Flow

Answer 14

Directly related to pressure difference
Inversely related to length of tube
Inversely related to viscosity of fluid
Directly related to radius of tube

(think of resistance)

Question 15

Discuss importance of pressure difference in creating flow of blood vessels

Answer 15

Question 16

Discuss importance of tube length in affecting flow of blood vessels

Answer 16

Longer vessels means less flow per unit time

Question 17

Discuss importance of viscosity in affecting flow of blood vessels

Answer 17

Think of it like drinking water vs millkshake from a straw

Question 18

Discuss importance of tube radius in affecting flow of blood vessels

Answer 18

The greater the diameter, the greater the flow

Think resistance

Flow related to r^4 (Remember) - exponential change

Question 19

Which blood vessels have the greatest capacity to change radius - Resistance vessels

Answer 19

Small arteries & arterioles

Question 20

When is the blood flow pulsatile and when is it steady

Answer 20

At capillaries it is steady but upstream of that it is more pulsatile

Question 21

Role of small arteries and arterioles in terms of pressure

Answer 21

Dissipating the pressures and preventing the pressure form overwhelming the capillaries

Question 22

Calculate total peripheral resistance and renal vascular resistance

Answer 22

Question 23

Why must peripheral resistance be less than the parallel individual resistances

Answer 23

Think of parallel circuits

Question 24

Issue of turbulent flow in terms of force and flow

Answer 24

More force is needed to acheive the same flow when flow is turbulent

Question 25

Compliance (vessels) and how is it related to distensibility

Answer 25

Change in volume for a given change in pressure

Less compliant = Less distensible

Question 26

Role of Arterial compliance

Answer 26

Provides ‘filtering’/smoothing of pressure for smaller vessels

Question 27

Role of Venous compliance

Answer 27

Provides ‘capacity’ for storage

Question 28

What happens to venous compliance as veins are constricted

Answer 28

Constriction of veins reduces venous capacity and increases return of blood to heart - increases effective circulating blood volume

Question 29

Factors affecting venous return

Answer 29

Venomotor tone (constriction)
Venous valve competence

Skeletal muscle pump
Respiration