4. Cardiovascular mechanisms 3

Question 1

Function of pulmonary circulation

Answer 1

allows blood to be oxygenated

Question 2

Function of systemic circulation

Answer 2

Pumps blood to rest of body

Question 3

Why do small arteries and arterioles have extensive smooth muscle in their walls?

Answer 3

to regulate their diameters and resistance to blood flow

Question 4

What do capillaries provide?

Answer 4

Large SA

Thin walls for diffusion to occur

Question 5

Which vessels are described as capacitance vessels?

Answer 5

Veins and venules
highly compliant
act as a reservoir for blood volume

Question 6

Equation for MAP (including cardiac output and resistance)

Answer 6

MAP = Cardiac output x Resistance
MAP = Q x R

Question 7

What 3 assumptions mean the equation for MAP can only give an approximation?
(eq. Q x R)

Answer 7

Steady flow (which does not occur due to the intermittent pumping of the heart)
Rigid vessels
Right atrial pressure is negligible

Question 8

How does pressure change with distance through circulation?

Answer 8

Pressure falls
Due to viscous pressure losses.
Small arteries and arterioles present most resistance to flow.
High pressure in arteries, markedly drops in arterioles, further drops in capillaries.
Pressure difference allows blood to flow through capillaries

Question 9

What 3 factors influence the resistance of a tube to flow?

Answer 9

Fluid viscosity
Length of the tube
Inner radius of the tube

Question 10

Poiseuilles equation

Answer 10

R= (8 x L x fluid viscosity) / pi x r^4

Question 11

What can be ignored in poiseuilles equation when calculating resistance in circulatory system?

Answer 11

Viscosity- doesn’t change

Length- doesn’t change

Question 12

What is the simplified version for poiseuilles equation when calculating resistance in circulatory system?

Answer 12

Resistance = 1 / r^4

Question 13

How is blood flow distribution determined?

Answer 13

By metabolic need

Question 14

Laminar flow

Answer 14

Linear, Healthy
Velocity of the fluid is constant at any one point and flows in layers
Blood flows fastest closest to the centre of the lumen.
Flows slower near walls due to resistance from hitting side walls of vessel

Question 15

Turbulent flow

Answer 15

Less healthy
Blood flows erratically, forming eddys, and is prone to pooling
Associated with pathophysiological changes to the endothelial lining of the blood vessels

Question 16

What gives blood a parabolic velocity profile?

Answer 16

Adhesive forces between fluid and surface slow flow

Velocity of layers increases as distance from wall increases

Question 17

How is the shear rate determined?

Answer 17

Gradient of velocity profile

Question 18

Shear stress equation

Answer 18

Shear rate x Viscosity

Question 19

What does shear stress govern?

Answer 19

How well endothelial cells work

Endothelial cells release molecules that govern resistance to flow and govern laminar flow

Question 20

Laminar shear stress

Answer 20

High shear stress
Promotes endothelial cell survival and quiescence
Cells aligned in direction of flow
Secretions promote vasodilation and anticoagulation
GOOD

Question 21

Disturbed shear stress

Answer 21

Low shear stress
Promotes endothelial proliferation, apoptosis and shape change
Secretions promote vasoconstriction, coagulation and platelet aggregation
BAD

Question 22

What causes turbulent flow to increase in carotid arteries?

Answer 22

Age

Question 23

What does slow deflation of a cuff when measuring BP cause?

Answer 23

Turbulent flow, which can be heard with a stethoscope

Question 24

What causes the dichroic notch when graphing BP?

Answer 24

Closure of aortic valve

Question 25

Equation for pulse pressure

Answer 25

PP= SBP - DBP

Question 26

Equation for MAP (including DBP and PP)

Answer 26

MAP = DBP + 1/3 (PP)

Question 27

When the aortic valve closes, why does ventricular pressure fall rapidly but aortic pressure fall slowly?

Answer 27

Windkessel effect: | Elasticity in aorta allows blood flow to be sustained, less pulsatile, maintains diastolic pressure

Question 28

During ejection blood enters the aorta and other downstream vessels at what relative speed?

Answer 28

Enters faster than it leaves them

Question 29

What happens of arterial compliance decreases? (become stiffer e.g. with age)

Answer 29

The damping effect of the Windkessel effect is reduced | Pulse pressure increases.

Question 30

Circumferential stress

Answer 30

= Tension (T) / Wall thickness (h)

Question 31

Equation for pressure gradient

Answer 31

P1 (start of vessel) - P2 (end of vessel)

Question 32

Pathological example of Law of Laplace

Answer 32

Vascular aneurysms increase radius of the vessel. So, for the same internal pressure, the inward force exerted by the muscular wall must also increase. However, if muscle fibres have weakened, the force needed can’t be produced, so the aneurysm will continue to expand until it ruptures

Question 33

Compliance

Answer 33

The relationship between transmural pressure and vessel volume Depends on vessel elasticity

Question 34

Venous compliance relative to arterial compliance at low pressure

Answer 34

Venous compliance 10-20x greater

Question 35

What can decrease radius and venous volume, thereby increasing venous pressure

Answer 35

Increased innervation and increasing smooth muscle contraction

Question 36

Describe the effects of gravity when standing up

Answer 36

Increases hydrostatic pressure in legs | Blood transiently pools in veins due to their high compliance, reducing venous return

Question 37

What is the approximate increase in hydrostatic pressure in vessels due to gravity?

Answer 37

100mmHg

Question 38

How does pressure ensure unidirectional flow?

Answer 38

Pressure gradient from left heart to right heart is maintained

Question 39

What is the difference between the blood pressure in the ankle compared to the hand?

Answer 39

BP in the ankle is much greater than in the hand

Question 40

Why don't we faint every time we stand up due to blood pooling in our leg veins?

Answer 40

Standing causes activation of the SNS, which stiffens and constricts the veins resulting in greater venous return to the heart. Constricted arteries means there is an increase in TPR to maintain BP. Also a slight increase in HR and force of contraction.

Question 41

What are the 2 pumps that facilitate the movement of venous blood back to the heart?

Answer 41

Skeletal muscle pump | Respiratory pump