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LSS Cadiovascular System > circulation > Flashcards

circulation Flashcards

flow: explain the physical principles, recall Poiseuille's equation, explain the effect of gravity, explain the control of capillary blood flow, and explain the concept of vascular capacitance and compliance

1
Q

2 types of blood flow

A

laminar and turbulent

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2
Q

define laminar flow

A

velocity of fluid is constant at any one point and flows in layers; flows fastest closest to lumen centre due to friction with endothelial lining

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3
Q

define turbulent flow

A

blood flows erratically, forming eddys at branching, and is prone to pooling; associated with pathophysiological changes to endothelial lining

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4
Q

what is parabolic velocity profile

A

the further from the wall, the faster the velocity

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5
Q

what is the tangent at any point on the parabolic velocity profile

A

shear rate (change in velocity/change in radius)

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6
Q

how to calculate shear stress

A

shear rate x viscosity

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7
Q

diagram of parabolic velocity profile

A

benjis

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8
Q

what does shear stress govern

A

how well endothelial cells work

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9
Q

when does laminar shear stress occur

A

at a high level of shear stress

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10
Q

what does laminar shear stress promote

A

endothelial cell survival, allowing secretions to promote vasodilation and anticoagulation

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11
Q

when does turbulent shear stress occur

A

at a low level of shear stress

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12
Q

what does turbulent shear stress promote

A

endothelial proliferation, apoptosis and shape change, allowing secretions to promote vasoconstriction, coagulation and platelet aggregation

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13
Q

what can turbulent shear stress lead to

A

occlusion

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14
Q

turbulent shear stress and age

A

worsens with age

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15
Q

how do you use turbulent flow to measure blood pressure

A

release of cuff leads to turbulent flow that can be heard with a stethoscope

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16
Q

where is blood pressure ususally measured and why

A

upper arm as easily accessed and at heart-level

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17
Q

Poiseuille’s equation

A

resistance = (8 x length x viscosity)/(pi x radius^4)

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18
Q

how is regulation of flow achieved

A

variation in resistance in vessels while pressure remains relatively constant

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19
Q

explanation of Poiseuille’s equation

A

changing radius changes amount of flow, so relatively small changes in vascular tone can produce large changes in flow

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20
Q

in Pouiseuille’s equation, what can be taken as effectively constant

A

length and viscosity of blood vessels, so only radius changes rapidly

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21
Q

Poiseuille’s equation for blood flow

A

R = 1/r^4 (so halving radius decreases flow 16 times)

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22
Q

define vascular capacitance/compliance

A

ability of a vessel to distend and increase its volume with increasing transmural pressure

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23
Q

at a given pressure, what happens to volume at high and low compliance

A

at high compliance, volume increases by large degree; at low compliance, volume doesn’t increase much

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24
Q

compliance equation

A

change in volume/change in pressure

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25
Q

define elastance

A

ability of a vessel to return to original shape

26
Q

elastance equation

A

change in pressure/change in volume

27
Q

what produces elastance in vessels

A

elastin fibres in vascular wall

28
Q

compliance properties of veins

A

very compliant so can dilate substantially and store a large volume of blood inside

29
Q

compliance properties of arteries

A

low compliance so do not distendas they have a larger elastic layer so have high elastance, recoiling to maintain pressure

30
Q

what is the Windkessel effect

A

recoil of arteries ensures continual flow despite pulastile effect of heart (e.g. during diastole); gets less significant with age

31
Q

clinical external modulation of compliance

A

stockings apply external pressure to veins, preventing large increase in volume and reducing risk of pooling

32
Q

internal modulation of compliance

A

renin-angiotensin aldosterone system, endogenous vasodilators/constrictors, vasoactive drugs

33
Q

what does gravity do to blood

A

pulls it towards ground

34
Q

effect on hydrostatic pressure by gravity when standing and outcome

A

standing causes increased hydrostatic pressure, so blood transiently pools in veins due to high compliance

35
Q

what happens to venous return in response to pooling and further outcomes

A

decreases, so without compensation will reduce cardiac output and blood pressure, causing fainting

36
Q

why is pressure gradient from left to right heart maintained

A

ensure unidirectional flow

37
Q

effect of small leg movement on venous return

A

activates skeletal muscle pump to increase venous return

38
Q

what ensures unidirectional blood flow in veins

A

valves

39
Q

effect of respiratory pump on venous return

A

negative intrathoracic pressure increases venous return

40
Q

define varicose veins

A

incompetent valves causing dilated superficial veins in leg

41
Q

cause of oedema in feet due to gravity

A

prolonged elevation of venous pressure even with intact compensatory mechanisms

42
Q

what are the local mechanisms of flow intrinsic to

A

smooth muscle (important for reflexive control)

43
Q

wht are the systemic mechanisms extrinsic to

A

smooth muscle (hormones and autonomic nervous system to control radius)

44
Q

define flow autoregulation

A

intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance

45
Q

myogenic theory of autoregulation to decrease resistance to increase flow

A

smooth muscle fibres respond to tension in vessel wall, so increased pressure caues contraction, and reduced perfusion causes relaxation

46
Q

metabolic theory of autoregulation to decrease resistance to increase flow (active hyperaemia)

A

as blood flow decreases, metabolites accumulate, causing dilation to increase flow and wash metabolites away

47
Q

how does injury cause constriction

A

serotonin release from platelets causes constriction

48
Q

endoelium derived vasodilators

A

nitric oxide, prostacyclin

49
Q

non-endothelium derived vasodilators

A

kinins, ANP

50
Q

endothelium-derived vasoconstrictors

A

thromboxane A2, endothelins

51
Q

non-endothelium derived vasoconstrictors

A

ADH, (nor)adrenaline, angiotensin II

52
Q

calculate flow rate

A

pressure gradient/resistance

53
Q

what is the pressure gradient in capillary blood flow

A

difference in pressure between arteriole and capillary

54
Q

what is the normal venous pressure

A

37 mmHg

55
Q

capillary beds in different tissues

A

highly metabolically active tissues have denser capilarry networks; skeletal muscle have large capacity limited flow at rest; myocardium and brain are most heavily perfused except lung

56
Q

function of pre-capillary sphincters and relevance to skeletal muscle beds

A

allow some capillaries to be completely closed off, allowing skeletal muscle bed flow to be reduced at rest and larger during exercise

57
Q

features of continuous capillaries

A

junctions between endothelial cells are filled with water; water soluble and small molecules diffuse over gap junctions; large and water soluble molecules require transport proteins; small and lipid soluble molecules can diffuse straight across

58
Q

features of fenestrated capillaries

A

many small gaps (fenestrations) make walls leaky e.g. glomerulus

59
Q

features of discontinuous capillaries

A

large gaps between cells e.g. bone marrow/liver

60
Q

what type of capillaries are involved in the blood-brain barrier

A

continuous capillaries with tight rather than gap junctions, and many transporter proteins

LSS Cadiovascular System (40 decks)

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