circulation

Question 1

2 types of blood flow

Answer 1

laminar and turbulent

Question 2

define laminar flow

Answer 2

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

Question 3

define turbulent flow

Answer 3

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

Question 4

what is parabolic velocity profile

Answer 4

the further from the wall, the faster the velocity

Question 5

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

Answer 5

shear rate (change in velocity/change in radius)

Question 6

how to calculate shear stress

Answer 6

shear rate x viscosity

Question 7

diagram of parabolic velocity profile

Answer 7

benjis

Question 8

what does shear stress govern

Answer 8

how well endothelial cells work

Question 9

when does laminar shear stress occur

Answer 9

at a high level of shear stress

Question 10

what does laminar shear stress promote

Answer 10

endothelial cell survival, allowing secretions to promote vasodilation and anticoagulation

Question 11

when does turbulent shear stress occur

Answer 11

at a low level of shear stress

Question 12

what does turbulent shear stress promote

Answer 12

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

Question 13

what can turbulent shear stress lead to

Answer 13

occlusion

Question 14

turbulent shear stress and age

Answer 14

worsens with age

Question 15

how do you use turbulent flow to measure blood pressure

Answer 15

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

Question 16

where is blood pressure ususally measured and why

Answer 16

upper arm as easily accessed and at heart-level

Question 17

Poiseuille’s equation

Answer 17

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

Question 18

how is regulation of flow achieved

Answer 18

variation in resistance in vessels while pressure remains relatively constant

Question 19

explanation of Poiseuille’s equation

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Poiseuille’s equation for blood flow

Answer 21

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

Question 22

define vascular capacitance/compliance

Answer 22

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

Question 23

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

Answer 23

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

Question 24

compliance equation

Answer 24

change in volume/change in pressure

Question 25

define elastance

Answer 25

ability of a vessel to return to original shape

Question 26

elastance equation

Answer 26

change in pressure/change in volume

Question 27

what produces elastance in vessels

Answer 27

elastin fibres in vascular wall

Question 28

compliance properties of veins

Answer 28

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

Question 29

compliance properties of arteries

Answer 29

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

Question 30

what is the Windkessel effect

Answer 30

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

Question 31

clinical external modulation of compliance

Answer 31

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

Question 32

internal modulation of compliance

Answer 32

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

Question 33

what does gravity do to blood

Answer 33

pulls it towards ground

Question 34

effect on hydrostatic pressure by gravity when standing and outcome

Answer 34

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

Question 35

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

Answer 35

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

Question 36

why is pressure gradient from left to right heart maintained

Answer 36

ensure unidirectional flow

Question 37

effect of small leg movement on venous return

Answer 37

activates skeletal muscle pump to increase venous return

Question 38

what ensures unidirectional blood flow in veins

Answer 38

valves

Question 39

effect of respiratory pump on venous return

Answer 39

negative intrathoracic pressure increases venous return

Question 40

define varicose veins

Answer 40

incompetent valves causing dilated superficial veins in leg

Question 41

cause of oedema in feet due to gravity

Answer 41

prolonged elevation of venous pressure even with intact compensatory mechanisms

Question 42

what are the local mechanisms of flow intrinsic to

Answer 42

smooth muscle (important for reflexive control)

Question 43

wht are the systemic mechanisms extrinsic to

Answer 43

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

Question 44

define flow autoregulation

Answer 44

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

Question 45

myogenic theory of autoregulation to decrease resistance to increase flow

Answer 45

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

Question 46

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

Answer 46

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

Question 47

how does injury cause constriction

Answer 47

serotonin release from platelets causes constriction

Question 48

endoelium derived vasodilators

Answer 48

nitric oxide, prostacyclin

Question 49

non-endothelium derived vasodilators

Answer 49

kinins, ANP

Question 50

endothelium-derived vasoconstrictors

Answer 50

thromboxane A2, endothelins

Question 51

non-endothelium derived vasoconstrictors

Answer 51

ADH, (nor)adrenaline, angiotensin II

Question 52

calculate flow rate

Answer 52

pressure gradient/resistance

Question 53

what is the pressure gradient in capillary blood flow

Answer 53

difference in pressure between arteriole and capillary

Question 54

what is the normal venous pressure

Answer 54

37 mmHg

Question 55

capillary beds in different tissues

Answer 55

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

Question 56

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

Answer 56

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

Question 57

features of continuous capillaries

Answer 57

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

Question 58

features of fenestrated capillaries

Answer 58

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

Question 59

features of discontinuous capillaries

Answer 59

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

Question 60

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

Answer 60

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