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Mechanics 3 Flashcards

1
Q

What is the function of the circulation?

A

transport blood around body (deliver O2, nutrients, hormones, clear CO2/metabolites)
regulate temperature

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2
Q

What is the physiological function of the heart?

A

muscular pump that generates pressure gradient to propel blood through blood vessels

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3
Q

What are the adaptations of capillaries?

A

diffusion is effective over short distances
capillary is 10 micrometres from each cell
highly branched structure
reservoir for blood volume
largest SA in CVS

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4
Q

What are the functions of veins?

A

reservoir during exercise as cardiac output increases
veins have a large capacitance for blood
venules and veins are highly compliant

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5
Q

How do small arteries/arterioles regulate diameters and resistance to blood flow?

A

elastic

have smooth muscle in walls

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6
Q

What is blood pressure physiologically?

A

force that drives circulation by a pressure difference

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7
Q

What is the function of small arteries and arterioles?

A

present most resistance to flow
alter perfusion to the vascular bed (gatekeeping)
useful during exercise - redirect flow to working muscles

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8
Q

Why does pressure fall across the circuit?

A

due to viscous pressure losses

i.e. frictional pressure losses

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9
Q

% of circulation to pulmonary?

A

17%

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10
Q

% of circulation to heart?

A

9%

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11
Q

% of circulation to arterioles and capillaries?

A

7%

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12
Q

% of circulation to arteries ?

A

11%

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13
Q

% of circulation to venules and veins?

A

61%

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14
Q

What is Darcy’s Law?

A 
defines blood flow between particular resistances and pressures 
P = Q X R
Q = volumetric flow
R = resistance 
P= pressure difference
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15
Q

Formula for MAP?

A

cardiac output x resistance

= Q x R

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16
Q

Why is the formula for MAP only an approximation?

A

assumes steady flow (heart is pulsatile)
assumes vessels are rigid (resistance may change)
assumes right arterial pressures is negligible (it may change)

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17
Q

What happens in reality?

A

flow is regulated by changing R to keep the BP constant
Q = P/R
Q is inversely proportional to resistance

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18
Q

What is Poiseuille’s Equation?

A

R = 8Ln/πr4

Resistance to blood flow depends on:

  • fluid viscosity (n) that is usually constant
  • length of tube (L) fixed
  • inner radius of tube (r) that changes
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19
Q

What would a half in radius of a vessel do to flow?

A

reduce flow 16x

therefore small changes in vascular tone (vasodilation/vasoconstriction) produce large changes in flow

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20
Q

Why does blood flow distribution to organs differ?

A

according to metabolic needs

arterioles/arteries vasoconstrict/dilate to reroute blood supply to more active orgsans

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21
Q

How does CO change during exercise ?

A

5 –> 20 L (increase total blood supply - less venous reservoir)
skeletal muscles receive 30 fold increase in supply
decrease reservoir in veins to increase venous return
increase preload
increase stretch
increase CO via contractility
divert blood to skeletal muscles

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22
Q

Blood flow to digestion and kidney at rest?

A

1L

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23
Q

Blood flow to digestion and kidney at exercise?

A

0.75L

1L

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24
Q

Blood flow to heart at rest/exercise?

A

0.25L —> 1.25L

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25
Blood flow to brain/skin at rest and exercise?
NO CHANGE 0. 75L 0. 25L
26
Blood flow to bone at rest and exercise?
0.15L ---> 0.25L
27
Blood flow to skeletal muscle at rest and exercise?
0.75L ---> 16L
28
What is the flow like in arteries?
pulsatile that becomes more continuous along the circulation
29
What is the normal circulatory flow described as?
laminar flow blood flows in layers velocity is constant throughout flow faster at centre, slow near walls due to friction and adhesive forces between fluid and walls
30
What is the flow associated with pathophysiological changes (atheroma)?
turbulent flow irregular eddys form, prone to pooling velocity not constant due to changes in SHEAR STRESS
31
What is the shear rate?
velocity gradient difference between fastest and slowest velocity in lumen s = difference in v/difference in r
32
What is the formula for shear stress?
T = s x n | governs how well endothelial cells work
33
What is high shear stress?
laminar flow endothelial cells align normally produce substances normally
34
What is low shear stress?
turbulent flow - associated with endothelial dysfunction cells mix up produce wrong substances more granules
35
What is the velocity profile of laminar flow?
parabolic
36
What physical signs are typical of laminar flow?
not heard high shear stress promote endothelial cell quiescence and survival cells aligned in direction of flow secretions promote vasodilation and anticoagulation
37
What physical signs are typical of turbulent flow?
low shear stress promote cell proliferation, apoptosis, shape change secretions promote vasoconstriction, coagulation, platelet aggregation --> increase clotting and blood vessel occlusion
38
What do age related changes do to flow?
increase turbulent flow in carotid arteries | decline in endothelial function
39
What is blood pressure a measure of?
turbulent flow
40
Describe how BP is measured?
1. Stop blood flow using a cuff - occlude arterial pressure 2. Decrease cuff pressure so that at SBP blood flows through turbulently 3. Hear using stethoscope on brachial artery 4. When sound disappears flow is laminar --> DBP reached
41
Formula for PP
DBP - SBP
42
Formula for MAP
DBP + 1/3PP
43
Why is there a dichrotic notch when measuring SBP and DBP?
from closure of aortic valve
44
What does increases elasticity mean?
increased compliance
45
Why does pressure fall slowly in arteries? What effect is this?
elasticity buffers change in PP to sustain diastolic blood pressure Windkessel effect - buffering
46
What happens to the Windkessel effect with age?
arterial compliance decreases elasticity decreases reduced buffering (WK effect) increase PP
47
Describe how the WK effect works?
1. ejection - blood enters aorta faster than it leaves (40% of SV stored by elastic arteries) 2. AV valve closes 3. elastic arteries recoil so pressure decreases slowly - they absorb pressure during systole 4. Ensures diastolic flow is pulsatile and continuous in downstream circulation
48
Vascular Law of Laplace?
T = P x r | transmural pressure causes tension in the wall
49
Formula for circumferential stress?
``` s = P x r /h h = wall thickness ```
50
What determines flow
pressure difference between 2 points | transmural pressure
51
What is compliance?
relationship between TMP and vessel volume | depends on vessel elasticity
52
What is the consequence of maintained high circumferential stress?
vessel distension ---> aneurysm overtime vessel walls weaken balloon like distension
53
Describe a vascular aneurysm?
increase vessel radius for same internal pressure inward force exerted by muscle wall increases (increase circumferential stress) if fibre weakened no force produced aneurysm expands till rupture
54
How to cure an aneurysm?
mesh around it
55
What do compliance curves show?
propensity of vessel to stretch under pressure veins compliant at low P - small changes in venous pressure distend veins and blood volume stored there - venous compliance 10-20x greater than arterial at low P arteries compliant over range of P
56
How do decrease venous compliance?
increase smooth muscle contraction | decrease venous volume, increase pressure
57
What is the effect of venous compliance? Consequence of standing?
blood pooling standing increase hydrostatic pressure in legs due to gravity blood pools in veins with high compliance and reduces venous return with time CO and BP decrease fainting
58
How much does gravity increase hydrostatic pressure in veins by?
100mmHg
59
How can pooling be prevented?
activate SNS constrict veins and arteries to increase total peripheral resistance increases BP standing HR increases and contractility increases to return more blood to heart
60
Hows does low pressure blood return to the heart?
skeletal muscle pump - contract to compress veins (positive pressure) respiratory pump - inhalation causes negative intrathoracic pressure so blood returns to central veins quickly -> extravascular pressure decreases in thorax but increases in abdominal cavity -> pressure gradient drived flow valves ensure unidirectional flow
61
What affects venous volume distribution?
venous tone (constriction) gravity skeletal muscle and respiratory pump
62
What are two issues with standing ?
1. varicose veins - dilated superficial veins - incompetent valves 2. oedema - prolonged elevated venous pressure - failed venous valves 3. fainting due to blood pooling
63
Tropys of the heart?
Chronotropic (Heart rate) Dromotropic (Conduction velocity) Inotropic (Contractility) Bathmotropic (Excitability) Lusitropic (Relaxation)
64
How is ESPVR generated?
IVC occlusion | progressive fall in preload

CVS (16 decks)

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