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3/ CVS > Coronary, Cerebral and Cutaneous Circulations > Flashcards

Coronary, Cerebral and Cutaneous Circulations Flashcards

1
Q

What is a-vO2 difference?
Where is a large a-vO2 difference found?
Where is a small a-vO2 difference found?

A

The difference in O2 between the arteries and veins
It represents the amount of O2 that a particular tissue extracts
Large difference in heart
Small difference in kidney/skin

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2
Q

What are the 2 main tasks of the coronary circulation?

A
  1. maintain secure O2 supply to coronary muscle (low capacity for anaerobic metabolism)
  2. alter local flow according to activity - functional hyperaemia (metabolic regulation)
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3
Q

What is meant by the coronary reserve?

A

flow can increase 4-5x when CO increases

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4
Q

What is a typical CO in the following situations?:

  • rest
  • moving around house
  • walking briskly
  • light jogging
  • strenuous running
A
  • 5 L/min
  • 10
  • 15
  • 20
  • 25
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5
Q

In the coronary circulation there is a very large a-vO2 difference.
What consequences does this have e.g. in angina?

A

The heart is extracting almost maximum amount of O2 possible at rest
Increased demand for O2 must be met by large flow increase

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6
Q

Why is flow to coronary muscle is intermittent?

A

For blood to flow through a coronary vessel
- Pa > Pv this to leads to directional flow
- Pi > Po so that vessels remain open
Pi = pressure in aorta
Po = pressure in ventricles
So if ventricular pressure > aortic pressure, blood will not flow

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7
Q

Describer coronary blood flow on the left side of the heart.

A

SYSTOLE = vessels are compressed by high pressure in the ventricle
Most blood flows to left myocardium during diastole
Aortic pressure during diastole determines flow
Max during early diastole
At high HR, diastole is shortened and reduces time for perfusion.

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8
Q

Draw graphs for coronary blood flow in the left side of the heart

A

flow may reverse during systole

greatest flow during diastole

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9
Q

Explain when blood might travel backwards in the coronary circulation

A

During systole
Extravascular compression in the left ventricular wall
Contracting myocutes collapse vesssle
Arterial blood is foes backward toward aorta

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10
Q

Describe blood flow in the right side of the heart

A

Right coronary flow highest during systole

They is constant flow to the right ventricle because ventricular pressure never exceeds aortic pressure

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11
Q

In what range do coronary arterioles exhibit myogenic regulation?
How else is coronary flow controlled?

A

60-180mmHg

  • some sympathetic control but overridden by local control
  • adenosine, prostaglandins, low O2, NO, K+,
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12
Q

What are the 2 tasks of the cerebral circulation?

A
  1. Maintain totally secure O2 supply to brain tissue (myogenic autoregulation)
  2. Alter local flow according to activity functional hyperaemia (metabolic regulation)
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13
Q

What are the structural adaptions of the cerebral circulation?

A
  • Circle of Willis - ensures supply even if one artery becomes blocked
  • short arterioles, dense capillary network
  • relatively high vascular resistance
  • cerebral perfusion maintained if carotid artery obstructed
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14
Q

What is the cellular basis of the blood brain barrier?

Why is this important?

A
  • brain capillary endothelial cells connected by tight junctions
  • controls bulk flow
  • no vesicular transport
  • protects neurones
  • maintains environment
  • responsible for long-lasting effects of heroine
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15
Q

What can pass through the BBB?

A 
lipophilic solutes - O2, CO2, alcohol, nicotine, caffeine 
amino acids via transport proteins 
glucose 
Na+ via Na+K+ATPase
ion channels
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16
Q

What are the 7 adaptations of the cerebral circulation?

A
  1. High basal flow
  2. Regulation of other organs safeguards cerebral circulation
  3. Autoregulation
  4. Cerebral vessels are VERY responsive to arterial CO2
  5. Cerebral vessels are less response to arterial O2
  6. Neuronal activity-evoked functional hyperaemia
  7. Nervous control not important in determining cereal flow
17
Q
  1. High basal flow

- What % of CO?

A

15% of CO

high extraction of O2

18
Q
  1. Regulation of other organs safeguards cerebral circulation
A
  • peripheral vasoconstriction (except heart) can maintain arterial pressure
19
Q
  1. Autoregulation
    - What is it?
    - What is the autoregulatory range?
A
  • a change in blood pressure is met by a change in resistance to maintain perfusion
  • 60-170mmHg
20
Q
  1. Cerebral vessels are VERY responsive to Co2
A

Hypercapnia (>40mmHg) –> vasodilation (endothelial NO, fall in myocyte pH, H+ rather than CO2 per se
Hypocapnia (<40mmHg) –> vasoconstriction
lose ability to autoregulate high PaCO2
This is responsible to dizziness during hyperventilation

21
Q
  1. Cerebral vessels are less responsive to levels arterial O2
A

Moderate hypoxia evokes little change in cerebral flow
Severe hypoxia leads to vasodilation: adenosine, K+, NO
- systemic hypoxia evokes hyperventilation so hypoxic vasodilation often masked by hypocapnic vasoconstriction

22
Q
  1. Neuronal activity-evoked functional hyperaemia

- What factors are important in coupling tissue metabolism to local flow?

A
  • CO2
  • increased interstitial [K+] due to increased K+ permeability
  • adenosine
  • nitric oxide
23
Q
  1. Is nervous control importnant in determining cerebral flow?
A
  • maximal sympathetic stimulation increases resistance by only 20-30%
  • baroreceptors have little influence on cerebral flow
  • sympathetic stimulation shifts autoregulatory curve to right
24
Q

REMEMBER TO LOOK OVER GRAPHS IN LECTURE

A

remember to look over graphs in lecture

25
Q

What are the 2 potential problems associated with cerebral vasculature?

A
  • raised intracranial pressure (ICP)

- postural syncope

26
Q

What is ICP increased by?

What is the result of increased ICP?

A
  • intracranial bleeding, cerebral edema, tumour

- collapses veins, decreases effective CPP reduces blood flow

27
Q

What is CPP?

What is the formula?

A

Cerebral Perfusion Pressure
= mean ABP - ICP
(Inside pressure - outside pressure)

28
Q

What is postural syncope?

A
  • when baroreflex/autonomic activity is impaired e.g. ageing
  • fainting when you stand up
29
Q

What are the 2 tasks of the cutaneous circulation?

A
  1. Regulate body temperature. Skin is the major thermoregulator
  2. Respond to trauma
30
Q

What are the two structural adaptations of the cutaneous circulation?

A

receives approx 10% of CO and has moderately high resistance
has a unique microvascular network
- venous plexus close to arterioles –> countercurrent exchange
- AV anastamoses - bypass capillary beds when cold

31
Q

What kind of control are arterioles in the skin under?

A

they are under sympathetic control rather than metabolic control
when warm –> removal alpha-adrenoceptor mediated sympathetic tone –> cutaneous vasodilation –> heat loss

32
Q 
Where AV anastomoses (AVAs) present?
What is their diameter?
What is their function?
What adrenoreceptors are on them?
What is the mechanism by which they work?
A
  • hands, feet, face (ears, nose and lips)
  • 50microns diameter with thick smooth muscle
  • shunt blood from arterioles - venules
  • alpha1 adrenoreceptors
  • warm –> decrease alpha-1 sympathetic activity –> dilation of AVA’s –> increase blood flow into venous plexus –> heat loss
33
Q

What is the mechanism followed by vasoldailtion enhanced by bradykinin?

A 
decrease systemic vascular resistance 
decrease ABP
baroreceptors
increase heart
increase CO
ABP = CO x SVR
34
Q

What happens when it is cold?

A

stimulation of alpha-adrenergic receptors
vasoconstriction
blood directed to interior vessels
heat gain

35
Q

Describe the graph that shows the effect of ambient temperature on skin blood flow

A

Over a 20 minute period of cooling by ice

  • cold-induced vasoconstriction
  • paradoxical cold vasodilation (extreme cold)
  • due to paralysis of NA transmission
36
Q

Describe the concept of countercurrent exchange in the cutaneous circulation

A
  • cold blood in veins returning from extremities can be 13 degrees cooler than in trunk
  • radiation from warm arterial to cold venous blood flowing in opposite directions
  • ‘traps’ heat near trunk
37
Q

What is Raynaud’s disease?

A 
skins vessel 'overactive'
to cold and stress
- cold/emotional stimuli lead to vasoconstriction (ischaemic attacks)
- white, blue, then red 
- numbness, pain and burning sensation
38
Q

What is the triple response?

A

Pointed object drawn over skin or small burn

  1. white reaction - blanching due to mechanical stimulation
  2. red reaction - local vasodilation, histamine?
  3. ‘flare’ - wider intense vasodilation
  4. Wheals/ local oedema

3/ CVS (19 decks)

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