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Cardiovascular 2018 > Special Circulations: Coronary, Cerebral, Pulmonary & Skeletal Muscle > Flashcards

Special Circulations: Coronary, Cerebral, Pulmonary & Skeletal Muscle Flashcards

1
Q

Where do the left and right coronary arteries arise from?

A

The base of the aorta

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2
Q

Where does coronary venous blood drain to and via?

A

Drains into the right atrium via the coronary sinus

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3
Q

What are the special adaptations of the coronary circulation?

A

High capillary density
High basal blood flow
High oxygen extraction (75%)

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4
Q

What are the intrinsic mechanisms of coronary blood flow regulation?

A
  • Decreased PO2 causes vasodilatation
  • metabolic hyperaemia matches flow to demand
  • adenosine (from ATP) is a potent vasodilator
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5
Q

What are the extrinsic mechanisms of coronary blood flow regulation?

A
  • Coronary arterioles are supplied by sympathetic vasoconstrictor nerved BUT this is overriden by metabolic hyperaemia as a result of increased HR and SV
  • sympathetic stimulation of the heart results in coronary vasodilatation despite direct vasoconstrictor effect (functional sympatholysis)
  • circulating adrenaline activates B2 adrenergic receptors which causes vasodilatation
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6
Q

What is coronary blood flow like during systole?

A

in the left coronary artery it is low due to the constriction of the sub-endocardial arteries when the ventricle contracts

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7
Q

What is coronary blood flow like during diastole?

A

left coronary blood flow is increased and most occurs during diastole due to the high pressures of the left ventricle

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8
Q

What happens if you shorten diastole?

A

tachycardia shortens the left coronary artery flow period, causing chest pain although the don’t have ischaemic heart disease

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9
Q

When does right coronary flow peak?

A

Peaks in systole but occurs in diastole too

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10
Q

What supplies the brain?

A

brain is supplied by internal carotids and vertebral arteries

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11
Q

Why does the brain need a secure supply of oxygen?

A

Grey matter is very sensitive to hypoxia, consciousness will be lost after a few seconds and permanent damage occurs in minutes

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12
Q

What are the special adaptations of the cerebral circulations?

A

Basilar & carotid arteries anastomose to form circle of willis

major cerebral arteries arise from circle of willis

cerebral perfusion should be maintained even if one carotid artery gets obstructed

obstruction of a smaller branch would deprive a smaller region

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13
Q

What are the two types of stroke?

A

Haemorrhage

Ischaemic

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14
Q

What does auto regulation of cerebral blood flow do?

A

guards against changes in cerebral blood flow as mean arterial blood pressure changes within a range

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15
Q

What has little affect on cerebral blood flow?

A

direct sympathetic stimulation

baroreceptor is negligible

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16
Q

What happens to resistance vessels if MABP rises?

A

automatically constrict to limit blood flow

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17
Q

What happens to resistance vessels if MABP falls?

A

automatically dilate to maintain blood flow

18
Q

What is the range of MABP auto regulation allows for?

A

below 60- above 160mmHg

19
Q

What happens if MABP drops bellow 50mmHg

A

confusion, fainting, and brain damage if not quickly corrected

20
Q

What is special about the brain during ischaemic?

A

blood flow increases to active parts of the brain (regional hyperaemia).

mechanism is unknown. may be due to rise in [K+]O due to potassium efflux from repeatedly active firing neurones?

21
Q

What is contained within the skull?

A

brain 80%, blood 12% and CSF 8%

22
Q

What is normal intracranial pressure?

A

8-13mmHg

23
Q

What is cerebral perfusion pressure?

A

Mean arterial pressure (MAP) - ICP

24
Q

What does increasing ICP cause?

A

decrease CPP and cerebral blood flow

if regulation fails then injury

25
Q

What is the blood brain barrier?

A

cerebral capillaries have very tight intercellular junctions- the blood brain barrier
they only allow certain substances to go into the brain

26
Q

What are cerebral capillaries permeable to?

A

O2 and CO2

27
Q

How does glucose enter the brain?

A

facilitated diffusion using specific carrier molecules

28
Q

Where does the pulmonary flow come from?

A

Right ventricle

29
Q

What must meet the oxygen requirements of the airways?

A

Systemic Bronchial circulation

30
Q

What is pulmonary resistance like in comparison to systemic resistance?

A

-10%

31
Q

What is pulmonary artery BP typically?

A

20-25/6-12 mmHg

32
Q

What are the special adaptations of the pulmonary circulation?

A

pulmonary capillary pressure is low (-8-11 mmHg) compared to systemic capillary pressure (17-25mmHg)

absorptive forces exceed filtration forces- protects against pulmonary oedema

hypoxia causes vasoconstriction of pulmonary arterioles

33
Q

What % of body mass is skeletal muscle?

A

approx 40

34
Q

What regulates resting blood flow to skeletal muscle?

A

Sympathetic vasoconstrictor tone

35
Q

When is sympathetic vasoconstrictor activity overriden in skeletal muscle?

A

during exercise

36
Q

What overcomes sympathetic vasoconstrictor activity during exercise?

A
  • circulating adrenaline causes vasodilatation (B2 adrenergic receptors)
  • increased CO during exercise, these could increase skeletal muscle blood flow by many folds
37
Q

What are the overall changes to BP and pulse pressure during exercise?

A

systemic blood pressure will increase but diastolic BP may not change or even drop

pulse pressure will be wide during steady state exercise

38
Q

What is the skeletal muscle pump?

A
  • large veins in limbs lie between skeletal muscles
  • contraction of muscle aids venous return
  • one-way valves allow blood to move towards the heart
39
Q

What does the skeletal muscle pump reduce the chance of?

A

postural hypotension & fainting

40
Q

What happens when the venous valves become incompetent?

A

blood pools in lower limb veins- varicose veins

41
Q

What will varicose veins due to cardiac output?

A

because of compensatory increase in blood volume

Cardiovascular 2018 (39 decks)

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