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Cardio > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

right and left coronary arteries arise from the ___ of the aorta.

A

base

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2
Q

Where does most coronary venous blood drain via and to?

A

coronary sinus

right atrium

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3
Q

name some special adaptations of coronary circulation

A

High capillary density
high basal blood flow
High O2 extraction
increasing coronary BF

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4
Q

what is the value of o2 extraction in heart compared with body? What does this mean?

A

75%
body avg 25%
means extra O2, when required eg exercise cannot be supplied by increasing o2 extraction

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5
Q

coronary BF is controlled via intrinsic/extrinsic mechanisms?

A

both

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6
Q

d; hyperaemia

A

excess of blood in organ

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7
Q

describe the intrinsic mechanisms that control coronary BF/

A

decrease  Po2 causes vasodilatation of the coronary arterioles
Metabolic hyperaemia matches flow to demand
Adenosine (from ATP) is a potent vasodilator

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8
Q

describe extrinsic controls of coronary BF

A

Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT
Over-ridden by metabolic hyperaemia as a result of increased heart rate and stroke volume
So sympathetic stimulation of the heart results in coronary vasodilatation despite direct vasoconstrictor effect (functional sympatholysis)
Circulating adrenaline activates 2 adrenergic receptors, which cause vasodilatation

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9
Q

what are the two receptors in coronary arteries?

A

alpha and beta 2

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10
Q

What is the only thing that causes vasoconstriction on coronary arteries?

A

sympathetic stimulation

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11
Q

when is flow low in CA?

A

systole

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12
Q

When is there peak BF in LCA?

A

during diastole

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13
Q

What does shortening diastole do to HR and coronary flow?

A

very fast HR

decreases coronary flow

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14
Q

When does most of coronary BF and myocardial perfusion occur and why?

A

occurs in diastole when the subendocardial vessels from the left coronary artery are not compressed

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15
Q

What arteries supply the brain?

A

internal carotids and vertebral arteries

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16
Q

Why is consciousness lost a few seconds after ischaemia in brain/

A

grey matter verysensitive to hypoxia

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17
Q

after what time is there irreversible to brain/

A

after 3 mins

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18
Q

How is stroke caused?

A

by interruption/ cut off of BS to region of the brain

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19
Q

what pressure range must MAP occur within , whilst its changing, for autoregulation of cerebral BF?

A

60-160mmHg

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20
Q

What two things have very little effect on cerebral BF?

A

direct sympathetic stimulation
baroreceptor
reflexes

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21
Q

what happens if MABP rises

A

resistance vessels automatically constrict to limit blood flow

22
Q

what happens if MABP falls

A

resistance vessels automatically dilate to maintain blood flow

23
Q

Why is the pressure change range of MAP between 60-160mmHG?

A

Autoregulation fails if MABP falls below ~ 60mmHg (cerebral blood flow falls) or rise above ~ 160mmHg (cerebral blood flow rises)

24
Q

What does a MAP below 50mmHg result in?

A

results in confusion, fainting, and brain damage if not quickly corrected

25
Q

Why could hyperventilation lead to fainting?

A

increase in PCO2 causes cerebral vasodilation

decrease in PCO2 causes vasoconstriction

26
Q

How does BF possibly increase to active parts of the brain?

A

Blood flow increases to active parts of the brain (regional hyperaemia). Mechanism unknown. May be due to rise in [K+]O as a result of K+ efflux from repetitively active neurones?

27
Q

how much of the brain is blood?

A

12%

28
Q

what is normal intercranial pressure ICP?

A

8-13mmHg

29
Q

What is the equation for cerebral perfusion pressure CPP?

A

MAP-ICP

30
Q

What is effect of increasing intercranial pressure/

A

Increasing ICP (e.g. due to head injury, or brain tumour) decreases CPP and cerebral blood flow

31
Q

What are the potential consequences of increasing ICP?

A

can lead o failure of autoregulation of cerebral BF

32
Q

what is the tight intercellular junctions between cerebral capillaries called?

A

blood brain barrier

33
Q

cerebral capillaries are ______ ________ to O2 and CO2

A

highly permeable

34
Q

How does glucose cross the blood brain barrier?

A

via facilitated diffusion using special carrier molecules

35
Q

what is the BBB impermeable to?

A

to hydrophilic substances such as ions, catecholamines, proteins etc

36
Q

How does the fact brain is impermeable to other hydrophilic substances protect bran?

A

helps protect brain neurones from fluctuating levels of ions etc in blood

37
Q

What type of pressure system is pulmonary circulation?

A

low pressure

38
Q

What is the typical pressure in a pulmonary artery?

A

(20-25)/(6-12)

39
Q

what is the pressure range of pulmonary circulation?

A

8-11mmHg

40
Q

what is the pressure range of the systemic capillary pressure?

A

17-25mmHg

41
Q

what protects against pulmonary oedema?

A

absorptive forces exceed filtration forces

42
Q

What does hypoxia cause in pulmonay arterioles?

A

vasoconstriction

43
Q

Hypoxia causes vasoconstriction of pulmonary arterioles. COMPLETELY OPPOSITE TO EFFECT OF HYPOXIA ON SYSTEMIC ARTERIOLES. WHY?

A

would help divert blood from poorly ventilated areas of lung

44
Q

what percentage of the body is made up by the skeletal muscle?

A

40%

45
Q

What does the resistance of the skeletal muscle vascular bed do to BP?

A

has large impact on blood pressure

Resting blood flow is low because of sympathetic vasoconstrictor tone

46
Q

during exercise what overcomes vasoconstrictor activity?

A

metabolic hyperaemia

also increased CO could increase skeletal muscle BF

47
Q

what does circulating adrenaline cause to BV and via what?

A

vasodilation

beta 2 adrenergic receptors

48
Q

describe the skeletal muscle pump?

A

Large veins in limbs lie between skeletal muscles

Contraction of muscles aids venous return

One-way venous valves allow blood to move forward towards the heart

Skeletal muscle pump reduces the chance for postural hypotension & fainting

49
Q

If Blood pools in lower limb veins if venous valves become incompetent, what is this called?

A

varicose veins

50
Q

why doesn’t varicose veins not lead to reduction of CO?

A

because of chronic compensatory increase in blood volume

Cardio (28 decks)

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