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3 CVS > 9 Special Circulation > Flashcards

9 Special Circulation Flashcards

1
Q

What is the blood flow like to the heart and brain compared to skin and muscle?

A

much higher

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2
Q

how much of the available oxygen goes to the heart?

A

1/3-2/3

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3
Q

What does a large a-vO2 difference suggest?

A

the vascular bed has a high oxygen consumption

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4
Q

What parts of the heart have a high blood supply?

A

the ventricles, particularly the left ventricle

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5
Q

What do coronary veins drain into?

A

the coronary sinus, and then into the right atrium

some is drained via thesbian veins

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6
Q

When might there be an increased demand for oxygen in the heart?

How is this met?

A

any increase in heart rate or contracitlity

this is met by an increase in flow

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7
Q

What is the distribution of blood vessels like in cardiac muscles compared to skeletal muscle?

A

much much denser in cardiac muscle, 3000/mm2 compared to 400/mm2 in skeletal muscle

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8
Q

How does myoglobin help cardiac muscle?

A

it has a much higher affinity to oxygen than haemoglobin, even if it can only bind to one molecule

the oxygen is passed along a chain of myoglobin, to maintin the diffusion of oxygen to mitochondria

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9
Q

How would you increase coronary flow?

A

vasodilating coronary vessels

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10
Q

What is the coronary flow reserve?

A

the difference between the resting level of flow, and the maximum flow that can be made by dilating the vessels

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11
Q

What does the coronary flow reserve allow?

A

blood flow to increase by up to 5x than resting autoregulated levels when cardiac output is increased (this ability is reduced in some cardiac conditions)

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12
Q

What would stimulate the coronary release of adenosine?

what does adenosine do?

A

increased metabolic activity
fall in coronary blood flow
fall in myocardial PO2

vasodilation - increase flow

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13
Q

What effect does extracellular potassium have on flow?

A

it contributes to the inital increase in coronary perfusion, although it is unlikely to contribute much to the sustained rises in coronary flow

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14
Q

How can acidosis alter vascular resistance?

A

changes in O2 and CO2 may cause acidosis, which can act to lower vascular resistance and increase oxygen supply

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15
Q

Where does stenosis usually occur?

how significant does it need to be to have effect?

A

large epicardial arteries, needs to exceed 60-70% reduction in lumen diameter to have a significant impact on flow

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16
Q

What happens in coronary artery disease?

A

affects artery lumen and causes endothelial damage and dysfunction

falls in NO and prostacyclin, which act as vasodilators

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17
Q

How might you treat unstable angina?

A

balloon angioplasty
implanting a stent
coronary bypass graft

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18
Q

Does grey or white matter receive more blood flow?

A

grey matter, despite the fact that there is less of it

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19
Q

What is the effect of grey matter being sensitive to hypoxia?

A

fainting occurs within seconds of hypoxia

hypoxia for over 4 minutes leads to neuronal damage

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20
Q

where do peel arteries go?

A

run over the brain surface

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21
Q

What is the benefit to the grey matter having a dense network of capillaries?

A

large surface area

low diffusion distance

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22
Q

Where are the fenestrations in cerebral blood vessels?

A

there are none, they are completely sealed by tight junctions

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23
Q

How can substances pass into the brain?

A

over the 2 cell membranes and cytoplasm of the endothelial cells

24
Q

How do O2, Co2, alcohol, nicotine, and caffeine pass over the blood endothelium into the brain?

A

they are lipophilic, so passive diffusion

25
Q

How do glucose and amino acids pass into the brain?

A

transport proteins

26
Q

What happens to excess K+ in the brain?

what adaptation facilitates this?

A

it is pumped out via Na+/K+ ATPase

endothelial cells in the brain have 5x more mitochondria than muscle endothelium

27
Q

how is high cerebral basal flow maintained?

A

peripheral vasoconstriction sacrifices perfusion to the peripheries, but not the heart

28
Q

What is the autoregulatory range in the brain?

A

60-150mmHg

29
Q

What happens in extreme cerebral hypoxia?

A

mental confusion

syncopy

30
Q

What does cerebral hypercapnia cause?

How?

A

vasodilation, especially in small peel arteries

endothelial NO
fall in myocyte pH

31
Q

What does cerebral hypocapnia cause?

what effect will an arterial CO2 of 2kPa have on cerebral flow?

A

vasoconstriction

this will halve total cerebral flow

32
Q

How can cerebral flow be measured?

A

retinal flow, as the retina is an embryological derivative of the nervous system

33
Q

What does severe hypoxia in the cerebrum stimulate?

A

vasodilation

hyperventilation via stimulation of carotid chemoreceptors

34
Q

What is the effect of hyperventilation in response to systemic hypoxia?

A

systemic hypoxia evokes hyperventilation so hypoxic dilation is often masked by hypocapnic vasocontriction

35
Q

What is the effect of systemic hypoxia on blood flow?

what might have a different effect?

A

only a minor effect, it has to be really really hypoxic before an increase in cerebral flow is observed

it is much more susceptible to changes in CO2 though

36
Q

what can astrocytes do?

A

they surround the synapses and may also be stimulated, signalling to smooth muscle to control vessel diameter

37
Q

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

A 
increased interstitial [K+]
adenosine
neuronal NO
metabolites released from astrocytes during increased activity
CO2 (not as significant as the others)
38
Q

What might ICP be increased by?

A

Intracranial Pressure

intracranial bleeding
cerebral edema
tumour

39
Q

What might the effects of increased ICP be?

A

venous collapsing

decreased effective CPP, causing a reduced blood flow

40
Q

How would we calculate CPP?

A

Central Perfusion Pressure = mean ABP - ICP

41
Q

When might postural hypotention lead to syncopy?

A

only really if the baroreceptor reflex is impaired

42
Q

What is a TIA?

A

transcient ischaemic attack

temporary reduction in flow (minutes to hours)

43
Q

what is a stroke?

A

total interruption in blood flow

44
Q

What is the range of blood flow exhibited by the skin?

A

1-200 ml/min/100g

45
Q

What is the structure of cutaneous blood supply?

A

small arteries give rise to arterioles penetrating into the dermis
these give rise to capillaries looping under the epidermis
venules return the blood to the venous plexus

the venous plexus could also receive blood directly from subcutaneous arteries via atriovenous anastomoses

46
Q

What do atriovenous anastomoses allow?

A

the blood to bypass cutaneous circulation

47
Q

How much of cutaneous blood volume is in the venous plexus?

A

most of it

can be up to 1.5L

48
Q

What affects changes in AVAs?

A

sympathetic activity, alpha adrenoreceptors

they do not show functional hyperaemia or autoregulation

49
Q

What happens when temperature rises?

A

sympathetic nervous system stimulates vasodilation and sweat release

50
Q

What stimulates sweat release and what effect does it have?

A

hypothalamic stimulation of sympathetic cholinergic fibres innervating the sweat glands

evaporates to remove heat
has an enzyme telling tissue to release bradykinin, a vasodilator acting on smooth muscle

51
Q

How does an increased temperature affect baroreceptor afferent activity to CNS?

A

vasodilatoin of arterioles and AVAs
decreases TPR
decreases ABO
decreases baroreceptor afferent activity to CNS

52
Q

What effect does decreasing baroreceptor afferent activity to CNS have?

A

decreased vagal activity to SA node

increased sympathetic activity to SA node

53
Q

What happens to cutaneous circulation when temperature drops?

A

increase in sympathetic activity and noradrenaline release causes vasoconstriction of cutaneous arterioles

increased sympathetic activity to arteriovenous anastomoses causes constriction to prevent flow to veins

this increases resistance to blood flow, diverting flow to the interior deeper veins in fat

54
Q

What happens in prolonged exposure to cold?

A

vasoconstriction in cutaneous circulation changes to a paradoxical cold circulation

55
Q

What causes paradoxical cold circulation?

A

paralysis of noradrenergic neurotransmission in response to cold, and the release of vasodilators like prostacyclin

redness caused by increased affinity of O2 for haemoglobin
(left shift of O2 dissociation curve)

56
Q

Why is it useful to have arteries and veins next to each other?

A

counter-current heat exchange preserves body temperature

57
Q

What happens in Raynaud’s disease?

A

cold / emotional stimuli lead to vasoconstriction
white, blue, then red

numbness, pain, burning sensation

3 CVS (24 decks)

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