Special Circulations

Question 1

perfusion is determined by

Answer 1

pressure gradient/resistance

Question 2

what drives local perfusion

Answer 2

alterations in vascular tone

1/r^4

Question 3

vascular tone reacts to

Answer 3

intrinsic - local

extrinsic - systemic factors

Question 4

examples of intrinsic mechanical stimuli

Answer 4

stretch
shear
endothelial regulation
metabolites

Question 5

examples of extrinsic systemic regulation

Answer 5

nerves

hormones

Question 6

primarily intrinsic organs

Answer 6

brain
kidney
heart - local control regulating flow
benefit: local autonomy

Question 7

primarily extrinsic organs

Answer 7

skin

Question 8

coronary artery supply what tissue and drain where

Answer 8

myocardium and drain in the right atrium

Question 9

most of the coronary arteries are ..

Answer 9

end arteries and some collaterals between arterioles
- high O2 demand
no alternative routes
blockage means no oxygen

Question 10

how does coronary artery type be a risk

Answer 10

increased risk of ischaemia

Question 11

heart receives what %age of cardiac output

Answer 11

5%

Question 12

how does perfusion across the heart and its arteries occur in conjunction with diastole and systole

Answer 12

perfusion occurs in diastole - arteries compressed in systole
increased activity - increased perfusion
typical O2 extraction more than 65% compared to 25% of rest of body

Question 13

why the difference between left and right circulations

Answer 13

right ventricle is so small on the left we dont get same compression

Question 14

how is high capillary to myocyte density seen as a coronary adaptation coronary adaptation

Answer 14

high capillary to myocyte density - low diffusion distance high myoglobin
very efficient oxygen exchange
control mostly intrinsic via metabolite induced vasodilation

Question 15

how does intrinsic metabolite induced vasodilation help adapt the coronary arteries

Answer 15

work by myocytes - K+ and H+ made, muscles use ATP - more adenosine - dilators
increases flow - more NO via shear stress
interact smooth muscle cells decrease resistance
increased perfusion

Question 16

how is extrinsic effect via SNS adapt to coronary arteries

Answer 16

beta adrenoreceptors SNS action can constrict - alpha AR and dilate beta AR
SNS action increase heartwork - increase metabolites and dilation

Question 17

coronary adaptation

Answer 17

High capillary to myocyte density
Control mostly intrinsic via metabolite-induced vasodilatation
Extrinsic effects via the SNS

Question 18

O2 extraction of cerebral circulation

Answer 18

35%

Question 19

if one artery of cerebral circulation is blocked what allows perfusion

Answer 19

circle of willis

Question 20

Mean cerebral O2 consumption

Answer 20

7 ml/min/100 g

Question 21

when will irreversible damage occur in cerebral circulation

Answer 21

by around 4 mins of ischaemia

Question 22

• Basal grey matter flow ≈

Answer 22

100 ml/min/100 g

Question 23

how is basal grey matter flow maintained

Answer 23

across physiological range of arterial pressure

Question 24

calculate cerebral perfusion pressure

Answer 24

mean arterial pressure minus the
intracranial pressure
– CPP = MAP – ICP

Question 25

how will increased intracranial pressure affect cerebral perfusion

Answer 25

decrease cerebral perfusion | tumour/oedema

Question 26

Cerebral blood flow calculation

Answer 26

cerebral perfusion pressure divided by the cerebral vascular resistance – CBF = CPP / CVR (which is the same as Q = ΔP/R or I = V/R)

Question 27

how is blood flow is cerebral tissue maintained

Answer 27

by constriction and dilatation in response to challenge | – can better deal with high pressure than with low pressures

Question 28

nerve firing in cerebral tissue is linked to what substances and in what practice is this beneficial

Answer 28

nerve firing linked to vasoactive K+, adenosine and NO | – this is the basis of functional MRI

Question 29

cerebral structural adaptations benefits

Answer 29

connected to circle of willis and high capillary density neurovascular coupling SNS fibres present lack alpha 1 at LIMIT response

Question 30

how is SNS fibres present but lack of α1 | -AR limit response beneificial for cerebral tissue

Answer 30

– thus brain spared from baroreceptor activation | – PNS releasing ACh and VIP may contribute to vasodilatation

Question 31

cerebral autoregulation via..

Answer 31

via myogenic activity and those of local mediators

Question 32

when will cerebral arteries contract and for what purpose

Answer 32

will contract when stretched | – constricting to increased pressure, limits blood flow

Question 33

what happens to cerebral arteries when low PaO2

Answer 33

an increase in cerebral blood flow involving NO and local | adenosine release leading to dilatation

Question 34

how is systemic hypoxia complicated and explain how

Answer 34

by changes in ventilation and CO2 | • CO2 is potent cerebrovascular dilator (get more perfusion) and hypoxic-induced hyperventilation will decrease PaCO2

Question 35

difference of local hypoxia and systemic hypoxia

Answer 35

local hypoxia - increase dilation and increase perfusion | systemic hypoxia - decrease CO2 and cerebral perfusion

Question 36

cerebral challenges

Answer 36

• Vascular dilatation (headaches/migraine) Postural hypotension/syncope Cerebrovascular accidents (strokes) Changes to intracranial pressure

Question 37

how can change to intracranial pressure negatively impact cerebral perfusion

Answer 37

increased pressure from space occupying lesion can decrease perfusion

Question 38

how can Postural hypotension/syncope negatively impact cerebral perfusion

Answer 38

transient fall in cerebral perfusion on standing | – usually prevented by baroreflex – indicative of dehydration

Question 39

Cerebral Ischaemic Response

Answer 39

redistributes blood to the brain away from periphery to brain drop in arterial pressure -> sympathetic vasoconstriction from baroreceptor reflex resistance increases -> few cerebral resistance brain has few SNS receptors

Question 40

cushing reflex occurs when

Answer 40

brain volume increases and ICP increases - decreases perfusion and constrict cerebral vessels

Question 41

for cushing reflex what does increased ICP lead to

Answer 41

increased SNS constriction and MAP

Question 42

2 problems with cushing reflex

Answer 42

more blood in the cerebral circulation raises the ICP and risk of oedema systemic pressure control perceives MAP too high and triggers baroreceptor medicated bradycardia

Question 43

splanchnic circulation supplies blood to

Answer 43

liver and GI tract

Question 44

splachnic circulation receives what percentage of cardiac output

Answer 44

25%

Question 45

when does blood flow increase in splanchnic circulation

Answer 45

with food digestion under extrinsic hormonal control

Question 46

what dilates splachnic arterioles and what affect will that have on blood flow

Answer 46

``` gastric hormones (gastrin & CCK) dilate splanchnic arterioles can double the GI blood flow – functional hyperaemia ```

Question 47

splanchnic circulation is innervation with what nerves

Answer 47

sympathetic innervation

Question 48

how is blood redistributed during sympathetic activation

Answer 48

During sympathetic activation (exercise, fight/flight) vasoconstriction redistributes blood away from GI tract to the heart and skeletal muscle

Question 49

how can prolonged redistribution of splanchnic circulation affect the liver and GI tract give an example of when this scene would be happen

Answer 49

necrosis of microvilli | in haemorrhage