Physiology of stroke

Question 1

what percentage of O2 intake does the brain consume at rest

Answer 1

20%

Question 2

what percentage of cardiac output does the brain consume at rest

Answer 2

14%

Question 3

why is high cerebral blood flow important

Answer 3

there is no where to store energy in the brain and the brain is intolerable to ischemia

Question 4

what component on the brain uses most of the energy

Answer 4

neurones (grey matter)

Question 5

why do neurons require such high levels of ATP

Answer 5

to maintain ion gradients and for synaptic transmission

Question 6

where is glucose stored in the brain

Answer 6

in astrocytes (as glycogen)

Question 7

how much glucose is oxidised by the brain daily?

Answer 7

100g

Question 8

where does the biggest energy expenditure occur in the brain?

Answer 8

synaptic transmission

Question 9

what are the structural adaptations that ensure a constant blood supply?

Answer 9

the circle of willis; the micro circulation

Question 10

what is an anastomosis

Answer 10

a connection or opening between two things that are normally diverging or branching

Question 11

how does the circle of willis safeguard from hypoxia

Answer 11

it ensures blood can continue to reach all vessels even if there is a blockage in one

Question 12

what are the source arteries of the brain

Answer 12

2 internal carotid, 2 vertebral

Question 13

what is the microcirculation

Answer 13

the capillary bed of the brain that is the primary site from oxygen and nutrient exchange; high capillary density optimised O2 transport

Question 14

what happens to the microcirculation during hypoxia

Answer 14

capillary density increases in an attempt to combat hypoxia

Question 15

what is the effect of hypertension on the microcirculation

Answer 15

decreases the number of capillaries - vascular resistance

Question 16

how is mean arterial pressure (MAP) regulated?

Answer 16

-ve feedback loop e.g. increased pressure results in decreased vasodilation and decreased HR

Question 17

what is cerebral perfusion pressure (CPP)?

Answer 17

the amount of pressure needed to maintain blood flow through the brain; regulated by 2 opposing forces

Question 18

What forces regulate CPP?

Answer 18

Mean arterial pressure and intercranial pressure; CPP = MAP - ICP

Question 19

is CPP raised during hypertension?

Answer 19

no, CPP is maintained by autoregulation at a constant cerebral blood flow (CBF) of 50-150mmHg

Question 20

what can increase ICP

Answer 20

intercranial bleeding, cerebral oedema, tumour

Question 21

what can increased ICP result in?

Answer 21

collapsed veins; decreased effectiveness of CPP; reduced blood flow

Question 22

what is the response of the vasculature during hypoxia?

Answer 22

the vessels become maximally dilated; CPP is increased; autoregulation is lost

Question 23

how is ICP maintained when vasodilation occurs

Answer 23

reciprocal volume changes occur everywhere else within the brain - a requirement of precise blood flow

Question 24

what is Cushing’s reflex?

Answer 24

increased ICP reduced cerebral perfusion; cerebral ischemia results and causes massive sympathetic activation - systemic blood pressure is increased in an effort to restore cerebral perfusion

Question 25

why is Cushing’s reflex necessary

Answer 25

an increase in ICP can compress blood vessels leading to the brain

Question 26

what is the blood brain barrier formed of?

Answer 26

capillary endothelial cells with tight junctions (instead of pores) and basement membrane; the neurovascular unit

Question 27

what kind of molecules can generally cross the blood brain barrier? (3)

Answer 27

lipid soluble molecules - O2, CO2, general anaesthetics etc.; D-glucose (via GLUT1); carriers for adenosine, metabolic acids, amino acids etc.

Question 28

what is the role of astrocytes with cerebral capillaries? (4)

Answer 28

regulate cerebral blood flow; upregulate tight junction proteins; contribute to ion and water homeostasis; interface directly with neurons

Question 29

what is the neurovascular unit?

Answer 29

neurons, glia and cerebral capillaries working together

Question 30

what is the NT for neurovascular coupling

Answer 30

glutamate

Question 31

what happens to neurovascular coupling after stroke?

Answer 31

it is damaged

Question 32

what is neurovascular coupling?

Answer 32

a unique mechanism that controls regional cerebral blood flow (CBF) and ensures a rapid increase in the rate of CBF to activated brain structures; alterations in local perfusion that occur in response to changes in neuronal activity

Question 33

what is the role of neuronal regulation in CBF

Answer 33

neuronal control is weak; the ANS (symp/para) has some control over modulating blood flow

Question 34

what is the role of metabolic regulation CBF

Answer 34

blood flow is sensitive to the metabolic needs of local cells and can change to accommodate them

Question 35

what ways can vasodilation be regulated metabolically? (4)

Answer 35

1. neural activity leads to ATP breaking down into adenosine which is a vasodilator;
2. decreased pH, pO2 and increased pCO2 levels result in vasodilation;
3. increased K+ levels cause vasodilation;
   (1-3 indicate that as more work is done by the brain blood flow increases)
4. the NV unit produces vasodilating compounds, the release of which is stimulated by Ca2+ waves, astrocytes use coupling to achieve this (see ppt!)

Question 36

what is the myogenic control of CBF?

Answer 36

independent of nerve supply; depends on perfusion pressure due to changes in vascular tone; increased pressure and the accompanying stretch of vascular smooth-muscle cells elicit vasoconstriction while decreased pressure elicits vasodilation

Question 37

what is the control of CBF a form of?

Answer 37

autoregulation