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LCRS - neuro > BBB and cerebral blood flow regulation > Flashcards

BBB and cerebral blood flow regulation Flashcards

1
Q

give approximate blood supply to brain

A

55ml/100g tissue/min.

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2
Q

What happens when blood flow to brain is reduced by more than 50%

A

insufficient oxygen delivery function becomes significantly impaired.

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3
Q

What period of interrupted CBF will result in unconsciousness?

A

4 seconds

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4
Q

What period of interrupted CBF will result in irreversible damage?

A

a few minutes.

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5
Q

What is syncope?

A

fainting - temporary CBF interruption.

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6
Q

Give some potential causes of syncope.

A

low BP, postural changes, vast-vagal attack, sudden pain, emotional shock.

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7
Q

Explain necessity of large glucose supply to brain.

A

Brain uses 50-60% body’s glucose. Brain cannot store/synthesise any other energy sauce (ketones in starvation)

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8
Q

Give three signs of reduced glucose supply to the brain.

A

Disorientation, slurred speech, impaired motor function.

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9
Q

What happens at glucose concentration levels fall below 2mM (normal fasting = 4-6)

A

unconsciousness, coma, death.

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10
Q

Why must CBF be maintained, efficient, and consistent?

A

because of the constant need of brain for oxygen and glucose.

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11
Q

What 2 types of mechanism regulate CBF

A

Mechanisms affecting total CBF mechanisms which relate activity to the requirement in specific brain regions by altered localised blood flow.

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12
Q

What is the range of auto regulation of total CBF?

A

60-160mm Hg

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13
Q

How is CBF auto regulated?

A

arteries/arterioles dilate/contract to change blood flow. Stretch sensitive cerebral vascular smooth muscle contracts at High BP and relaxes at lower BP.

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14
Q

What happens outside the auto regulatory range?

A

Below - insufficient supply –> compromised brain function Above - increased flow –> swelling of brain tissue –> increased intracranial pressure = dangerous.

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15
Q

Why is local auto regulation needed?

A

The local brain activity determines the local O2 and glucose demands, therefore local changes in blood supply

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16
Q

What two ways is CBF locally auto regulated?

A

-neural control -chemical control

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17
Q

Explain pattern of vascularisation in CNS

A

arteries enter CNS from branches of surface Pia vessels. Branches penetrate into parenchyma and branch into capillaries.

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18
Q

What’s the furthest a neurone might be from a capillary?

A

100micrometers.

19
Q

What 4 ways do neural factors regulate CBF?

A
  1. sympathetic nerve stimulation to main cerebral arteries –> vasoconstriction. 2. parasympathetic (facial nerve) stimulation –> slight vasodilation. 3. central cortical neurones release vasoconstrictor neurotransmitters e.g. catecholamines (e.g. NA, adrenaline) 4. dopaminergic neurones produce vasoconstriction (localised)
20
Q

What is the function of dopaminergic neurones (locally)?

A
  1. innervate penetrating arterioles and pericytes around capillaries.
  2. participate in diversion of CBF –> areas of high activity.
  3. dopamine can cause contraction of perictyes via amoinergic + serotoninergic receptors
21
Q

What chemical factors regulate CBF?

A

CO2 - vasodilator

lower pH - vasodilator

NO - vasodilator

K+ - vasodilator

adenosine - vasodilator

anoxia - vasodilator

other, e.g. kinins, histamines, endothelins, prostaglandins.

22
Q
A

What is the effect of pCO2 on CBF (diagram)?

23
Q

How does CO2 cause vasodilation.

A

CO2 –> carbonic acid –> increased H+ (carbonic anhydrase) –> relaxation –> increased blood flow.

(H+ cannot cross BBB)

24
Q

How can brain activity be mapped?

A

Imaging - look for increased blood flow.

Increased blood flow equates to increased neuronal activity in CNS.

25
Q

what is the function of the choroid plexus?

A

produce CSF.

26
Q

How does CSF act as a protective mechanism?

A

Provides insulation - brain effectively floating in CSF.

27
Q

What lines ventricles, aqueducts and canals of brain?

A

ependymal cells. Can form choroid plexus in ventricles.

28
Q

Label diagram of ventricles.

A
29
Q

What is the function of the CSF?

A

physical and chemical protection. Neurone nutrition. Molecule transport.

30
Q

What is the volume of CSF?

A

80-150ml

31
Q

How is CSF formed?

A

Capillaries leaky, but local ependymal cells have extensive tight junctions.

Secrete CSF into ventricles (lateral ventricles, 3rd ventricle via interventricular foramina, down cerebral aqueduct into 4th ventricle and into subarachnoid space via medial and lateral apertures) – circulates.

32
Q

Label diagram outlining CSF formation.

A
33
Q

Diagram showing relative CSF vs plasma concentrations.

A
34
Q

What is the level of the BBB (at which size of blood vessel is BBB formed)?

A

CNS capillaries.

35
Q

What are capillaries of CNS derived from?

A

surface pia vessels

36
Q

Give some features of BBB capillaries?

A

tight junctions - minimise solute and fluid leakage.

Dense pericyte coverage (maintain capillary function)

End feet from astrocytes (maintain BBB properties)

Influx and efflux transporters control solute flow

lipophilic molecules can cross.

37
Q

Give transport systems for water, glucose, aa and electrolytes across BBB.

A
  1. water - aquaporin (AAQP1, AQP4)
  2. glucose - GLUT1
  3. aa, 3 different transporters.
  4. electrolytes, via specific systems.
38
Q

what are circumventricular organs (CVOs)

A

Area where capillaries lack BBB properties.

39
Q

Give some properties of CVOs.

A

fenestrated (so leaky).

tight ependymal lining to control and limit exchange.

40
Q

Why do CVOs exist?

A

for secretion of substances into plasma, e.g. posterior pituitary, media eminence

for sampling of plasma. e.g. area postrema (vomiting)

41
Q

What can cause breakdown of BBB function?

A

trauma, inflammation, infection, stroke.

42
Q

Why does the BBB present an issue for pharmacology?

A

Do you want your drug to access the brain?

Many drugs cannot access the brain

Many drugs access it too readily.

43
Q

Why do old fashioned antihistamines make people drowsy?

A

histamine is important for wakefulness. Old fashioned antihistamiens are lipophilic and can cross BBB. Newer antihistamines are polar

44
Q

Why does the BBB affect Parkinsons treatment?

A

Dopamine cannot cross BBB, precusor L-DOPA can.

LCRS - neuro (16 decks)

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