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Year 2 - Neuroscience > Cerebral Blood Flow Regulation > Flashcards

Cerebral Blood Flow Regulation Flashcards

1
Q

When does unconsciousness occur and irreversible damage?

A

If CBF interrupted for 4secs = unconsciousness

Few minutes = irreversible damage

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2
Q

Syncope?

A

Fainting

Common manifestation of reduced BS to the brain

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3
Q

Main principle energy source for the brain?

A

Glucose

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4
Q

[glucose] concentrations and impact?

A

Normal fasting levels = 4-6mM

If <2mM = unconsciousness, coma and death

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5
Q

How is CBF regulated?

A

x mechanisms affecting TOTAL CBF

x mechanisms with alter LOCALISED BF depending on activity

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6
Q

Auto-regulation range for CBF?

A

MABP 60-160mmHg

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7
Q

How is the CBF autoregulated to maintain the MABP?

A

Stretch-sensitive cerebral vascular SM

High BP - contracts
Low BP - relax

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8
Q

What can happen to the brain if the BP is too high?

A

Swelling of brain tissue as ‘closed’ cranium = intracranial pressure increases

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9
Q

What is local regulation mediated by?

A

Neural control
AND
Chemical control

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10
Q

How can local changes to CBF be measured?

A

Imaged on PET scans & fMRIs

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11
Q

Explain the vascularisation of the CNS

A

Arteries from the pia mater penetrate into the brain parenchyma –> form capillaries

These brain into veins/venules –> into the surface pial vessels

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12
Q

Relationship betw. neurone and capillary in the CNS

A

No neurone is >100um (micro) from a capillary

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13
Q

4 neural factors affecting CBF regulation?

A
  1. SN nerve stimulation
  2. PSN (facial nerve) stimulation
  3. Central cortical neurones
  4. Dopaminergic neurones
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14
Q

SN nerve stimulation (neural factor)?

A

To main cerebral arteries

VasoCONSTRICTION when MABP is high

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15
Q

PSN facial nerve stimulation (neural factor)?

A

Produces sligh vasoDILATION

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16
Q

Central cortical neurones (neural factor)?

A

Releases various vasoCONSTRICTOR NTs

e.g. catecholamines (A & NA)

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17
Q

Dopaminergic neurones (neural factor)?

A

LOCALISED vasoCONSTRICTION

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18
Q

Explain what dopaminergic neurones innervate

A

Innervate
x penetrating arterioles
x pericytes around capillaries

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19
Q

Explain how dopaminergic neurones function

A

May participate in the diversion of CBS to areas of high activity

Dopamine may cause contraction of pericytes via. aminergic & serotoninergic receptors

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20
Q

Pericytes?

A

Brain macrophages that wrap around capillaries - maintaining integrity & function

Diverse activity inc. immune function, transport property, contractile

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21
Q

Chemical factors affecting CBF?

A

Generally localised

CO2 (indirect)
pH
NO
K+
Adenosine, anoxia, prostaglandins
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22
Q

Effect of pCO2 on CBF?

A

An increase in pCO2 = BF increases

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23
Q

Effect of CO2 on cerebral arteries?

A

VasoDILATION

Increase in H+ = decreases pH inside VSMCs = cell relaxes = vessels dilate = INCREASED BF

24
Q

Where can the H+ (in chemical factors) be derived from?

A

Higher CO2 in blood (NOT directly from H+ in blood)

Increased neural metabolic activity

25
Q

What produces CSF?

A

Choroid plexus (in the cerebral ventricles)

26
Q

Choroid plexus?

A

Modifies ependymal cells that normally line the ventricles, aqueducts and canals of the brain

27
Q

Capillaries of the choroid plexus vs. local ependymal cells?

A

Leaky vs. extensive tight junctions

28
Q

Path of CSF?

A
  1. Lateral ventricles
  2. 3rd ventricle via. interventricular foramina
  3. Central aqueduct
  4. 4th ventricle
  5. Subarachnoid space via. medial & lateral apertures

LEAVES via. arachnoid granulations into superior saggital sinus

29
Q

Volume of CSF?

30
Q

Function of CSF?

A

Protection
Nutrition
Transport

31
Q

What is similar in the composition of plasma & CSF?

A

pH (slightly more acidic in CSF) & osmolarity

32
Q

What is different in the composition of plasma & CSF?

A

CSF - very LOW protein levels

33
Q

At what level is the BBB present?

A

Level of CNS capillaries

34
Q

Why is the BBB important?

A

CNS neurones sensitive to local envrionment - homeostasis is key for the brain

35
Q

3 types of capillaries?

A

Continuous
Fenestrated
Sinusoid

36
Q

From what are the CNS capillaris derived from?

A

Derived from surface pial vessels

37
Q

What happens to the BBB capillaries the deeper it goes?

A

Extensive tight junctions at endothelial cell-cell contacts

remember capillary surrounded by endothelial and then pericytes

38
Q

Importance of the change in property of BBB capillary the deeper it goes?

A

Reduces solute & fluid leakage across the capillary wall

39
Q

BBB proper?

A

The deeper into the tissue, the less permeable BBB

Little transcellular vesicular transport

40
Q

Interendothelial junctions (IEJs)

A

More tightly knit - endothelial cells overlap on each other to give a tighter fit

41
Q

Other than pericytes what else are BBB capillaries covered with?

A

Astrocytes - ‘end-feet’

42
Q

Which part of the CNS do blood-borne infections normally affect?

A

Meninges - as vessels are NOT BBB

43
Q

Some evidence shows that loss of BBB can be good - why?

A

Can help with clearing some infections by allowing immune cells across

44
Q

Example of lipophillic molecules that can cross the BBB?

A

O2
CO2
Alcohol

45
Q

Examples of hydrophillic substances and specific transport mechanisms needed to cross BBB

A

Water - AQP1/4 channels

Glucose - GLUT1

AA - 3 diff transporters

Electrolytes - specific transporter systems

46
Q

Area of the brain that lacks BBB? Where it is found?

A

Circumventricular organs (CVO)

Found close to the ventricles

47
Q

What are the capillaries of the CVOs like?

A

Fenestrates (therefore leaky)

48
Q

Why do the CVOs capillaries have fenestrated type?

A

Need to sample blood
OR
secrete into the blood itself

49
Q

Relationship between CSF and CVOs?

A

Ventricular ependymal lining close to the CVOs often MUCH TIGHTER than other areas

To LIMIT exchange between them and the CSF

50
Q

Area posterma?

A

Samples plasma for toxins - induces vomiting if found (example of CVO)

51
Q

Antihistamines and BBB?

A

H1 blockers are hydrophobic so cross BBB by diffusion

As histamine invovled in wakefullness can cause people to become drowsy

52
Q

What have been changed about the antihistamines in regards to the BBB?

A

2nd-generation antihistamines

Are POLAR (have a hydrophillic attachment) so do NOT readily cross the BBB so do NOT cause drowsiness

53
Q

Issue with giving dopamine to treat Parkinson’s Disease?

A

Need to raise dopamine levels in brain to treat PDs

BUT

Dopamine CANNOT cross the BBB

54
Q

Issue with L-DOPA?

A

L-DOPA CAN cross the BBB via. aa transporter

BUT

Most of it is converted to dopamine peripherally so LESS AVAILABLE to access the brain

55
Q

How to overcome the issue with L-DOPA?

A

Co-administer with DOPA decarboxylase inhibitor

CANNOT cross BBB so does NOT interfere w conversion of L-DOPA in the brain

56
Q

Example of DOPA decarboxylase inhibitor?

Year 2 - Neuroscience (18 decks)

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