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Year 2 LCRS > Neurology 5 - Blood brain barrier > Flashcards

Neurology 5 - Blood brain barrier Flashcards

1
Q

How long does cerebral blood flow need to be interrupted for unconsciousness to result?

A

4 seconds

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2
Q

Define syncope and list its causes

A
  • Fainting due to temporarily reduced blood supply to the brain
  • Caused by low blood pressure, postural changes, vaso-vagal shock, sudden pain, emotional shock
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3
Q

List the symptoms of hypoglycaemia

A
  • Disorientation
  • Slurred speech
  • Impaired motor function
  • Below 2mM results in unconsciousness, coma and death
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4
Q

What is cerebral blood flow regulated by?

A
  • Mechanisms affecting total cerebral blood flow
  • Mechanisms which relate activity to the requirement in specific brain regions by altered localised blood flow (chemical and neural regulation)
  • Autoregulated between MAP 60-160mmHg
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5
Q

Describe the process of global autoregulation of cerebral blood flow

A
  • Arteries and arterioles dilate or contract to maintain blood flow.
  • Stretch-sensitive cerebral vascular smooth muscle contracts at high BP and relaxes at lower BP.
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6
Q

What happens above and below the autoregulatory pressure range?

A
  • Below there will be compromised brain function

- Above there will be swelling and increased intracranial pressure

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7
Q

Describe the pattern of vascularisation in the CNS tissues

A
  • Arteries enter CNS tissue as branches of surface pial vessels
  • These branches penetrate into the brain parenchyma
  • They branch into capillaries, which drain to venules and veins
  • The veins drain to surface pial veins
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8
Q

List the neural factors regulating cerebral blood flow

A
  • Sympathetic nerve stimulation (vasoconstriction of large arteries)
  • Parasympathetic facial nerve stimulation (vasodilation)
  • Central cortical neurones (vasoconstrictor neurotransmiters released)
  • Dopaminergic neurons (vasoconstriction related to increased brain activity, more localised)
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9
Q

Describe how dopaminergic neurones have local effect on cerebral blood flow

A
  • Innervate penetrating arterioles and pericytes around capillaries
  • May participate in diversion of blood to areas of high activity
  • May cause contraction of pericytes via aminergic and serotinergic receptors
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10
Q

List the chemical factors that cause vasodilation in local autoregulation of CBF

A
  • CO2
  • pH
  • Nitric oxide
  • K+
  • Adenosine
  • Anoxia
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11
Q

Describe the formation of CSF

A
  • Formed by the choroid plexus
  • Leaky capillaries but local ependymal cells have extensive tight junctions
  • CSF secreted into ventricles
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12
Q

Describe the pathway of CSF

A
  • Lateral ventricles to 3rd ventricle via interventricular foramina
  • Down cerebral aqueduct into 4th ventricle and into subarachnoid space via medial and lateral apertures
  • It circulaties to eventually reach arachnoid granulations
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13
Q

What are the functions of CSF?

A
  • Protection as it surrounds the brain
  • Nutrition of neurones
  • Transport of molecules
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14
Q

Compare the composition of plasma and CSF

A
  • CSF has lower potassium, higher magnesium, lower calcium, higher chloride and lower bicarbonate ions
  • CSF has lower amino acids
  • CSF has a similar pH and osmolarity
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15
Q

Why is it clinically important that CSF has little protein?

A

If there is more protein in the CSF this can indicate a bacterial infection or damage to the blood-brain barrier

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16
Q

Why is the blood brain barrier important?

A
  • Activity of neurones is highly sensitive to composition of local environment
  • CNS needs to be protected from fluctuations in blood composition
17
Q

Where are the capillaries of the blood brain barrier derived from?

A

Surface pial vessels - the branches get more like the blood brain barrier the deeper they get into the brain

18
Q

List the differences between BBB capillaries and normal capillaries

A
  • Many tight junctions and cell-cell contacts
  • Little transport
  • Dense pericyte coverage in BBB, to maintain capillary integrity and function
  • Covered with the end feet of astrocytes which produce growth factors to induce blood-brain barrier qualities
19
Q

What are circumventricular organs?

A
  • Areas close to the ventricles where the capillaries lack BBB properties
  • Capillaries are fenestrated, and the organs are involved in secretion or need to sample the plasma
  • There is limited exchange between these vessels and the CSF, as ependymal lining cells are much tighter
20
Q

Give examples of circumventricular organs

A
  • Posterior pituitary
  • Median eminence
  • Area postrema (samples plasma for toxins to induce vomiting)
21
Q

What is the clinical importance of the blood brain barrier?

A
  • Breaks down in inflammation, infection, trauma and stroke
  • Do you want a drug to cross the BBB and get to the brain or not?
  • Antihistamine initially crossed the blood brain barrier and caused drowsiness, so now non-drowsy versions are available that cannot cross the blood brain barrier as they are polar
22
Q

How does the BBB affect treatment of Parkinsons Disease?

A
  • Raising dopamine levels is a therapy for parkinsons
  • Dopamine cannot cross the blood brain barrier as it is very hydrophilic
  • L-DOPA can cross the blood brain barrier, but it is often converted to dopamine peripherally (in the blood)
  • It must therefore be co-administered with carbidopa, which blocks DOPA decarboxylase in the blood, so DOPA is not converted to dopamine. Carbidopa cannot cross the blood brain barrier
23
Q

How does carbon dioxide cause cerebral arterial vasodilation?

A
  • H+ can’t cross the blood brain barrier
  • CO2 from neural metabolic activity is converted to hydrogen ions by carbonic anhydrase
  • H+ can enter smooth muscle
  • CO2 from the blood can be converted to hydrogen ions in the smooth muscle too
  • Lower pH causes smooth muscle to relax
24
Q

What are arachnoid granulations?

A

Openings in the arachnoid mater allowing circulation between the plasma and CSF

25
Q

How can lipophilic and hydrophilic molecules cross the blood brain barrier?

A
  • Lipophilic molecules by simple diffusion, such as oxygen, carbon dioxide and anaesthetics
  • Hydrophilic substances need specific transport mechanisms (water via aquaporins, glucose via GLUT1, amino acids and electrolytes)

Year 2 LCRS (128 decks)

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