Neuro 5: Regulation of blood flow + Blood Brain Barrier Flashcards
(42 cards)
Give values of blood flow to the brain.
high at 55ml/100g tissue/min
__ seconds of CBF interruption = unconsciousness
4 seconds of CBF interruption = unconsciousness
after few mins –> irreversible damage
what are some causes of syncope?
- reduced blood supply to the brain
- low BP
- postural changes
- vasovagal attack
- sudden pain
- emotional shock
Why is supply of glucose vital to the brain?
- because the brain can’t store, synthesis, or utilize any other source of energy
other than glucose, but is the other source of energy?
- ketones
What happens to brain function in HYPOglycaemia?
- if glucose conc <2mM
- can result in unconsciousness, coma, + death
What are some symptoms of HYPOglycaemia ?
- disoriented, slurred speech, impaired motor function.
What is the range for normal fasting levels?
4-6 mM
How is the 2 mechanisms by which cerebral blood flow regulated ?
- mechanism affecting total cerebral blood flow
2. mechanisms that relate activity to requirement in specific brain regions through altering localized blood flow.
How is total cerebral blood flow auto regulated?
- autoregulation occurs over MABP 60-160 mmHg
- through myogenic response
- Increase in vessel wall pressure –> causes smooth muscle contraction
(decreasing cerebral blood flow) - stretch sensitive cerebral vascular smooth muscle CONTRACTS at HIGH BP
RELAXES at LOW BP
Below the autoregulatory pressure range, what happens to the brain?
- leads to compromised brain function
Above the autoregulatory pressure range, what happens to the brain?
- increased blood flow –> causes swelling of brain tissue
- causes increase in intracranial pressure
local brain activity determines O2 + glucose demand –> so local changes in blood supply =
local auto regulation.
What are the 2 methods of local regulation of CBF ?
- neural control
- chemical control
What are the 4 neural factors that regulates CBF
a) Sympathetic Nerve Stimulation to main cerebral arteries –> causing vasoconstriction
b) Parasympathetic Stimulation
- -> causes slight vasodilation
c) Central Cortical Neurones –> releases a variety of vasoconstrictor neurotransmitters (e.g catecholamines)
d) Dopaminergic Neurones –> produces vasoconstriction
How does dopaminergic neurones help with regulation of CBF?
- they innervate penetrating arterioles + pericytes around capillaries
- and they participate in the diversion of cerebral blood –> to areas of high activity
Dopamine causes contraction of pericytes via _______ and _____ receptors
Dopamine causes contraction of pericytes via aminergic and serotoninergic receptors
The main arteries of the brain = innervated by
sympathetic fibres
note: CNS = densely vascularized.
No neurone = more than 100um from a capillary
-
List examples of chemical factors that regulates CBF
- CO2
- PH
- Nitric Oxide
- K+
- Adenosine
- Anoxia
(vasodilators)
Describe the graph
for the effect of pCO2 on Cerebral Blood Flow
CO2 has strong effect on cerebral blood flow
- sharp rise
Describe the mechanism of cerebral arterial vasodilation by CO2
- H+ ions can’t cross the BBB
BUT - H+ ions can be generated in the brain
- so CO2 can move through the BBB
- in smooth muscle cells + neural tissue: CO2 + H2O —> HCO3- + H+ (in presence of Carbonic anhydrase)
- so H+ produced –> PH decreases –> acts as vasodilator –> causes relaxation of smooth muscle cells –> causes increase in Blood Flow
How is CSF produced?
- CSF = produced by the choroid plexus
- capillaries are surrounded by ependymal cells (tight junctions)
- ependymal cells secrete molecules into the ventricles
- to make CSF
The ventricles, aqueducts + canals of brain = lined with ________ cells
The ventricles, aqueducts + canals of brain = lined with ependymal cells
