Neuro 5 - Central Blood Flow Regulation and Blood-Brain Barrier Flashcards
How much oxygen is supplied to the brain per minute?
55ml/100g of tissue/min
Why is there a vast surplus of glucose delivery to the brain?
Because the brain can only metabolise glucose
Ketone bodies can only be metabolized if shortage of glucose
Blood glucose below what value will lead to a loss in consciousness?
2mM
On what levels do you get regulation of cerebral blood flow?
Total cerebral blood flow
localised blood flow
Between what range in mean arterial blood pressure can autoregulation maintain a constant cerebral blood flow?
60-160mmHg
Name one important factor to do with muscle lining arterioles that allow regulation of blood flow.
Myogenic Mechanism - smooth muscle surrounding arterioles is stretched, contract to maintain a constant blood flow
What are the two types of control of cerebral blood flow regulation?
Neural and Chemical
What are the 4 types of neural control of cerebral blood flow?
Sympathetic - causes vasoconstriction
Parasympathetic - facial - can cause slight vasodilation
Central cortical neurons - neurons within the brain can release neurotransmitters to cause vasoconstriction
Dopaminergic neurons - produce vasoconstriction means blood goes to other areas
What feature do capillaries in the brain have that allow them to contract?
Have pericytes which are contractile cells
What do the dopaminergic neurons affecting cerebral blood flow?
Pericytes around capillaries and smooth muscle around arterioles
Dopaminergic neurons cause contraction of pericytes vis which receptors?
aminergic and serotonergic neurons
Which fibres innervate the main arteries in the brain?
Sympathetic
Name some chemical factors that cause an increase in blood flow to particular tissues.
carbon dioxide NO pH anoxia adenosine K+
all vasodilators
How does change in pH affect blood flow?
the lower the pH the more the vessel vasodilates
Describe how carbon dioxide indirectly causes vasodilation in the cerebral vessels.
H+ ions can’t cross BBB but carbon dioxide can
Carbon dioxide moves into smooth muscles
reacts with water to form bicarbonate and H+ ions
H+ ions cause vasodilation
Describe how NO causes vasodilation.
Nitric oxide stimulates guanylyl cyclase
converts GTP –> cGMP
cGMP causes vasodilation
Where is CSF produced?
Choroid plexus
What name is given to parts of the brain that receive blood flow like anywhere else but do not have a blood brain barrier?
Circumventricular organs
Describe the passage of CSF through the ventricular system.
Lateral ventricle 3rd ventricle cerebral aqueduct 4th ventricle subarachnoid space
What is the volume of CSF in a normal person?
80-150ml
What is the volume of CSF produced per day?
450ml a day
State the 3 functions of CSF.
Protection
Nutrients
Transport
Describe the structure of the blood brain barrier?
capillaries in the brain have endothelial cells with very tight junctions
pericytes can also contract making it more likely for molecules to leave the capillary
What types of molecules can cross the blood brain barrier easily?
Lipophillic molecules
How do water and glucose cross the BBB?
WATER - aquaporin molecules
GLUCOSE - GLUT1 transporters
Name 3 circumventricular organs.
Median eminance
Subfornical
Organum vasculosum
State four components that have a lower concentration in the CSF than the plasma.
K+
Calcium
Amino acids
Bicarbonate
State two components have a high concentration in the CSF than the plasma?
Magnesium
Chloride
How is osmolarity different between the CSF and plasma?
The same
How is pH different in the CSF compared to plasma?
CSF is slightly more acidic.
