Central Blood Flow Regulation and the Blood-Brain Barrier Flashcards
How much oxygen is supplied to the brain per minute?
55 ml/100g of tissue/min
Why is there a vast surplus of glucose delivery to the brain?
Because the brain can only metabolise glucose
Brain can’t store, synthesise or utilise any other source
(Ketone bodies can be metabolized if there is a shortage)
Blood glucose below what value will lead to loss of consciousness, coma and death?
2 mM
On what levels do you get regulation of cerebral blood flow?
Mechanisms affecting total CBF
Mechanisms that relate activity to requirement in specific brain regions by altered localised blood flow
Between what range in mean arterial blood pressure can autoregulation maintain a constant cerebral blood flow?
60-160 mm Hg
Name one important factor to do with the smooth muscle lining arterioles that allows regulation of blood flow.
Myogenic Mechanism – when smooth muscle surrounding arterioles is stretched, it will contract to maintain a constant blood flow
Occurs when there is a change in BP in the body
What are the 2 types of control of cerebral blood flow regulation?
Neural
Chemical
What are the 4 types of neural control of cerebral blood flow?
Sympathetic innervation of the main cerebral arteries: causes vasoconstriction when arterial BP is high
Parasympathetic (facial nerve) stimulation: can cause slight vasodilation
Central cortical neurons: release vasoconstrictor neurotransmitters e.g. catecholamines (A + NA)
Dopaminergic neurons: produce vasoconstriction (localised effect related to increased brain activity)
What feature do capillaries in the brain have that allow them to contract?
Surrounded by pericytes:
a type of brain macrophage that have several functions e.g. contractile, immune function, transport properties
What do the dopaminergic neurons affecting cerebral blood flow innervate?
Pericytes around capillaries + smooth muscle around arterioles
Dopaminergic neurons cause contraction of pericytes via which receptors?
Aminergic + serotoninergic neurons
Name 7 chemical factors that increase blood flow to particular tissues.
CO2 NO pH Anoxia Adenosine K+ Other (e.g. kinins, prostaglandins, histamine, endothelins)
How does change in pH affect blood flow?
The lower the pH (the higher the H+ concentration) the more the vessel vasodilates, resulting in increased blood flow
Describe how carbon dioxide indirectly causes vasodilation in the cerebral vessels.
H+ ions can’t cross the BBB, but CO2 can
CO2 moves from the blood through the BBB into the smooth muscle cells
Within the smooth muscle cells, in the presence of carbonic anhydrase, CO2 reacts with water to form bicarbonate + H+ ions
Internally generated H+ ions within the smooth muscle cells cause smooth muscle relaxation (vasodilation)
Where is CSF produced?
Choroid plexus: specific cells associated with the ventricles (particularly the lateral ventricles)
What name is given to parts of the brain that receive blood flow like anywhere else but do NOT have a BBB?
Circumventricular organs
Describe the passage of CSF through the ventricular system.
CSF produced by specialized ependymal cells of the choroid plexus (mainly in lateral ventricles)
From lateral ventricles, goes through interventricular foramina to 3rd ventricle
Then flows down the cerebral aqueduct to 4th ventricle
Enters subarachnoid space (via medial + lateral apertures)
Drains back into venous system via arachnoid granulations
What is the volume of CSF in a normal person?
80-150 mL
What is the volume of CSF formed per day?
450 mL/day
State 3 functions of the CSF.
Protection (chemical + physical)
Nutrient provision to neurons
Transport of molecules
Describe the structure of the blood-brain barrier. Which cells are involved?
Capillaries in the brain have endothelial cells with very tight junctions so there is tight control of what can pass through the walls
Capillaries are also surrounded by pericytes with end-feet of astrocytes running along the capillary wall
What type of molecule can cross the blood-brain barrier easily?
Lipophilic molecules
How do water and glucose cross the blood-brain barrier?
Water: aquaporin channels
Glucose: GLUT-1 transporters
Name 3 circumventricular organs.
Median eminence region of the hypothalamus
Subfornical organ
Organum vasculosum of the lamina terminalis
