CBF, CSF, Brain Metabolism
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Blood is supplied to the brain via 4 large arteries...what are these? and what do they merge to form?
- 1. two carotid and two vertebral arteries
- 2. merge to form the Circle of Willis
The arteries from the Circle of Willis travel and are than called ____ arteries.
Pial arteries turn into ______ arteries or arterioles.
The penetrating vessels of the brain are separated slightly from the brain tissue by an extension of the subarachnoid spaced called the ____ ____ ____.
Normal blood flow through the brain of the adult person averages ____ - ___ ml per 100gram of brain tissue per minute.
The brain makes up __% of body weight and receives ___% of cardiac output.
What four metabolic factors contribute to the regulation of cerebral blood flow?
- 1. CO2 concentration
- 2. H ion concentration
- 3. O2 concentration
- 4. substances released from astroyctes
How does CO2 increase the blood flow to the brain?
CO2 combines with water to form carbonic acid which dissociates to form H ions. H ions cause vasodilation which can increase the blood flow to the brain to 2 x the normal.
An increase in hydrogen ions has what effect on the neuro system if there was no increase in blood flow??
it decrease neural activity.
When H ions cause dilation to increase blood flow what else happens??
the increased blood flow causes an increase in the removal of carbonic acid from tissues deducing the amount of H ions back to normal which in return maintains constant neuronal activity.
How does oxygen deficiency cause increased blood flow??
decrease o2 causes vasodilation even with intense brain activity to return the blood flow back to a normal rate.
*this concept is basically the same as what occurs in coronary circulation to improve blood flow to the heart.
A decrease in oxygen < ____ almost immediately causes an increase in cerebral blood flow.
Brain function becomes deranged below ___ mmHg. This can result in coma.
Blood flow is autoregulated well between ___ and ___ mmhg.
60 and 140
What is the SNS role in controlling blood flow to the brain?
Mild to moderate stimulation of the SNS causes little change to the cerebral blood flow. However when arterial pressure rise acutely, the SNS will constrict large and intermediate size brain arteries to prevent the high pressures from reaching the smaller vessels preventing stokes from occurring.
In the brain, there are more capillaries where the ____ are the greatest.
Metabolic rate of gray matter when neuronal cell bodies lie is ___ x as great as white matter. The number of capillaries and the rate of blood flow is also ____ x as great.
What are present in the brain capillaries to prevent them from being "leaky" as the other capillaries in the body are??
glial feet support the capillaries on all sides!
these feet prevent over stretching of capillaries in cases of high capillary blood pressures. they provide support to the vessels.
Almost all elderly patients have small artery blockages in the brain.. what % of these individuals will have a stoke at some point in their life?
Blockage of what artery is the cause of most strokes??? and what does this artery supply?
Middle cerebral artery
supplies the mid portion of one brain hemisphere
There is a lot of fluid surrounding the brain and spinal cord. The capacity if 1600-1700ml. What mls of this is CSF?
What is the job of the CSF??
to cushion the brain and allow it to flow
What is the specific gravity of CSF? what about the pH?
1.002 to 1.009
What does coup mean in relation to head injuries??
Means that when you have a blow to the head or have an acceleration/deceleration injury... you will see injury to the brain on the same side of the head where the blow occurred.
What does contrecoup mean in relation to head injuries??
injury to the brain will occur on the opposite side of the blow to the head
With the force of trauma, the brain moves towards the side of injury, as the brain is pulled away from the skull, a vacuum force tries to pull the brain back, once the blow is no longer occurring, the vacuum collapses and the brain smashes back against the opposite side of the head causing increase to the brain on the opposite side of head where the blow/trauma occurred.
CSF is formed at a rate of ____ ml a day.
____ of CSF originates as secretion from the choroid plexus.
**small amount also comes from brain itself and ependymal cells
Describe the flow of CSF starting with the choroid plexus...
- 1. choroid plexus
- 2. lateral ventricles
- 3. third ventricle
- 4. downward along the duct of sylvius into 4th ventricle
- 5. through 3 small openings (2 lateral formina of Luschka and a mideline foramen of Magendie)
- 6. then enters the cisterna magna
What is the cisterna magna?
a fluid space between the medulla and the cerebellum.
Secretion of CSF depends mainly on what mechanism???
the active transport of sodium ions through epithelial cells
What does the increase of NaCl in the CSF cause???
immediate osmosis of water leading to fluid secretion of CSF
How does the osmotic pressure in the CSF compare to the pressure in the plasma???
it is almost equal
How does the sodium concentration in the CSF compare to the sodium concentration in the plasma???
it is equal
How does the chloride concentration in the CSF compare to the chloride concentration in the plasma???
Chloride is about 15% greater in the CSF than in the plasma.
How does the K concentration in the CSF compare to the K concentration in the plasma???
K is about 40% less in the CSF than in the plasma.
**FYI---this is wrong in our note and study guide... see pg. 747 under Secretion by the Choroid Plexus
How does the glucose concentration in the CSF compare to the glucose concentration in the plasma???
glucose is about 30% less in the CSF than in the plasma
CSF pressure is regulated by ____ ___.
What is the normal CSF pressure?
5-15mmHg which is close to 130 mm of H20
How does the arachnoidal villi control a constant rate of formation and pressure of CSF?
the villi has valves just like the heart that allows for CSF to flow forward and not backward. if the pressure increases, the valves will open widely to allow CSF to flow. Pressure only has to be slightly greater than venous pressure to flow.
What is hydrocephalus?
excess water in the cranial vault
What is communicating hydrocephalus?
communicating fluid flows freely from the ventricular system into the subarachnoid space bc of a blockage of fluid flow in the space or in the villi. fluid will collect outside the brain.
What is noncommunicating hydrocephalus?
fluid build up due to a blockage of flow in one of the ventricles, normally a block is in the sylvius from closure before birth or because of a tumor.
The brain is not capable of anaerobic metabolism...therefore, a lack of blood flow can cause unconsciousness within _____.
5 to 10 seconds.
How does the brain get its energy???
from glucose supplied in the blood..
the brain does not need insulin to get glucose to the brain.... this prevents the lose of mental function in diabetic patients.
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