Cerebral metabolism- Exam 1
At what rate is CSF formed? Total made per day (on average)?
0.3-0.4 mL/min 500 mL
CBF reaches a new steady state within __ min after a step-change in PaCO2?
1 -CO2 diffuses very easily!
CBF increases/decreases __ mL/100 g/min per __ torr increase/decrease in PaCO2 within normal limits of PaCO2. At what torr is this process attenuated?
1 1 25 torr MEMORIZE this fact
What are the four types of receptors that cerebral vessels are innervated by?
1. Adrenergic 2. Cholinergic 3. Serotonergic 4. GABAminergic
What does flow-metabolism coupling depend on?
1. Buildup of metabolites causing vasodilation of the cerebral vasculature (arterials) 2. Endothelium derived factors (NO)
What are the five "purposes" of CSF within the subarachnoid space?
1. Cushioning for brain and SC 2. Excretory pathway (secretion of waste products into the venous blood thru arachnoid villi) 3. Provide buoyancy 4. Nutrient pathway 5. Serves as a route of communication (carries NTs and hormones)
What are the two types of cells in the CNS?
1. Neurons 2. Glial cells
How is the CBV manipulated?
1. Physiologic 2. Pharmacologic methods (us)
How does CSF volume increase (2)?
1. Production increases (rare) 2. Reabsorption is decrease
What is the CBF in which there is loss of cellular integrity in the brain?
10 mL/100 g/min
CBF can vary from __ to __ mL/100 g/min
10-300
Ischemia longer than 2 hours below __ mL/100 g/min is probably irreversible
12
How many grams does the brain weigh?
1400
What is the CBF in which there is disappearance of evoked potentials and synaptic transmission?
15 mL/100 g/min
How much CO does the brain receive?
15% (large amount compared to overall weight)
How much CSF does an average person have? Distribution?
150 mL 1/2 in cranial vault and 1/2 in spinal subarachnoid space
How many ATP molecules per molecule of glucose does the anaerobic pathway produce?
2
What percentage of TBW does the brain weigh?
2%
Vertebral arteries supply __% of the cerebral blood flow to the brain?
20
At rest, what is the total percentage of O2 uptake of the brain?
20%- brain is the most metabolically active tissue in the body
What is the CBF in which functional impairment would occur?
23 mL/100 g/min
The Na+/K+ pump itself accounts for __-__% o the ATP utilization in the brain?
25-40%
What is the normal value for cerebral blood flow?
50 mL/100 gram brain tissue/min
At what MAP pressure is CBF kept constant?
50-150 torr
Changes in CBF due to PaCO2 returning to normal occurs in __-__ hrs?
6-8
When PaO2 falls below __ torr, CBF begins to increase?
60
At rest, the brain is ___ times more active in metabolism than any other organ in the body.
7.5
Gray matter CBF value? White matter CBF value?
80 mL/100 gram/min 20 mL/100 gram/min *Overall average is 50 mL/100 gram/min
Brain accounts for __% of intracranial contents, CSF accounts for __% of intracranial contents and CBV accounts for __% of intracranial contents?
85 10 5
How do substances that don't easily cross the BBB get across?
Active and passive transport (carrier mediated transport)
What is the mechanism that explains why hypoxemia (PaO2<50 torr) begins to cause a dramatic increase in CBF?
Adenosine release and accumulation
Glial cells (specifically astrocytes) are located where in the brain? What's their purpose?
Border all of our cerebral blood vessels Control of extracellular K+ concentrations (helps with vasodilation in the cerebral tissue)
What characteristic of CSF reduces the weight of the brain to 25 grams vs 1400 grams?
Buoyancy
What are some examples of lipid soluble substances that pass easily from the blood to the brain?
CO2 O2 VAs
What structure supplies 80% of blood flow to the brain?
Carotid arteries
Where does protein metabolism and synthesis occur in the CNS?
Cell bodies in GRAY matter
What happens to the brain when MAP<50 torr?
Cerebral ischemia and decreased energy levels
What is flow metabolism coupling in the brain?
Changes in cerebral metabolic rate is rapidly matched by changes in cerebral blood flow
Where is CSF formed?
Choroid plexus in the cerebral ventricles
The arteries that supply the blood flow to the brain terminate where?
Circle of Willis
What is the structure in the brain the permits collateral circulation?
Circle of Willis
An increase in an intracranial component does what to the CSF? (number one thing) What other two things does it affect?
Expands it Number one thing is translocation of CSF to a more distensible spinal arachnoid space 1. Increase absorption 2. Decrease production (this is rare tho)
T/F There is storage capacity in the brain for glucose?
False! There is none
T/F Glial cells appear unnecessary for the maintenance and development of the BBB?
False... glial cells (astrocytes specifically) appear NECESSARY
T/F CMRO2 is greatest in white matter?
False... gray matter (bc of all the protein synthesis going on there)
T/F CSF is an ultrafiltrate of the plasma?
False... is not bc the choroid plexus specifically secretes CSF
What must oxidative phosphorylation have for fuel?
Glucose... cerebral metabolism requires mostly an aerobic pathway
What does glial mean?
Glue (cells that hold everything together in the brain)
CO2 effects on CBF are due to ___
H+ ion (or pH) concentration **H+ ions are the reason for vasodilation (not the CO2). They are easily transmitted across the BBB and affect the medulla chemoreceptors
CSF absorption is a sensitive function of ___
ICP
Acute hypotonicity: Net movement of water __ the brain. What does this do to brain tissue?
INTO swells
What's the mechanism of mannitol on the brain?
Increases tonicity of the plasma, decreasing brain water and increases movement of water OUT of the brain
What's the mechanism of Lasix on formation of CSF?
Inhibition of Na+ and Cl- transporters
What's the mechanism of Acetazolamide (Diamox) on formation of CSF?
Inhibition of the HCO3- transporter (Carbonic anhydrase inhibitor)
Which ions are actively transported to the inside of the cell after each action potential?
K+ and Cl-
What prevents passage of polar molecules in the BBB? Give examples of some polar molecules that to not pass?
Lipid bilayer ions, glucose, aa, proteins, mannitol
What is the formula for CPP?
MAP-ICP
What are the normal "housekeeping" functions of the brain?
Metabolism of: 1. Lipids 2. Proteins 3. Carbs and maintenance of membranes
What principle states that "the central nervous system and its accompanying fluids are enclosed in a rigid container whose total volume tends to remain constant. An increase in volume of one component (e.g., brain, blood, or cerebrospinal fluid) will elevate pressure and decrease the volume of one of the other elements."
Monro-Kellie
What factors is cerebral auto regulation controlled by?
Myogenic and metabolic factors
CSF is formed by transport of what four things? What is the mechanism of formation of CSF?
Na+ Cl- HCO3- osmotic movement of water *Increases osmolarily of CSF, which pulls water into CSF
Which ions are actively transported to the outside of the cell after each action potential?
Na+ and Ca++
What happens to neurons when there are decreased stores of ATP available?
Neurons become nonfunctional and may become damaged
What two substrates MUST the brain have sufficient supply of to meet metabolic demands?
O2 and glucose
Acute hypertonicity: Net movement of water __ the brain. What does this do to brain tissue?
OUT of shrinks
What is the most potent physiologic determination of CBF?
PaCO2 (arterial)
What element plays the greatest role in volume compensation to maintain normal ICP?
Redistribution of CSF!!!
What happens to the brain when MAP>150 torr?
There is disruption of the BBB and cerebral edema or hemorrhage occurs
What structures are present in the capillary endothelium of the BBB? What's their purpose?
Tight junctions Prevention of extracellular substances from passing from the blood-> brain
What's the purpose of the blood brain barrier?
To maintain bran milieu
In chronic HTN pts, their cerebral autoregulation curve is shifted ___, meaning they require a ___ BP to maintain cerebral auto regulation.
To the right HIGHER- don't use hypotensive techniques on these pts
T/F Brain metabolism increases with increased brain activity?
True
T/F CBV can change very rapidly?
True
T/F Long term antihypertensive therapy can restore normal auto regulation?
True
In what instances can the brain increase in solid material?
Tumor Cerebral edema (increase in tissue water)
What conditions would not allow a person to maintain normal cerebral auto regulation?
Tumors AVMs Ruptured aneurysms Stroke (STAR)
What arteries are responsible for the "posterior circulation" of the brain?
Vertebral
Absorption of CSF occurs via ___, primarily found in ___ of the brain?
arachnoid villi superior saggital sinus (which a venous sinus)
Water freely moves across the BBB due to ___
bulk flow
Internal carotid arteries enter into the cranium thru the ___, then bifurcates in to ____ cerebral and ____ artery. This is known as the "____" of the brain.
carotid canal anterior (supplies the front of the brain) middle (supplies the temporal region of the brain) "anterior circulation"
Definition: Cerebral metabolic rate of oxygen=
cerebral metabolic requirement for O2
When neurons depolarize, extracellular K+ increases/decreases?
increases
Approximately 60% of the brains O2 consumption is used to support what? How about the other 40%?
ionic gradients that are necessary for the electrical activity of the brain. Other 40%- normal housekeeping functions of neurons and glial cells.
Auto regulation of the brain: maintenance of CBF regardless of changes in ____
perfusion pressure
CSF production is relatively insensitive to ___
pressure
Above or below 50-150 torr, CBF becomes ____, relying on ___.
pressure dependent CPP
In the aerobic pathway, glucose is metabolized into ___? This takes place in the ___ and produces how many ATP molecules per glucose molecule? This entire process is known as the _____.
pyruvate mitochondria 38 Kreb's cycle (aka citric acid cycle)
Vertebral arteries come off the __ and go into the __ of the cervical vertebrae, enter thru the ___ and then coalesce into the ___, which supplies blood flow to the cerebellum and the ____.
subclavian artery transverse processes foramen magnum basilar artery posterior cerebrum
The common carotid arteries come off ____?
the aorta
There is free movement of what substances across the blood-CSF barrier?
water gases lipid soluble substances
