03. CSF and Brain Homeostasis (Karius) Flashcards
How does O2 affect blood flow to the brain?
It largely stays the same in response to increasing levels of O2, except at the extremes.
Too low of O2 will cause blood flow to the brain to dramatically increase.
Too high of O2 will cause blood flow to the brain to decrease.
How does the parasympathetic nervous system affect blood flow to the brain, and what neurotransmitters are used by it?
Parasympathetics will cause vasodilation when blood pressure is low to increase the portion of the blood reaching the brain via acetylcholine, vasoactive intestinal peptide, PMH-27
How might a decrease in CSF cause an increase in blood flow to the brain?
Cerebral circulation is highly sensitive to pain in response to torsion. A decrease in CSF makes the brain less bouyant. This can cause torsion on blood vessels which leads to pain. This in turn causes an increase in blood flow to the brain, potentially to increase CSF
Substance P, Neurokinin A and CGRP are in charge of this signaling.
What is the blood brain barrier highly permeable to, slightly permeable to, and basically not permeable to?
- Highly permeable:
- CO2
- O2
- Lipid soluble substances (like unbound steroid hormones)
- Slightly permeable:
- Na+
- Cl-
- K+
- Basically not, but still kind of permeable:
- Plasma proteins
- Non-lipid-soluble organic molecules.
What are the cellular components of the blood brain barrier?
- Pericytes
- Can regulate passage across the blood brain barrier based upon their level of contraction around the fenestra of the capillaries.
- Astrocytes
- Have foot processes that block the fenestra.
- Endothelial cells
How does an increase in intracranial pressure affect cerebral blood flow?
An increase in intracranial pressure causes the veins in the cerebrum to become compressed. This leads to a reduction in venous return, and a concomitant reduction in cerebral blood flow.
What four transporters are responsible for carrying glucose across the blood brain barrier, and on which cells are they found?
- Glut 1 has two isoforms:(not insulin depend.)
- 45 kD Glut 1 – Astrocytes
- 55 kD Glut 1 – Microvessels, choroid plexus, ependymal cells.
- Glut 3 is found on neurons.
- Glut 5 is found on microglia.
How do the blood vessels of the brain respond to changes in cerebral perfusion pressure?
As cerebral perfusion pressure goes up or down, the blood vessels will constrict or dilate to compensate – maintaining blood flow at a plateau. However, at the extremes, increased cerebral perfusion pressure will increase cranial blood flow, and decreased pressure will reduce cranial blood flow.
How does the sympathetic nervous system affect cerebral blood flow and why?
What neurotransmitters are used by it?
Sympathetic innervation protects the brain by constricting when blood pressure is high via norepinephrine and neuropeptide Y.
This protects the brain.
leads to constriction when systemic cardiac output/blood pressure increases ONLY
What are the four circumventricular organs and their functions?
- Posterior pituitary
- Has secretory functions – we already know about this.
- Area postrema
- Initiates vomiting in response to chemical triggers.
- Organum vasculosum of the lamina terminalis (OVLT)
- Regulates total body water/thirst important as a target of angiotensin II
- Subfornical organ
- Thirst/water
When intracranial pressure increases or decreases, how does the body modify CSF levels to adapt to the change?
It either increases or decreases absorption to respond to the change.
At equilibrium, what is the relationship of sodium and total osmolarity of CSF to the blood?
What is CSF richer in than the blood?
What is blood richer in the than the CSF?
At equilibrium, the level of sodium and the overall osmolarity of CSF is roughly equal to that of the blood.
However, CSF is richer in Cl-, and CO2. As a result, CSF is more acidic (pH ≅ 7.33)
On the other hand, protein, and glucose cannot enter the CSF, so the CSF will not have as much of these substances as the blood. Blood also contains more K+, Ca2+ and HCO3-(slightly)
What protein is responsible for taking drugs out of the ventricles that have passed through the blood brain barrier but don’t belong there?
P-glycoprotein
How does CO2 affect cerebral blood flow, and what causes the change?
As CO2 goes up, cerebral blood flow goes up (H+ is a vasodilator).
What allows water to cross BBB?
What allows water to get into CSF/ventricles?
AQ4
AQ1
Where is the sensory innervation of the blood vessels?
NTMs
Distal
substance P, neurokinin, CGRP all dilate BV in response to pain
Na/K/2Cl transporters for BBB
moves all these ions from CSF to blood
seems to be related to [K]csf
electrolyte in BBB
maintains composition, esp. related to K and membrane potential
protects from toxins
absorption of CSF is proportional to what?
intracranila pressure
control pt is at absorption not production
Production is constant over wide ranges of intracranial pressures
CSF pressure equilibration
- fluid moves from teh blood vessels into the ventricles
hydrostatic pressure=blood pressure and pushes fluid out of the vessels
tissue hydrostatic pressure pushes fluid into capillary (small forces, overcome by hydrostatic pressure)
oncotic pressure=osmotic pressure pulls fluid into capillary
- modification of ion composition controlled by channels and aquaporins
How is cerebral blood flow controlled?
It is autoregulated over a wide range of systemic (mean arterial) pressures
it will decrease below a mean arterial BP of 60mmHg and increase at a mean of 140mmHg (which is really high)
sympathetic stimulation extends the “safe” range where no change occurs
Explain vasoconstriction in the brain
in the face of high BP which could damage the BBB, sympathetics in the brain will vasoconstrict the vasculature
this increases the systemic vascular resistance, but it protects the capillaries in the brain and the BBB resists damage
Discuss the effects of cerebral edema on blood flow in the brain
cerebral blood flow is influenced by intracranial pressure; as it goes up, venous outflow is blocked, thus arterial flow is blocked
this decreases brain perfusion and triggers the CV portion of the medulla to increases systemic BP to try to force blood thru any obstruction without worrying about BBB
What is the problem with phosphorylating elF2a kinase during a repurfusion event?
leads to a further decrease in protein synthesis
increases activation of caspase 3
increases apoptotic signaling
