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Neuro test 2 > 3. Cerebral Vasculature and Brain homeostasis > Flashcards

3. Cerebral Vasculature and Brain homeostasis Flashcards

1
Q

What are the functions of CSF?

A

cushioning, distribution of secretory signals, regulates neurogenesis, waste clearance, fluid movement

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2
Q

What does the flow of CSF pass through?

A

ventricles, cistern, and subarachnoid space

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3
Q

What is important about the CSF in the brain?

A

makes the weight of the brain like a golf ball (1.4 Kg–> 50g)–> its BUOYANT

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4
Q

What is the polarity of choroid plexus epithelial cells?

A

direction of water flow is from the basolateral (blood) side to the apical (ventricular lumen) side (opposite in renal tubules)

Na/K Atpase = main driver on apical/CSF side !!

NCBE= on blood/basolateral side

no reabsorption, instead water flow!!

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5
Q

What moves water from blood to the ventricles across teh choroid plexus?

A

An osmotic gradient (Na/K Atpase drives it all) for Na+

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6
Q

What is the final result of the electrochemical gradient for movement of water across the choroid plexus?

A

net flux of Na+, HCO3-, and Cl- from blood, crosses epithelium, and into ventricles–> creates osmotic gradient that drives water into ventricles

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7
Q

Describe the flow/polarity of choroid plexus epithelial cells (10 steps):

A
  1. Na+ low inside cells
  2. Na+ enters epithelial cells via two routes (NCBE= Na depdt Cl-/HCO3 exch.)
  3. intracellular Na actively pumped out of cell into ventricle side via Na/K ATPase
  4. Continuous action of two systems==> transmembrane gradient
  5. HCO3- accumulates intracellularly, creates concentration gradient (continuous hydration of CO2 by C.A. making more bicarb; Hydrogen exchanger also present)
  6. Gradient drives HCO3 out of cell down its concentration gradient via anion channel and HCO3 channel (apical membrane); leaves via transporters!
  7. Cl- accumulates intracellularly; creates electrochemical gradient; bc followed Na inside cell
  8. Cl- leaves cell via apically located Cl- channels and Na-K-Cl cotransporters
  9. Overall results in net movement of Na, Cl, HCO3 from blood across epithelial cell and into ventricles (OSMOTIC GRADIENT driving water same direction)
  10. Water fluxes through AQP1 channels
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8
Q

What ion is in equilibrium in both CSF and Serum?

A

Na+

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9
Q

where is pH more acidic, CSF or Serum?

A

CSF (more H+ abundant)

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10
Q

where is pH more basic, CSF or Serum?

A

Serum

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11
Q

What is found more in serum than CSF?

A

proteins and glucose (as well as K+, Ca, Mg, and HCO3)

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12
Q

Describe the production of CSF?

A

constant over wide range of intracranial pressure

CSF is reabsorbed by arachnoid villi, occurs by bulk flow with some evidence of pinocytosis

CSF absorption is proportional to intracranial pressure (ICP); if less than

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13
Q

Describe the absorption of CSF:

A

CSF absorption is proportional to intracranial pressure (ICP); if less than 68 mm ICP= NO absorption

normal = 112 mm ICP

but too much ICP = damaging neurons

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14
Q

What is the relationship bw CO2, H+ and cerebral blood flow?

A

Increasing CO2 in blood greatly increases cerebral BF

Because CO2 dissociates into carbonic acid–> H –> vessel vasodilation; which is why H+ ion concentration will greatly increase Cerebral BF

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15
Q

What is the relationship bw Oxygen concentration and cerebral BF?

A

as oxygen is being sensed, if oxygen is decreased, that can induce vasodilation to get more oxygen !! so increases Cerebral blood flow

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16
Q

What is the importance of astrocyte metabolites in Cerebral BF?

A

Metabolism of astrocytic processing results in number of vasodilatory activities, particularly whenever have excitatory with nearby neurons; there is very important coupling and activity of neurons/metabolic processes, and waste clearance by nearby astrocytes

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17
Q

What is the metabolic activity relating to cerebral BF?

A

if certain area of brain very active, that will increase local BF to that particular area of the brain; basis of fMRI

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18
Q

What do the sympathetics of cerebral circulation lead to? NTs used?

A

leads to VASOCONSTRICTION when systemic CO and BP INCREASE

NTs: NE and NPY; receptors: a-adrenergics

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19
Q

What do the parasympathetics of cerebral circulation lead to? NTs used?

A

leads to VASODILATION when systemic CO and BP decrease

NTs: Ach, VIP, CGRP, SP

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20
Q

Describe the sensory innervation of cerebral circulation? What are the NTs used?

A

Helping to monitor sensation of distal BVs

NTs: SP, CGRP, NKA

It renders BVs exquisitely sensitive to torsion/manipulation–> PAINFUL

decreased CSF volume–> brain heavier–> simple motion torques BVs==> pain

21
Q

What does reciprocal activation of sensory afferents affect?

A

reciprocal activation of sensory afferents activate vasodilation and increase BF, perhaps to increase CSF volume

22
Q

How does increased ICP influence cerebral BF?

A

increased ICP leads to obstruction of venous outflow bc blood vessels are squishy and it would squish them down–> leads to reduced arterial flow bc all pressure drained

23
Q

What can increase ICP?

A

hydrocephalus, edema, infection, intracranial bleeding, tumor blockage

24
Q

How does ICP affect cerebral BF?

A

As ICP goes up, CBF plummets

25
Q

How does Pa CO2 affect cerebral BF?

A

As CO2 goes up, CBF goes up

26
Q

How does Pa O2 affect cerebral BF?

A

O2 too low: CBF goes up

O2 too high: CBF goes down ( too much = bad)

27
Q

How does cerebral perfusion pressure affect cerebral BF?

A

autoregulation again

if too low, BF drops off

too high, BF also goes up

28
Q

How/why does autoregulation maintain BF?

A

to protect delicate interface/barrier of BBB

why have plateau region where BVs can constrict or dilate accordingly../but eventually get to cerebral perfusion pressure being too low that there is point of maximal dilation, and as result cerebral BF goes down

As cerebral perfusion gets too high, can only constrict so much and get maximal constriction and as reach that, cerebral blood flow goes up

BP to overcome autoregulation is very high (maybe >200)

29
Q

When systemic BP goes up, how does the system protect the BBB and the capillaries?

A

sympathetics VASOCONSTRICT vasculature!! it increases vascular resistance

30
Q

What happens in the event of reduced brain perfusion?

A

maybe in case of hemorrhage-decreased brain perfusion activates vasomotor centers, increasing systemic BP, driving blood to the brain!!!

sensory centers are monitoring the brain perfusion at all times!!

31
Q

What are some extrinsic factors that regulate cerebral BF?

A

baroreceptor reflexes regulate systemic BP

erythrocyte concentration regulates blood viscosity (anemia increases CBF and polycythemia decreases CBF)

Occlusions > 70-90% regulate carotid/vertebral vessel lumen

32
Q

What are some intrinsic factors regulating CBF?

A

autoregulation- tension in walls of small BVs, sympathetics

Arterial CO2 and O2- high PaCO2 increases CBF; very low PaO2 increases CBF

Acidosis increases CBF and alkalosis decreases CBF

33
Q

What is the BBB highly permeable to?

A

water, CO2, O2, and lipid-soluble substances

34
Q

What is the BBB slightly permeable to?

A

Na+, Cl-, and K+

35
Q

What is the BBB nearly permeable to?

A

plasma proteins and non-lipid-soluble organic molecules

36
Q

What is the function of BBB? what does it exclude and contain?

A

protection!!!

maintain electrolyte composition of CSF and neural parenchyma

excludes toxins from getting in

contains NTs

endothelium with much tighter pore with cells encapsulating around it

37
Q

What are the three cellular constituents of the BBB?

A

astrocyte endfeet, pericytes, and endothelial cells

pericytes- contractile ability; help regulate exactly how much can get across BBB based on how constricted/contracted they become

38
Q

How do things get across BBB?

A

Passive diffusion–> H20, CO2, O2, unbound steroid hormones, lipid soluble stuff (gaseous)

Paracellular, transcellular, transport proteins, lipid soluble, endocytosis, or transcytosis

39
Q

What is the major energy source of the brain? how does it get across?

A

GLUCOSE!! transport proteins (GLUT1= main transporter)

40
Q

What is the important about GLUT1?

A

main transporter of glucose across blood

non-insulin dependent, 2 isoforms

41
Q

What is important about the Na-K-2Cl- transporter?

A

transports ions across CSF to blood; expression tied to endothelin 1 and 3; endothelin pdtion tied to astrocyte signaling!!

42
Q

What is important about P-glycoprotein?

A

moves drugs that dont belong that crossed BBB back into blood; kicks stuff that doesnt belong out!!

43
Q

What does glut 3 and glut 5 associated with, respectively?

A

glut 3- neurons

glut 5- microglia

44
Q

What is glut 1 associated with?

A

everything else basically (except neurons and microglia)

- astrocytes, microvessels, choroid plexus, ependymal cells

45
Q

Where is the BBB and Blood-CSF barrier NOT present in?

A

circumventricular organs

46
Q

What are the different Circumventricular Organs?

A

posterior pituitary, area postrema, organum vasculosum of lamina terminalis (OVLT), subfornical organ

47
Q

Which CVO organ is the only secretory organ?

A

Posterior pituitary (endocrine)

48
Q

Which CVO organs are sensory organs? What do they do?

A

area postrema- initiation of vomiting in response to chemotactic triggers

OVLT- regulation of total body water and thirst; target of angiotensin 2

subfornical organ

Neuro test 2 (15 decks)

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