3. Cerebral Vasculature and Brain Homeostasis

Question 1

What are the main compositions within the skull?

Answer 1

10% CSF
10% blood/vasculature
80% brain (20% interstitial fluid, 60% intracellular fluid)

Question 2

CSF is renewed every 6hrs and can be found in ventricles, cisterns and subarachnoid space. What are 4 of its functions?

Answer 2

cushioning
distributing secretory signals
regulating neurogensis
waste clearance

Question 3

What does CSF do to the weight of the brain?

Answer 3

without CSF, the brain weighs as much as a toaster

with CSF, buoyancy allows the brain to float = gold ball weight

Question 4

Choroid plexus cells make CSF. What can be found on the ventricular lumen (apical) and then blood side (basolateral)?

Answer 4

Apical: Na/K ATPase and AQP1
Basolateral: NCBE (Na dependent chloride bicarbonate exchanger) and AQP1

Question 5

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

Answer 5

osmotic gradient

Question 6

the Na/K ATPase creates an electrochemical gradient for Na resulting in what which creates what? *******important

Answer 6

Net flux of Na, HCO3, and Cl from blood into ventricles creating the osmotic gradient that drives H20 into ventricles via AQP1

Question 7

What three things are greater in CSF than blood serum?

Answer 7

Cl-
CO2
pH more acidic (7.33)

Question 8

What 3 main things are greater in serum than CSF?

Answer 8

protein
glucose
pH more basic (7.41)

Question 9

What two things are equal after equilibration between CSF and blood serum?

Answer 9

Na and osmolarity

Question 10

Production of CSF is constant over a wide range of intracranial pressures. Absorption of CSF is proportional to what?

Answer 10

intracranial pressure (as ICP inc, so does CSF and vice versa)

Question 11

The brain receives 15% of cardiac output with blood flow of 750-900mL/min. What are the four main regulations of blood flow to the brain?

Answer 11

CO2 (inc in blood CO2= inc blood flow)**
[Hydrogen Ion] (inc=vasodi=inc blood)
[O2] (dec = inc blood)
Astrocyte Metabolites

Question 12

Sympathetics leads to vasoconstriction when BP/CO increase to protect brain from surges. What are the NT/ receptors?

Answer 12

A-adrenergic via NE/ neuropeptide Y

Question 13

Parasympathetics lead to vasodilation when CO/BP decreases to inc. blood to the brain. Via which NT and receptor? (4)

Answer 13

cholinergic via ACh, VIP, NO

Question 14

Sensory innervation via NT SP and CGRP, which makes cerebral circulation sensitive to pain under what circumstances?

Answer 14

torsion/manipulation
decreased CSF (increases brain weight)

Question 15

What do the following lead to… hydrocephalus, edema, infection, intracranial bleeding and tumor?

Answer 15

increased ICP

Question 16

Increased ICP leads to obstruction of venous outflow due to compression of brain leads to what?

Answer 16

reduced arterial flow

Question 17

Autoregulation maintains blood flow in presence of changing mean arterial blood pressure. What is autoregulation mediated by?

Answer 17

sympathetic stimulation

Question 18

What occurs to allow maximal dilation or constriction?

Answer 18

max dilation: when cerebral perfusion pressure dec
Max constriction: when cerebral perfusion P inc.

Note: when CPP is normal: there will be mix of constriction and dilation

Question 19

How would each of the follow regulate cerebral blood flow?
High Pa CO2
Low O2
Acidosis
Alkalosis

Answer 19

High Pa CO2: increase CBF (cerebral blood flow)
Low O2 : Increase cbf
Acidosis: Increase CBF (to increase blood flow)
Alkalosis: Decrease CBF

Question 20

The BBB and blood-CSF barrier (with ependymal cells) are not present in what?

Answer 20

circumventricular organs (CVOs)

Question 21

The BBB and blood-CSF barrier are highly permeable to water, CO2, O2 and lipid solubles. Slight permable to Na, Cl, K and impermeable to what?

Answer 21

plasma proteins and non-lipid-soluble organic molecules

Question 22

What is the difference between the normal capillary and brain capillary?

Answer 22

brain capillary does not have slit pores/intracellular clefts. They have very tight pores to monitor substances

Question 23

What are the three main components of the BBB?

Answer 23

astrocyte endfeet
Pericytes (contract to regulate what can pass)
Endothelial cells

Question 24

There are multiple pathways across the BBB. What are the 5 things that passive diffuse?

Answer 24

H20
CO2
O2
Unbound steroid hormones
Lipid soluble stuff

Question 25

What is the main transporter for glucose from blood in the brain, which is its main energy source?

Answer 25

GLUT 1 (NOT insulin dependent)

Question 26

the Na/K/2Cl transporter transports ions from CSF to blood, its expression is tied to what two things? which are tied to what?

Answer 26

Endothelin 1 and 3 increase expression of Na/K/CC, whose production are tied to astrocyte signals

Question 27

What moves drugs that dont belong that crossed the BBB back into the blood, like a bouncer?

Answer 27

P-glycoprotein

Question 28

GLUT1 is located in astrocytes(45kD) , microvessels, choroid plexus, and ependymal cells (55kD). Where are GLUT 3 and 5 located?

Answer 28

GLUT3: Neurons
GLUT5: Microglia

Question 29

What are the first two circumventricular organs which lack BBB and what do they do?

Answer 29

1. Posteiror pituitary - secretory- endocrine

2. Area Postrema - sensory - initiates vomitting

Question 30

What are the second two circumventricular organs which lack BBB and what do they do?

Answer 30

3. Organum vasculosum of the lamina terminalis (OVLT) sensory-regulation of total body water and thirst
4. Subfornical organ (SFO) - sensory