Cerebral Vasculature & Brain Homeostasis

Question 1

What connects the lateral ventricles to the 3rd ventricle?

Answer 1

Intraventricular foramen

Question 2

What connects the 3rd ventricle to the 4th ventricle?

Answer 2

Cerebral aquaduct

Question 3

What connects the 4th ventricle to the cisterna magna?

Answer 3

Median aperture

Question 4

What connects the 4th ventricle to the arachnoid space?

Answer 4

Lateral apertures (2)

Question 5

What produces CSF?

Answer 5

Choroid plexus (50-70%), mostly in the lateral ventricle

Question 6

What are the 2 steps of CSF production?

Answer 6

Passive filtration of serum and modification of ion composition

Question 7

The passive filtration of serum is dependent on what two pressures?

Answer 7

Hydrostatic pressure of the capillaries (pushes fluid out of capillaries in the brain) and oncotic pressure (dependent on solute concentration in the blood, is equal in brain)

Question 8

How much CSF do we have at any given moment? How much is produced per day?

Answer 8

150ml at any given moment

550ml made per day

Question 9

What ions are at the same concentration in CSF vs in the blood?

Answer 9

Na+ and HCO3

Question 10

What ions have a higher concentration in CSF vs in the blood?

Answer 10

Mg2+, Cl-, CO2

Question 11

What ions have a lower concentration in CSF vs in the blood?

Answer 11

K+, Ca2+, protein, glucose

Question 12

What reabsorbs the CSF?

Answer 12

Arachnoid villi (where pia and arachnoid mater have fused). Flow of CSF from subarachnoid space into sinuses

Question 13

The absorption of CSF is proportional to what?

Answer 13

ICP (normal pressure is 112 mm CSF). Absorption happens over 68 mm CSF

Question 14

Increased CSF pressure does what?

Answer 14

Damages neurons

Question 15

What are the two components of the BBB?

Answer 15

Tight junctions between endothelial cells and glial endfeet that come in contact with the blood vessel (cover capillary w/ lipid bilayers)

Question 16

What can cross the BBB via passive diffusion?

Answer 16

H20 (aquaporin 4), CO2, O2, and free steroid hormones

Question 17

How does glucose cross the BBB?

Answer 17

Glut1 transporter, is not insulin dependent
55K on capillaries
45K on astroglia

Question 18

How does glucose get into neurons?

Answer 18

Glut3 transporter (is also insulin independent)

Question 19

What is the Na/K/2Cl transporter?

Answer 19

Moves all those ions from CSF to blood when [K+] of CSF is too high

Question 20

What is P-glycoprotein?

Answer 20

Pump that binds to a wide variety of chemicals and moves them out of the CSF back into the blood

Question 21

Where are the circumventricular organs?

Answer 21

Posterior pituitary (releases hormones into the blood)
Area postrema (chemotactic trigger zone for toxins in blood)
Organum vasculosum of lamina terminalis (OVLT) and Subfornical organ (control of body osmolarity)

Question 22

What is the significance of the circumventricular organs?

Answer 22

Not as well protected by BBB as other neural tissue so they can be exposed to the blood.

Question 23

What NTs are involved in sympathetic innervation of cerebral circulation?

Answer 23

Norepinephrine and neuropeptide Y

Go to alpha-adrenergics (vasoconstriction)

Question 24

What NTs are involved in parasympathetic innervation of cerebral circulation?

Answer 24

Ach, VIP, and PHM-27 cause vasodilation

Question 25

What NTs are involved in sensory innervation of cerebral circulation?

Answer 25

Substance P, neurokinin A, and CGRP (all dilation)

Question 26

What is the clinical relevance of sensory fibers in the brain blood vessels?

Answer 26

Extremely sensitive to torsion/manipulation. Brain heavier in presence of reduced CSF volume and causes torsion of blood vessels. Induces vasodilation to increase blood flow and return intracranial volume closer to normal

Question 27

In response to high systemic BP, what do sympathetics in the brain do?

Answer 27

Vasoconstrict to protect capillaries in the brain and BBB from damage

Question 28

What does high ICP mean in terms of blood flow? What does the brain do to counteract this?

Answer 28

Means venous outflow from brain is obstructed so there is reduced arterial flow into the brain. Brain drives up systemic BP to force blood into the brain