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NeuroEndo Exam 2 > Cerebral Blood Flow & CNS Homeostasis (Karius) > Flashcards

Cerebral Blood Flow & CNS Homeostasis (Karius) Flashcards

1
Q

Describe the blood flow to the brain

A

The 2 internal carotid arteries & basilar artery join to form the Circle of Willis.

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2
Q

How does the cerebral circulation ensure survival in case theres damage to an artery

A

The vessels that contribute to the Circle of Willis do not mix but instead innervate separate regions of the brain. So disruption of one of the inputs produces localized areas of ischemia and not to the whole brain.

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3
Q

What are the innervations for cerebral circulation

A
  1. Sympathetic NS
  2. Parasympathetic NS
  3. Sensory Innervation
  4. Local control - Oxygen consumption
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4
Q

Explain Sympathetic Innervation to cerebral circulation

A
  • Only activated when there is an increase in cardiac ouput and blood pressure.
  • NT released are Norepinephrine & Neuropeptide Y (NPY) which are released from the postganglionic cell
  • NT bind to alpha 1 adregnergic receptors in the brain
  • Leads to constriction of blood vessels
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5
Q

Explain Parasympathetic innervation to Cerebral circulation

A
  • NT relased are Acetylcholine, Vasoactive Intestinal Polypeptide (VIP) & PHM-27 and innervate larger blood vessels (which are proximal to heart)
  • Causes vasodilation of blood vessels
  • Physiological relevance is uncertain (in day to day life how often are they active and are they doing anything)
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6
Q

Explain Sensory innervation to Cerebral circulation

A
  • Nociceptors (sensory nerve cells) release NTs: Substance P, Neurokinin A, CGRP.
  • The NTs cause the blood vessels to dilate which increases blood flow to the brain.

(In presence of low CSF in brain, the brain is heavier and simple motion causes pain)

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7
Q

Explain the role of local control in innervating Cerebral circulation

A

Oxygen consumption dictates where in the brain blood goes because increased O2 consumption = increased activity of the brain. Therefore blood is directed to those areas.

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8
Q

What does autoregulation of cerebral blood flow mean

A

The blood flow in the brain is held constant at varying systemic pressures btw 60 mmHg - 140 mmHg and even higher with sympathetic innervation

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9
Q

How are the cerebral capillaries protected from changes in systemic blood pressure

A

Cerebral blow flow is strongly autoregulated. When blood pressure is high, the sympathetics in the brain will vasoconstrict the vasculature prior to reaching the capillaries so the thin capillary walls are not damaged.

This increases systemic vascular resistance, causing the heart to work harder BUT IT’S ALL ABOUT THE BRAIN

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10
Q

What infleunces cerebral blood flow

A

Intrancranial pressure – as intracranial pressure goes up, venous outflow is obstructued due to collapsed veins, leading to a reduced arterial flow.

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11
Q

What might increase intracranial pressure

A
  • Hydrocephalus of any variety (increased CSF)
  • Crebral Edema (swelling of brain tissue)
  • Intracranial Bleeding (brain tumors)
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12
Q

What are the changes in systemic circulation that occur when blood flow in the brain is reduced

A

The brain will drive systemic blood pressure up to force blood to the brain.

BECAUSE IT’S ALL ABOUT THE BRAIN, blood pressure can be driven to very high levels in order to perfuse the brain.

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13
Q

What is the role of CSF

A

To protect the brain. Makes the brain “lighter”

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14
Q

Route of CSF

A

Lateral ventricle –> (interventricular foramen) –> Third ventricle –> (cerebral aqueduct) –> fourth ventricle –> (lateral & median apeture) –> subarachnoid space —> arachnoid villi –> Superior sagittal sinus

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15
Q

Where is cerebral spinal fluid produced

A

50-70% is made by the choroid plexus while the remaining is made by the tissue that lines the ventricles & blood vessels.

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16
Q

Process of making CSF

A
  1. Passive filtration of serum (removal of clotting factor proteins from plasma)
  2. Modification of ion composition
17
Q

What does the passive filtration of serum depend on

A
  1. Hydrostatic pressure (DOMINATES)
  2. Oncotic pressure (the oncotic pressures cancel each other out)

Fluid moves from blood vessels into the ventricles

18
Q

What substances are in equal amounts in both the plasma and CSF

A

Sodium and bicarbonate

19
Q

What substances are in greater quantity in the CSF than plasma

A

Mg2+, Cl- (added)

CO2 (neuronal metabolism)

20
Q

What substances are found less in the CSF than in plasma

A

K+

Ca2+

Protein

Glucose (needed in brain)

21
Q

How does CSF enter the venous sinus

A

Arachnoid villi allows for bulk flow of CSF to venous sinuses. CSF flows in one direction.

22
Q

What is the role of the blood brain barrier

A

Protect the compostition of the CSF

23
Q

What are the structural adaptions that form the BBB and what are thri functions

A
  1. Tight junctions btw endothelial cells - prevents bulk flow
  2. Glial endfeet (podocytes) - form lipid bi-layer and increase distance of diffusion
24
Q

What substances can cross the BBB

A

H2O - Via aquaporins

CO2 - lipid soluble

O2 - needed by neurons

Free steroid hormones

25
Q

What is the major energy source for neurons

A

Glucose

26
Q

How does Glucose enter the brain

A

Glut 1 (55k) - moves glucose past endothelial cells of capillary (located on capillaries)

Glut 1 (45k) - moves glucose past glial end feet of capillary to CSF

(located on astroglia)

Glut 3 - moves glucose into neurons

27
Q

Mutation of what glucose transporter is not survivable

A

Glut 3 - moves glucose into neurons.

28
Q

What happens if neurons don’t get glucose

A

No glucose = No ATP = No Na/K ATPase activity = Depolarization = increased excitability = Seizures = Damged neurons

29
Q

Na/K/2Cl transporter

A

Transporter that moves all those ions from CSF to blood.

30
Q

What regulates Na/K/2Cl transporter

A

Concentration of K+ in CSF.

Increased K+ in CSF causes a repolarization that triggers endothelial cells of the blood vessels to express endothelin 1 & 3 to remove K+ from CSF

31
Q

What is p-glycoprotein (MDR-1)

A

Protein that shuttles substances that have gotten past the BBB back into the blood. Provided protection from toxins.

32
Q

Clinical consquence of p-glycoprotein

A

Removes drugs that we want to get across BBB

33
Q

What are the circumventricular organs

A

Organs that don’t have a BBB because they need access to plasma composition

  1. Posterior Pituitary
  2. Area Postrema
  3. OVLT
  4. Subfornical organ
34
Q

Posterior Pituitary

A

Releases hormones into the blood

35
Q

Area Postrema

A

Surface of brain where 4th ventricle opens up. Protects composition of blood by eliciting vomiting.

36
Q

OVLT & Subfornical organ

A

Control of total body water, thirst, blood volume control

NeuroEndo Exam 2 (13 decks)

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