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Neuroendocrine Exam 2 > Cerebral Blood Flow and CNS Homeostasis > Flashcards

Cerebral Blood Flow and CNS Homeostasis Flashcards

1
Q

Circle of Willis Source

A
  • Internal Carotid
  • Basilar
  • Vertebral
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2
Q

Circle of Willis Circulation

A
  • stratified blood flow to limit damage
  • little mixing of blood from the 3 major arteries
  • blockage of blood flow in Circle causes localized ischemia vs global ischemic event
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3
Q

Sympathetic Innervation of Cerebral Circulation

A
  • NE and NPY released from post-ganglionic pre-synaptic terminal
  • alpha 1 adrenergic receptors
  • vasoconstriction and increased blood pressure
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4
Q

Parasympathetic Innervation of Cerebral Circulation

A
  • ACH
  • VIP and its PHM-27 pre-cursor
  • vasodilation of larger blood vessels proximal to heart
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5
Q

Nociceptors

A

provide sensory innervation of distal blood vessels

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6
Q

Vasodilator Neurotransmitters

A
  • substance P
  • neurokinin A
  • CGRP
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7
Q

Role of Sensory Innervation of Cerebral Circulation

A
  • regulate sensitivity of brain vessels to painful torsion/manipulation
  • reduced CSF volume = heavier brain and pain with motion
  • activation of afferents causes vasodilation and increased blood flow to restore normal intracranial volume
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8
Q

Oxygen-Mediated Cerebral Circulation

A
  • flow locally controlled by oxygen consumption

- more metabolically active areas = more O2 consumption and vasodilation for O2 delivery

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9
Q

Autoregulation

A

brain controls own blood flow which is held constant over range of systemic/mean arterial BP

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10
Q

Mean Arterial BP vs Cerebral Blood Flow

A
  • as MABP increases, cerebral flow increases
  • direct relationship until autoregulation
  • when autoregulation range is exceeded, direct relationship resumes
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11
Q

Sympathetic Autoregulation

A
  • range of autoregulation is extended to a higher MABP to protect capillaries from damage, esp in BBB
  • vasculature will vasoconstrict to protect capillaries in brain, although systemic vascular resistance increases
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12
Q

Intercranial Pressure vs Cerebral Blood Flow

A

as intercranial pressure increases, venous outflow is obstructed and arterial flow is reduced

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13
Q

Effects on Systemic Blood Pressure

A

decreased brain perfusion activates CV control in medulla to increase systemic BP drastically ( >200) to try to force veins open for blood entry

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14
Q

Increased Intercranial Pressure

A
  • hydrocephalus: increased CSF volume
  • cerebral edema: swelling of brain tissue
  • intracranial bleeding: blockage of CSF flow from space-occupying mass
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15
Q

CSF Quantities

A
  • 150 mL in a given moment
  • 500 mL / day
  • no recirculation
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16
Q

Four Ventricles

A
  • 2 lateral
  • Third Ventricle
  • Fourth Ventricle
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17
Q

Ventricular System

A
  • Intraventricular Foramen: lateral to third
  • Cerebral Aqueduct: third to fourth
  • Median Aperture: fourth to cisterna magna
  • Lateral Aperture: fourth to arachnoid space
18
Q

Choroid Plexus

A

specialized tissue in lateral ventricles producing most CSF, remainder made by tissues lining ventricles and vessels

19
Q

Passive Filtration of Serum

A
  • first step of CSF production
  • dependent on hydrostatic and oncotic pressure
  • oncotic pressures cancel
  • blood pressure in capillaries > tissue hydrostatic pressure
  • fluid moves from vessels to ventricles
  • capillary pressure dominates and pushes fluid into ventricle
20
Q

Hydrostatic Pressure

A
  • pressure in capillary > pressure in ventricle
  • pressure in capillary (blood pressure) favors movement out of ventricle
  • pressure around capillary (tissue hydrostatic pressure) favors movement into ventricle
21
Q

Oncotic Pressure

A
  • osmotic pressure
  • depends on solute concentration
  • inside capillary = pulls fluid into capillary
  • surrounds fluid = pulls fluid out of capillary
  • equal and opposite at choroid plexus
22
Q

Modification of Ion Composition

A
  • second step of CSF formation
  • HCO3, Cl, and K concentrations controlled by channels in choroid plexus epithelia
  • Aquaporin 1 permits water passage
23
Q

Capillary Hydrostatic Pressure vs Intercranial Pressure

A

capillary hydrostatic pressure is higher than intercranial pressure would ever reach which drives CSF production

24
Q

[X] CSF = [X] plasma

A
  • Na (ranges overlap)

- HCO3

25
Q

[X] CSF > [X] plasma

A
  • Mg: interacts with Ca, added by choroid plexus
  • Cl: added by choroid plexus
  • CO2: from neuronal metabolism
26
Q

[X] CSF < [X] plasma

A
  • K: tightly controlled bc changes potential
  • Ca: tightly controlled because toxic in high quantities
  • Protein
  • Glucose: fuel for neurons
27
Q

CSF Flow

A

-via ventricular system unidirectionally
-reabsorbed by arachnoid villi
-bulk flow into venous sinuses driven by pressure inside villi
returns to general circulation

28
Q

CSF Absorption vs Intracranial Pressure

A
  • CSF absorption proportional to intracranial pressure
  • no absorption at 68 mm CSF
  • normal pressure at 112 mm CSF
  • pressure of CSF drives movement into sinuses
  • body prevents reabsorption of CSF at low pressures bc movement is not driven
29
Q

CSF Role

A
  • brain protection and “floatation”

- reduces weight of lipid/myelin rich brain so brain is not subject to motion/shock

30
Q

Limited Exchange Mechanisms of BBB Capillaries

A
  • tight junctions between endothelial cells

- glial endfeet

31
Q

Glial Endfeet

A
  • close contact with blood vessels
  • cover capillaries
  • increase distance over which substance diffuses from blood to CSF to reduce diffusion
32
Q

Chemical Mechanisms of BBB

A

lipophilic bilayer membranes to prevent passage of hydrophilic materials in blood

33
Q

Passive Diffusion of Substances Across BBB

A
  • H2O: via AQP4
  • CO2: moves from CSF to capillary for removal
  • O2: leave capillaries to neurons
  • free steroid hormones
34
Q

Glut-1 Transporter

A
  • non-insulin dependent transporter of glucose across BBB

- larger transporter on capillaries vs astroglia

35
Q

Glut-3 Transporter

A

non-insulin dependent transporter to move glucose into neurons

36
Q

Na/K/2Cl Transporter

A
  • electroneutral movement of ions from CSF to blood unidirectionally to keep K in CSF low
  • expression regulated by endothelin 1 and 2
37
Q

P-Glycoprotein/MDR-1

A
  • transports drugs that cross BBB back into blood

- binds wide variety of substances with diff structures

38
Q

Circumventricular Organs

A
  • neural tissue not protected by BBB due to capillaries lacking tight junctions
  • Four: Posterior Pituitary, Area Postrema, Organum Vasculosum of Lamina Terminalis, and subfornical organ
39
Q

Circumventricular Organs: Posterior Pituitary

A

exposure to plasma blood for hormone release and control

40
Q

Circumventricular Organs: Area Postrema

A
  • cluster of neurons at surface of brain where fourth ventricle opens
  • triggers vomiting in response to chemical detection
41
Q

Circumventricular Organs: Organum Vasculosum of Lamina Terminalis and Subfornical Organ

A

control water/thirst/blood volume to regulate blood osmolarity

Neuroendocrine Exam 2 (11 decks)

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