Transport within the CSF

Question 1

describe how the composition of CSF and plasma differ

Answer 1

• concentrations of protein, glucose, K and Ca ions are lower in CSF than plasma
• concentrations of Cl and Mg ions are higher in CSF
• pH is lower in CSF

Question 2

name 4 adverse effects of elevated ICP

Answer 2

1. nausea
2. bradycardia
3. systemic hypertension
4. papilledema

Question 3

describe the BBB

Answer 3

• BBB arises from the endothelial cells, capillary basement membranes and astrocytic endfeet
• capillaries of the BBB are distinct, lacking fenestrations that otherwise would allow paracellular transport
• there are tight junctions between the endothelial cells

Question 4

explain the oil/water partition coefficient

Answer 4

• lipid-soluble materials cross the endothelial cell membranes
• the higher the oil/water coefficient, the more effective the transfer across the BBB is

Question 5

describe facilitated diffusion and active transport across the BBB

Answer 5

• glucose crosses the BBB faster than predicted by its oil/water partition coefficient because both endothelial cell membranes express the glucose transporter Glut-1, which promotes facilitated diffusion
• L-DOPA, the precursor for dopamine, also crosses the BBB by facilitated diffusion, using a carrier for neutral amino acids
• Glycine crosses the BBB (from brain to blood) by a Na-dependent cotransporter
  
  • secondary active transport

Question 6

name situations where the tight junctions between vascular endothelial cells become “leaky”

Answer 6

• hypertension
• hyperosmolality
  
  • the BBB can reversibly weaken with brief exposure to hypertonic infusions that shrink endothelial cells and compromise tight junctions
    
    • the procedure may permit delivery of lipid-insoluble drugs to the CNS
• trauma, ischemia, inflammation
• infection

Question 7

describe what circumventricular organs are

Answer 7

• circumventricular organs are areas in the brain that lack tight junctions in capillaries and have an incomplete BBB
  
  • area postrema
  • median eminence
  • neurohypophysis
  • organum vasculosum
  • pineal body
  • subcommissural organ
  • subfornical organ

Question 8

describe the secretion of CSF

Answer 8

• most CSF is secreted by the choroid plexus
  
  • there are transporters and pumps that move ions into ventricle
    
    • water follows passively and through aquaporins

Question 9

describe the reabsorption of CSF

Answer 9

• CSF flow over the surface of the spinal cord and brain for passage through the arachnoid granulations (villi) into the lumen of the superior sagittal sinus
• this transcellular transport process involves intracellular vacuoles that engulf and emit small volumes of CSF

Question 10

describe the changes in CSF during pathological conditions

Answer 10

Question 11

describe the 2 types of hydrocephalus

Answer 11

• communicating (non-obstructive)
  
  • overproduction
    
    • choroidal tumor
  • insufficient drainage
    
    • malfunction of arachnoid villi
  • ex vacuo
    
    • enlargement secondary to tissue loss
• non-communicating (obstructive)
  
  • blockage within ventricular system
    
    • congenital
    • cellular debris