CSF physiology
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This document discusses cerebrospinal fluid (CSF) physiology and summarizes a presentation given by Dr. Kaushal Deep Singh. It outlines the history of CSF discovery. CSF is formed primarily by the choroid plexuses in the ventricles and circulates through the ventricles and subarachnoid spaces before being reabsorbed into the venous sinuses. The composition, circulation, and factors regulating CSF formation and reabsorption are described. Alterations in CSF dynamics can occur in various pathologies.
![Vf AND ICP/MAP
• As long as MAP remains >70 mm of Hg,
increase of ICP [upto 20 mm of Hg] has no
major impact on Vƒ
• When MAP is significantly lowered → CBF↓
→ CPP↓, Vƒ↓](https://image.slidesharecdn.com/kaushalcsfphysiologypresentation-180405172422/85/CSF-physiology-18-320.jpg)
![CSF RESORPTION
• CSF is absorbed primarily by arachnoid villi
(granulations) that extend into the dural venous
sinuses.
• Arachnoid Villi are protrusion of the arachnoid matter
through perforations in the dura into the lumina of
venous sinuses
• Other sites of absorption include the choroid plexuses
and lymphatics.
• Intracranial-Superior sagittal sinus[85%-90%]
• Spinal-dural sinusoids on dorsal nerve roots[15%]](https://image.slidesharecdn.com/kaushalcsfphysiologypresentation-180405172422/85/CSF-physiology-19-320.jpg)
![MECHANISM OF CSF
REABSORPTION
• High velocity of blood flow through the fixed
diameter of the sinuses & the low intraluminal
pressure that develops @ the circumference of
the sinus wall where the arachnoid villi enter,
cause a suction –pump action
• Rate of reabsorption (Va); @ ICPs > 7 cms of
H2O, Va ↑ directly as ICP ↑[relation linear upto
ICP of 30 cms of H2O]](https://image.slidesharecdn.com/kaushalcsfphysiologypresentation-180405172422/85/CSF-physiology-21-320.jpg)
![DETERMINANTS OF
REABSORPTION
• Endothelium covering the villus acts as a CSF-
blood barrier
• If through endothelium:(1)pinocytic vesicles
(2)transcellular openings
• Trans villous hydrostatic pressure gradient [CSF
pressure-Venous sinus pressure]
• Resorption remains normal upto a CSF pressure
of 30 cm of H2O; above this it decreases](https://image.slidesharecdn.com/kaushalcsfphysiologypresentation-180405172422/85/CSF-physiology-22-320.jpg)
![METABOLIC REGULATION
HYPOTHERMIA: ↓ Vf – By decreasing
secretory and transport process and by ↓ing
CBF
between 41310 C: each 10 C↓in
temperature, ↓ Vf by 11%
HYPOCAPNIA: acutely ↓ Vf [mechanism :
↓ CBF, ↓ H+ for exchange with Na]](https://image.slidesharecdn.com/kaushalcsfphysiologypresentation-180405172422/85/CSF-physiology-34-320.jpg)
CSF physiology
- 1. CSF PHYSIOLOGY Presenter: Dr Kaushal Deep Singh MCh Senior Resident Department of Neurosurgery Sher-i-Kashmir Institute of Medical Sciences (SKIMS), Srinagar Date: 08/03/2018
- 2. HISTORY Emanuel Swedenborg who discovered CSF, referred to it as “highly gifted juice” that is dispensed from the roof of the fourth ventricle to the medulla oblongata, and the spinal cord. Albrecht von Haller found that that the “water” in the brain, in case of excess secretion, descends to the base of the skull resulting in hydrocephalus.
- 3. OUTLINE • CSF SPACES AND CSF CIRCULATION • CSF FORMATION, REABSORPTION AND FACTORS AFFECTING THEM • ALTERATION IN CSF DYNAMICS IN PATHOLOGIES
- 4. CSF SPACES • Two lateral ventricles • Foramina of Monro • Third ventricle • Cerebral Aqueduct of Sylvius • Fourth ventricle • Central canal of spinal cord • Central Foramen of Magendie and Lateral Foramen of Luschka • Subarachnoid spaces
- 6. MECHANISM OF CIRCULATION OF CSF • Hydrostatic pressure of CSF formation • Cilia of ependymal cells • Respiratory variations • Vascular pulsations of cerebral arteries, choroid plexus
- 7. CSF FORMATION • 80% of CSF is produced by the choroid plexuses, located in both lateral ventricles and in the 4th ventricle. • Most of the rest of intracranial production occurs in the interstitial space. • A small amount may also be produced by the ependymal lining of the ventricles. • In the spine, it is produced primarily in the dura of the nerve root sleeves.
- 8. CSF FORMATION • CSF is “turned over” ≈ 3-4 times every day. • Rate of formation is independent of the intracranial pressure. • Except in the limiting case when ICP becomes so high that cerebral blood flow is reduced.
- 9. CSF FORMATION: Choroid Plexus • Invagination of blood vessels & leptomeninges covered by a layer of modified ependyma • Epithelium forms the blood-CSF barrier • Carbonic anhydrase present in the epithelium & Na+-K+ pump in luminal plasma membrane play major role in CSF formation
- 10. ANATOMY • Choroid plexus projects into The temporal horn of each lateral ventricle, the posterior portion of the third ventricle & the roof of the fourth ventricle.
- 12. CSF PRODUCTION, VOLUMES AND PRESSURES
- 13. COMPOSITION
- 14. VARIATION IN CSF COMPOSITION WITH AGE
- 15. VARIATION IN CSF COMPOSITION • Vary according to sampling site • Altered during neuroendoscopy
- 16. MOVEMENT OF GLUCOSE • Glucose concentration is 60% that of plasma. • Remains constant, unless blood glucose >270- 360. • Enters CSF quickly by facilitated transport. • Rate ∝ Serum glucose.
- 17. MOVEMENT OF PROTEIN • CSF protein concentrations are ≤ 0.5% of plasma protein concentration. • If structural barrier between ECF & CSF spaces are not intact, it enters, but then also cleared from CSF spaces into dural sinuses - because of the sink effectof flowing CSF. VENTRICLES 26mg/100ml CISTERNA MAGNA 32mg/100ml LUMBAR SAC 42mg/100ml
- 18. Vf AND ICP/MAP • As long as MAP remains >70 mm of Hg, increase of ICP [upto 20 mm of Hg] has no major impact on Vƒ • When MAP is significantly lowered → CBF↓ → CPP↓, Vƒ↓
- 19. CSF RESORPTION • CSF is absorbed primarily by arachnoid villi (granulations) that extend into the dural venous sinuses. • Arachnoid Villi are protrusion of the arachnoid matter through perforations in the dura into the lumina of venous sinuses • Other sites of absorption include the choroid plexuses and lymphatics. • Intracranial-Superior sagittal sinus[85%-90%] • Spinal-dural sinusoids on dorsal nerve roots[15%]
- 21. MECHANISM OF CSF REABSORPTION • High velocity of blood flow through the fixed diameter of the sinuses & the low intraluminal pressure that develops @ the circumference of the sinus wall where the arachnoid villi enter, cause a suction –pump action • Rate of reabsorption (Va); @ ICPs > 7 cms of H2O, Va ↑ directly as ICP ↑[relation linear upto ICP of 30 cms of H2O]
- 22. DETERMINANTS OF REABSORPTION • Endothelium covering the villus acts as a CSF- blood barrier • If through endothelium:(1)pinocytic vesicles (2)transcellular openings • Trans villous hydrostatic pressure gradient [CSF pressure-Venous sinus pressure] • Resorption remains normal upto a CSF pressure of 30 cm of H2O; above this it decreases
- 23. CSF DRAINAGE & CEREBRAL EDEMA • Vasogenic edema resolves partly by drainage of fluid into ventricular CSF • Factors influencing: (1) pressure gradient between brain tissue andCSF (2)sink action of CSF • Brain ECF proteins cleared by glial uptake
- 24. FUNCTIONS OF CSF- SUPPORT,NUTRITION • The low specific gravity of CSF (1.007) relative to that of the brain (1.040) reduces the effective mass of a 1400g brain to only 47g. • Stable supply of nutrients, primarily glucose; also vitamins, eicosanoids, monosaccharides, neutral & basic amino acids.
- 25. CONTROL OF THE CHEMICAL ENVIRONMENT • Exchange between neural tissue & CSF is easy upto a diffusion distance 15mm (max) & ISF space and CSF spaces are continuous
- 26. CONTROL OF THE CHEMICAL ENVIRONMENT
- 27. Control of the chemical environment
- 28. EXCRETION • Removes metabolic products, unwanted drugs • BBB excludes out toxic large, polar and lipid insoluble drugs, humoral agents.
- 29. INTRACEREBRAL TRANSPORT CSF Neurohormone releasing factors formed in hypothalamus MEDIAN EMINENCE
- 31. NEUROGENIC REGULATION Adrenergic nerves from superior and lower cervical ganglia innervate CP 3rd ventricle rich in cholinergic innervation, whereas 4th ventricle devoid of it Peptidergic nerves contain VIP and substance-P : both are potent vasodilators
- 32. ADRENERGIC SYSTEM α constriction βdilatation Decrease carbonic anhydrase activity Norepinephrine:↓ Vf high α mediated vasoconstriction Low β1 mediated inhibitory action on CP
- 33. CHOLINERGIC SYSTEM Also ↓ Vf Receptors presumably muscarinic Act on CP epithelium, rather than on vasculature
- 34. METABOLIC REGULATION HYPOTHERMIA: ↓ Vf – By decreasing secretory and transport process and by ↓ing CBF between 41310 C: each 10 C↓in temperature, ↓ Vf by 11% HYPOCAPNIA: acutely ↓ Vf [mechanism : ↓ CBF, ↓ H+ for exchange with Na]
- 35. METABOLIC REGULATION Metabolic alkalosis ↓ Vf due to pH effect Metabolic acidosis: no change
- 36. VF IN CHANGE OF OSMOLARITY ↑osmolarity of serum ↓osmolarity of ventricular CSF
- 39. THANK YOU