3. Cerebrospinal fluid Flashcards
3 roles of the CSF
- PROTECTION (buoyancy, protects against impact, surface tension between dura and arachnoid)
- NUTRITION
- COMPLIANCE (Monroe-Kellie doctrine)
2 main sources of CSF production
CAPILLARIES between pia and arachnoid
CHOROID PLEXI in each ventricle
Constituents of a choroid plexus
- Capillary loop (fenestrated endothelium)
- Pia-arachnoid
- Ependymal cells
2 mechanisms of CSF production
- Passive (mainly)
- Active (minimally)
What is the rate of CSF production in dogs vs cats
Dogs: 0.047 ml/ml
Cats: 0.017 ml/min
What mainly influences the rate of CSF PRODUCTION?
Plasma osmotic pressure (e.g. hyperosmolar therapy)
What mainly influences CSF ABSOPRTION?
ICP (primary homeostatic mechanism)
2 main routes of CSF absorption?
- Arachnoid villi
- Veinules in the subarachnoid space
Other alternate routes of CSF absorption?
Lymphatic pathways surrouding:
* Spinal nerves at intervertebral foramina
* Cranial nerves I, II, VIII as they exit the skull
Glymphatic system, draining into the retropharyngeal lymph nodes
Where are arachnoid villi mostly concentrated?
Dorsal sagittal sinus
Describe the structure of an arachnoid villi
Prolongation of arachnoid membrane + subarachnoid space into the lumen of venous sinuses
1-way valve (opens when CSF pressure > venous pressure)
What are the two driving forces of CSF circulation?
- Blood pulses in the choroid plexuses
- Motile cilia on ependymal cells
Main direction of CSF circulation
Random, but dominantly CAUDAL
What kind of hydrocephalus will cause an obstruction to …
1. CSF absorption?
2. CSF circulation?
- EXTERNAL hydrocephalus (accumulates in subarachnoid space)
- INTERNAL hydrocephalus (accumulates in ventricular system, rostral to the obstruction) +/- hydromyelia
Describe CSF circulation pathways
- Lateral ventricules
- Interventricular foramina (foramen of monro)
- 3rd ventricle
- Mesencephalic aqueduct
- Fourth ventricle
- Lateral apertures +/- median aperture
- Central canal