CSF: Production, Circulation and Pathology Flashcards
What is cerebrospinal fluid (CSF)?
Clear, colourless liquid composed mostly of water
Production of CSF?
By the secretory epithelium of the choroid plexus
500-600 ml are produced per day and, in the CNS, there is 150ml that is replaced 3-4 times daily
What does the CSF supply and remove from the CNS?
Supplies water, amino acids and ions
Removes metabolites
3 major functions of the CSF?
- Mechanical protection - it is a shock-absorbing medium in which the brain floats
- Homeostatic functions:
• pH of CSF affects pulmonary ventilation and cerebral blood flow
• Transports hormones - Circulation - it is a medium for minor exchange of nutrients and waste products between blood and brain tissue
How can clinical CSF analysis be carried out and why is this useful?
Obtained via a lumbar puncture; aids in the diagnosis of brain, meninges, and spinal cord issues
Characteristics of normal CSF?
Clear and colourless
Contains little protein, few Igs and only 1-5 cells
Consequences of conditions that cause CSF accumulation?
Serious neurological deficits, e.g: hydrocephalus (fetus or newborn)
Embryonic development of the brain and ventricular system?
At 3 weeks, the developing NS consists of a tube (neural canal); its cavity gives rise to the adult brain ventricules and spinal cord’s central canal
Choroid plexus develops from cells in the walls of the ventricules
Function of the choroidal cells?
Specialised secreting cells that produce CSF
What is the choroid plexus?
Networks of capillaries in the walls of the ventricles
Development of the choroid plexus?
Developing arteries invaginate the roof of the centricle to form the choroid fissure
Involuted ependymal cells along with the vessel enlarge into villi and form the choroid plexus
Location of the choroid plexus in the adult brain?
Found in the 3rd, 4th and lateral ventricles
Label the choroid plexus?
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Ions involved with CSF production?
CSF secretion inv. transport of ions across the epithelium, from blood to CSF:
Na+
Cl-
HCO3-
Ion movement drives water into the CSF
How is CNS secretion possible?
Due to the polarised distribution of specific ion transporters in the apical or basolateral membrane of the epithelial cells
Action of the active Na+ transporter in CSF production?
Electrical gradient pulls along CL- and both ions drag water by osmosis
Compare ion concentrations in CSF to plasma?
Lower K+, glucose and much lower protein
Higher Na+ and Cl-
Relationship of CSF production to arterial blood pressure?
CSF production in the choroid plexuses is an active secretory process
It is not directly dependent on the arterial BP
Label the ventricular system
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How are the ventricles connected to one another?
Intraventricular foramina (of Monroe) - connects lateral ventricles to 3rd ventricle
Cerebral aqueduct (of Sylvius) - connects 3rd ventricle to the 4th
How are the ventricles connected to the subarachnoid space?
Foramen of Magendie (median aperture) - connects the 4th ventricle to subarachnoid space
Foramina of Luschka (lateral aperture) - connects the 4th ventricle to the subarachnoid space
Pathway of CSF circulation following its production?
- Produced in the choroid plexuses of each lateral ventricle
- Flows to third ventricle through 2 interventricular foramina
- More CSF added by choroid plexus in roof of third ventricle
- Then flows through cerebral aqueduct (midbrain) and into the 4th ventricle
- Another choroid plexus in the 4th ventricle adds more CSF
- Enters the subarachnoid space through the roof of the 4th ventricle, via:
• Single median aperture
• Paired lateral apertures - Circulates in the central canal of the spinal cord
Where is the subarachnoid space?
Between the pia and dura mater
Outflow of the CSF?
- Returns to venous blood through arachnoid granulations into the superior sagittal sinus (SSS)
- Brain intersitial fluid makes up the final portion of the CSF and drains into the CSF via perivascular spaces
