Physiology of CSF Flashcards
what is CSF
a clear, colourless liquid composed mostly of water
where is CSF produced
the secretory epithelium of the choroid plexus (in the ventricles)
what is the volume of CSF at one time (replaced every 3-4 days)
150 ml
what does the CSF circulate in
subarachnoid space
between the arachnoid and pia mater
what does the CSF supply/remove from the brain
supplies water, amino acids, ions
removes metabolites
what are the 3 main functions of CSF
- mechanical protection (shock absorbing medium that protects brain tissue)
- homeostatic function (pH of CSF affects pulmonary ventilation and cerebral blood flow - transports hormones
- circulation (minor exchange of nutrients and waste products between blood and brain tissue)
how is clinical CSF analysis obtained
lumbar puncture
aids the diagnosis of the brain, meninges and spinal cord
what does normal CSF look like
clear
colourless
contains little protein and little immunoglobulins
how many cells are there per 1 cml of CSF
1-5
what does the developing nervous system look like at 3 weeks
the neural canal/tube
what does the neural canal give rise to in the human brain
the ventricles and the central canal of the spinal cord
what does the choroid plexus develop from c
cells in the walls of the ventricles
what cells produce CSF
Choroidal cells (in the choroid plexus)
how is the choroid fissure formed
developing arteries press the roof of the ventricle inside out to produce the choroid fissure
this then develops into the choroid plexus
where is the choroid plexus found in the adult brain
the 3rd and 4th and lateral ventricles
what ions are transported across the epithelium from blood to CSF to allow CSF secretion
Na+
Cl-
HCO3-
transferred across the epithelium from blood to CSF
what is the circulation of CSF
choroid plexuses of the lateral ventricles
then to 3rd ventricle via the inerventricular foramen
more CSF is added by the choroid plexuses of the 3rd ventricle
then flows through aqueduct of midbrain (cerebral duct) into 4th ventricle
choroid plexus un 4th ventricle adds more CSF
then enters subarachnoid space via 4th ventricle - goes through the lateral apertures or the median aperture
circulated in the central canal of the spinal cord
how does CSF return to venous blood
through arachnoid granulation into the dural sinus
what restricts the blood supply to the majority of the brain
blood brain barrier
how does the brain interstitial fluid drain into the CSF
via the perivascular spaces
what makes up the blood brain barrier
endothelial cells in brain capillaries
tight junctions between brain endothelial cells prevent paracellular movement of molecules
what parts of the brain do not have a blood brain barrier
circumventricular organs
pineal gland
what does the BBB protect the brain from
bacterial infections and toxins
what pathology can affect the ventricles, choroid plexus and CSF
Tumours
Ventricular haemorrhage (accumulation of blood in the ventricles)
Hydrocephalus
Idiopathic intracranial hypertension
what tumours can affect the ventricles, choroid plexus and CSF
- colloid cysts (often found in inter ventricular foramen)
- ependyomonas (arising from ependymal cells lining the ventricles)
- choroid plexus tumours
where are common haemorrhages which can affect the ventricles, choroid plexus and CSF found
epidural hematoma (arterial bleed between skull and dura)
subdural hematoma (venous bleed between dura and arachnoid)
subarachnoid haemorrhage
what is hydrocephalus
accumulation of CSF in the ventricular system or around the brain (either due to obstruction or overproduction)
Subsequent enlargement of one or more ventricles and increase in CSF pressure
what is idiopathic intracranial hypertension/pseudotumour cerebri
symptoms include headache and visual disturbances due to papilloadema (bulging of optic disc)
increased CSF pressure but no imaging features of hydrocephalus
what does hydrocephalus look like on MRI
Swelling of the lateral ventricles
what is papilloedema
optic disc swelling due to increased intracranial pressure
visual symptoms of papilloedema
enlarged blind spot
blurring of vision
visual obscurations
loss of vision
what is aqueous humour
specialised fluid that bathes try structures within the eye
provides oxygen and metabolites and contains bicarbonate
why does aqueous humour contain bicarbonate
to buffer the H+ produced in the cornea and lens by anaerobic glycolysis
where is aqueous humour produced
ciliary body
via an energy dependent process in the epithelial later
what route does aqueous humour take after it has been secreted
ciliary body — posterior chamber — anterior chamber (via pupil) — lacrimal canal/canal of schlep –nasolacrimal duct
what two juxtaposed layers of epithelia calls cover the ciliary body and posterior surface of the iris
pigmented epithelium of the retina
non pigmented epithelium of the retina
why must the aqueous humour contain bicarbonate
so it can be exchanged for Na+ and Cl- ions to come into the ciliary body and bring water
how can you control the levels of aqueous humour
by blocking the production of bicarbonate with carbonic anhydrase inhibitors
these therefore reduce ocular pressure in glaucoma
what are 2 commonly used carbonic anhydrase inhibitors
dorzolamide (eye drops)
acetazolomide (oral- also targets kidneys)
