Physiology Flashcards
Colour and components of CSF
clear and colourless composed mainly of water
what produces CSF
secretory epithelium of the choroid plexus in the ventricles of the brain
How much CSF is there and how often is it replaced?
there is about 150cm3 and it is replaced 3-4 times daily
what does the CSF supply/remove
supplied ions, water and amino acids
removes metabolites
circulation of CSF
produced in the choroid plexus in the ventricles, circulates in the subarachnoid space and is absorbed in the venous circulation
How do you obtain CSF fluid to analyse
lumbar puncture
major functions of the csf
1) mechanical protection- shock absorber so the brain floats in the cranial cavity
2) homeostatic function- pH of the CSF affects pulmonary ventilation and cerebral blood flow. also transports hormones
3) circulation- minor exchange for nutrients and waste products between circulation and brain tissue
in embryonic development what gives rise to the brain and spinal cord?
the neural canal cavity
What are choroid cells and what are they produced from?
Choroid cells are specialised secretory cells that produce CSF. the choroid plexus develops from cells in the walls of the ventricle.
How does the choroid plexus develop?
Developing arteries invaginate the roof of the ventricles to form the choroid fissure. the ependymal cells involved along with the artery enlarge into villi (finger like projections) and from the choroid plexus
Where are choroid plexuses found in the adult brain?
lateral ventricles and 3rd and 4th ventricle
What ions are transported across the epithelium from blood to CSF in CSF secretion? How does this work?
Na, Cl and HCO3
Depends on active Na transport across cells into the csf and the electrical gradient pulls along CL
both ions drag water via osmosis
Is CSF production active or passive? does it depend on arterial BP?
It is an active secretory process
It is NOT DIRECTLY dependent on arterial BP
Ion differences between blood and CSF
CSF has lower K, glucose and much lower protein than blood but higher Na and higher Cl
what allows CSF to be secreted from the ventricles?
Pores:
mainly the medial and lateral aperture but there are 4 in total:
interventicular foramina of Monroe (lateral ventricles to 3rd ventricle)
cerebral aqueduct of sylvius ( 3rd ventricle to 4th)
foramen of magendie (median aperture): fourth ventricle to subarachnoid space
foramen of luschka (lateral aperture) fourth ventricle to subarachnoid space
Production and circulation of CSF
CSF is formed in the choroid plexus of each lateral ventricle. it flows to the third ventricle through the interventricular foramen. more CSF is added by the choroid plexus in the ROOF of the 3rd ventrcicle. It then flows through the cerebral aqueduct into the 4th ventricle- more CSF is added by the choroid plexus in the 4th ventricle. CSF then enters the subarachmoid space through 3 opening in the roof of the 4th ventricle
What are the 3 openings in the roof of the 4th ventricle
single median aperture: foramen of magendie
paired lateral aperture: foramen of luschka
How much CSF is produced and absorbed every day
500- pressure and volume remains constant
Where does CSF flow to after the ventricular system
CSF flows into the subarachnoid space between the arachnoid and pia mater then goes to venous circulation through arachnoid granulations into the superior sagittal sinus
What is tighter the BBB or BCSFB
BBB
What is the BBB made up of
capillary endothelium and its basal membrane
perivascular astrocytes
What junctions are present at the BBB and what is their purpose?
tight junctions- prevents paracellular movement of molecules (eg through the intracellular space in contrast to transcellular transport where it travels through the wall)
What are circumventricular organs and an example
No BBB- allow the link between the CNS and peripheral blood flow eg pineal gland
what are colloid cysts
tumours arising almost always at the interventricular foramen
what are ependymonas
tumours arising from ependymal cells lining ventricles
What are the different types of ventricular haemorrhages
Epidural: arterial bleed between skull and dura mater
Subdural: venous bleed between the dura mater and arachnoid
What is hydrocephalus
accumulation of CSF in the ventricular system (obstruction/overproduction) resulting in inc ICP
What is idiopathic intracranial HT
increase in ICP with no detectable cause. Symptoms include headache and visual disturbances.
what is papilloedema
Optic disc swelling due to increased intracranial pressure causing pressure in the subarachnoid space surrounding the optic nerve
where is aqueous humour produced and does it require energy?
energy dependent process in the ciliary body
Flow of aqueous humour
Aqueous humour is produced in the ciliary body and flows into the posterior chamber of the eye. It then flows into the anterior chamber and drains into the scleral venous sinus through the canal of schlemm.
where is the canal of schlemm
At the iridocorneal angle- angle between iris and cornea
Histology of ciliary body and posterior iris
a forward continuation of the pigmented epithelium of the retina (layer closest to sclera) and an inner non-pigmented epithelial layer (layer closer to retina)
Movement of Na and CL across the ciliary body in CSF production
Na and Cl from plasma are taken into pigmented epithelial cells and move into non-pigmented epithelial cells of the ciliary body through gap junctions and are then transported into the posterior chamber
Normal intraocular pressure
17mmHg above atmospheric
Conc of Na Cl and bicarbonate in aquaeous compared with plasma
Increased conc of Na and CL and decreased conc of bicarbonate in aquaeous humour compared with plasma
What are CA inhibitors, how do they work and what diseases do they work for?
carbonic anhydrase inhibitors that block the production of bicarbonate so decrease the production of aquaeous humour. They are used in glaucoma.
Examples of CA inhibitors?
Dorzolamide: eye drops
acetazolamide: oral admin and also targets kidney
