Physiology - CSF Flashcards
Where is CSF produced
The secretory epithelium in the choroid plexus of the ventricles
What is CSF composed of
- clear, colourless ultra-filtrate of plasma
- mostly water & some ions/ AA’s
Where is CSF contained
subarachnoid space and the central canal of the spinal cord
What are the 3 roles of CSF
- mechanical protection of brain
- circulate function
- nutrient exchange between blood & brain - homeostatic function
- pH affects pulmonary ventilation & cerebral blood flow
- Hormone transport
What structure does the ventricles of the brain and central canal of the spinal cord originate from embryologically
The cavity of the neural canal
What gives rise to the choroid plexus embryologically
cells in the walls of the ventricles & nearby arteries
Describe the choroid plexus
- capillaries next to the walls of the ventricles
- ependymal (secretory) cells of the ventricle walls
Describe the production of CSF
- Na+ is transported across the basolateral membrane of the ependymal cells from the capillaries of the choroid plexus in exchange of H+ & HCO3-
- This creates an electrical gradient which pulls Cl- along too, as well as water (by osmosis)
- Na+ & K+ is then transported across the apical membrane of the ependymal cells into the ventricles by the NaKCl contransporter & NaK ATPase
Describe the flow of CSF
- Secreted by ependymal cells of lateral ventricles
- Flows into third ventricles where more CSF is added
- Flows into fourth ventricles where more CSF is added
- CSF flows into subarachnoid space via medial & lateral apertures of the fourth ventricle
i.e. Ependymal cells => lateral ventricle => third ventricle => fourth ventricle => subarachnoid space => spinal cord canal
Describe the flow of CSF from the subarachnoid space into the blood stream
CSF from the subarachnoid space passes through the arachnoid granulations into the superior sagittal sinus
CSF from interstitial fluid drains into the subarachnoid space via the perivascular space in order to drain through the mechanisms above
What are the three components of the blood brain barrier
- The capillary endothelium
- The capillary basal membrane
- The perivascular astrocytes
How does the BBB prevent paracellular movement of undesirable molecules
Tight junction between the capillary endothelial cells (that are made from parts secreted by astrocytes)
How does the BBB allow cellular transport of desirable molecules
By cellular transport channels
What is hydrocephalus
accumulation of CSF in the ventricular system or around the brain (either due to obstruction of drainage or overproduction), causing ventricular enlargement and increased CSF pressure
What is idiopathic cranial hypertension/pseudotumor cerebri
Increased CSF pressure but no imaging features of hydrocephalus
What is papilloedema
optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
