CSF, BBB and intracranial pressure Flashcards
where is CSF found in the CNS?
-fills the subarachnoid space (between arachnoid and pia mater of brain and spinal cord)
-also fills the ventricles
what are the functions of CSF?
-supports and provides mechanical cushioning
-maintains constant external environment for neuron’s & glia
-distributor of hormones
-major route for removing harmful brain metabolites
what is CSF formed by?
-choroid plexus
what are the characteristics of the wall of the choroid plexus?
-the choroid plexus capillaries are fenestrated and have no tight junctions
- the ependyma act as a continuous sheath of tissue covering and sealing the capillary wall
what does the choroid plexus have low permeability to?
lipid insoluble solutes eg ions, glucose and amino acids
- ie these molecules have restricted movement and are tightly regulated
what does the movement of lipid insoluble solutes through the choroid plexus depend on?
presence of transported in the walls of the ependyma eg glucose transporter GLUT1
what do the choroid plexus have high permeability to?
-lipid soluble solutes eg fats, O2, CO2, lipid soluble drugs etc
-ie these molecules have unrestricted mvt and they can move freely
what is the blood - CSF barrier?
-barrier by the choroid plexus and certain other brain capillaries and their associated transporters
- the transporters promote entry of some substances and restrict entry of others into CSF from blood
how can a sample of CSF be obtained in a human?
- a needle is inserted between the 3rd and 4th or 4th and 5th lumbar vertebrae so that the tip lies in the subarachnoid space
what effect does meningitis have on CSF composition?
-increased number of WBC in the CSF
what can happen to the CSF after a subarachnoid haemorrhage?
CSF becomes discoloured and yellowish a few hours later
how does the CSF flow through the ventricles?
-produced in the choroid plexus in lateral ventricle
-flows from lateral ventricle into the 3rd ventricle via the interventricular foramen
-flows from the 3rd ventricle to the 4th ventricle through the cerebral aqueduct
-flows from the 4th ventricle into the subarachnoid space via the lateral and medial aperture
what is the pressure of CSF in mmHg normally?
10mmHg
what is hydrocephalus?
excessive accumulation of CSF in the ventricles of the brain
-this can lead to brain damage
what are examples of causes of hydrocephalus in infants vs adults?
infants:
-stenosis or inflammation of the aqueduct between 3rd and 4th ventricle
adults:
-obstruction of aqueduct between 3rd and 4th
what is the blood brain barrier (BBB)?
- a highly specialised system of cells and blood vessels that serve as a protective barrier between the bloodstream and the brain
how are the blood CSF and blood brain barrier similar?
-functionally the 2 barriers are the same but structurally they are different
what is the function of the BBB?
-maintain a constant environment for the neurons of the CNS to function effectively
-exclusion of toxic substances
-protects brain from circulating neurotransmitters
what is intracranial pressure?
Intracranial pressure (ICP) refers to the pressure exerted by the cerebrospinal fluid (CSF) within the skull and on the brain tissue.
what are examples of things that could cause an increase in ICP?
-brain swelling due to injury or infection
-excess CSF eg hydrocephalus
-bleeding in the brain - eg aneurysm / traumatic head injury
-tumours - can cause increased in ICP by compressing the brain
what can happen to the cerebral vessels and flow as a result of an increased ICP?
–increased ICP- cerebral vessels compression - reduction in cerebral flow and therefore can eventually lead to cerebral ischemia
what are examples of symptoms associated with an increase in ICP initially and as the condition worsens?
-initially- headache, nausea and restlessness
-as condition worsens, there can be neural dysfunction eg confusion and drowsiness
-as ICP rises further, the cerebral pressure becomes very low and cushings reflex occurs
what is cushings reflex?
a set of physiological responses that occur when the ICP rises
what are the 3 components of cushings reflex?
-increase in ICP compresses the brain and can cause compression of the medulla oblongata - ie the cardioresp centre - causing bradycardia
-increase in ICP - causes compensatory mechs by the body to increase flow to the brain - therefore increased BP
- compression of brain can also lead to abnormal respiratory conditions eg cheyne stokes respiration
in simple words , what are the 3 components / physical symptoms of a patient with a cushings reflex due to increased ICP? ie the cushings triad
-increased BP
-bradycardia
-decrease in respiration
