Physiology of CSF Flashcards
how much CSF is found in the CNS
150ml
where is CSF found in the body
CSF occupies the subarachnoid space and ventricular system around and inside brain and spinal cord.
what are the 3 major functions of CSF
mechanical protection: shock-absorbing medium that portects brain tissue
homeostatic function: pH of CSF affects pulmonary ventilation and cerebral blood flow, also transports hormones
circulation: medium for minor exchange of nutrients and waste products between blood and brain tissue
how can CSF be clinically analysed
lumbar puncture
what can a lumbar puncture reveal
intra cranial pressure
what does normal CSF look like
clear, colourless and little protein
Embryonic Development of the Brain and Ventricular System
describe the formation of the ventricules and spinal cord central channel
neural tube is the first structure to form (neural progenitor cells form the neural plate, which forms neural groove and finally neural tube)
the hollow centre of the tube becomes the ventricules and spinal cord central channel
Embryonic Development of the Brain and Ventricular System
describe the formation of the choroid plexus
develops from ependymal cells in the walls of the ventricules
developing arteries invaginate into the roof of the ventricle to form the choroid fissure. The involuted ependymal cells and vessels form the choroid plexus
where is CSF produced from
Ventricles are lined by choroid plexus, which is composed of ependymal cells that secrete CSF. The main function of the ventricles is the production and distribution of CSF.
how is CSF made and moved from choroid plexus into ventricles
active transport of sodium from blood to CSF creates an electrical gradient which pulls chlorine across. water follows by osmosis
compare the constituency of CSF to that of blood
lower concentration of potassium, glucose and protein
higher concentrations of Sodium and Chlorine
which structure in the choroid plexus prevents substances flowing freely into CSF
tight junctions between ependymal cells
describe the ventricular system
lateral ventricles via Foramen of Munro to 3rd ventricle
to 4th ventricle via cerebral aqueduct (of Sylvius)
to subarachnoid space via median and lateral apertures
what are the median and lateral apertures also called
and how many of them are there
3 apertures - one median and two lateral
median = foramen of Magendie
lateral = foramen of Luschka
describe the CSF circulation in the ventricules
it then circulates the central canal of spinal cord in subarachnoid space
how much CSF is produced and absorbed every day (continuous process)
500ml
how much CSF is there in the body at any one time
125 ml
describe the reabsorption of CSF
returns to venous blood by entering the dural venous sinuses through arachnoid granules into the superior sagittal sinus
blood-CSF barrier
The blood-CSF barriers separate the peripheral and cerebral blood from the CSF
Composed of epithelial cells of the choroid plexus at the peripheral blood-CSF boundary and the arachnoid membrane at the cerebral blood-CSF boundary.
BBB
Highly selective semi-permeable membrane that separates the circulating blood from the brain and extracellular fluid in the CNS.
what is the BBB formed of
- Central component is tight junctions between endothelial cells that make up blood vessels. Restrict diffusion across.
- Astrocytes (star shaped glial cells – homeostasis) surround blood vessels and help form BBB. Involved in signalling.
give some examples of parts of the brain that don’t have a BBB
- Circumventricular organs have no BBB as their functions require access to blood stream e.g. posterior pituitary releases hormones straight into blood stream
- circumventricular organs (linkage between CNS and peripheral blood flow)
- pineal gland (secretes melatonin directly into systemic circulation)
what does the BBB allow across
BBB endothelial cells allow the diffusion of hydrophobic molecules (O2, CO2) into the CSF
Restrict the diffusion of microscopic, large or hydrophilic molecules.
signs of raised ICP
- bilateral papilloedema
- morning headache, worse on sneezing/coughing
- vomiting without nausea
- altered level of consciousness
Munro Kellie hypothesis
The Munro-Kellie hypothesis states that the cranial compartment is rigid incompressible and volume of brain, CSF and blood inside it is fixed. Therefore, a state of volume equilibrium exists. The main buffers to increased volume are CSF, and blood volume to a lesser extent.
