Download Cerebrospinal fluid

Cerebrospinal fluid
Definition
• The serum like fluid that circulates through
the ventricles of the brain, the cavity of the
spinal cord, and the subarachnoid space
• Since the brain floats in CSF, the fluid acts in
effect to reduce the weight of the brain from
some 1000 g to about 50 g, and also protects
the brain from knocks on the head
The subarachnoid space on the outside of the
brain is in continuity with a similar space around
the spinal cord and also with the series of
interconnected cerebral ventricles within the
brain (see figure).
Each of the paired lateral ventricles, in the
cerebral hemispheres, contains a leaf-like, highly
vascular choroid plexus. It is from these
structures that the bulk of the CSF is secreted.
From the lateral ventricles CSF drains into the central
third ventricle, and thence through the aqueduct in
the midbrain into the fourth ventricle.
From the fourth ventricle, the CSF exits into the
subarachnoid space through several openings, and fills
the ‘basal cisterns’ beneath the brain.
hence the flow of CSF is mainly up and over the whole
brain surface, whilst some flows down around the
spinal cord. Completing the circuit back to the
bloodstream
Secretion and volume:
• The secretion of CSF is an active transport process that
moves fluid and solutes from the blood plasma into the
ventricles, the choroid plexuses being a specialized part
of the blood-brain barrier.
• CSF secretion involves the pumping of ions and
specialized ion channels, with the energy coming from
glucose and oxygen in the blood.
• In the adult human CSF is formed at a rate of about 0.5
ml/min; the total volume is about 200 ml, of which 30
ml is in the ventricles and the remainder in the
subarachnoid space. The circulation of CSF leads to the
fluid being completely replaced about every 4 hours.
Composition and appearance:
• CSF is a weak salt solution with similar
inorganic ion concentrations to plasma (Ca2+,
Na+, Cl , K+, and Mg2+), but with small and
significant differences
• whereas the protein content is about 100
times less than that of plasma (0.5 g/liter
compared to 50-70 g/liter).
• Glucose concentration is also lower than that of
blood 50-85 mg/dl, it’s the major source of
energy for the brain.
• CSF is normally a clear, amazingly ‘bright’ fluid,
and if it is cloudy or contains a raised level of
protein or traces of blood this is usually an
indication of brain infection, some types of brain
or spinal cord tumour, or trauma.
Function
1. The major function of the CSF is to cushion
the brain within its solid vault.
2. It carries nutrients to the brain and the spinal
cord.
3. The CSF also acts as a drainage route for
waste products of brain metabolism.
Diagnosis and therapy:
• Abnormalities of the CSF can be important in diagnosis of
some medical conditions; the fluid can be sampled by
lumbar puncture from the extension of the subarachnoid
space (the lumbar sac) below the lower end of the spinal
cord. usually between the third and fourth lumbar
vertebrae
• Detecting the levels of protein and glucose in CSF may be
extremely beneficial in the diagnosis of subarachnoid
hemorrhage and central nervous system infections (such as
meningitis).
• A cerebrospinal fluid culture examination may yield the
microorganism that has caused the infection.
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