Cerebrospinal fluid (CSF) is produced by the choroid plexus in the brain ventricles and circulates around the brain and spinal cord, providing buoyancy and protection. Approximately 500 ml of CSF is produced per day, with most produced in the lateral ventricles and circulating through all ventricles before draining into the subarachnoid space. CSF is eventually absorbed into venous blood through arachnoid villi. It acts to flush metabolic waste from the brain and maintain chemical stability in the central nervous system. Alterations in CSF volume can help compensate for changes in intracranial pressure from issues like hemorrhage or edema.

1. NAME : hament sharma
GROUP : 239
TOPIC : THE CIRCULATION OF THE CEREBRO
SPINAL FLUID

2. Cerebrospinal Fluid (CSF)
 Cerebrospinal fluid (CSF) is a clear fluid that
surrounds the brain and spinal cord. There is about 150
milliliters of CSF within the cerebral cavity that
encloses the brain and spinal cord which allows the
brain to “float” in the fluid.

5. CSF Production
 CSF is produced in the brain by modified ependymal
cells in the choroid plexus (approximately 50% to 70%)
and the remainder is formed around blood vessels and
along ventricular walls

6.  The CSF is produced at a rate of 500 ml / day. Since the
subarachnoid space around the brain and spinal cord
can contain only 135 to 150 ml, large amounts are
drained primarily into the blood through arachnoid
granulations in the superior sagittal sinus. Thus the
CSF turns over about 3.7 times a day. This continuous
flow into the venous system dilutes the concentration
of larger, lipid-insoluble molecules penetrating the
brain and CSF. The CSF contains approximately
0.3% plasma proteins, or approximately 15 to 40 mg /
dL, depending on the sampling site.

11. Formation of Cerebrospinal Fluid
(CSF)
 Most of the CSF is secreted by the choroid plexus of
the four ventricles. This accounts for about two-thirds
of the 500 to 700 milliliters of CSF that are produced
in a day. The remaining quantities of CSF are secreted
by the ependymal surfaces of the ventricles and
the arachnoids mater. A small amount of CSF also
comes from the blood flow in the brain.

12. Formation of Cerebrospinal Fluid
(CSF)
 CSF is formed by an active process where sodium ions
are transported across the epithelial cells and pushed
outside of the choroid plexus. The positive sodium
ions then attract negative chloride ions. This changes
the osmotic gradient and the CSF with the higher ion
concentration draws water across the choroid plexus
membrane (osmosis). Glucose, bicarbonate ions and
sodium are then transported out of the blood
capillaries by other processes. This brings the
composition of CSF similar to that of plasma, although
the quantities of chloride ions, potassium ions and
glucose are lower in the CSF.

13. QUANTITY OF GLUCOSE AND
PROTEIN
 The quantity of protein in the CSF may vary between
15mg/dL to 40mg/dL and glucose concentration is
approximately 50 to 80mg/dL.

15. Circulation of the Cerebrospinal
Fluid
 The CSF is formed in the lateral ventricles, circulates
through the interventricular foramens into the third
ventricle, and then via the cerebral aqueduct into the
fourth ventricle. Here the fluid scapes via the lateral
apertures of the fourth ventricle and the medial
foramen of the fourth ventricle into the subaracnoid
spaces, where it difuses over the brain and spinal cord.
It has been calculated that 430 to 450 ml of CSF are
produced every day, so the fluid must be changes
every 6 to 7 hours (Neter, 31).Respiratory and
circulatory changes are belivied to change the
pressure within the closed system and promote the
mixing and diffusion of fluid.

17. Flow of Cerebrospinal Fluid
 Fluid secreted from the choroid plexus of the lateral passes
through the first and third ventricles and into the fourth
ventricle. Minute amounts of CSF are added to the bulk
from the lateral ventricles in the third and fourth ventricle.
By exiting the fourth ventricle through the two lateral
foramina (of Luschka) and the midline foramen (of
Magendie), the cerebrospinal fluid enters the cisterna
magna. This then drains into the subarachnoid space which
surrounds the entire brain and spinal cord. Eventually CSF
flows through the arachnoidal villi and is emptied into the
several venous sinuses of the cerebrum. It is then returned
into the venous circulation.

21.  Alterations in the volume of CSF is a compensatory
mechanism to deal with raised intracranial pressure
associated with a hemorrhage (bleeding in the cranial
cavity), hematoma (accumulation of blood) or cerebral
edema (swelling of the brain).

22.  Since the brain lacks a true lymphatic system, excess
protein in the brain tissue spaces (which cannot enter
into the veins of the brain) are carried through the
perivascular spaces and into the subarachoid spaces by
the cerebrospinal fluid. By passing through the
arachnoid villi, the CSF carries the protein back into
the venous blood stream. This route via the
perivascular spaces may also be utilized to flush out
cellular debris in the brain following an infection and
other metabolic wastes.

23. Functions of CSF
 The functions of CSF include:
 Buoyancy: The actual mass of the human brain is about 1400 grams;
however, the net weight of the brain suspended in the CSF is equivalent
to a mass of 25 grams. The brain therefore exists in neutral buoyancy,
which allows the brain to maintain its density without being impaired
by its own weight.
 Protection: CSF protects the brain tissue from injury when jolted or
hit.
 Chemical stability: CSF flows throughout the inner ventricular system
in the brain and is absorbed back into the bloodstream, rinsing the
metabolic waste from the central nervous system through the blood–
brain barrier. This allows for homeostatic regulation of the distribution
of neuroendocrine factors, to which slight changes can cause problems
or damage to the nervous system.
 Prevention of brain ischemia: The prevention of brain ischemia is
made by decreasing the amount of CSF in the limited space inside the
skull. This decreases total intracranial pressure and facilitates

24. Blood Brain Barrier
 Neurons of the brain and spinal cord are protected from
many chemical damage and biological substances by
"blood brain barrier", interposed between the blood and
the CSF by the endothelial cells of the capillaries and the
choroid plexus. This is clinically important because some
drugs cannot penetrate the barrier. This protective device
has many elements, ranging from junctions between
endothelial cells in the capillaries of the brain, restricting
permeability of larger molecules to neuroglia. Large blood
vessels penetrating the brain tissue are lined with an inner
layer of endothelium reinforced by fibromuscular tissue.

25. CSF as a Diagnostic Tool
 When CSF pressure is elevated, cerebral blood flow may be
constricted. When disorders of CSF flow occur, they may
therefore affect not only CSF movement but also
craniospinal compliance and the intracranial blood flow,
with subsequent neuronal and glial vulnerabilities. The
venous system is also important in this equation. Infants
and patients shunted as small children may have
particularly unexpected relationships between pressure
and ventricular size, possibly due in part to venous pressure
dynamics. This may have significant treatment
implications, but the underlying pathophysiology needs to
be further explored.

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