THE CIRCULATION OF THE CEREBRO SPINAL FLUID

THE CIRCULATION OF THE CEREBRO SPINAL FLUID

1. SEMEY STATE MEDICAL UNIVERSITY NAME : hament sharma GROUP : 239 TOPIC : THE CIRCULATION OF THE CEREBRO SPINAL FLUID

2. C erebrospinal 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.

3. 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

4. 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.

5. 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 .

6. 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.

7. 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 .

8. 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.

9. 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.

10. 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 ).

11. 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.

12. 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 blood  perfusion .

13. 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.

14. 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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