CSF.pdf

CEREBROSPINAL FLUID [CSF] CEREBRAL CIRCULATION The Circle of Willis is the joining area of several arteries at the bottom (inferior) side of the brain. At the Circle of Willis, the internal...

CEREBROSPINAL FLUID [CSF] CEREBRAL CIRCULATION The Circle of Willis is the joining area of several arteries at the bottom (inferior) side of the brain. At the Circle of Willis, the internal carotid arteries branch into smaller arteries that supply oxygenated blood over 80% of the cerebrum. CEREBRAL CIRCULATION CEREBROSPINAL FLUID The cerebrospinal Fluid [CSF] is a clear, colorless transparent, tissue fluid present in the cerebral ventricles, spinal canal, and subarachnoid spaces. CEREBROSPINAL FLUID  CEREBROSPINAL FLUID [FORMATION] CSF is largely formed by the choroid plexus of the lateral ventricle and remainder in the third and fourth ventricles. About 30% of the CSF is also formed from the ependymal cells lining the ventricles and other brain capillaries. The choroid plexus of the ventricles actively secrete cerebrospinal fluid. The choroid plexuses are highly vascular tufts covered by ependyma. MECHANISM OF FORMATION OF CSF CSF is formed primarily by secretion and also by filtration from the net works of capillaries and ependymal cells in the ventricles called choroid plexus. Various components of the choroid plexus from a blood- cerebrospinal fluid barrier that permits certain substances to enter the fluid, but prohibits others. Such a barrier protects the brain and spinal cord from harmful substances. MECHANISM OF FORMATION OF CSF The entire cerebral cavity enclosing the brain and spinal cord has a capacity of about 1600 to 1700 milliliters About 150 milliliters of this capacity is occupied by cerebrospinal fluid and the remainder by the brain and cord. MECHANISM OF FORMATION OF CSF Rate of formation: About 20-25 ml/hour 550 ml/day in adults. Turns over 3.7 times a day Total quantity: 150 ml: 30-40 ml within the ventricles About 110-120 ml in the subarachnoid space [of which 75-80 ml in spinal part and 25-30 ml in the cranial part].  MECHANISM OF FORMATION CSF is formed at a rate of about 550 milliliters each day,. About two thirds or more of this fluid originates as secretion from the choroid plexuses in the four ventricles, mainly in the two lateral ventricles. Additional small amount of fluid is secreted by the ependymal surfaces of all the ventricles and by the arachnoidal membranes Small quantity comes from the brain itself through the perivascular spaces that surround the blood vessels passing through the brain.  MECHANISM OF FORMATION Secretion by the Choroid Plexus. The choroid plexus, is a cauliflower-like growth of blood vessels covered by a thin layer of epithelial cells. Secretion of fluid by the choroid plexus depends mainly on active transport of sodium ions through the epithelial cells lining the outside of the plexus. The sodium ions in turn pull along large amounts of chloride ions because the positive charge of the sodium ion attracts the chloride ion's negative charge. The two of these together increase the quantity of osmotically active sodium chloride in the cerebrospinal fluid, which then causes almost immediate osmosis of water through the membrane, thus providing the fluid secretion. MECHANISM OF FORMATION Less important transport processes move small amount of glucose into the cerebrospinal fluid and both potassium and bicarbonate ions out of the cerebrospinal fluid into the capillaries. The resulting characteristics of the CSF are: Osmotic pressure approximately equal to that of plasma sodium ion concentration Approximately equal to that of plasma chloride ion About 15 per cent greater than in plasma potassium ion approximately 40 per cent less glucose  ABSORPTION OF CSF THROUGH ARACHNOID VILLI The arachnoidal villi are fingerlike inward projections of the arachnoidal membrane through the walls into venous sinuses. villi form arachnoidal granulations can protruding into the sinuses. The endothelial cells covering the villi have vesicular passages directly through the bodies of the cells large enough to allow relatively free flow of (1) cerebrospinal fluid, (2) dissolved protein molecules, and (3) even particles as large as red and white blood cells into the venous blood. COMPOSITION OF CSF Proteins = 20-40 mg/100 ml Glucose = 50-65 mg/100 ml Cholesterol = 0.2 mg/100 ml Na+ = 147 meq/Kg H2O Ca+ = 2.3 meq/kg H2O Urea = 12.0 mg/100 ml Creatinine = 1.5 mg/100 ml Lactic acid = 18.0 mg/100 ml CHARACTERISTICS OF CSF Nature: Colour = Clear, transparent fluid Specific gravity = 1.004-1.007 Reaction = Alkaline and does not coagulate Cells = 0-3/ cmm Pressure = 60-150 mm of H2O The pressure of CSF is increased in standing, coughing, sneezing, crying, compression of internal Jugular vein (Queckenstedt’s sign  CIRCULATION OF CSF Circulation: CSF is mainly formed in choroid pleaxus of the lateral ventricle. CSF passes from the lateral ventricle to the third ventricle through the interventricular foramen (foramen of Monro). From third ventricle it passes to the fourth ventricle through the cerebrol aqueduct. The circulation is aided by the arterial pulsations of the chroid plexuses. From the fourth ventricle (CSF) passes to the sub arachnoid space around the brain and spinal cord through the foramen of magendie and foramina of luschka. CIRCULATION OF CSF Lateral ventricle Foramen of Monro [Interventricular foramen] Third ventricle: Cerebral aqueduct Fourth ventricle: Foramen of megendie and formen of luschka Subarachnoid space of Brain and Spinal cord  CIRCULATION OF CSF Circulation: CSF slowly moves cerebromedullary cistern and pontine cisterns and flows superiorly through the interval in the tentorium cerebelli to reach the inferior surface of the cerebrum. It moves superiority over the lateral aspect of each cerebrol hemisphere. FUNCTIONS OF CSF A shock absorber A mechanical buffer Act as cushion between the brain and cranium Act as a reservoir and regulates the contents of the cranium Serves as a medium for nutritional exchange in CNS Transport hormones and hormone releasing factors Removes the metabolic waste products through absorption