lecture : physiology of cerebrovascular fluid (CSF)

Lecture: physiology of cerebrovascular fluid (CSF) students' reference

1. Dr Shamshad

2. Functions Protection/Cushion effect: Protects the brain from damage by buffering the brain. Cushion effect to brain & reduces the impact by blow. Coup and counter coup mechanisms Buoyancy :Brain in immersed in CSF, the net wt. of the brain is reduced from 1400 to 50 gm. Thus, pressure at the base of the brain is reduced. Nutrition and Excretion : Provides nutrition Na2+,glucose,K+ to the brain and removes waste metabolites. Maintain homeostasis Unidirectional flow of CSF takes away harmful metabolites(Lactic acid/urea) & drugs away from brain.

3. CUSHIONING Effect : Major function protects brain within its solid skull. The brain and the CSF have about the same specific gravity ,so the brain simply floats in the fluid. A blow to the head, if it is not too intense, moves the entire brain simultaneously with the skull, causing no one portion of the brain to be momentarily contorted by the blow. Coup injury : Same side contusion as the impact injury.

4. Contrecoup : Severe blow to the head may not damage the brain on the side of the head where the blow is struck but may damage the opposite side. The poles & the inferior surfaces of the frontal & temporal lobes,(brain comes into contact with bony protuberances in the base of the skull) often the sites of injury & contusions after a severe blow to head ( boxer).

5. May also be caused by rapid acceleration or deceleration alone in the absence of physical impact by blow to head. Here the brain may bounce off the wall of the skull, causing a coup injury, and then also bounce off the opposite side, causing a contrecoup contusion. Such injuries are thought to occur, for example, in “shaken baby syndrome” or sometimes in vehicular accidents.

6. Composition of CSF 10% of total volume of body fluid. Average vol.: 150 cc in adult (90cc in children) Osmotic Pressure: same as plasma Rate of secretion: 450-500ml/day Normal CSF pressure: 90-180 mmH 2 O/<15mmHg Formation: ≥70% from choroid plexus. ͠ 30% transepndymal movement fluid from brain to ventricles. Pressure increases in : standing , intrathoracic pr or compress of Internal jugular vein( Queckenstedt’s sign)

7. Normal physical examination Appearance and color Clear, colorless pH 7.4 Sp.g 1.006-1.007 Normal Microscopic examination Lymphatics 1-5/HPF Normal chemical examination Protein 15-45mg/dl <serum Glucose 50-80mg/dl << 30%plasma Chloride 130meq/l >15%plasma Calcium 2.3meq/l <plasma Phosphorus 0.4-.0.7mmol/l Magnesium 1.2-1.5mmol/l Potassium 2.9meq/l <plasma by 40% Sodium 150meq/l =plasma Bicarbonate ions 21.0meq/l

8. Protein: CSF:Serum albumin ratio::1:200 Cl importance : RBC+ indicates traumatic tap /hemorrhage. Froin syndrome : Spinal cord tumor :protein≥1000mg/dl. ↑ lumbar CSF protein is nonspecific but sensitive indicator of CNS diseases. Glucose:↓CSF/plasma glucose Cl Importance : CNS pyogenic infection, brain tumors, or TB meningitis or sarcoidosis In viral CNS infection the ratio usually normal .

9. FORMATION, FLOW & ABSORPTION OF CSF ≥2/3 rd originates as secretion from the choroid plexuses in the four ventricles, mainly in the two lateral ventricles. 1/3rd of fluid are secreted by the ependymal surfaces of all the ventricles and by the arachnoidal membranes & through the perivascular spaces ( Virchow-Robin spaces ) that surround the blood vessels passing through the brain.

10. Absorption: Arachnoid villi in venous sinuses. Allow CSF dissolved proteins and particles like RBCs/ WBCs to be easily absorbed. Force of circulation: Movement of the CSF is by pulsating blood vessels ,respiration and changes of posture.

11. Absorption of Cerebrospinal Fluid Through the Arachnoidal Villi. The arachnoidal villi are microscopic fingerlike inward projections of the arachnoidal membrane through the walls and into the venous sinuses. Conglomerates of these villi form macroscopic structures called arachnoidal granulations that can be seen protruding into the sinuses.

12. 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. Perivascular Spaces and Cerebrospinal Fluid.

13. The large arteries and veins of the brain lie on the surface of the brain but their ends penetrate inward, carrying with them a layer of pia mater, the membrane that covers the brain. The pia is only loosely adherent to the vessels, so a space, the perivascular space, exists between it and each vessel. Follow both the arteries and the veins into the brain as far as the arterioles and venules go.

14. Analysis the effects of change in composition & pressure of CSF

15. High CSF pressure In diseases the villi get blocked by fibrosis, or by excesses of blood cells that have leaked into the CSF in brain diseases can cause high CSF pressure, A large brain tumor elevates the CSF pressure by decreasing its reabsorption back into the blood. As a result, the CSF pressure can rise to as much as 500 mm of water (37 mm Hg) . The CSF pressure also rises considerably when hemorrhage or infection occurs in the cranial vault. Where large numbers of blood cells can cause serious blockage of the small absorption channels through the arachnoidal villi.

16. Some babies are born with high CSF pressure, which is often caused by abnormally high resistance to fluid reabsorption through the arachnoidal villi, due to either few arachnoidal villi or abnormal absorptive villi Leading to Hydrocephalus. Low pressure: Severe Dehydration Leakage of CSF.

17. Blood–CSF and Blood ­Brain Barriers The blood CSF barrier / the blood-brain barrier, exist between the blood and the CSF and brain fluid. Certain substances in the CSF are tightly regulated by specific transport systems Due to the tight junctions BBB occurs in all places in brain ECECPT Some areas of hypothalamus Pineal gland Area postrema Importance: here sensory receptors for pressure, glucose osmolality etc. present.

18. The blood– cerebrospinal fluid and blood-brain barriers often make it impossible to achieve effective concentrations of therapeutic drugs, such as protein antibodies and non-lipid-soluble drugs, in the CSF or parenchyma of the brain. The cause of the low permeability of the blood CSF and BBB is the manner in which the endothelial cells of the brain tissue capillaries are joined to one another. The membranes of the adjacent endothelial cells are tightly fused rather than having large slit pores between them, as is the case for most other capillaries of the body. Called tight junction .

19. Causes: Concussion or blockage Result: Compression of vessels Less oxygen supply Vasodilation More edema sodium pump turned off Treatment: Mannitol Ventricular pump

20. Brain Edema :Accumulation of extra fluid compresses the blood vessels, to cause decreased blood flow and destruction of brain tissue. Brain edema is increased capillary pressure or damage to the capillary wall that makes the wall leaky to fluid. EX:Brain concussion, brain tissues and capillaries are traumatized and capillary fluid leaks into the traumatized tissues. Once brain edema begins, it often initiates two vicious circles because of the following positive feedbacks:

21. 1. Edema compresses the vasculature, Decreases blood flow and causes brain ischemia. The ischemia in turn causes arteriolar dilation with still further increase in capillary pressure. The increased capillary pressure then causes more edema fluid, so the edema becomes progressively worse. 2. The decreased cerebral blood flow also decreases oxygen delivery, increases the permeability of the capillaries, allowing still more fluid leakage.

22. It also turns off the sodium pumps of the neuronal tissue cells, further swelling. Treatment: Immediately Infuse IV a concentrated osmotic substance, mannitol , which pulls fluid by osmosis from the brain tissue Remove fluid quickly from the lateral ventricles of the brain by means of ventricular needle puncture, relieving the intracerebral pressure