CSF and it's production and normal composition
- 1. Cerebrospinal Fluid (CSF) INTRODUCTION PROPERTIES AND cOMPOSITION FORMATION SITE OF FORMATION MECHANISM OF FORMATION SUBSTANCES AFFECTINGTHE FORMATION CIRCULATION ABSORPTION PRESSURE EXERTED FUNCTIONS COLLECTION LUMBAR PUNCTURE BLOOD-BRAIN BARRIER STRUCTURE FUNCTIONS BLOOD-CEREBRoSPINAL FLUIDBARRIER APPLIED PHYSIOLOGY HYDROCEPHALUS than potassium. CSF also contains some lymphocytes. CSF secreted by ventricle does not contain any celI. Lymphocytes are added when CSF flows in the spinal INTRODUCTION Cerebrospinal fluid (CSF) is the clear, colorless and transparent fluid that circulates through ventricles of brain, subarachnoid space and central canal of spinal cord. It is a part of extracellular fluid (ECF). cord. FORMATION OF CEREBROSPINAL FLUID PROPERTIES AND COMPOSITION OF CEREBROSPINAL FLUID SITE OF FORMATION CSF is formed by choroid plexuses, situated within the ventricles. Choroid plexuses are tuft of capillary projections present inside the ventricles and are covered by pia mater and ependymal covering. A large Properties Volume 150 mL (100 mL to 200 mL) Rate offormation 0.3 mL per minute Specific gravity 1.005 Reaction amount of CSF is formed in the lateral ventricles. :Alkaline. MECHANISM OF FORMATION Composition Composition of CSF is given in Figure 163.1. Since CSF is a part of ECF, it contains more amount of sodium CSF is formed by the process of secretion that involves active transport mechanism. Formation of CSF does not involve ultrafiltration or dialysis.
- 2. ABSORPTION OF CEREBROSPINAL FLUID Cerebrospinal fluid CSF is mostly absorbed by the arachnoid villi into dural sinuses and spinal veins. Small amount is absorbed along the perineural spaces into cervical lymphatics and into the perivascular spaces. The mechanism of absorption is by filtration due to pressure gradient between hydrostatic pressure in the subarachnoid space fluid and the pressure that exists in the dural sinus blood. Colloidal substances pass slowly and crystalloids are absorbed rapidly. Normally, about 500 mL of CSF is formed everyday and an equal amount is absorbed. Water 99.13%)Solids-0.87% Organic substances Inorganic substances 1. Proteins 2. Amino acids 1. Sodiumn 2. Calcium 3. Sugar 3. Potassium 4. Magnesium 5. Chlorides 6. Phosphate 7. Bicarbonates 4. Cholesterol Urea . 6. Uricacid 7. Creatinine 8. Lactic acid PRESSURE EXERTEDBY CEREBROSPINAL FLUID 8. Sulfates Lymphocytes in CSF: 6/cu mm Pressure exerted by CSF in man varies in different position, viz. Lateral recumbent position Lying position Sitting position Certain events like coughing and crying increase FIGURE 163.1: Composition of cerebrospinal fluid 10 to 18 cm of H,O 13 cm of H,0 30 cm of H,O SUBSTANCES AFFECTING THE FORMATION OF cSF 1. Plocarpine, ether and extracts of pituitary gland e pressure by decreasing absorption. Compression of stimulate the secretion of CSF by stimulating choroid plexus internal jugular vein also raises the CSF pressure. 2. Injection of isotonic saline also stimulates cSF FUNCTIONS OF CEREBROSPINAL FLUID formation 1. Protective Function 3. Injection of hypotonic saline causes greater rise in capillary pressure and intracranial pressure and CSF acts as fluid buffer and protects the brain from fall in osmotic pressure, leading to increase in shock. Since, the specific gravity of brain and CSFis CSF formation more or less same, brain floats in CSF. When head 4. Hypertonic saline decreases CSF formation and receives a blow, CSF acts like a cushion and prevents decreases the CSF pressure. The increased intracranial pressure is reduced by injection of thereby, prevents the damage of brain. 30% to 35% of sodium chloride or 50% sucrose. the movement of brain against the skull bone and However, if the head receives a severe blow, the brain moves forcefully and hits against the skull bone, leading to the damage of brain tissues. Brain strikes against the skull bone at a point opposite to the point where the blow was applied. So, this type of damage CIRCULATION OF CEREBROSPINAL FLUID Major quantity of CSF is formed in lateral ventricles to the brain is known as countercoup injury. and enters third ventricle by passing through foramen of Monro (Figs.163.2and163.3). From here,itpasses 2. Regulation ofCranial Content Volume to fourth ventricle through aqueductus Sylvius. From fourth ventricle, CSF enters the cisterna magna and Regulation of cranial content volume is essential cisterna lateralis through foramen of Magendie (central because, brain maybe affected if the volume of cranial opening) and foramen of Luschka (lateral opening). From cisterna magna and cisterna lateralis, CSF and brain tumors. circulates through subarachnoid space over spinal cord and cerebral hemispheres. It also flows into by greater absorption of CSF to give space for the central canal of spinal cord. content increases. It happens in cerebral hemorrhage Increase in cranial content volume is prevented increasing cranial contents.
- 3. Dura mater Superior sagittal - venous sinus -Arachnoid mater Subarachnoid space Pia mater ---Choroid plexus Lateral ventricle Third ventricle Foramen of Luschka - Aqueductus Sylvius Foramen of Magendie - Fourth ventricle Choroid plexus Central canal of spinal cord - Dura mater Arachnoid mater Pia mater FIGURE 163.2: Circulation of cerebrospinal fiuid 3. Medium of Exchange back of the subject by joining the highest points of iliac crests of both sides. Opposite to midplane, this line crosses the fourth lumbar spine. After determining the area of fourth lumbar spine, third lumbar spine is palpated. The needle is introduced into subarachnoid space by passing through soft tissue space between the two spines. CSF is the medium through which many substances particularly nutritive substances and waste materials are exchanged between blood and brain tissues. COLLECTION OF CEREBROSPINAL FLUID cSF is collected either by cisternal puncture or lumbar puncture. In cisternal puncture, the CSF is collected by passing a needle between the occipital bone and atlas, so that it enters cisterna magna. In lumbar puncture, the lumbar puncture needle is introduced into subarachnoid space in lumbar region, between the third and fourth lumbar spines Reasons for selecting this site 1. Spinal cord will not be injured, because, it terminates below the lower border of the first lumbar vertebra. Cauda equina may be damaged. But it is regenerated. 2. Subarachnoid space is wider in this site. It is because the pia mater is reduced very much. LUMBAR PUNCTURE Uses of Lumbar Puncture Posture ofBody for Lumbar Puncture The reclining body is bent forward, so as to flex the vertebral column as far as possible. Then the body is brought near edge of a table. The highest point of iliac crest is determined by palpation. A line is drawn on the Lumbar puncture is used for: 1. Collecting CSF for diagnostic purposes 2. Injecting drugs (intrathecal injection) for spinal anesthesia, analgesia and chemotherapy 3. Measuring the pressure exerted by CSF.
- 4. capillaries of other organs, adjacent endothelial cells leave the cleft called fenestra, which allows transcytosis ofseveral substancesthrough endothelium (Chapter 111). However, in capillaries of brain, fenestra are absent because, the endothelial cells fuse with each Formation ofcerebrospinal fluid in lateral ventricle other bytight junctions (Fig. 163.4). Tight junctions are formed between endothelial cells of the capillaries at childhood. At the same time, cytoplasmic foot processes of astrocytes (neuroglial cells) develop around capillaries and reinforce the barrier. Astocytes envelop the vasculature almost completely. Pericytes also form the important cellular constituent of BBB. These cells play an important role in formation and maintenance of tight junction and structural stability of the barrier. In brain, pericytes function as macrophages and play an important role in Foramen of Monro Third ventricle Aqueductus Sylvius Fourth ventricle Foramen of Magendie and foramen of Luschka the defense. FUNCTIONS OF BLOOD-BRAIN BARRIER Cisterna magna and cisterna lateralis BBB acts as both a mechanical barrier and transport mechanisms. It prevents potentially harmful chemical substances and permits metabolic and essential materials into the brain tissues. By preventing injurious materials and organisms, BBB provides healthy environment for the nerve cells of brain. Central canal Subarachnoid spaces Over cerebral Substances which can Pass through Blood-Brain Barrier Over spinal cord hemispheres 1. Oxygen FIGURE 163.3: Cerebrospinal fluid circulation 2. Carbon dioxide 3. Water BLOOD-BRAIN BARRIER 4. Glucose 5. Amino acids Blood-brain barrier (BBB) is a neuroprotective structure that prevents the entry of many substances and pathogens into the brain tissues from blood. It was observed more than 50 years ago, that when trypan blue, the acidic dye was injected into living animals, all the tissues of body were stained by it, except the brain and spinal cord. This observation suggested that there was a hypothetical barrier, which prevented the diffusion of trypan blue into the brain tissues from the capillaries. This barrier was named as blood-brain barrier (BBB). It exists in the capillary membrane of all parts of the brain, except in some areas of hypothalamus. 6. Electrolytes 7. Drugs such as L-dopa, 5-hydroxytryptamine sulfo- namides, tetracycline and many lipid-soluble drugs 8. Lipid-soluble anesthetic gases such as ether and nitrous oxide 9. Other lipid-soluble substances. Substances which cannot Pass through Blood-Brain Barrier 1. Injurious chemical agents 2. Pathogens such as bacteria 3. Drugs such as Penicillin and the catecholamines. Dopamine also cannot pass through BBB. So, parkinsonism is treated with L-dopa, instead of dopamine. STRUCTURE OFBLOOD-BRAIN BARRIER Tightjunctionsinthe endothelial cells of brain capillaries are responsible for BBB mechanism.
- 5. Capillary in other organ Capillary in brain Pericyte --- Pericyte Tight junctions Capillary lumen Endothelial - Endothelial cell cell Foot process of astrocytes Fenestra FIGURE 163.4: Blood-brain barrier 4. Bile pigments: However, since the barrier is notwell APPLIED PHYSIOLOGY developed in infants, the bile pigments enter the brain tissues. During jaundice in infants, the bile pigments enter brain and causes damage of basal ganglia, leading to kernicterus (refer Chapter 21 for details). HYDROCEPHALUS Abnormal accumulation of CSF in the skull, associated with enlargement of head is called hydrocephalus. During obstruction of any foramen, through which CSF escapes, the ventricular cavity dilates and this condition is called internal hydrocephalus. It is also known as non-communicating hydrocephalus. On the other hand, if the arachnoid villi are blocked, BLOOD-CEREBROSPINAL FLUID BARRIER Blood-CSF barrier is the barrier between blood and cerebrospinal fluid that exists at the choroid plexus. The function of this barrier is similar to that of BBB. It external or communicating hydrocephalus occurs. Hydrocephalus alongwith increased intracranial pressure causes headache and vomiting. In severe conditions, it leads to atrophy of brain, mental weakness does not allow the movement of many substances from blood to cerebrospinal fluid. It allows the movement of only those substances which are allowed by BBB. and convulsions.