Continued… As CSF is part of ECF therefore it contain more amount of Sodium than Potassium. Contains some lymphocytes. CSF secreted by ventricles does not contain any cell. The lymphocytes are added when it flows in the spinal cord.
Formation of CSF Site of formation Formed by the choroid plexus situated within the ventricles. The choroid plexus are tuft of capillary projections present inside ventricles and covered by: Pia mater Ependymal covering.
Continued... Mechanism of formation Formed by process of secretion. Does not involve ultrafiltration or dialysis. Uses energy. Active transport mechanism is involved in secretion.
Continued… Substances affecting the formation of CSF Pilocarpine, ether and extracts of pituitary gland stimulates the secretion of CSF by stimulating choroid plexus. Injection of isotonic saline also stimulates CSF formation.
Continued… Injection of hypotonic saline Causes greater rise in capillary pressure and intracranial pressure, Fall in osmotic pressure leading to increase in CSF formation. Hypertonic saline Decreases CSF formation Decreases CSF pressure
Absorption of CSF Mostly absorbed by the Arachnoid villi into Dural sinuses and Spinal veins. Small amount is absorbed along the perineural spaces into cervical lymphatics and in to the perivascular spaces. Normally, 500 mL of CSF is formed everyday and equal amount is absorbed.
Mechanism of absorption of CSF By filtration due to pressure gradient between hydrostatic pressure in the subarachnoid space fluid And the pressure that exists in the Dural sinus blood. The colloidal substances pass slowly and crystalloids are absorbed rapidly.
Pressure exerted by CSF Varies in different position: Lateral recumbent position = 10-18 cm of H2O Lying position = 13 cm of H2O Sitting position = 30 cm of H2O Coughing and crying increases the pressure by decreasing the absorption. Compression of internal jugular vein also raises the CSF pressure.
Function of CSF Protective Function: Acts as buffer Protects the brain from shock If brain receives severe blow , countercoup injury may take place.
Continued… Regulation of Cranial Content Volume Is very essential because When substances are absorbed into the venous sinuses, intracranial pressure is raised, Intracranial pressure in turn interferes with the cerebral circulation causing Asphyxia. It is prevented by greater absorption of CSF to give space for increasing cranial contents.
Continued… Medium of Exchange CSF is the medium through which substances like : Nutritive substances Waste materials are exchanged between blood and brain tissues.
Collection of CSF Collected by : Cisternal puncture or Lumbar puncture In Cisternal puncture CSF is collected by passing needle between Occipital bone and Atlas, so it enters the cisterna magna.
Continued… In Lumbar puncture The Lumbar puncture needle is introduced into the subarachnoid space in the Lumbar region , between the third and fourth Lumbar spines. Uses of Lumbar puncture Collecting CSF for diagnostic purpose. Injecting drugs for spinal anesthesia, analgesia and chemotherapy. Measuring pressure exerted by CSF.
Blood–Cerebrospinal Fluid Barrier Barrier between the blood and cerebrospinal fluid . Exists at the Choroid plexus. Similar to Blood-Brain Barrier(BBB) Allows the movement of only those substances, which are allowed by BBB.
Substances which can pass through Blood-Cerebrospinal Fluid Barrier Oxygen Carbon dioxide Water Glucose Amino acids Electrolytes Drugs such as L-dopa, 5-hydroxytryptamine sulfonamides, tetracycline and other lipid soluble drugs
Continued… Anesthetic gases such as ether, nitrous oxide which are lipid soluble Other lipid soluble substances.
Substances which can’t pass through Blood-Cerebrospinal Fluid Barrier Injurious chemical agents. Pathogens such as bacteria. Drugs such as Penicillin and the Catecholamines. Dopamine also can’t pass therefore Parkinsonism is treated with L-dopa instead of dopamine.
Continued… Bile pigments However barrier is not well developed in infants. The bile pigments enter the brain tissues . During jaundice in infants, the bile pigments enter the brain and causes damage of Basal ganglia leading to Kernicterus.
CSF disorders Hydrocephalus Abnormal accumulation of CSF in the skull with enlargement of head. 2 types of Hydrocephalus 1. non-communicating 2. communicating
Continued… Non-communicating Hydrocephalus or Internal Hydrocephalus Due to the obstruction of any of the foramen through which CSF escapes results in dilation of ventricular cavity. Communicating Hydrocephalus or External Hydrocephalus Due to blockage of Arachnoid villi.
Continued… Symptoms of Hydrocephalus: Headache Vomiting Atrophy of brain Mental weakness Convulsions
Continued… Normal pressure Hydrocephalus Same as Communicating Hydrocephalus but it is due to decreased CSF absorption. Symptoms : Gait instabiltiy Urinary incontinence Dementia