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Y2 s1 csf
 

Y2 s1 csf

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    Y2 s1 csf Y2 s1 csf Presentation Transcript

    • cerebrospinal fluid (CSF) Prof. Vajira Weerasinghe Dept of Physiology
    • cerebral blood flow
      • 750 ml/min (15% of cardiac output)
    • cerebrospinal fluid
      • The cavity enclosing the brain & spinal cord, and the central canal: filled with CSF
      • This fluid is in
        • ventricles
        • cisterns
        • subarachnoid space
        • central canal
    •  
    • cushioning function
      • brain is floating in the fluid
      • this provides a protective function
    • contrecoup injury
      • when there is a severe blow on the head
      • brain is lushed so that the opposite side is struk on the skull to cause an injury
      • volume of CSF
        • 150 ml
      • rate of production
        • 500 ml/day
      • formed
        • mainly in the choroid plexuses of the ventricles
        • small amounts in the ventricles, arachnoid membranes & perivascular spaces
    •  
    • formation
      • choroid plexus projects into
        • horn of lateral ventricle
        • posterior portion of 3rd ventricle
        • roof of the 4th ventricle
      • Mechanism:
        • active transport of Na through the epithelial cells, Cl follows passively
        • osmotic outflow of water
        • glucose moves in to CSF
        • K and HCO3 moved out of CSF
    • absorption
      • arachnoid villi in the walls of venous sinuses
    • circulation
      • fluid secreted in the lateral ventricles into the 3rd ventricle (secretes here)
      • pass along the aqueduct of Sylvius into the 4th ventricle
      • through foramina of Luschka & Magendie into the cisterna magna (behind the medulla)
      • subarachnoid spaces around the brain & spinal cord
      • arachnoid villi in the venous sinuses
    •  
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    • composition
      • similar to plasma
            • CSF Plasma
            • Na 147 (similar) 150 mmol/l
            • K 2.9 (less) 4.6 mmol/l
            • HCO3 25 24.8 mmol/l
            • Cl 113 (more) 99 mmol/l
            • Pco2 50 40 mmHg
            • pH 7.33 7.4
            • osmolality 289 (similar) 289 mosm
            • protein 20 (less) 6000 mg/dl
            • glucose 64 (less) 100 mg/dl
            • urea 12 (less) 15 mg/dl
      • some substances do not pass into CSF
    • blood brain barrier
      • tight junctions between capillary endothelial cells & epithelial cells in the choroid prevent some substances entering CSF
      • small molecules & lipid soluble substances pass through easily
      • blood-brain barrier exists between blood & brain tissue
      • blood-CSF barrier is present in choroid
      • these barriers are
        • highly permeable to water, CO 2 , O 2 , lipid soluble substances (such as alcohol), most anaesthetics,
        • slightly permeable to electrolytes
        • impermeable to proteins, large organic molecules
        • drugs (variable)
    • Blood brain barrier
    • blood brain barrier
          • CO 2 & O 2 crosses easily
          • H+ & HCO3- slow penetration
          • glucose
            • passive: slow penetration
            • active transport system by glucose transporter GLUT
          • Na-K-Cl transporter
          • transporters for other substances
    • blood brain barrier
        • No blood brain barrier in the hypothalamus & posterior pituitary
          • substances diffuses easily
          • these areas contain chemoreceptors for various substances to detect changes in conc
    • CSF pressure
      • lumbar CSF pressure: 70-180 mmH 2 O
      • this is regulated by absorption through arachnoid villi
      • rate of CSF formation is constant
    • CSF pressure rises
        • if the arachnoid villi are blocked by a disease process
        • brain tumour may compresses the brain and blocks the absorption
        • haemorrhage into the brain tissue can block small channels in the arachnoid villi
        • babies are born with high CSF (as in hydrocephalus) due to a defect before birth
          • blocking the aqueduct of Sylvius
          • blocking of arachnoid villi
    •  
    •  
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    • cerebral oedema
        • because brain is enclosed in a solid cranial vault, accumulation of fluid compresses brain tissue and have serious effects
        • happens due to increased capillary pressure or damage to the capillaries
        • causes
          • compresses vasculature, decreases blood flow, brain ischaemia, arteriolar dilatation, increased capillary pressure, oedema worsens
          • decreases blood flow, deceases oxygen supply, increases capillary permeability, more fluid leakage
    • Cerebral oedema
      • A 45-year-old man was brought to the emergency department by his friends
      • because of a 1-day history of a severe headache and "bizarre behavior.“
      • CT scan of his brain revealed
        • acute intracranial hemorrhage
        • with cerebral edema
        • evidence of midline shift
        • increased intracranial pressure
      • The patient was admitted to the intensive care unit (ICU)
      • young patient
      • was found belatedly after a collapse
      • secondary to drug overdose
      • Note the extensive cerebral oedema
      • with loss of normal grey-white matter differentiation.
      • The patient never regained consciousness
      • eventually died with increased intracranial pressure.
    • brain metabolism
      • brain metabolism is 15% of total metabolism of the body (although brain mass is 2% of total body mass)
      • therefore brain has an increased metabolic rate
      • this is due to increased activity of neurons (AP)
      • requires oxygen
      • brain is not capable of anaerobic metabolism
      • energy supply is by glucose
      • glucose entry is not controlled by insulin
    • Lumbar puncture
      • This is the method of obtaining access to the subarachnoid space This is done for the following purposes
        • To obtain CSF for examination
        • To estimate CSF pressure
      • Patient lying on one side
      • LP needle is inserted between 3 rd and 4 th or 4 th and 5 th lumbar spinous processes
      • Fluid is withdrawn
      • Manometer is connected and pressure measured
    • Lumbar puncture