Dr Mohammed Jeelani Specific learning outcomes Explain the blood brain barrier Mention the normal volume of cerebral blood flow Describe the autoregulation of cerebral blood flow Describe the metabolic regulation of cerebral blood flow ID: 1007234
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1. Cerebral blood flow & blood-brain barrierDr Mohammed Jeelani
2. Specific learning outcomesExplain the blood- brain barrier.Mention the normal volume of cerebral blood flowDescribe the autoregulation of cerebral blood flowDescribe the metabolic regulation of cerebral blood flowExplain the role of intracranial pressure in the regulation of cerebral blood flow
3. Blood- Brain BarrierRestricts the movement of large molecules and highly charged ionsFormed : CNS capillary endothelial cells, their intercellular junctions and lack of vesicular transportSubstances crossed are not lipid soluble (specific carrier-mediated transport system)
4. Some areas of the brain do not have a BBBPosterior pituitary and circumventricular organs. Isolated from the rest of the brain by specialized ependymal cells called tanycytes.
5. Disruption of blood–brain barrier Brain tumours and Bacterial meningitis. Detected : radiologically
6. Normal cerebral blood flowIn an adult averages 50–65 mL/100 g, or about 750–900 mL/min. Brain receives approximately 15% of the total resting cardiac output
7. REGULATION OF CEREBRAL BLOOD FLOWFactors which affect the cerebral blood flow are:Arterial blood pressureIntracranial pressureResistance, i.e. viscosity of the bloodDiameter of the cerebral blood vessels
8. Metabolic regulationThe important metabolic factors which play important role are:(i) Carbon dioxide.(ii) pO2.(iii) K+ ions.
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10. Autoregulation of cerebral blood flow60 and 140 mm Hg blood pressure below 60 mm Hg extremely compromised and syncopeabove 140 mm Hgdisruption of blood–brain barrier and cerebral oedema or cerebral haemorrhage
11. Role of intracranial pressure in regulation ofcerebral blood flowMonro-Kellie doctrine: the brain, CSF and blood in the cerebral vessels are three elements enclosed in a rigid cranial cavity and when any of them increases, it is at the expense of other Helps to maintain the cerebral blood flow when changes in the arterial blood pressure occur at the level of head.
12. (ii) Cushing reflex: When intracranial pressure is increased and becomes equal to the arterial pressure, it compresses the arteries in the brain and blood supply to vasomotor area is compromised. The hypoxia and hypercapnia produced increases the discharge from VMCThe resultant rise in a systemic pressure tends to restore the cerebral blood flow
13. Nervous regulation of cerebral blood flowInnervated by the noradrenergic vasoconstrictor fibres and cholinergic vasodilator fibres. Normal Conditions :do not regulate the cerebral blood flow. In severe hypertension: vasoconstriction In severe hypotension: vasodilation
14. ReferenceIndu khurana. Medical physiology for UG, 1st edition, Elsevier publication chapter 4.6 page 272-273, chapter 10.6 page 775-776