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Blood brain barrier

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  • 1. MICROENVIRONMENT OF NEURONS- REVIEW OF BLOOD BRAIN BARRIER & IMPORTANT RK GOIT, LECTURER DEPARTMENT OF PHYSIOLOGY
  • 2. Cerebral blood flow • the principal arterial inflow to the brain in human is via four arteries: two internal carotids & two vertebrals • blood flow to the brain is about 750 ml/min (15% of the cardiac output) • cerebral blood flow is 50ml/100g/min of brain tissue • three metabolic factors have potent effects in controlling cerebral blood flow: • CO2 concentration • H+ concentration • O2 concentration
  • 3. Autoregulation of cerebral blood flow • cerebral blood flow is “autoregulated” extremely well between arterial pressure limits of 60 & 140 mm Hg
  • 4. Cerebral microcirculation • the number of blood capillaries in the brain is greatest where the metabolic needs are greatest • the number of capillaries & rate of blood flow are about four times as great as that of white matter in the gray matter • brain capillaries are much less “leaky” than the blood capillaries in almost any other tissue of the body • the capillaries are supported on all sides by “glial feet,” & provide physical support to prevent overstretching of the capillaries
  • 5. Cerebrospinal fluid • a clear, colorless, almost protein free filtrate of blood • volume is about 150 ml & rate of production is 550ml/d • 50-70% of the CSF is formed in the choroid plexuses & the remainder is formed around blood vessel & along ventricular walls • is present around the brain & spinal cord (in the subarachnoid space) as well as inside the brain & spinal cord (in its ventricles & the central canal respectively) • all these chambers are connected with one another, & the pressure of the fluid is maintained at a constant level
  • 6. Functions of CSF 1. Mechanical protection • serves as a cushion between the CNS & surrounding bones, thus protecting it against mechanical trauma • also buoys the brain so that it “floats” in cranial cavity 2. Homeostatic function • pH of the CSF affects pulmonary ventilation & cerebral blood flow • CSF also serves as a transport system for polypeptide hormones secreted by hypothalamic neurons 3. Circulation • CSF is a medium for minor exchange of nutrients & waste products between the blood & adjacent nervous tissue
  • 7. Formation CSF is formed mainly in the choroid plexuses of the lateral, third, & fourth ventricles; some originates from the ependymal cells lining the ventricles & from the brain substance through the perivascular spaces
  • 8. Absorption some of the CSF is absorbed directly into the veins in the subarachnoid space, & some escapes through the perivascular spaces into the subarachnoid spaces
  • 9. • brain requires a very stable environment in order to function normally • barriers, called the blood-cerebrospinal fluid barrier & the blood-brain barrier, exist between the blood & cerebrospinal fluid & brain fluid, respectively (except in some areas of the hypothalamus, pineal gland & area postrema) • barriers are highly permeable to water, carbon dioxide, oxygen, & most lipid-soluble substances; slightly permeable to electrolytes; & almost totally impermeable to plasma proteins & most non–lipid-soluble large organic molecules
  • 10.

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