Cerebral Circulation

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Information about Cerebral Circulation
Healthcare

Published on May 31, 2014

Author: ttylim

Source: slideshare.net

  Izatty Lim 0308188 SALIENT FEATURES REGULATION

 15% of cardiac output  10 seconds of interruption in blood flow leads to unconsciousness  Most neurologic disorders are due to vascular lesions

 Posterior communicating artery (part of the Circle of Willis) o Allow cross-over flow during impairment of blood flow http://www.youtube.com/watch?v=MPcO2ibO75o

 brain capillaries are surrounded by the endfeet of astrocytes  closely applied to the basal lamina of the capillaries,  do not cover the entire capillary wall  gaps of about 20 nm occur between endfeet  induce the tight junctions in the capillaries

 controlled almost entirely by local metabolites  exhibits autoregulation o between arterial pressure limits of 60 and 140 mm Hg.  many circulating vasoactive substances do not affect the cerebral circulation because their large molecular size prevents them from crossing the blood-brain barrier.

 Intracranial pressure(ICP) rises → Cerebral vessels compressed  Change in venous pressure → a similar change in ICP  Rise in venous pressure decreases cerebral blood flow by o decreasing the effective perfusion pressure o compressing the cerebral vessels  helps to compensate for changes in arterial blood pressure at the level of the head o the body is accelerated upward, blood moves toward the feet & arterial pressure at the level of the head decreases. o However, venous pressure also falls and intracranial pressure falls o so that the pressure on the vessels decreases and blood flow is much less severely compromised  Monro–Kellie doctrine

 most important local vasodilators o ↑ in cerebral Pco2 o formation of carbonic acid →dissociation → H+ o ↑ in H+ concentration = ↓ in pH o causes vasodilation of the cerebral arterioles o results in an ↑ in blood flow to remove the excess CO2.  Any other substance that ↑ the acidity of the brain tissue  ↑ hydrogen ion concentration  ↑ cerebral blood flow o lactic acid o pyruvic acid o other acidic material formed during the course of tissue metabolism.

 By ↑ the blood flow o Remove hydrogen ions, carbon dioxide, and other acid- forming  Maintain constant hydrogen ion concentration in the cerebral fluids o maintain a normal, constant level of neuronal activity.  ↑ hydrogen ion concentration greatly depresses neuronal activity.

 Oxygen deficiency (hypoxia) mechanism → vasodilation o Hypoxia-induced drop in ATP open KATP channels on smooth muscle o causing hyperpolarization and vasodilation o returning the brain blood flow o transport of oxygen to the cerebral tissues to near normal.  mechanism is almost exactly the same in the brain as in o coronary blood vessels, in skeletal muscle and in most other circulatory areas of the body

 Strong sympathetic innervation from the superior cervical sympathetic ganglia in the neck & then into the brain along with the cerebral arteries.  supplies both the large brain arteries and the arteries that penetrate into the substance of the brain.  Autoregulation mechanism can override the nervous effects.  *mean arterial pressure rises acutely to an exceptionally high level o the sympathetic nervous system constricts the large- and intermediate-sized brain arteries o prevent the high pressure from reaching smaller brain blood vessels o prevent cerebral stroke

 Textbook of Medical Physiology Eleventh Edition o By Arthur C. Guyton and John E. Hall  Ganong’s Review of Medical Physiology 23rd edition o By Kim E. Barrett, Susan M. Barman, Scott Boitano and Heddwen L. Brooks  Control of Cerebral Blood Flow o http://www.ncbi.nlm.nih.gov/books/NBK53082/

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