Published on May 31, 2014
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/
Mitos y realidades de las sustancias psicoactivas
Mitos y realidades de las sustancias psicoactivas.
This presentation describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic ...
When your cerebral circulation is impaired, less oxygen and glucose reach your brain. This can cause brain damage and neurological problems. Some ...
NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health. Cipolla MJ. The Cerebral Circulation. San Rafael (CA): Morgan ...
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Results. Speed of cervical-cerebral circulation was routinely measured from innominate and subclavian arteries to the appearance of diatrizoate in the ...
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