1.  
Izatty Lim
0308188
SALIENT FEATURES REGULATION

2.  15% of cardiac output
 10 seconds of interruption in blood flow leads to
unconsciousness
 Most neurologic disorders are due to vascular lesions

3.  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

4.  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

5.  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.

7.  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

8.  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.

9.  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.

10.  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

11.  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

12.  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/