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1. U N I T XI
Textbook of Medical Physiology, 11th Edition
GUYTON & HALL
Copyright © 2006 by Elsevier, Inc.
Chapter 61:
Cerebral Blood Flow, Cerebral Spinal Fluid,
and Brain Metabolism
Slides by David J. Dzielak, Ph.D.

2. Copyright © 2006 by Elsevier, Inc.
Blood Flow to the Brain
• brain is highly dependent on blood flow
• cessation of flow for 5-10 seconds results in a
loss of consciousness
• highly dependent on oxygen delivery

3. Copyright © 2006 by Elsevier, Inc.
Cerebral Blood Flow
• 15% of the resting cardiac output (750-900 ml/min)
• related to the metabolic rate of the brain
• 3 metabolic factors have potent effects on blood flow
- CO2
- H+
- O2

4. Copyright © 2006 by Elsevier, Inc.
Cerebral Blood Flow
• An increase in CO2 increases blood flow.
• This is thought to work through an increase in the
H+ ion concentration.
– CO2 + H2O H2CO3 H+ + HCO3
-
• An increase in H+ concentration depresses
neuronal activity.
• Normal PO2 35 - 40 mm Hg.
• Below 30 mm Hg begin to see increase in flow,
below 20 mm Hg coma.

5. Copyright © 2006 by Elsevier, Inc.
Cerebral Blood Flow
• cerebral blood flow is autoregulated
– nearly constant over a pressure range of 60 to
140 mm Hg
– below 60 mm Hg blood flow begins to fall
rapidly
– above 140 mm Hg the blood flow increases but
most importantly the blood vessels begin to
stretch, which can lead to damage and eventual
rupture (stroke)

6. Copyright © 2006 by Elsevier, Inc.
Cerebrospinal Fluid
• performs a cushioning function
• total volume is about 150 ml
• 500 ml are produced each day by the choroid
plexus of the ventricles of the brain
• reabsorption of this fluid occurs through the
arachnoid villi
• normal cerebrospinal fluid pressure 10 mm Hg

7. Copyright © 2006 by Elsevier, Inc.
Cerebrospinal Fluid Flow
Figure 61-4; Guyton & Hall

8. Copyright © 2006 by Elsevier, Inc.
Brain Metabolism
• highly metabolic organ
– 2% of total body mass, yet has 15% of total
metabolism of the body
• limited anaerobic metabolism
– anaerobic breakdown of glycogen cannot
supply the energy requirements of the brain
– most neuronal activity depends on the second
by second delivery of oxygen to the brain

9. Copyright © 2006 by Elsevier, Inc.
Brain Metabolism
• mostly glucose dependent
• uptake of glucose into the brain is not
dependent on insulin
• blood glucose must be maintained for the brain
to receive the proper amount of this substrate