1. Chapter 61: Cerebral Blood Flow, CSF, And Brain Metabolism
Unit Eleven: The Nervous System: C. Motor and Integrative Neurophysiology
Chapter 61: Cerebral Blood Flow, CSF,
And Brain Metabolism
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Cerebral Blood Flow
Cerebral Blood Flow
Blood flow to the brain is supplied by four large arteries:
two carotid and two vertebral arteries.
Merge to form the circle of Willis at the base of the brain
Arteries then travel along the surface and branch
extensively

3. Cerebral Blood Flow
Normal Rate of Cerebral Blood Flow
50-65 ml/100 g brain tissue per minute
For the entire brain, ml/min
Brain constitutes about 2% of the body weight but
receives 15% of the resting cardiac output

4. Cerebral Blood Flow
Regulation of Cerebral Blood Flow
Metabolic factors that contribute to cerebral blood flow
regulation
Carbon dioxide concentration
Hydrogen ion concentration
Oxygen concentration
Substances released from astrocytes

5. Cerebral Blood Flow Fig. 61.1
Fig Relationship between arterial PCO2 and cerebral blood flow

6. Cerebral Blood Flow
Importance of Control by Carbon Dioxide and Hydrogen Ions
Increased H+ concentration depresses neuronal activity but increases blood flow, which then carries H+ , CO2, and other acids away from the brain tissues
Loss of carbon dioxide removes carbonic acid from the tissues and reduces the hydrogen ion
concentration back toward normal

7. Cerebral Blood Flow
Oxygen Deficiency as a Regulator
a. If blood flow to the brain becomes insufficient to supply the needed amount of oxygen, vasodilation occurs returning the brain blood flow and transport of oxygen to the brain

8. Cerebral Blood Flow
Substances Released from Astrocytes- series of metabolites mediate local vasodilation
Cerebral Blood Flow Autoregulation Protects the Brain from Fluctuations in Artrial Pressure
Changes
Role of the Sympathetic Nervous System in Controlling Cerebral Blood Flow

9. Cerebral Blood Flow
Cerebral Microcirculation
The number of capillaries is greatest where the metabolic needs are the greatest
Less leaky than the blood capillaries
Supported on all sides by glial cells
Cerebral “Stroke” Occurs When Cerebral Blood Vessels are Blocked

10. Cerebrospinal Fluid
Cerebrospinal Fluid System
Cushioning function of the CSF
Formation, flow, and absorption of CSF
Secretion by the choroid plexus
Absorption through the arachnoid villi
Perivascular spaces and CSF
1. Lymphatic function

11. Cerebrospinal Fluid
Fig Drainage of a perivascular space into the
subarachnoid space

12. Cerebrospinal Fluid
Cerebrospinal Fluid Pressure
Regulation of CSF pressure by the arachnoid villi
Obstruction can cause “hydrocephalus”
Blood-CSF and Blood-Brain Barriers
Barriers exist at the choroid plexus and at the
tissue capillary membranes in all areas of the
brain except: hypothalamus and pineal gland
Exception areas: have sensory function that respond
to changes in the body as well as hormone functions

13. Cerebrospinal Fluid
Highly permeable to water, carbon dioxide, oxygen,
and most lipid soluble substances
Slightly permeable to electrolytes such as sodium,
chloride, and potassium
Brain Edema- most commonly caused by concussion
Compresses the vasculature-decreases blood flow
Decreases oxygen delivery
Increases permeability of capillaries, allowing more
leakage

14. Brain Metabolism
Total Brain Metabolic Rate and Metabolic Rate of
Neurons
Special Requirement for Oxygen-Lack of Anaerobic
Metabolism
Most Brain Energy is Supplied by Glucose