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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
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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
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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
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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
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Cerebral Blood Flow Fig. 61.1
Fig Relationship between arterial PCO2 and cerebral blood flow
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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
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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
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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
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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
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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
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Cerebrospinal Fluid Fig Drainage of a perivascular space into the subarachnoid space
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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
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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
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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
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