Unit Four: The Circulation
Chapter 18: Nervous Regulation of the Circulation, and Rapid Control of Arterial
Pressure
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Autonomic Nervous System
• Sympathetic Nervous System
a. Sympathetic innervation of the blood vessels
b. Sympathetic nerve fibers to the heart
c. Sympathetic vasoconstrictor system
• Parasympathetic Control of Heart Function
Autonomic Nervous System
• Sympathetic Nervous System
Fig. 18.1
Autonomic Nervous System
• Sympathetic Nervous System
Fig. 18.2 Sympathetic innervation of the systemic circulation
ANS (cont.)
• Vasomotor Center in the Brain and its Control of the Vasoconstrictor System
a. Located bilaterally in the reticular substance of the medulla and lower third of the pons; contains
1. vasoconstrictor area2. vasodilator area3. sensory area
Fig. 18.3 Areas of the brain that play important roles in the nervous regulation of the circulation. Dashed lines represent inhibitory pathways.
ANS (cont.)
• Continuous partial constriction of the blood vessels is normally caused by sympatheticvasoconstriction (Fig. 18.4)
• Control of heart activity by the vasomotor center
• Control of the vasomotor center by higher nervecenters (Fig. 18.3)
• Norepinephrine-the vasoconstrictor substance
Fig. 18.4 Effect of total spinal anesthesia on the arterial pressure, showing marked decrease in pressure resulting from loss of “vasomotor” tone
Role of the Nervous System in Rapid Control of Arterial Pressure
• Most arterioles of the systemic circulation are constricted
• The veins are especially strongly constricted
• The heart is directly stimulated by the ANS,further enhancing cardiac pumping
Role of the Nervous System in Rapid Control of Arterial Pressure
• Rapidity of Nervous Control of Arterial Pressure
a. Increase in arterial pressure during muscle exerciseand other types of stress
• Reflex Mechanism for Maintaining Normal Arterial Pressure
• Baroreceptor Reflexes
Baroreceptor Reflexes
• Physiological Anatomy and Innervation
Fig. 18.5
Baroreceptor Reflexes (cont.)
• Response to Arterial Pressure
Fig. 18.6
Baroreceptor Reflexes (cont.)
• Circulatory Reflex Initiated by Baroreceptors
a. Vasodilation of the veins and arterioles
b. Decreased heart rate and strength of contraction
Fig. 18.7 Typical carotid sinus reflex effect on aortic arterial pressure by clamping both common carotid arteries
Baroreceptor Reflexes (cont.)
• Functions of the Baroreceptors During Changes inBody Posture
• Pressure “Buffer” Function of the Baroreceptor Control System
Baroreceptor Reflexes (cont.)
Fig. 18.8 Two hour records of arterial pressure in a normal dog and in the same dog several weeks after the baroreceptors have been denerved
Baroreceptor Reflexes (cont.)
Fig. 18.9 Frequency distribution curves of the arterial pressure for a 24 hr period in a normal dog and in the same dog several weeks after the baroreceptors have been denerved
Baroreceptors (cont.)
• Control of Arterial Pressure by the Carotid andAortic Chemoreceptors
a. Effect of the lack of oxygen on arterial pressure
• Atrial and Pulmonary Artery Reflexes RegulateArterial Pressure
• Atrial Reflexes That Activate the Kidneys- thevolume reflex
• Atrial Reflex Control of Heart Rate- theBainbridge Reflex
CNS Ischemic Response
• Control of Arterial Pressure by the Brain’sVasomotor Center in Response to DiminishedBrain Blood Flow
a. Importance of the CNS ischemic response as a regulator of arterial pressure
b. Cushing Reaction to increased pressure aroundthe brain
Nervous Control of Arterial Pressure
• Abdominal Compression Reflex
• Increased Cardiac Output and Arterial PressureCaused by Skeletal Muscle ContractionDuring Exercise
• Respiratory Waves in the Arterial Pressure
• Arterial Pressure “Vasomotor” Waves
a. Oscillation of the baroreceptor and chemoreceptorreflexes
b. Oscillation of the CNS ischemic response
