Nervous Regulation of the Circulation - Guyton and Hall Physiology PDF

Nervous Regulation of the Circulation General Overview Local Tissue Control Mechanisms: Main function for adjusting blood flow in tissues and organs. Nervous Control: More global functions, including: Redistributing blood flow Modulating heart pumping activity...

Nervous Regulation of the Circulation General Overview Local Tissue Control Mechanisms: Main function for adjusting blood flow in tissues and organs. Nervous Control: More global functions, including: Redistributing blood flow Modulating heart pumping activity Rapid control of systemic arterial pressure Autonomic Nervous System (ANS) Sympathetic Nervous System (SNS) Primary Role: Regulating circulation. Pathways: 1. Sympathetic Nerves: Innervate internal viscera and heart. 2. Peripheral Spinal Nerves: Distributed to peripheral areas. Innervation of Blood Vessels: Innervated Vessels: All except capillaries. Small Arteries and Arterioles: Increase resistance, decreasing blood flow. Veins: Sympathetic stimulation decreases volume, aiding heart pumping. Parasympathetic Nervous System (PNS) Role: Minor in vascular function; significant in heart rate control (via vagus nerves). Effects: Decreases heart rate and slight reduction in contractility. Control Centers in the Brain Vasomotor Center Location: Reticular substance in the medulla and lower third of the pons. Functions: Parasympathetic impulses to the heart. Sympathetic impulses to arteries, arterioles, and veins.  Areas Identified: 1. Vasoconstrictor Area: Upper medulla, excites vasoconstrictor neurons. 2. Vasodilator Area: Lower medulla, inhibits vasoconstrictor activity. 3. Sensory Area: Nucleus tractus solitarius, reflex control of circulatory functions. Sympathetic Vasoconstrictor System Fibers: Predominantly vasoconstrictor with fewer vasodilator fibers. Powerful Effect Areas: Kidneys, intestines, spleen, and skin. Sympathetic Tone: Continuous firing maintaining partial vessel constriction (vasomotor tone). Nervous Regulation of Arterial Pressure Sympathetic Stimulation: Increases heart rate and contractility. Constricts veins, increasing blood volume to the heart. Directly stimulates the heart. Increases During Exercise Heavy Exercise: Local vasodilation and nervous system-induced arterial pressure rise. Alarm Reaction: Sharp pressure increase during stress (e.g., fright). Reflex Mechanisms Baroreceptor Reflex Function: Maintains near-normal arterial pressure. Location: Carotid sinus and aortic arch. Mechanism: Stretch receptors detect arterial pressure changes. Signals sent to CNS, reducing arterial pressure. Response to Pressure Changes: Rapid firing during high pressure to induce relaxation (vasodilation). Slow firing during low pressure to induce constriction and increased cardiac output. Chemoreceptor Reflex Function: Responds to low oxygen, high CO2, and H+ levels. Location: Carotid and aortic bodies. Mechanism: Stimulates vasomotor center to elevate arterial pressure during low blood pressure situations. Atrial and Pulmonary Artery Reflexes Low-Pressure Receptors: Minimize pressure changes from blood volume changes. Volume Reflex: Responds to increased atrial pressure, adjusting kidney functions to regulate fluid volume. Bainbridge Reflex: Increases heart rate in response to elevated atrial pressure and increased blood volume. CNS Ischemic Response Emergency Mechanism: Activated by severe blood flow decrease to the brain. Result: Sharp elevation in arterial pressure to ensure blood flow to the brain. Cushing Reaction: Special case where cerebrospinal fluid pressure compresses brain arteries, triggering a rise in arterial pressure. Skeletal Muscle Contribution Abdominal Compression Reflex: Increases cardiac output by compressing abdominal vessels. Muscle Contraction during Exercise: Enhances cardiac output and arterial pressure by relocating blood from peripheral vessels to the heart. Respiratory Waves in Arterial Pressure Mechanism: Arterial pressure rises and falls with respiratory cycles due to changes in thoracic pressures and cardiac output.