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This 8 page Class Notes was uploaded by Jess Graff on Tuesday March 1, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 29 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 03/01/16
BMS 508.03 2/29/16 Chapter 20 (cont) Blood Vessels and Circulation (cont) Cardiovascular Regulation • Tissue Perfusion • Blood flow through the tissues • Carries O 2nd nutrients to tissues and organs • Carries CO a2d wastes away • Affected by: • Cardiac output • Peripheral resistance • Blood pressure • Cardiovascular Regulation Changes Blood Flow to a Specific Area • At an appropriate time • In the right area • Without changing blood pressure and blood flow to vital organs • Controlling Cardiac Output and Blood Pressure • Autoregulation • Causes immediate, localized homeostatic adjustments • Neural mechanisms • Respond quickly to changes at specific sites • Endocrine mechanisms • Direct long-term changes • Autoregulation of Blood Flow within Tissues • Adjusted by peripheral resistance while cardiac output stays the same • Local vasodilators accelerate blood flow at tissue level • Low O o2 high CO leve2s • Low pH (acids) • Nitric oxide (NO) • High K or H concentrations • Chemicals released by inflammation (histamine) • Elevated local temperature • Local vasoconstrictors • Examples: prostaglandins and thromboxanes • Released by damaged tissues • Constrict precapillary sphincters • Affect a single capillary bed • Neural Mechanisms • Cardiovascular (CV) centers of the medulla oblongata • Cardiac centers • Cardioacceleratory center increases cardiac output • Cardioinhibitory center reduces cardiac output • Vasomotor Center • Control of vasoconstriction • Controlled by adrenergic nerves (NE) • Stimulates smooth muscle contraction in arteriole walls • Control of vasodilation • Controlled by cholinergic nerves (NO) • Relaxes smooth muscle • Vasomotor Tone • Produced by constant action of sympathetic vasoconstrictor nerves • Reflex Control of Cardiovascular Function • Cardiovascular centers monitor arterial blood • Baroreceptor reflexes • Respond to changes in blood pressure • Chemoreceptor reflexes • Respond to changes in chemical composition, particularly pH and dissolved gases • Baroreceptor Reflexes • Stretch receptors in walls of: • Carotid sinuses (maintain blood flow to brain) • Aortic sinuses (monitor start of systemic circuit) • Right atrium (monitors end of systemic circuit) • When blood pressure rises, CV centers: • Decrease cardiac output • Cause peripheral vasodilation • When blood pressure falls, CV centers: • Increase cardiac output • Cause peripheral vasoconstriction • Chemoreceptor Reflexes • Peripheral chemoreceptors in carotid bodies and aortic bodies monitor blood • Central chemoreceptors below medulla oblongata • Monitor cerebrospinal fluid • Control respiratory function • Control blood flow to brain • Changes in pH, O , an2 CO concen2rations • Produced by coordinating cardiovascular and respiratory activities • CNS Activities and the Cardiovascular Centers • Thought processes and emotional states can elevate blood pressure by: • Cardiac stimulation and vasoconstriction • Hormones and Cardiovascular Regulation • Hormones have short-term and long-term effects on cardiovascular regulation • Example: E and NE from adrenal medullae stimulate cardiac output and peripheral vasoconstriction • Antidiuretic Hormone (ADH) • Released by neurohypophysis (posterior lobe of pituitary) • Elevates blood pressure • Reduces water loss at kidneys • ADH responds to: • Low blood volume • High plasma osmotic concentration • Circulating angiotensin II • Angiotensin II • Responds to fall in renal blood pressure • Stimulates: • Aldosterone production • ADH production • Thirst • Cardiac output and peripheral vasoconstriction • Erythropoietin (EPO) • Released at kidneys • Responds to low blood pressure, low O content 2n blood • Stimulates red blood cell production • Natriuretic Peptides • Atrial natriuretic peptide (ANP) • Produced by cells in right atrium • Brain natriuretic peptide (BNP) • Produced by ventricular muscle cells • Respond to excessive diastolic stretching • Lower blood volume and blood pressure • Reduce stress on heart Cardiovascular Adaptation • Blood, Heart, and Cardiovascular System • Work together as unit • Respond to physical and physiological changes (for example, exercise and blood loss) • Maintain homeostasis • The Cardiovascular Response to Exercise • Light Exercise • Extensive vasodilation occurs, increasing circulation • Venous return increases with muscle contractions • Cardiac output rises • Venous return (Frank–Starling principle) • Atrial stretching • Heavy Exercise • Activates sympathetic nervous system • Cardiac output increases to maximum • About four times resting level • Restricts blood flow to “nonessential” organs (e.g., digestive system) • Redirects blood flow to skeletal muscles, lungs, and heart • Blood supply to brain is unaffected • Exercise, Cardiovascular Fitness, and Health • Regular moderate exercise • Lowers total blood cholesterol levels • Intense exercise • Can cause severe physiological stress • The Cardiovascular Response to Hemorrhaging • Entire cardiovascular system adjusts to: • Maintain blood pressure • Restore blood volume • Short-Term Elevation of Blood Pressure • Carotid and aortic reflexes • Increase cardiac output (increasing heart rate) • Cause peripheral vasoconstriction • Sympathetic nervous system • Triggers hypothalamus • Further constricts arterioles • Venoconstriction improves venous return • Hormonal effects • Increase cardiac output • Increase peripheral vasoconstriction (E, NE, ADH, angiotensin II) • Shock • Short-term responses compensate after blood losses of up to 20% of total blood volume • Failure to restore blood pressure results in shock • Long-Term Restoration of Blood Volume • Recall of fluids from interstitial spaces • Aldosterone and ADH promote fluid retention and reabsorption • Thirst increases • Erythropoietin stimulates red blood cell production • Vascular Supply to Special Regions • Through organs with separate mechanisms to control blood flow • 3 important examples • Brain • Heart • Lungs • Blood Flow to the Brain • Top priority • Brain has high oxygen demand • When peripheral vessels constrict, cerebral vessels dilate, normalizing blood flow • Stroke • Also called cerebrovascular accident (CVA) • Blockage or rupture in a cerebral artery • Stops blood flow • Blood Flow to the Heart • Through coronary arteries • Oxygen demand increases with activity • Lactic acid and low O lev2ls • Dilate coronary vessels • Increase coronary blood flow