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Cardiovascular System

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Cardiovascular System Cardiovascular System BLOOD VESSELS 2 Blood Pressure Main factors influencing blood pressure: Cardiac output (CO) Peripheral resistance (PR) Blood volume Peripheral resistance is a major factor regulating BP and tissue perfusion Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2 Blood Baroreceptors Chemoreceptors volume Venous Activation of vasomotor and cardiac return acceleration centers in brain stem Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length Cardiac output Peripheral resistance Initial stimulus Physiological response Result Mean systemic arterial blood pressure Copyright © 2010 Pearson Education, Inc. Figure 19.11 Regulation of Peripheral Resistance Local control Arterioles and capillaries vary diameters = autoregulation A response to the chemical composition of the blood Faster flow = faster removal of wastes Regulation of Peripheral Resistance Local control Localized hypoxia metabolites (CO2, lactic acid, adenosine) acidic pH inhibit smooth muscle vasodilation increased blood flow Precapillary sphincters Respond to local stimuli and vasoactive hormones Endothelial cells & platelets Vasodilators NO, prostacyclin Vasoconstrictors Endothelians, seratonin, thromboxane A2 Brain Heart Skeletal muscles Skin Kidney Abdomen Other Total blood flow at rest 5800 ml/min Total blood flow during strenuous exercise 17,500 ml/min Copyright © 2010 Pearson Education, Inc. Figure 19.13 Intrinsic mechanisms Extrinsic mechanisms (autoregulation) • Maintain mean arterial pressure (MAP) • Distribute blood flow to individual • Redistribute blood during exercise and organs and tissues as needed thermoregulation Amounts of: pH Sympathetic Nerves O2 α Receptors Epinephrine, Metabolic β Receptors norepinephrine controls Amounts of: CO2 K+ Angiotensin II Hormones Prostaglandins Adenosine Antidiuretic hormone (ADH) Nitric oxide Endothelins Atrial natriuretic Myogenic Stretch peptide (ANP) controls Dilates Constricts Figure 19.15 Peripheral Resistance Example of autoregulation Blood flow to skeletal muscles During muscle activity, blood flow increases in direct proportion to the metabolic activity Blood flow can increase 10× or more during physical activity Peripheral Resistance Neural control Directed by ANS via sympathetic innervation Vascular smooth muscle lacks parasympathetic input Peripheral Resistance Neural control Vasomotor center Baroreflex Chemoreflex Ischemic reflex Peripheral Resistance Baroreflex Baroreceptors (pressure receptors) in Carotid sinuses Aortic arch Inhibitory signals sent to vasomotor center while stimulatory signals sent to cardioinhibitory center 3 Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory 4a Sympathetic center) and inhibit vasomotor impulses to heart center. cause HR, contractility, and CO. 2 Baroreceptors in carotid sinuses and aortic arch are stimulated. 4b Rate of vasomotor impulses allows vasodilation, causing R 5 CO and R 1 Stimulus: return blood Blood pressure pressure to (arterial blood homeostatic range. pressure rises above Homeostasis: Blood pressure in normal range normal range). 1 Stimulus: Blood pressure (arterial blood pressure falls below normal range). 5 CO and R return blood pressure 4b Vasomotor to homeostatic range. fibers stimulate vasoconstriction, causing R Baroreceptors 2 in carotid sinuses and aortic arch are inhibited. 4a Sympathetic impulses to heart cause HR, Impulses from baroreceptors stimulate contractility, and 3 CO. cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. Figure 19.9 Peripheral Resistance Chemoreflex Excitatory or inhibitory signals to vasomotor center Chemoreceptors are located in the Carotid bifurcation Aortic arch Large arteries of the neck Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2 Blood Baroreceptors Chemoreceptors volume Venous Activation of vasomotor and cardiac return acceleration centers in brain stem Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length Cardiac output Peripheral resistance Initial stimulus Physiological response Result Mean systemic arterial blood pressure Copyright © 2010 Pearson Education, Inc. Figure 19.11 Peripheral Resistance Medullary Ischemic Reflex Triggered by low perfusion of the medulla Hypoxia and hypercapnia vasoconstriction in extremities blood flow directed to head and upper body Peripheral Resistance Hormonal controls Angiotensin II Generated by kidney release of renin Causes vasoconstriction Atrial natriuretic peptide/factor Causes blood volume and blood pressure to decline Causes generalized vasodilation Antidiuretic hormone (ADH, vasopressin) Causes intense vasoconstriction in cases of extremely low BP Epinephrine Causes generalized vasoconstriction and increase cardiac output Arterial pressure Direct renal Indirect renal mechanism mechanism (hormonal) Baroreceptors Sympathetic stimulation promotes renin release Kidney Renin release catalyzes cascade, resulting in formation of Angiotensin II Filtration ADH release Aldosterone by posterior secretion by pituitary adrenal cortex Water Sodium reabsorption reabsorption by kidneys by kidneys Blood volume Vasoconstriction ( diameter of blood vessels) Initial stimulus Physiological response Result Arterial pressure Figure 19.10 Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2 Blood Baroreceptors Chemoreceptors volume Venous Activation of vasomotor and cardiac return acceleration centers in brain stem Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length Cardiac output Peripheral resistance Initial stimulus Physiological response Result Mean systemic arterial blood pressure Figure 19.11 Questions? 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