Blood Pressure Dynamics PDF

BLOOD PRESSURE DYNAMICS Dr. Samantha Solecki, DC, MS Instructor, Biology Thinker. Learner. Motivator. Lover of Anatomy & Physiology [email protected] © 2019 Pearson Education, Inc.1 Learning Objectives...

BLOOD PRESSURE DYNAMICS Dr. Samantha Solecki, DC, MS Instructor, Biology Thinker. Learner. Motivator. Lover of Anatomy & Physiology [email protected] © 2019 Pearson Education, Inc.1 Learning Objectives 2 *Acquired from the Human Anatomy and Physiology Society (HAPS) with personal additions  Define blood flow, blood pressure and peripheral resistance.  State and interpret the equation that relates blood flow to pressure and resistance.  List the local, hormonal and neuronal factors that affect peripheral resistance and explain the importance of each.  Interpret relevant graphs to explain the relationships between vessel diameter, cross-sectional area, blood pressure and blood viscosity.  Using a graph of pressures within the systemic circuit, interpret the pressure changes that occur in the arteries, capillaries and veins.  Given values for systolic and diastolic blood pressure, calculate pulse pressure (PP) and mean arterial pressure (MAP).  With respect to regulation of blood pressure:  During the baroreceptor reflex, explain how cardiac output and peripheral resistance are regulated to maintain adequate blood pressure on a moment-to-moment basis.  During the chemoreceptor reflex, explain how the respiratory and cardiovascular systems are coordinated to provide flow and oxygen to body tissues.  Explain the role of the sympathetic nervous system in regulation of blood pressure and volume  Provide specific examples to demonstrate how the cardiovascular system responds to maintain homeostasis in the body.  Explain how the cardiovascular system relates to other body systems to maintain homeostasis.  3 CIRCULATION  4 Physiology of Circulation: Definition of Terms  Blood flow  Volume of blood flowing through vessel, organ, or entire circulation in given period  Measured as ml/min  Equivalent to cardiac output (CO) for entire vascular system  Relatively constant when at rest  Varies widely through individual organs, based on needs  5 Physiology of Circulation: Definition of Terms  Blood pressure (BP)  Force per unit area exerted on wall of blood vessel by blood  Expressed in mm Hg  Measured as systemic arterial BP in large arteries near heart  Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas Physiology of Circulation: 6 Definition of Terms  Resistance (peripheral resistance)  Opposition to flow  Measure of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation  Three important sources of resistance 1.Blood viscosity 2.Total blood vessel length 3.Blood vessel diameter  7 Resistance  Factors that remain relatively constant:  Blood viscosity  The "stickiness" of blood due to formed elements and plasma proteins  Increased viscosity = increased resistance  Blood vessel length  Longer vessel = greater resistance encountered  Blood vessel diameter  Greatest influence on resistance  Frequent changes alter peripheral resistance  Varies inversely with fourth power of vessel radius  E.g., if radius is doubled, the resistance is 1/16 as much  E.g., Vasoconstriction  increased resistance  8 Resistance  Small-diameter arterioles major determinants of peripheral resistance  Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance  Disrupt laminar flow and cause turbulent flow  Irregular fluid motion  increased resistance  9 Relationship Between Blood Flow, Blood Pressure, and Resistance  Blood flow (F) directly proportional to blood pressure gradient ( P)  If  P increases, blood flow speeds up  Blood flow inversely proportional to peripheral resistance (R)  If R increases, blood flow decreases: F =  P/R  R more important in influencing local blood flow because easily changed by altering blood vessel diameter  1 0 Review...  Define blood flow.  Identify what factors effect resistance.  Explain what blood pressure is.  1 1 BLOOD PRESSURE  1 2 Systemic Blood Pressure  Pumping action of heart generates blood flow  Pressure results when flow is opposed by resistance  Systemic pressure  Highest in aorta  Declines throughout pathway  0 mm Hg in right atrium  Steepest drop occurs in arterioles  Figure 19.6 Blood pressure in various blood vessels of the systemic circulation. 1 3 120 Blood pressure (mm Hg) Systolic pressure 100 Mean pressure 80 60 Diastolic 40 pressure 20 0 es ies les ies ae i ns rta i ol av lar nu ter Ao Ve ter ec pil Ve Ar Ar na Ca Ve  1 4 Arterial Blood Pressure  Reflects two factors of arteries close to heart  Elasticity (compliance or distensibility)  Volume of blood forced into them at any time  Blood pressure near heart is pulsatile  1 5 Arterial Blood Pressure  Systolic pressure: pressure exerted in aorta during ventricular contraction  Averages 120 mm Hg in normal adult  Diastolic pressure: lowest level of aortic pressure  Pulse pressure = difference between systolic and diastolic pressure  Throbbing of arteries (pulse)  1 6 Arterial Blood Pressure  Mean arterial pressure (MAP): pressure that propels blood to tissues  MAP = diastolic pressure + 1/3 pulse pressure  Pulse pressure and MAP both decline with increasing distance from heart  Ex. BP = 120/80; MAP = 93 mm Hg  1 7 Capillary Blood Pressure  Ranges from 17 to 35 mm Hg  Low capillary pressure is desirable  High BP would rupture fragile, thin-walled capillaries  Most very permeable, so low pressure forces filtrate into interstitial spaces  1 8 BLOOD PRESSURE MAINTENANCE  1 9 Maintaining Blood Pressure  Requires  Cooperation of heart, blood vessels, and kidneys  Supervision by brain  Main factors influencing blood pressure 1.Cardiac output (CO) 2.Peripheral resistance (PR) 3.Blood volume  2 0 Maintaining Blood Pressure  F =  P/R; CO =  P/R;  P = CO × R  Blood pressure = CO × PR (and CO depends on blood volume)  Blood pressure varies directly with CO, PR, and blood volume  Changes in one variable quickly compensated for by changes in other variables Figure 19.8 Major factors enhancing cardiac output. 2 1 Exercise BP activates cardiac centers in medulla Activity of respiratory pump Sympathetic activity Parasympathetic activity (ventral body cavity pressure) Activity of muscular pump (skeletal muscles) Epinephrine in blood Sympathetic venoconstriction Venous return Contractility of cardiac muscle EDV ESV Stroke volume (SV) Heart rate (HR) Initial stimulus Physiological response Result Cardiac output (CO = SV x HR)  2 2 BLOOD PRESSURE CONTROL Regulation of Blood 2 Pressure 3  Recall that CO = SV × HR, so if MAP = CO × R, then MAP  SV HR R  Anything that increases SV, HR, or R will also increase MAP  SV is effected by venous return (EDV)  HR is maintained by medullary centers  R is effected mostly by vessel diameter  2 4 Control of Blood Pressure 1. Short-term neural and hormonal controls  Counteract fluctuations in blood pressure by altering peripheral resistance and CO  Hormonal  Water-soluble hormones  Neural Controls  Baroreceptor Reflexes  Chemoreceptor Reflexes 2. Long-term renal regulation  Counteracts fluctuations in blood pressure by altering blood volume  Hormonal  Steroid hormones  2 5 Major Factors That Increase MAP Figure 19.10 Major factors that increase MAP.  2 6 The Cardiovascular Center  Clusters of sympathetic neurons in medulla oversee changes in CO and blood vessel diameter  Consists of cardiac centers and vasomotor center  Vasomotor center sends steady impulses via sympathetic efferents to blood vessels  moderate constriction called vasomotor tone  Receives inputs from baroreceptors, chemoreceptors, and higher brain centers Short-term Mechanisms: 2 7 Baroreceptor Reflexes  Baroreceptors located in  Carotid sinuses  Aortic arch  Walls of large arteries of neck and thorax  Increased blood pressure stimulates baroreceptors to increase input to vasomotor center  Inhibits vasomotor and cardioacceleratory centers, causing arteriolar dilation and venodilation  Stimulates cardioinhibitory center   decreased blood pressure Figure 19.9 Baroreceptor reflexes that help maintain blood pressure homeostasis. Slide 1 3 Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor 2 center. 8 4a Sympathetic impulses to heart cause HR, contractility, and CO. 2 Baroreceptors in carotid sinuses and aortic arch are stimulated. 4b Rate of vasomotor impulses allows vasodilation, IMB causing R. ALA 5 CO and R 1 Stimulus: NC return blood E Blood pressure pressure to (arterial blood homeostatic range. pressure rises above Homeostasis: Blood pressure in normal range normal range). 1 Stimulus: Blood pressure IMB (arterial blood ALA pressure falls below NC E normal range). 5 CO and R return blood pressure to 4b Vasomotor homeostatic range. fibers stimulate vasoconstriction, causing R. 2 Baroreceptors in carotid sinuses and aortic arch are inhibited. 4a Sympathetic impulses to heart cause HR, contractility, and 3 Impulses from baroreceptors CO. activate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center.  2 Short-term Mechanisms: 9 Hormonal Controls  Cause increased blood pressure  Epinephrine and norepinephrine from adrenal gland  increased CO and vasoconstriction  Angiotensin II stimulates vasoconstriction  High ADH levels cause vasoconstriction  Cause lowered blood pressure  Atrial natriuretic peptide causes decreased blood volume by antagonizing aldosterone  3 Effects of Selected 0 Hormones on Blood Pressure Table 19.2 Effects of Selected Hormones on Blood Pressure Long-term Mechanisms: 3 1 Renal Regulation  Baroreceptors (short-term) quickly adapt to chronic high or low BP so are ineffective  Long-term mechanisms control BP by altering blood volume via kidneys  Kidneys regulate arterial blood pressure 1. Direct renal mechanism 2. Indirect renal (renin-angiotensin-aldosterone) mechanism Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure. Direct renal mechanism Indirect renal mechanism (renin-angiotensin-aldosterone) 3 Arterial pressure Arterial pressure Initial stimulus Physiological response 2 Result Inhibits baroreceptors Sympathetic nervous system activity Filtration by kidneys Angiotensinogen Renin release from kidneys Angiotensin I Angiotensin converting enzyme (ACE) Angiotensin II Urine formation ADH release by Thirst via Vasoconstriction; Adrenal cortex posterior pituitary hypothalamus peripheral resistance Secretes Aldosterone Blood volume Sodium reabsorption Water reabsorption Water intake by kidneys by kidneys Blood volume Mean arterial pressure Mean arterial pressure Figure 19.11 Factors that increase MAP. Activity of muscular Release of ANP Fluid loss from hemorrhage, Crisis stressors: exercise, trauma, Vasomotor tone; bloodborne Dehydration, high hematocrit Body size 3 pump and excessive body chemicals 3 respiratory sweating temperature (epinephrine, pump NE, ADH, angiotensin II) Conservation Blood volume Blood pH of Na+ and Blood pressure O2 water by kidneys CO2 Blood Baroreceptors Chemoreceptors volume Venous Activation of vasomotor and cardio- return acceleratory centers in brain stem Diameter of Blood Blood vessel Stroke Heart blood vessels viscosity length volume rate Cardiac output Peripheral resistance Initial stimulus Physiological response Result Mean arterial pressure (MAP)  3 4 CIRCULATORY EFFICIENCY  3 5 Monitoring Circulatory Efficiency  Vital signs: pulse and blood pressure, along with respiratory rate and body temperature  Pulse: pressure wave caused by expansion and recoil of arteries  Radial pulse (taken at the wrist) routinely used  Pressure points where arteries close to body surface  Can be compressed to stop blood flow  3 6 Measuring Blood Pressure  Systolic pressure, normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery  Diastolic pressure, normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely  3 7 Variations in Blood Pressure  Transient elevations occur during changes in posture, physical exertion, emotional upset, fever.  Age, sex, weight, race, mood, and posture may cause BP to vary  3 8 Review...  Identify the three factors that influence blood pressure.  What short term controls are in place to balance BP?  Identify the difference between the direct and indirect renal mechanisms for long-term BP control.