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Pengaturan Tekanan Darah

C h a p t e r20

2012 Pearson Education, Inc.

Mahasiswa mampu menjelaskan mekanisme pengaturan tekanan darahMahasiswa mampu menjelaskan pengaruh sistem saraf dan hormon pada jantungTujuan pembelajaran

Function of ArteriesVasoconstriction and VasodilationAffect:Afterload on heartPeripheral blood pressureCapillary blood flow

Function of ArteriesArtery Diameter Change with sympathetic or endocrine stimulationConstricted arteries oppose blood flowResistance (R)Resistance vessels - arterioles

Blood VesselsThe Distribution of BloodHeart, arteries, and capillaries3035% of blood volumeVenous system6065% 1/3 of venous blood is in the large venous networks of the liver, bone marrow, and skin

Figure 21-7 The Distribution of Blood in the Cardiovascular SystemPulmonary arteries 3%Large venousnetworks (liver,bone marrow, skin)21%Venules andmedium-sized veins25%Pulmonarycircuit 9%Heart 7%SystemicPulmonary capillaries 2%Pulmonary veins 4%Heart 7%Aorta 2%Elastic arteries 4%Systemic capillaries 7%Muscular arteries 5%Arterioles 2%Large veins18%Systemiccapillaries 7%arterialsystem13%Systemic

venous

system

64%

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21-1 Blood VesselsCapacitance of a Blood VesselThe ability to stretchRelationship between blood volume and blood pressureVeins (capacitance vessels) stretch more than arteries

21-1 Blood VesselsVenous Response to Blood LossVasomotor centers stimulate sympathetic nervesSystemic veins constrict (venoconstriction) Veins in liver, skin, and lungs redistribute venous reserve

21-2 Pressure and ResistanceTotal Capillary Blood FlowEquals cardiac outputIs determined by:Pressure (P) and resistance (R) in the cardiovascular system

Figure 21-8 An Overview of Cardiovascular PhysiologyCardiac OutputVenous ReturnRegulation(Neural and Hormonal)VenousPressureArterial BloodPressurePeripheralResistanceCapillary PressureCapillary exchangeInterstitial fluid

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21-2 Pressure and ResistancePressure (P)The heart generates P to overcome resistance Absolute pressure is less important than pressure gradientThe Pressure Gradient (P)Circulatory pressureThe difference between:Pressure at the heartAnd pressure at peripheral capillary beds

21-2 Pressure and ResistanceFlow (F) Is proportional to the pressure difference (P) Divided by R

21-2 Pressure and ResistanceMeasuring PressureBlood pressure (BP)Arterial pressure (mm Hg) Capillary hydrostatic pressure (CHP)Pressure within the capillary bedsVenous pressurePressure in the venous system

21-2 Pressure and ResistanceCirculatory PressureP across the systemic circuit (about 100 mm Hg)Circulatory pressure must overcome total peripheral resistance R of entire cardiovascular system

21-2 Pressure and ResistanceTotal Peripheral ResistanceVascular resistanceBlood viscosityTurbulence

21-2 Pressure and ResistanceVascular ResistanceDue to friction between blood and vessel wallsDepends on vessel length and vessel diameterAdult vessel length is constantVessel diameter varies by vasodilation and vasoconstrictionR increases exponentially as vessel diameter decreases

21-2 Pressure and ResistanceViscosity R caused by molecules and suspended materials in a liquidWhole blood viscosity is about four times that of water

21-2 Pressure and ResistanceTurbulence Swirling action that disturbs smooth flow of liquidOccurs in heart chambers and great vesselsAtherosclerotic plaques cause abnormal turbulence

Table 21-1 Key Terms and Relationships Pertaining to Blood Circulation

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Table 21-1 Key Terms and Relationships Pertaining to Blood Circulation

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Table 21-1 Key Terms and Relationships Pertaining to Blood Circulation

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21-2 Pressure and ResistanceAn Overview of Cardiovascular PressuresVessel diametersTotal cross-sectional areasPressuresVelocity of blood flow

Figure 21-10a Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Vesseldiameter(cm)Vessel diameter

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Figure 21-10b Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Total cross-sectional area of vesselsCross-sectionalarea(cm2)

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Figure 21-10c Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Average blood pressureAveragebloodpressure(mm Hg)

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Figure 21-10d Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Velocity of blood flowVelocityof bloodflow(cm/sec)

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21-2 Pressure and ResistanceArterial Blood PressureSystolic pressurePeak arterial pressure during ventricular systoleDiastolic pressureMinimum arterial pressure during diastole

21-2 Pressure and ResistanceArterial Blood PressurePulse pressure Difference between systolic pressure and diastolic pressure Mean arterial pressure (MAP)MAP = diastolic pressure + 1/3 pulse pressure

21-2 Pressure and ResistanceAbnormal Blood PressureNormal = 120/80HypertensionAbnormally high blood pressureGreater than 140/90Hypotension Abnormally low blood pressure

21-2 Pressure and ResistanceElastic ReboundArterial wallsStretch during systole Rebound (recoil to original shape) during diastole Keep blood moving during diastole

21-2 Pressure and ResistancePressures in Small Arteries and ArteriolesPressure and distanceMAP and pulse pressure decrease with distance from heart Blood pressure decreases with friction

21-2 Pressure and ResistanceVenous Pressure and Venous ReturnDetermines the amount of blood arriving at right atrium each minuteLow effective pressure in venous system

21-2 Pressure and ResistanceVenous Pressure and Venous ReturnLow venous resistance is assisted by:Muscular compression of peripheral veinsCompression of skeletal muscles pushes blood toward heart (one-way valves) The respiratory pumpThoracic cavity action Inhaling decreases thoracic pressureExhaling raises thoracic pressure

21-2 Pressure and ResistanceCapillary Pressures and Capillary ExchangeVital to homeostasisMoves materials across capillary walls by:DiffusionFiltrationReabsorption

21-3 Cardiovascular RegulationTissue Perfusion Blood flow through the tissuesCarries O2 and nutrients to tissues and organsCarries CO2 and wastes awayIs affected by:Cardiac outputPeripheral resistanceBlood pressure

21-3 Cardiovascular RegulationCardiovascular Regulation Changes Blood Flow to a Specific AreaAt an appropriate timeIn the right areaWithout changing blood pressure and blood flow to vital organs

Hypertension. 1991 Aug;18(2):199-210.

21-3 Cardiovascular RegulationControlling Cardiac Output and Blood PressureAutoregulationCauses immediate, localized homeostatic adjustmentsNeural mechanismsRespond quickly to changes at specific sitesEndocrine mechanismsDirect long-term changes

21-3 Cardiovascular RegulationAutoregulation of Blood Flow within TissuesAdjusted by peripheral resistance while cardiac output stays the sameLocal vasodilators accelerate blood flow at tissue levelLow O2 or high CO2 levelsLow pH (acids)Nitric oxide (NO)High K+ or H+ concentrationsChemicals released by inflammation (histamine)Elevated local temperature

21-3 Cardiovascular RegulationAutoregulation of Blood Flow within TissuesAdjusted by peripheral resistance while cardiac output stays the sameLocal vasoconstrictorsExamples: prostaglandins and thromboxanesReleased by damaged tissuesConstrict precapillary sphinctersAffect a single capillary bed

21-3 Cardiovascular RegulationNeural MechanismsCardiovascular (CV) centers of the medulla oblongataCardiac centersCardioacceleratory center increases cardiac outputCardioinhibitory center reduces cardiac output

21-3 Cardiovascular RegulationVasomotor Center Control of vasoconstriction Controlled by adrenergic nerves (NE)Stimulates smooth muscle contraction in arteriole walls Control of vasodilationControlled by cholinergic nerves (NO)Relaxes smooth muscle Vasomotor ToneProduced by constant action of sympathetic vasoconstrictor nerves

21-3 Cardiovascular RegulationReflex Control of Cardiovascular FunctionCardiovascular centers monitor arterial bloodBaroreceptor reflexesRespond to changes in blood pressureChemoreceptor reflexesRespond to changes in chemical composition, particularly pH and dissolved gases

21-3 Cardiovascular RegulationBaroreceptor ReflexesStretch 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)

21-3 Cardiovascular RegulationBaroreceptor ReflexesWhen blood pressure rises, CV centers: Decrease cardiac output Cause peripheral vasodilationWhen blood pressure falls, CV centers: Increase cardiac output Cause peripheral vasoconstriction

21-3 Cardiovascular RegulationChemoreceptor Reflexes Peripheral chemoreceptors in carotid bodies and aortic bodies monitor bloodCentral chemoreceptors below medulla oblongata:Monitor cerebrospinal fluidControl respiratory functionControl blood flow to brain

21-3 Cardiovascular RegulationChemoreceptor Reflexes Changes in pH, O2, and CO2 concentrations Produced by coordinating cardiovascular and respiratory activities

21-3 Cardiovascular RegulationCNS Activities and the Cardiovascular CentersThought processes and emotional states can elevate blood pressure by:Cardiac stimulation and vasoconstriction

21-3 Cardiovascular RegulationHormones and Cardiovascular RegulationHormones have short-term and long-term effects on cardiovascular regulationFor example, E and NE from adrenal medullae stimulate cardiac output and peripheral vasoconstriction

21-3 Cardiovascular RegulationAntidiuretic Hormone (ADH)Released by neurohypophysis (posterior lobe of pituitary) Elevates blood pressureReduces water loss at kidneysADH responds to:Low blood volumeHigh plasma osmotic concentrationCirculating angiotensin II

21-3 Cardiovascular RegulationAngiotensin II Responds to fall in renal blood pressureStimulates: Aldosterone productionADH productionThirstCardiac output and peripheral vasoconstriction

21-3 Cardiovascular RegulationErythropoietin (EPO)Released at kidneys Responds to low blood pressure, low O2 content in bloodStimulates red blood cell production

21-3 Cardiovascular RegulationNatriuretic PeptidesAtrial natriuretic peptide (ANP) Produced by cells in right atriumBrain natriuretic peptide (BNP) Produced by ventricular muscle cellsRespond to excessive diastolic stretchingLower blood volume and blood pressureReduce stress on heart