Hematocrit, plasma & serumSystemic, pulmonary circulationsPressure, flow & resistanceResistanceHeart structureHeart valve structureHeart muscle structureConducting systemConducting system propertiesCardiac action potential (ventricular muscle)Cardiac action potential (conducting tissue)Excitation contraction couplingSlide 13Excitation contraction: cardiac vs. skeletal muscleElectrocardiogramCardiac cycle1. Ventricular filling2. Isovolumetric ventricular contraction3. Ventricular ejection3. Isovolumetric ventricular relaxationRight heart mechanicsCardiac output & ejection fractionRegulation of cardiac outputRegulation of heart rate: autonomics & epinephrineSlide 25Slide 26Regulation of stroke volume: Frank-Starling effectRegulation of stroke volume: sympathetic NS & epinephrineFrank Starling vs. sympathetic/epinephrineSympathetic effects on contractionAutonomic nerves on heartSlide 32ArteriesArteries as pressure reservoirsMean arterial pressureArterial complianceArteriolesRegulation of arteriolar toneRegulation of arteriolar tone: active hyperemiaRegulation of arteriolar tone: flow autoregulationRegulation of arteriolar tone: autonomicsRegulation of arteriolar tone: hormonesCapillaries: anatomyMicrocirculation structureCapillary flow velocityFluid exchange across capillary wallFluid exchange across capillary wall (Starling forces)Starling forces: the numbersVeinsRegulation of venous return (VR) to heartRegulation of venous returnLymphBlood pressure = Cardiac output X Peripheral resistanceBaroreceptor locationBaroreceptor responseResponse to hemorrhageResponse to standing up (from lying position)Slide 58Exercise (blood flow)Exercise (cardiovascular changes)1Hematocrit, plasma & serumfig 12-1Hematocrit = volume of red cells (~45%)Plasma = fluid in fresh bloodSerum = fluid after blood has clottedPlasma = serum + fibrinogen (& other clotting factors)Normal volumes:blood ~5.5L, plasma ~3L, rbc’s ~2.5L2Systemic, pulmonary circulationsfig 12-22 hearts, each with 2 chambersLeft heart to all body except lungs (systemic)Right heart to lungs (pulmonary)Systemic arteries: oxygenated bloodPulmonary arteries: deoxygenated bloodSystemic veins: deoxygenated bloodPulmonary veins: oxygenated bloodAtria: receive blood from veinsVentricles: pump blood to arteries3Pressure, flow & resistanceflow = Δ pressure / resistance Later you will see that: blood pressure = cardiac output (flow) x peripheral resistanceIt is Δ pressure that drives flow4Resistanceresistance = 8 x  x L x r4where: = viscosity (“eta” mostly depends on hematocrit)L = length of vesselr = radius of vesselconclusion:the body regulates blood flow by altering vessel radiushalving the radius  16x resistance5Heart structurefig 12-66Heart valve structurefig 12-7atrioventricular valves: like parachutesaortic & pulmonary valves: like pockets7Heart muscle structurefig 12-9striated, branched cells, 1 nucleus/cell, connected by intercalated discsspontaneous contraction, regulated by autonomic NS, hormonescoronary blood flow regulated by active hyperemia (see later)8Conducting systemconsists of modified cardiac muscle cellsfig 12-10Sequence:sinoatrial nodeatrial pathwaysatrioventricular nodeBundle of Hisonly path to ventriclesR & L bundle branchesPurkinje fibers9Conducting system propertiesSpontaneous depolarizationall conducting system shows spontaneous depolarizationintrinsic rates:SA node (70/min), AV node (40/min), Purkinje fibers (20/min)therefore SA node sets heart rateConduction ratesslowest: AV node, ~ 100 msec delay between atrial & ventricular contractionfastest: Purkinje fibersall ventricular muscle contracts together (apex slightly ahead)10Cardiac action potential (ventricular muscle)RMP close to K+ equilibrium potentialdepolarization: Na+ channels open/inactivateplateau phase: Ca++ channels open, K+ channels closerepolarization:Ca++ channels close, K+ channels openrefractory period ~250 millisecondsvalue of plateau & refractory period:heart must relax before contracting againfig 12-1211Cardiac action potential (conducting tissue)RMP drifts to threshold (pacemaker potential)K+ channels closingfunny Na+ channels open/closeT-type Ca++ channels opendepolarization: L-type Ca++ channels openrepolarization:Ca++ channels close, K+ channels openplateau phase: Ca++ channels open, K+ channels closerepolarization:Ca++ channels close, K+ channels openrefractory period ~250 millisecondsfig 12-1312Excitation contraction couplingfig 12-1813Excitation contraction couplingL-type channel Ca++ channel acts as voltage gated channelCa++ enters cytosol from T tubulesCa++ from T tubules stimulates opening of ryanodine receptor Ca++ channelCa++ enters cytosol from sarcoplasmic reticulum  contractionfig 12-1714Excitation contraction: cardiac vs. skeletal muscleCa++ channels 1. L-type Ca++ channels (DHP receptor) in T tubule membrane 2. Ryanodine receptor Ca++ channels in wall of sarcoplasmic reticulumSkeletal muscle: L-type (DHP) Ca++ channel acts as voltage sensor (not as channel) L-type (DHP) mechanically opens ryanodine receptor channel Ca++ enters cytosol from sarcoplasmic reticulum  contractionCardiac muscle L-type channel Ca++ channel acts as voltage gated channel Ca++ enters cytosol from T tubules Ca++ from T tubules stimulates opening of ryanodine receptor Ca++ channel Ca++ enters cytosol from sarcoplasmic reticulum  contractionWhy is this important? Skeletal muscle will contract even if there is no extracellular Ca++ Ca++ channel blocking drugs (DHP derivatives):cardiac contractility, but do not  skeletal muscle strength15Electrocardiogramfig 12-14P wave: atrial depolarizationQRS complex: ventricular depolarizationT wave: ventricular repolarizationAtrial repolarization wave obscured by QRS complexnote voltage (compare with ic electrode)16Cardiac cycleSystole = contraction (~ *0.3 sec)Diastole = relaxation (~ *0.5 sec) *resting rate4 phases:1. ventricular filling (diastole)2. isovolumetric ventricular contraction (systole)3. ventricular ejection (systole)4. isovolumetric ventricular relaxation (diastole)171. Ventricular fillingAV valvesA&P valvesatrial P > ventricular P AV valves openaortic P > ventricular P A&P valves closedatrial contraction adds ~15% more blood182. Isovolumetric ventricular contractionventricular P > atrial P  AV valves closedaortic P > ventricular P  A&P valves closed1st heart sound: closing of AV valves193. Ventricular ejectionventricular P > atrial P  AV valves