Cardiac MuscleCardiac Muscle

Found only in Found only in heartheart StriatedStriated Each cell usually has Each cell usually has one nucleusone nucleus Has intercalated disks and gap junctionsHas intercalated disks and gap junctions AutorhythmicAutorhythmic cells cells Action potentials of longer duration and Action potentials of longer duration and

longer refractory periodlonger refractory period CaCa2+2+ regulates contraction regulates contraction

Cardiac MuscleCardiac Muscle

Elongated, branching cells containing 1-2 centrally located nucleiElongated, branching cells containing 1-2 centrally located nuclei Contains actin and myosin myofilaments Contains actin and myosin myofilaments Intercalated disksIntercalated disks: Specialized cell-cell contacts: Specialized cell-cell contacts Desmosomes hold cells together and gap junctions allow action Desmosomes hold cells together and gap junctions allow action

potentialspotentials Electrically, cardiac muscle behaves as single unitElectrically, cardiac muscle behaves as single unit

Cardiac myocyte action Cardiac myocyte action potential:potential:

Refractory PeriodRefractory Period

AbsoluteAbsolute: Cardiac muscle cell : Cardiac muscle cell completely insensitive to further completely insensitive to further stimulationstimulation

RelativeRelative: Cell exhibits reduced : Cell exhibits reduced sensitivity to additional stimulationsensitivity to additional stimulation

Long refractory period prevents Long refractory period prevents tetanic contractionstetanic contractions

AP-contraction AP-contraction relationship:relationship:

AP in skeletal muscle is AP in skeletal muscle is very short-livedvery short-lived AP is basically over before AP is basically over before

an increase in muscle an increase in muscle tension can be measured.tension can be measured.

AP in cardiac muscle is AP in cardiac muscle is very long-livedvery long-lived AP has an extra AP has an extra

component, which extends component, which extends the duration.the duration.

The contraction is almost The contraction is almost over before the action over before the action potential has finished.potential has finished.

Functions of the HeartFunctions of the Heart Generating Generating bloodblood pressure pressure Routing Routing bloodblood

Heart separates pulmonary and Heart separates pulmonary and systemic circulationssystemic circulations

Ensuring one-way Ensuring one-way bloodblood flow flow Heart valves ensure one-way flowHeart valves ensure one-way flow

Regulating Regulating bloodblood supply supply Changes in contraction rate and Changes in contraction rate and

force match blood delivery to force match blood delivery to changing metabolic needschanging metabolic needs

Orientation of cardiac Orientation of cardiac muscle fibres:muscle fibres:

Unlike skeletal Unlike skeletal muscles, cardiac muscles, cardiac muscles have to muscles have to contract in more than contract in more than one direction.one direction.

Cardiac muscle cells Cardiac muscle cells are striated, meaning are striated, meaning they will only contract they will only contract along their long axis.along their long axis.

In order to get In order to get contraction in two contraction in two axis, the fibres wrap axis, the fibres wrap around.around.

Circulation circuits:Circulation circuits:

Heart WallHeart Wall

Three layers of tissueThree layers of tissue EpicardiumEpicardium: This serous membrane : This serous membrane

of smooth outer surface of heartof smooth outer surface of heart MyocardiumMyocardium: Middle layer composed : Middle layer composed

of cardiac muscle cell and of cardiac muscle cell and responsibility for heart contractingresponsibility for heart contracting

EndocardiumEndocardium: Smooth inner surface : Smooth inner surface of heart chambersof heart chambers

Valve function:Valve function:

Coronary circulation:Coronary circulation:

Cardiac conducting Cardiac conducting system:system:

Pacemaker potential:Pacemaker potential:

EKG:EKG:

Heart sounds:Heart sounds:

Heart SoundsHeart Sounds

First heart sound or “lubb”First heart sound or “lubb” Atrioventricular valves and surrounding fluid Atrioventricular valves and surrounding fluid

vibrations as valves close at beginning of vibrations as valves close at beginning of ventricular systoleventricular systole

Second heart sound or “dupp”Second heart sound or “dupp” Results from closure of aortic and pulmonary Results from closure of aortic and pulmonary

semilunar valves at beginning of ventricular semilunar valves at beginning of ventricular diastole, lasts longerdiastole, lasts longer

Third heart sound Third heart sound (occasional)(occasional) Caused by turbulent blood flow into ventricles and Caused by turbulent blood flow into ventricles and

detected near end of first one-third of diastoledetected near end of first one-third of diastole

Cardiac ArrhythmiasCardiac Arrhythmias

TachycardiaTachycardia: Heart rate in excess of : Heart rate in excess of 100bpm100bpm

BradycardiaBradycardia: Heart rate less than 60 : Heart rate less than 60 bpmbpm

Sinus arrhythmiaSinus arrhythmia: Heart rate varies 5% : Heart rate varies 5% during respiratory cycle and up to 30% during respiratory cycle and up to 30% during deep respirationduring deep respiration

Premature atrial contractionsPremature atrial contractions: : Occasional shortened intervals between Occasional shortened intervals between one contraction and succeeding, one contraction and succeeding, frequently occurs in healthy peoplefrequently occurs in healthy people

Cardiac CycleCardiac Cycle

Heart is two pumps that work Heart is two pumps that work together, right and left halftogether, right and left half

Repetitive contraction (Repetitive contraction (systolesystole) and ) and relaxation (relaxation (diastolediastole) of heart chambers) of heart chambers

Blood moves through circulatory Blood moves through circulatory system from areas of higher to lower system from areas of higher to lower pressure.pressure. Contraction of heart produces the Contraction of heart produces the

pressurepressure

Pressure relationships:Pressure relationships:

Mean Arterial Pressure Mean Arterial Pressure (MAP)(MAP)

Average blood pressure in aortaAverage blood pressure in aorta MAP=CO x PRMAP=CO x PR

CO is amount of blood pumped by heart CO is amount of blood pumped by heart per minuteper minute CO=SV x HRCO=SV x HR

SVSV: Stroke volume of blood pumped during each : Stroke volume of blood pumped during each heart beatheart beat

HRHR: Heart rate or number of times heart beats per : Heart rate or number of times heart beats per minuteminute

Cardiac reserve: Difference between CO at Cardiac reserve: Difference between CO at rest and maximum COrest and maximum CO

PR is total resistance against which PR is total resistance against which blood must be pumpedblood must be pumped

Factors Affecting MAPFactors Affecting MAP

Regulation of the HeartRegulation of the Heart Intrinsic regulationIntrinsic regulation: Results from : Results from

normal functional characteristics, not normal functional characteristics, not on neural or hormonal regulationon neural or hormonal regulation Starling’s law of the heartStarling’s law of the heart

Extrinsic regulationExtrinsic regulation: Involves neural : Involves neural and hormonal controland hormonal control Parasympathetic stimulationParasympathetic stimulation

Supplied by vagus nerve, decreases heart rate, Supplied by vagus nerve, decreases heart rate, acetylcholine secretedacetylcholine secreted

Sympathetic stimulationSympathetic stimulation Supplied by cardiac nerves, increases heart rate Supplied by cardiac nerves, increases heart rate

and force of contraction, epinephrine and and force of contraction, epinephrine and norepinephrine releasednorepinephrine released

Heart HomeostasisHeart Homeostasis Effect of blood pressureEffect of blood pressure

Baroreceptors monitor blood pressureBaroreceptors monitor blood pressure Effect of pH, carbon dioxide, oxygenEffect of pH, carbon dioxide, oxygen

Chemoreceptors monitorChemoreceptors monitor Effect of extracellular ion concentrationEffect of extracellular ion concentration

Increase or decrease in extracellular KIncrease or decrease in extracellular K++ decreases heart ratedecreases heart rate

Effect of body temperatureEffect of body temperature Heart rate increases when body temperature Heart rate increases when body temperature

increases, heart rate decreases when body increases, heart rate decreases when body temperature decreasestemperature decreases

Baroreceptor and Baroreceptor and ChemoreceptorChemoreceptor

ReflexesReflexes

Cardian Cardian innervatiinnervati

on:on:

Pacemaker regulation:Pacemaker regulation:

Once the pacemaker cells reach threshold, Once the pacemaker cells reach threshold, the magnitude and duration of the AP is the magnitude and duration of the AP is always the same.always the same.

In order to change the frequency, the time In order to change the frequency, the time between APs must vary.between APs must vary. The interval can only be changed in two ways.The interval can only be changed in two ways.

The rate of depolarization can be changedThe rate of depolarization can be changed The amount of depolarization required to reach The amount of depolarization required to reach

threshold can be changed.threshold can be changed.

Vascular physiology:Vascular physiology:

Peripheral Circulatory Peripheral Circulatory SystemSystem

Systemic vesselsSystemic vessels Transport blood through most all body Transport blood through most all body

parts from left ventricle and back to right parts from left ventricle and back to right atriumatrium

Pulmonary vesselsPulmonary vessels Transport blood from right ventricle Transport blood from right ventricle

through lungs and back to left atriumthrough lungs and back to left atrium Blood vessels and heart regulated to Blood vessels and heart regulated to

ensure blood pressure is high enough ensure blood pressure is high enough for blood flow to meet metabolic needs for blood flow to meet metabolic needs of tissuesof tissues

Blood Vessel StructureBlood Vessel Structure ArteriesArteries

Elastic, muscular, arteriolesElastic, muscular, arterioles CapillariesCapillaries

Blood flows from arterioles to capillariesBlood flows from arterioles to capillaries Most of exchange between blood and Most of exchange between blood and

interstitial spaces occurs across the wallsinterstitial spaces occurs across the walls Blood flows from capillaries to venous Blood flows from capillaries to venous

systemsystem VeinsVeins

Venules, small veins, medium or large Venules, small veins, medium or large veinsveins

Structure of Arteries Structure of Arteries and Veinsand Veins

Three layers except for Three layers except for capillaries and venulescapillaries and venules

Tunica intima (interna)Tunica intima (interna) EndotheliumEndothelium

Tunica mediaTunica media VasoconstrictionVasoconstriction VasodilationVasodilation

Tunica adventitia Tunica adventitia (externa)(externa) Merges with connective Merges with connective

tissue surrounding blood tissue surrounding blood vesselsvessels

Note mistake on figureNote mistake on figure

Structure of ArteriesStructure of Arteries

Elastic or conducting arteriesElastic or conducting arteries Largest diameters, pressure high and Largest diameters, pressure high and

fluctuatesfluctuates Muscular or medium arteriesMuscular or medium arteries

Smooth muscle allows vessels to regulate Smooth muscle allows vessels to regulate blood supply by constricting or dilatingblood supply by constricting or dilating

ArteriolesArterioles Transport blood from small arteries to Transport blood from small arteries to

capillariescapillaries

Structure of VeinsStructure of Veins Venules and small veinsVenules and small veins

Tubes of endothelium on delicate Tubes of endothelium on delicate basement membranebasement membrane

Medium and large veinsMedium and large veins ValvesValves

Allow blood to flow toward heart but Allow blood to flow toward heart but not in opposite directionnot in opposite direction

Atriovenous anastomosesAtriovenous anastomoses Allow blood to flow from arterioles to Allow blood to flow from arterioles to

small veins without passing through small veins without passing through capillariescapillaries

Blood Vessel Blood Vessel Comparison:Comparison:

Capillaries:Capillaries: Capillary wall Capillary wall

consists mostly of consists mostly of endothelial cellsendothelial cells

Types classified by Types classified by diameter/permeabilitydiameter/permeability ContinuousContinuous

Do not have fenestraeDo not have fenestrae FenestratedFenestrated

Have poresHave pores SinusoidalSinusoidal

Large diameter with Large diameter with large fenestraelarge fenestrae

Capillary Network:Capillary Network:

Blood flows from Blood flows from arterioles through arterioles through metarteriolesmetarterioles, then , then through through capillary capillary networknetwork

Venules drain Venules drain networknetwork

Smooth muscle in Smooth muscle in arterioles, arterioles, metarterioles, metarterioles, precapillary precapillary sphincterssphincters regulates regulates blood flowblood flow

Muscular contractions aid Muscular contractions aid venous return:venous return:

Pulmonary CirculationPulmonary Circulation

Moves blood to and from the lungsMoves blood to and from the lungs Pulmonary trunkPulmonary trunk

Arises from right ventricleArises from right ventricle Pulmonary arteriesPulmonary arteries

Branches of pulmonary trunk which Branches of pulmonary trunk which project to lungsproject to lungs

Pulmonary veinsPulmonary veins Exit each lung and enter left atriumExit each lung and enter left atrium

Systemic Circulation: Systemic Circulation: ArteriesArteries

AortaAorta From which all arteries are derived From which all arteries are derived

either directly or indirectlyeither directly or indirectly PartsParts

Ascending, descending, thoracic, abdominalAscending, descending, thoracic, abdominal

Coronary arteriesCoronary arteries Supply the heartSupply the heart

Systemic Circulation: Systemic Circulation: VeinsVeins

Return blood from body to right Return blood from body to right atriumatrium

Major veinsMajor veins Coronary sinus (Coronary sinus (heartheart)) Superior vena cava (Superior vena cava (head, neck, thorax, head, neck, thorax,

upper limbsupper limbs)) Inferior vena cava (Inferior vena cava (abdomen, pelvis, abdomen, pelvis,

lower limbslower limbs)) Types of veinsTypes of veins

Superficial, deep, sinusesSuperficial, deep, sinuses

Dynamics of Blood Dynamics of Blood CirculationCirculation

Interrelationships betweenInterrelationships between PressurePressure FlowFlow ResistanceResistance Control mechanisms that regulate blood Control mechanisms that regulate blood

pressurepressure Blood flow through vesselsBlood flow through vessels

Blood PressureBlood Pressure

Measure of force exerted by blood Measure of force exerted by blood against the wallagainst the wall

Blood moves through vessels Blood moves through vessels because of blood pressurebecause of blood pressure

Measured by listening for Korotkoff Measured by listening for Korotkoff sounds produced by turbulent flow sounds produced by turbulent flow in arteries as pressure released from in arteries as pressure released from blood pressure cuffblood pressure cuff

Pressure and Pressure and ResistanceResistance

Blood pressure Blood pressure averages averages 100 mm 100 mm HgHg in aorta and in aorta and drops to 0 mm Hg drops to 0 mm Hg in the right atriumin the right atrium

Greatest drop in Greatest drop in pressure occurs in pressure occurs in arterioles which arterioles which regulate blood flow regulate blood flow through tissuesthrough tissues

No large No large fluctuations in fluctuations in capillaries and capillaries and veinsveins

Blood Pressure Blood Pressure MeasurementMeasurement

Pulse PressurePulse Pressure Difference between Difference between

systolic and systolic and diastolicdiastolic pressures pressures

Increases when Increases when stroke volume stroke volume increases or increases or vascular vascular compliance compliance decreasesdecreases

Pulse pressure can Pulse pressure can be used to take a be used to take a pulse to determine pulse to determine heart rate and heart rate and rhythmicityrhythmicity

Blood Flow, Poiseuille’s Blood Flow, Poiseuille’s LawLaw

and Viscosityand Viscosity Blood flowBlood flow

Amount of blood Amount of blood moving through a moving through a vessel in a given vessel in a given time periodtime period

Directly Directly proportional to proportional to pressure pressure differences, differences, inversely inversely proportional to proportional to resistanceresistance

Poiseuille’s LawPoiseuille’s Law Flow decreases when Flow decreases when

resistance increasesresistance increases Flow resistance Flow resistance

decreases when decreases when vessel diameter vessel diameter increasesincreases

ViscosityViscosity Measure of Measure of

resistance of liquid resistance of liquid to flowto flow

As viscosity As viscosity increases, pressure increases, pressure required to flow required to flow increasesincreases

Critical Closing Critical Closing Pressure, Laplace’s Law Pressure, Laplace’s Law

and Complianceand ComplianceCritical closing Critical closing

pressurepressure Pressure at which a Pressure at which a

blood vessel collapses blood vessel collapses and blood flow stopsand blood flow stops

Laplace’s LawLaplace’s Law Force acting on blood Force acting on blood

vessel wall is vessel wall is proportional to proportional to diameter of the vessel diameter of the vessel times blood pressuretimes blood pressure

Vascular complianceVascular compliance Tendency for blood Tendency for blood

vessel volume to vessel volume to increase as blood increase as blood pressure increasespressure increases

More easily the More easily the vessel wall stretches, vessel wall stretches, the greater its the greater its compliancecompliance

Venous system has a Venous system has a large compliance and large compliance and acts as a blood acts as a blood reservoirreservoir

Physiology of Systemic Physiology of Systemic CirculationCirculation

Determined byDetermined by Anatomy of circulatory systemAnatomy of circulatory system Dynamics of blood flowDynamics of blood flow Regulatory mechanisms that control Regulatory mechanisms that control

heart and blood vesselsheart and blood vessels Blood volumeBlood volume

Most in the veinsMost in the veins Smaller volumes in arteries and Smaller volumes in arteries and

capillariescapillaries

Laminar and Turbulent Laminar and Turbulent FlowFlow

Laminar flowLaminar flow StreamlinedStreamlined Outermost layer Outermost layer

moving slowest and moving slowest and center moving center moving fastestfastest

Turbulent flowTurbulent flow InterruptedInterrupted Rate of flow exceeds Rate of flow exceeds

critical velocitycritical velocity Fluid passes a Fluid passes a

constriction, sharp constriction, sharp turn, rough surfaceturn, rough surface

Aging of the ArteriesAging of the Arteries

ArteriosclerosisArteriosclerosis General term for General term for

degeneration degeneration changes in changes in arteries making arteries making them less elasticthem less elastic

AtherosclerosisAtherosclerosis Deposition of Deposition of

plaque on wallsplaque on walls

Capillary Exchange andCapillary Exchange andInterstitial Fluid Volume Interstitial Fluid Volume

RegulationRegulation

Blood pressure, capillary Blood pressure, capillary permeability, and osmosis affect permeability, and osmosis affect movement of fluid from movement of fluid from capillariescapillaries

A net movement of fluid occurs from A net movement of fluid occurs from blood into tissues. Fluid gained by blood into tissues. Fluid gained by tissues is removed by tissues is removed by lymphatic lymphatic systemsystem..

Fluid Exchange Across Fluid Exchange Across Capillary WallsCapillary Walls

Vein Characteristics andVein Characteristics andEffect of Gravity on Effect of Gravity on

Blood PressureBlood PressureVein Vein

CharacteristicsCharacteristics Venous return to Venous return to

heart increases heart increases due to increase in due to increase in blood volume, blood volume, venous tone, and venous tone, and arteriole dilationarteriole dilation

Effect of GravityEffect of Gravity In a standing In a standing

position, hydrostatic position, hydrostatic pressure caused by pressure caused by gravity increases gravity increases blood pressure blood pressure below the heart and below the heart and decreases pressure decreases pressure above the heartabove the heart

Control of Blood Flow by Control of Blood Flow by TissuesTissues

Local controlLocal control In most tissues, blood flow is In most tissues, blood flow is

proportional to metabolic needs of proportional to metabolic needs of tissuestissues

Nervous SystemNervous System Responsible for routing blood flow and Responsible for routing blood flow and

maintaining blood pressuremaintaining blood pressure Hormonal ControlHormonal Control

Sympathetic action potentials stimulate Sympathetic action potentials stimulate epinephrine and norepinephrineepinephrine and norepinephrine

Local Control of Blood Flow Local Control of Blood Flow by Tissuesby Tissues

Blood flow can increase 7-8 times as a result of Blood flow can increase 7-8 times as a result of vasodilation of metarterioles and precapillary vasodilation of metarterioles and precapillary sphincters in response to increased rate of metabolismsphincters in response to increased rate of metabolism Vasodilator substances produced as metabolism increasesVasodilator substances produced as metabolism increases Vasomotion is periodic contraction and relaxation of Vasomotion is periodic contraction and relaxation of

precapillary sphinctersprecapillary sphincters

Nervous Regulation of Nervous Regulation of Blood VesselsBlood Vessels

Short-Term Regulation Short-Term Regulation ofof

Blood PressureBlood Pressure Baroreceptor reflexesBaroreceptor reflexes

Change peripheral resistance, heart rate, and Change peripheral resistance, heart rate, and stroke volume in response to changes in blood stroke volume in response to changes in blood pressurepressure

Chemoreceptor reflexesChemoreceptor reflexes Sensory receptors sensitive to oxygen, carbon Sensory receptors sensitive to oxygen, carbon

dioxide, and pH levels of blooddioxide, and pH levels of blood

Central nervous system ischemic Central nervous system ischemic responseresponse Results from high carbon dioxide or low pH levels Results from high carbon dioxide or low pH levels

in medulla and increases peripheral resistancein medulla and increases peripheral resistance

Baroreceptor Reflex Baroreceptor Reflex ControlControl

Local mechanisms affect Local mechanisms affect MAP:MAP:

Effects of pH and GasesEffects of pH and Gases

Long-Term Regulation Long-Term Regulation of Blood Pressureof Blood Pressure

Renin-angiotensin-aldosterone Renin-angiotensin-aldosterone mechanismmechanism

Vasopressin (ADH) mechanismVasopressin (ADH) mechanism Atrial natriuretic mechanismAtrial natriuretic mechanism Fluid shift mechanismFluid shift mechanism Stress-relaxation responseStress-relaxation response

General control of MAP:General control of MAP:

Renin-Angiotensin-Renin-Angiotensin-AldosteroneAldosteroneMechanismMechanism

Vasopressin (ADH) Vasopressin (ADH) MechanismMechanism

Long Term MechanismsLong Term MechanismsWhich Lower Blood Which Lower Blood

VolumeVolume Atrial natriuretic Atrial natriuretic

factorfactor Hormone released Hormone released

from cardiac muscle from cardiac muscle cells when atrial cells when atrial blood pressure blood pressure increases, simulating increases, simulating an increase in an increase in urinary production, urinary production, causing a decrease causing a decrease in blood volume and in blood volume and blood pressureblood pressure

Fluid shiftFluid shift Movement of fluid Movement of fluid

from interstitial from interstitial spaces into spaces into capillaries in capillaries in response to response to decrease in blood decrease in blood pressure to maintain pressure to maintain blood volumeblood volume

Stress-relaxationStress-relaxation Adjustment of blood Adjustment of blood

vessel smooth vessel smooth muscle to respond muscle to respond to change in blood to change in blood volumevolume

Chemoreceptor Reflex Chemoreceptor Reflex ControlControl

ShockShock

Inadequate blood flow throughout bodyInadequate blood flow throughout body Three stagesThree stages

CompensatedCompensated: Blood pressure decreases only a : Blood pressure decreases only a moderate amount and mechanisms able to moderate amount and mechanisms able to reestablish normal blood pressure and flowreestablish normal blood pressure and flow

ProgressiveProgressive: Compensatory mechanisms : Compensatory mechanisms inadequate and positive feedback cycle develops; inadequate and positive feedback cycle develops; cycle proceeds to next stage or medical treatment cycle proceeds to next stage or medical treatment reestablishes adequate blood flow to tissuesreestablishes adequate blood flow to tissues

IrreversibleIrreversible: Leads to death, regardless of medical : Leads to death, regardless of medical treatmenttreatment

Fetal circulation:Fetal circulation: