Pathophysiology 1 ( Exam 2 : Cardiac Function and Conduction)

Great Vessels

Superior and inferior venae cavae

ØBring deoxygenated blood from the systemic circulation to the right atrium

Right and left pulmonary arteries

ØTransport unoxygenated blood from the right heart to the right and left lungs

ØBranch into pulmonary capillaries

Pulmonary veins

ØCarry oxygenated blood from the lungs to the left side of the heart

Aorta

ØDelivers oxygenated blood to systemic vessels that supply the body

Valves of the Heart

Ensure one way blood flow

Atrioventricular valves (AVs)

ØOne-way flow of blood from the atria to the ventricles

ØTricuspid valve: three leaflets or cusps

ØBicuspid (mitral) valve: two leaflets or cusps

Semilunar valves

ØOne-way flow from the ventricles to either the pulmonary artery or to the aorta

ØPulmonic semilunar valve

ØAortic semilunar valve

Structures That Support Cardiac Metabolism: Coronary Circulation

Coronary circulation

ØSupplies oxygen and other nutrients to the myocardium

Right coronary artery

ØConus artery

ØRight marginal branch

ØPosterior descending branch

Left coronary artery

ØLeft anterior descending artery

ØCircumflex artery

Collateral arteries

ØAre connections, or anastomoses, between the branches of the coronary circulation

ØProtects the heart from ischemia

Are formed by arteriogenesis or angiogenesis

Coronary capillaries

ØWhere the exchange of oxygen and other nutrients takes place

Coronary veins

ØCoronary sinus

ØGreat cardiac vein

ØPosterior vein of the left ventricle

CARDIAC CYCLE

Atrial systole

Atrial diastole

Ventricular systole

Ventricular diastole

Quiescent period

The Five Phases of the Cardiac Cycle

ØPhase 1: atrial systole or ventricular diastole

ØPhase 2: isovolumetric ventricular systole

ØPhase 3: ventricular ejection (semilunar valves open)

ØPhase 4: isovolumetric ventricular relaxation (aortic valve closes)

ØPhase 5: passive ventricular filling (mitral and tricuspid valves open)

What make up a heart beat ?

ØOne contraction and one relaxation

Blood Flow During the Cardiac Cycle

PART 1

Unoxygenated (venous) blood from systemic circulation enters the right atrium through the superior and inferior venae cavae.

From the atrium, the blood passes through the right AV (tricuspid) valve into the right ventricle.

In the ventricle, the blood flows from the inflow tract to the outflow tract and then through the pulmonic semilunar valve (pulmonary valve) into the pulmonary artery, which delivers it to lungs for oxygenation.

Blood Flow During the Cardiac Cycle

Part 2

Oxygenated blood from the lungs enters the left atrium through the four pulmonary veins (two from the left lung and two from the right).

From the left atrium, the blood passes through the left AV valve (mitral valve) into the left ventricle.

In the ventricle, the blood flows from the inflow tract to the outflow tract and then through the aortic semilunar valve (aortic valve) into the aorta, which delivers it to the entire body.

Atrial systole

Atria contract

Blood pressure in atria increases

Blood forced into ventricles

Isovolumetric contraction

Ventricles contract

Ventricular pressure increases

AV valves close

Heart sound S1

No blood ejected yet

Ventricular ejection

Ventricular pressure exceeds arterial pressure

Semilunar valves open

Blood ejected into arteries

Not all blood expelled

Amount ejected = stroke volume

% = Ejection fraction

Isovolumetric relaxation

Early in ventricular diastole

Blood briefly flows backwards

Semilunar valves close

Heart sound s2

AV valves not yet open

No blood taken in yet

Ventricular filling

Ventricular pressure drops

AV valves open

Ventricles begin to fill

(Completely filled by atrial systole)

Where do the coronary lymphatic vessels fluid ?

Paratracheal lymph nodes

Structures That Control Heart Action

Cardiac action potentials

ØTransmission of electrical impulses

Conduction system

ØSinoatrial (SA) node

•Pacemaker of the heart

•Intranodal pathways

ØAtrioventricular (AV) node

ØBundle of His (AV bundle)

ØRight and left bundle branches

ØPurkinje fibers

ØVentricular myocardium

Cardiac Myocytes

Autorhythmic

ØSpontaneous depolarization at regular intervals

Some specialized to generate action potentials

Ø"Cardiac conduction system"

ØSinoatrial (SA) node

ØAtrioventricular (AV) node

Sinoatrial (SA) Node

Myocytes in right atrium

"Pacemaker"

Initiates heartbeat

Determines heart rate

Firing rate is increased/decreased by nerves

70 - 80 beats per minute (bpm)

4 Phases of action potential of cardiac mucles

Phase 0 :

Rapid Na+ influx through open fast NA+ channels

Phase 1 :

Transient K+ CHANNELS OPEN AND k+ effluX RETURS tmp To Omv

Phase 2 :

Influx ca2+ through L-type channels is electrically balanced by K+ efflux through delayed rectifier K+ channels

Phase 3 = Ca2+ Channels close but delayed rectiferremain and return TMP to -90Mv

SA action potential

Spreads throughout atrial myocardium

Atria contract ~simultaneously

Signal reaches AV node (50msec)

Delayed at AV node (100 msec)

Ventricles fill during delay

Atrioventricular (AV) Node

Near Right AV Valve

Electrical Gateway To Ventricles

Distributes Signal To Ventricular Myocardium

ØAV Bundle

ØPurkinje Fibers

Signal travels from AV node through ventricular myocardium

Ventricles contract ~simultaneously

Cardiac Rhythm depends on

substances delivered to myocardium via coronary arteries

Nutrients and Oxygen

Hormones and Biochemicals

Electrocardiogram

Electrical currents generated in the heart travel weakly through all body tissues

These currents can be measured using electrodes applied to the skin

Normal electrocardiogram (ECG)

ØSum of all cardiac action potentials

ØP wave: atrial depolarization

ØPR interval: time from the onset of atrial activation to the onset of ventricular activation

•Time necessary to travel from the sinus node through the atrium, AV node, and His-Purkinje system to activate ventricular myocardial cells

ØQRS complex: sum of all ventricular depolarizations

ØST interval: ventricular myocardium depolarized

ØQT interval: "electrical systole" of the ventricles

•Varies inversely with the heart rate

Cardiac Output characteristics

Heart rate (HR) (beats/min)

Ø~75 bpm at rest

Stroke volume (SV)

Ø~70 ml/beat at rest

Cardiac output (CO)

ØCo = HR * SV

Ø75 * 70 = 5,000 ml/min at rest

ØCardiac output is not constant

Cardiac Output Resting

Ø~5 liters/min resting (total volume)

Cardiac Output Vigourus exercise

Ø~21 liters/min in good condition

Ø~35 liters/min Olympic athlete

Factors Affecting Cardiac Output

Ejection fraction

Preload

Afterload

Laplace's law

Frank-Starling law of the heart

Myocardial contractility

Ejection fraction

ØIs the amount of blood ejected per beat

ØNormal is 66% for women and 58% for men.

ØIs calculated by dividing the stroke volume by the end-diastolic volume

ØIs an indicator of ventricular function

Afterload

ØIs the resistance to ejection during systole

ØAortic systolic pressure is a good index of afterload for the left ventricle.

ØDecreased afterload: heart contracts more rapidly

ØIncreased afterload: slows contractions and increases work load

ØSystemic vascular resistance (SVR)

ØTotal peripheral resistance (TPR)

Frank-Starling law of the heart

ØIs the volume of blood at the end of diastole

ØMyocardial stretch determines the force of myocardial contraction.

•More stretch = Increased force of contraction

ØIs the major way that the right and left ventricles maintain equal minute outputs, despite stroke (beat) output variation

Laplace's law

ØContractile force within a chamber depends on the radius of the chamber and the thickness of its wall.

•Smaller chambers and thicker chamber walls equal increased contraction force.

•In ventricular dilation, the force needed to maintain ventricular pressure lessens available contractile force.

Positive inotropic agents

•: increase the force of contraction

Norepinephrine

Epinephrine

Negative inotropic agents

•decrease the force of contraction

Acetylcholine released from the vagus nerve

What is the effect of hypoxia on contractility?

It decreases contractility

HEART RATE

Easily measured (pulse)

70 - 80 average resting rate

Tachycardia: resting >100 bpm

Bradycardia: resting <60 bpm

Regulated by nervous system

Cardiac accelerator nerves

Secrete norepinephrine

Binds to receptors in heart

Increases heart rate

Vagus nerves

Secrete acetylcholine

Send signals to AV and SA nodes

Fire less frequently

STROKE VOLUME

Governed by three factors

ØPreload

ØContractility

ØAfterload

When do means arterial blood pressure increase ?

increases when there is an increase in cardiac output or when the diameter of the blood vessels (principally the arterioles) is decreased

flow of blood vessels

is laminar and the flow is smooth, and no sound is generated

Øthe radius of the vessel and the viscosity of the blood