Cardiac Anatomy and Physiology

Iris Ken R. Rico, OTRPLecturer

OUTLINE: Introduction Functions of the Heart Size, Form, and Location of the Heart Anatomy of the Heart

Pericardium External Anatomy Heart Chambers and Internal Anatomy

Right and Left AtriaRight and Left Ventricles

Heart ValvesAtrioventricular valves

• Tricupsid valve• Mitral valve

Semi-lunar valves• Aortic valve• Pulmonic valve

Route of Blood Flow Through the Heart Blood Supply to the Heart

Histology of the Heart Heart Wall Cardiac Muscle

Electrical Activity of the Heart Action Potentials in Cardiac Muscle Conduction System of the Heart Electrocardiogram

Cardiac Cycle Heart sounds Regulation of Heart Function

Intrinsic Regulation of the Heart Extrinsic Regulation of the Heart

Control of the Heart by Sympathetic and Parasympathetic Nerves Excitation of the Heart by Sympathetic Nerves Parasympathetic (Vagal) Stimulation of the Heart

Effect of Potassium and calcium Ions on heart Function Effect of Potassium Ions Effect of Calcium Ions

Effect of Temperature on Heart Function Systems Pathology

Effects of Aging on the Heart

FUNCTIONS OF THE HEART

Generating blood pressure.Routing blood.Ensuring one-way blood flow.Regulating blood supply.

SIZE, FORM, AND LOCATION OF THE

HEART

Blunt cone and size of a closed fist> age 65 LocationMediastinum = heart, trachea, esophagusKnowledge on the shape and location of the heart Lies obliquely in the mediastinum, with its base directed

posteriorly and slightly superiorly and the apex directed anteriorly and slightly inferiorly

Apex = directed to the left, approximately 2/3 pf the heart’s mass, lies left of the midline of the sternum, deep to the left 5th ICS, approximately 7-9 cm to the left of the sternum near the midclavicular line

Base = located deep to the sternum and extends to the level of the 2nd ICS

Size/dimensionsAt rest and during exercise

ANATOMY OF THE HEART

Pericardium

Pericardial cavityPericardium or pericardial sac

Two layers:Fibrous pericardiumSerous pericardium

Parietal pericardium Visceral pericardium or Epicardium Pericardial fluid

External Anatomy

Atria (R/L)Ventricles Coronary sulcusAnterior ventricular sulcusPosterior interventicular sulcus6 veins that carry blood to the heartPulmonary trunk and aorta

Heart Chambers and Internal Anatomy

Right (pulmonic) pump: circulates blood to the lungs

Left (systemic) pump: circulates blood to the body

Right Atrium

Thin muscle wallMost blood flow into the right atrium during

inspiration when RA pressure drops below that in IVC and SVC (higher to lower pressure)

High flow; low pressure systemFunction: Receives unoxygenated blood from

the venous systemInflow: Superior and inferior vena cavaOutflow: Tricuspid valve

Left Atrium

Slightly thicker than the right atriumBreathing does not affect fillingFunction: Receives oxygenated blood from the

lungsInflow: 4 Pulmonic veinsOutflow: Mitral (Bicuspid) valveNormal filling pressure: 4-12mmHg

Right Ventricle

Function: Delivers unoxygenated blood to the lungs

Inflow: Tricuspid valveOutflow: Pulmonic valveFour muscular bands:

Infundibulum septumParietal bandSeptal bandModerator band

Normal systolic pressure: 15– 28mmHgEnd diastolic pressure: 0-8mmHg

Left Ventricle

Function: Delivers oxygenated blood to the body

Inflow: Mitral valveOutflow: Aortic valveNormal systolic pressure: 120mmHg (100-140)End diastolic pressure: 4-12mmHg

Cardiac Skeleton

Anulus fibrosus – firm anchor to which most of the heart’s muscles and valves are attachedGives structure to the heart and acts as an insulator

to ensure that electrical impulses move through the AV node and bundle only

Consists of tough fibrous rings surrounding the AV valves, and the bases of the aortic and the pulmonary trunks connected by the tendon of the conus

Heart Valves

Atrioventricular valveTricuspid valveBicuspid or mitral valve

Semilunar valveAortic valvePulmonary valve

Papillary muscles – contract when ventricle walls contractDo not help the valves to closePull vanes inward toward the ventricles to

prevent bulging too far backward toward the atria

Chordae tendinae – connect valve leaflet to papillary muscles in the ventricles

Route of Blood Flow through the

Heart

Blood Supply to the Heart

Coronary Arteries

Left coronary artery – originates from the left side of the aorta 3 branches:

Anterior interventricular artery – lies in the anterior interventricular sulcus

Circumflex artery – extends around the coronary sulcus on the left to the posterior surface of the heart

Left marginal artery – extends inferiorly along the

lateral wall of the left coronary artery

Right coronary artery – originates on the right side of the aorta and extends around the coronary sulcus on the right to the posterior interventricular sulcus

2 branches:Posterior interventricular artery – lies in the posterior

interventricular sulcusRight marginal artery – extends inferiorly along the

lateral wall of the right ventricleResting person – heart gives approximately 70%

of its oxygen

Cardiac Veins

Drain blood form the cardiac musclePathways nearly parallel to the coronary

arteries and most drain blood into the coronary sinus (large vein located within the coronary sulcus on the posterior aspect of the heart)

Some drain directly into the right atrium

HISTOLOGY OF THE HEART

Heart Wall

Epicardium or visceral pericardiumMyocardium Endocardium Trabeculae carnea

Cardiac Muscle

Cardiac muscle cell3 major types of cardiac muscle

Atrial muscleVentricular muscleExcitatory and conducive muscle fibers

Specialized fibers that contract only feebly because of few contractile fibrils

Physiologic Anatomy

ELECTRICAL ACTIVITY OF THE

HEART

Action Potentials in Cardiac Muscle

105 millivoltsAfter the initial spike, the membrane remains

depolarized for about ___ second in atrial muscle and ____ second in ventricular muscle exhibiting a plateau followed by repolarization

Depolarization phaseEarly repolarization phasePlateau phaseFinal repolarization phase

What causes the long action potential and plateau?

2 types of channelsFast sodium channelsSlow calcium channels

Immediately after the onset of action potential, permeability of cardiac muscle for potassium ions decreases about fivefold

Conduction System of the Heart

Sinoatrial nodeAtrioventricular nodeAtrioventricular bundleRight and left bundle branchesPurkinje fibers

Sinoatrial node

Pacemaker of the Heart Is a small flattened, ellipsoidal strip of specialized

muscle about ___ millimeters wide, ___millimeters long, and ___ millimeter thick

Located in the superior posterolateral wall of the right atrium immediately below and slightly lateral to the opening of the SVC

Generates the normal rhythmical impulseSinus nodal fibers connect directly with the atrial

muscle fibersEctopic pacemaker Stokes-Adam syndrome

Atrioventricular node

Located in the posterior wall of the right atrium immediately behind the tricuspid valve and adjacent opening of the coronary sinus

Delay transmission of impulse from atria to ventricles to allow time for atria to empty their blood into the ventricles before ventricular contraction begins

Discharge at an intrinsic rhythmical rate

Atrioventricular bundle

Composed of multiple small fascicles passing through the fibrous tissue separating the atria from the ventricles

Delay from A-V node to bundle is about 0.13 second

Right and left bundle branches

Purkinje fibers

Very large fibersTransmit velocity about 6 times that in usual

ventricular muscle and 150 times that in some A-V nodal fibers

Rapid transmission of action potentialDischarge at an intrinsic rhythmical rate

Electrocardiogram

Recording device that detect the small electrical changes resulting form the action potentials in all of the cardiac muscle cells

Normal ECG consists of:

P waveAtrial depolarization

QRS complexVentricular depolarization

T waveVentricular repolarization

PQ/PR interval – beginning of the P wave and beginning of QRS complexAtria contract and begin to relaxEnd – ventricle begin to depolarizeNormal PQ interval is 0.16 second sometimes called

the PR interval cause the Q wave is frequently absentQT interval – beginning of the QRS complex to the

end of the T waveRepresents the length of time required for ventricular

depolarization and repolarization0.35 second

CARDIAC CYCLE

Beginning of one heartbeat to the beginning of the next beat

Includes systole, diastole, and a short pause called diastasis cordis

Duration depends on heart rateEntire heart rests for 0.4 seconds

Components of cardiac event:

Ventricular systoleIsometric contraction phaseRapid ejection phaseSlow ejection phase

Ventricular diastoleIsometric interval phaseAtrial systole phaseSlow ventricular filling phaseRapid ventricular filling phase

Isometric contraction phase

• Isovolumetric contraction phase = all valves closed and no ejection of blood

• Beginning of ventricular contraction• Increase in pressure = AV close• Atria fills with blood• Tension is increasing in the muscle but no shortening of

the muscle fibers is occuring

Rapid ejection phase

• Left ventricular pressure exceeds 80mmHg and right ventricular pressure exceeds 8mmHg = aortic and pulmonic valves open

• Pouring of blood from atria to ventricles• 70% emptied during first third of ejection period

Slow ejection phase

• Remaining 30% of blood in the ventricle is emptied during 2/3 of ejection phase

Isometric interval phase

• A.K.A. - Isovolumetric interval phase• Relaxation phase and is the beginning of diastole• Ventricular pressure lower than in the aorta and

pulmonary artery = momentary backflow of blood and closure of semilunar valves (2nd heart sound)

• Ventricular pressure drops to 00mmHg

Rapid ventricular filling phase

• Ventricular pressure falls below atrial pressure = AV valves open, blood rushes rapidly from atria to ventricles

Slow ventricular filling phase

• Diastasis or the last part of diastole• Small amount drain from the lungs and peripheral

circulation into the atria and added to ventricles• Towards ends= depolarization of atria begins

Atrial systole phase

• Atrial contraction or atrial kick• 25% more blood to the ventricle during last phase of

ventricular systole

HEART SOUNDS

Stethoscope First heart sound – “Lubb”

Lower pitchOccurs at the beginning of ventricular systole

and results form closure of the AV valvesSecond heart sound - “Dub”

Occurs at the beginning of ventricular systole and results from closure of semilunar valves

Murmurs

REGULATION OF HEART FUNCTION

Cardiac output (CO) – volume of blood puped by either ventricle of the heart each minuteCO = SV x HR

Stroke volume (SV) – volume of blood pumped per ventricle each time the heart contracts

Heart rate – number of times the heart contracts each minute

Resting conditions – 72 beats/min , SV = 70 mL/beat, CO – 5040 mL/min

Athletes - higher SV and lower HR

4 Interrelated factors that govern cardiac output:

PreloadAfterloadContractilityHeart rate

Preload

Ventricular fillingInfluenced by the total volume of circulating blood> venous return > stretch of myocardial fibersFRANK-STARLING’S LAW = the greater the

myocardial stretch, the greater the force of contraction

Afterload

Resistance to ejection of bloodAmount of tension the ventricles must develop to

eject the blood through the semilunar valvesResistance against which the heart must pump the

blood to all parts of the bodyFactors causing higher that normal resistance:

• Systemic and pulmonary arterioles• Increased blood viscosity• Pulmonary valve stenosis

Contractility

Refers to changes in the force of myocardial contraction and is a function of the interaction between the contractile elements

Depends on:• Amount of contractile proteins• Presence of ATP and calcium• Sympathetic stimulation• Pharmacologic agents

Heart Rate

Influenced by many factors:• Exercise• Person’s physical size• Age• Gender differences• Hypotension and hypertension• ANS via sympathetic and parasympathetic branches

Extrinsic Regulation of the Heart

Refers to mechanisms external to the heart, such as either hormonal or nervous regulation

Baroreceptors Plays an important role in regulating the function of the heart Are stretch receptors that monitor pressure in the aorta and in the wall

of the internal carotid arteries, which carry blood to the brain Changes in blood pressure result in changes in the stretch of the walls

of the blood vessels leading to changes in the frequency of action potentials produced by baroreceptors

Chemoreceptors Emotions influence heart function by increasing sympathetic

stimulation of the heart in response to exercise, excitement, anxiety, or anger and by increasing parasympathetic stimulation in response to depression

Alterations in body fluid levels of cardon dioxide, pH, and ion concentrations, as well as changes in body temperature, influence heart function

Control of the Heart by Sympathetic and Parasympathetic Nerves

Excitation of the Heart by Sympathetic NervesStrong = increase heart rate from the normal 70

beats for minute to 180 to 200 and rarely 250 beats per minute

Increase force of contraction, increasing the volume of blood pumped and increasing the ejection pressure

Increases cardiac output tp twofold to threefold

Parasympathetic (Vagal) Stimulation of the HeartStrong = stop heartbeat for a few seconds, but

then the heart usually escapes and beats at a rate of 20 to 40 beats per minute, 40 % normal

Decrease the strength of heart contraction by 20 to 30%

Decrease heart rate rather than to decrease greatly the strength of heart contraction

Effect of Potassium and Calcium Ions on heart Function

Effect of Potassium IonsExcess potassiumLarge quantities = block conduction from atria

to ventricles through the A-V bundleElevation to only 8 to 12 mEq/L

Effect of Calcium IonsOpposite the effect of potassium ions

Effect of Temperature on Heart Function

Increased temperature = increased heart rateDecreased temperature = decreased heart rateNear death due to hypothermiaHeat Contractile strength = enhanced temporarily by

a moderate increase in temperature, but prolonged elevation exhausts metabolic system of the heart and causes weakness

EFFECTS OF AGING ON THE HEART

Gradual changes in functionAge 70 = decreases approximately 1/3 Hypertrophy of the left ventricle = increase pressure in

the aorta against which the left ventricle must pumpGreater amount time to contract and relax, decrease in

maximum heart rateChanges in connective tissue of the heart valves = less

flexible and calcium deposits develop Increased in cardiac arrhythmiasDevelopment of CAD and heart failureAerobic exercise

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