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• right atrium: receives blood returning from systemic circuit
• left atrium: receives blood returning from pulmonary circuit

• right ventricle: pumps blood through pulmonary circuit
• left ventricle: pumps blood through systemic circuit

• mediastinum between second rib and fifth intercostal space
• superior surface of diaphragm
• anterior to vertebral column
• posterior to sternum

palpated between fifth and sixth ribs

toward left hip

right shoulder

• double walled sac
• superficial fibrous pericardium: protects anchors to surrounding structures, and prevents overfilling
• deep two layered serous pericardium (parietal and visceral layer)

lines internal surface of fibrous pericardium

also known as the epicardium on external surface of the heart

pericardial cavity filled with fluid to decrease friction

• inflammation of pericardium
• roughens membrane surfaces

excess fluid sometimes compresses heart, creating limited pumping ability

• epicardium (visceral layer of serous pericardium)
• myocardium
• endocardium

• spiral bundles of contractile cardiac muscle cells
• cardiac skeleton: crisscrosing, interlacing layer of connective tissue
• anchors cardiac muscle fibers
• suppots great vessels and valves
• limits spread of action potentials to specific paths

• continuous with endothelial lining of blood vessels
• lines heart chambers
• covers cardiac skeleton of valves

separates atria

separates ventricles

remnant of foramen ovale of fetal heart

encircles junction of atria and ventricles (atrioventricular groove)

anterior position of the interventricular septum

landmark on posteroinferior surface

appendages that increase atrial volume

• pectinate muscles
• posterior and anterior regions separated by crista terminalis

pectinate muscles only in auricles

• small, thin walled
• contribute little to propulsion of blood
• three veins empty into right atrium (superior vena cava, inferior vena cava, coronary sinus)
• four pulmonary veins empty into left atrium

• most of the volume of the heart
• right ventricle: most anterior surface
• left ventricle: posteroinferior surface
• trabeculae carneae: irregular ridges of muscle on walls
• papillary muscles: anchor chordae tendineae
• thicker walls than atria
• actual pumps of heart
• right ventricle: pumps blood into pulmonary trunk
• left ventricle: pumps blood into aorta

the aorta

• ensure unidirectional blood flow through heart
• open and close in response to pressure changes
• two atrioventricular (AV) valves and two semilunar (SL) valves

• prevent backflow into atria when ventricles contract
• tricuspid valve (right AV valve)
• mitral valve (left AV valve, bicuspid valve)
• chordae tendineae anchor cusps to papillary muscles (hold valve flaps in closed position)

• prevent backflow into ventricles when ventricles relax
• open and close in response to pressure changes
• aortic semilunar valve
• pulmonary semilunar valve

• incompetent balve: blood backflows so heart repumps same blood over and over
• valvular stenosis: stiff flaps, constrict opening so the heart must exert more force to pump blood

• right atrium > tricuspid valve > right ventricle
• right ventricle > pulmonary SL valve > pulmonary trunk > pulmonary arteries > lungs
• lungs > pulmonary veins
•  > left atrium

• left atrium > mitral valve > left ventricle
• left ventricle > aortic SL valve > aorta
• aorta > systemic circulation

• equal volumes of blood pumped to pulmonary and systemic circuits
• pulmonary circuit short, low pressure circulation
• systemic circuit, long high friction circulation
• anatomy of ventricles reflects differences (left ventricle walls 3x thicker than right and pumps with greater pressure)

• functional blood supply to heart muscle itself: delivered when heart is relaxed, left ventricle receives most blood supply
• arterial supply varies among individuals
• contains many anastomoses (junctions): provide additional routes for blood delivery, cannot compensate for coronary artery occlusion

• arteries arise from base of aorta
• left coronary arty branches to anterior interventricular arty and circumflex arty: supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left venticle
• right coronary artery branches to right marginal artery and posterior interventricular artery: supplies right atrium and most of right ventricle

• cardiac veins: collect blood from capillary beds
• coronary sinus: empties into right atrium; formed by merging cardiac veins (great cardiac vein, middle cardiac vein, small cardiac vein)
• several anterior cardiac veins empty directly into right atrium anteriorly

anterior interventricular sulcus

posterior interventricular sulcus

inferior margin

• thoracic pain caused by fleeting deficiency in blood delivery to myocardium
• cells weakened

• prolonged coronary blockage
• areas of cell death repaired with noncontractile scar tissue

• striated, short, branched, fat, interconnected
• connective tissue matrix (endomysium) connects to cardiac skeleton
• numerous large mitochondria
• intercalated discs: junctions between cells, anchor cardiac cells
• desmosomes prevent cells form separating during contraction
• gap junctions allow ions to pass from cell to cell; electrically couple adjacent cells
• gap junctions allow the heart to be functional syncytium (behaves as a single unit)

when no action potentials can occur during that period

• does not need nervous sytem stimulation, can start on its own
• all cardiomyocytes contract as a unit, or none do
• long absolute refractory period, prevents tetanic contractions

• presence of gap junctions
• intrinsic cardiac conduction system : network of noncontractile cells, initiate and distribute impulses, coordinated depolarization and contraction of heart

• have unstable resting membrane potentials due to opening of slow Na+ channels (continuously depolarize)
• at threshold, Ca2+ channels open
• explosive Ca2+ influx produces the rising phase of action potential
• repolarization results from inactivation of Ca2+ channels and opening of voltage gated K+ channels

• pacemaker potential: repolarization closes K+ channels and opens slow Na+ channels > ion imbalance
• depoalrization: Ca+ channels open > huge influx > rising phase of action potential
• repolarization: K+ channels open > efflux of K+

• sinoatrial node
• atrioventricular node
• atrioventricular bundle
• right and left bundle branches
• subendocardial conducting network (purkinje fibers)

• pacemaker of the heart in right atrial wall
• depolarizes faster than rest of myocardium
• generates impulses about 75x a minute (sinus rhythm)
• impulses spreads across atria and to AV node

• in inferior interatrial septum
• delays impulses approximately 0.1 second because fibers are smaller diameter, have fewer gap junctions, allows atrial contraction prior to ventricular contraction
• inherent rate of 50x per minute in absence of SA node input

• in superior interventricular septum
• only electrical connection between atria and ventricles
• atria and ventricles not connected via gap junctions

• two pathways in interventricular septum
• carry impulses toward apex of heart

• complete pathway through interventricular septum into apex and ventricular walls
• more elaborate on left side of heart
• AB bundle and subendocardial conducting network depolarize 30x a minute in absence of AV node input
• ventricular contraction immediately follows form apex toward atria

• irregular heart rhythms
• uncoordinated atrial and ventricular contractions

• rapid, irregular contractions
• useless for pumping blood, circulation ceases, brain death
• defibrillation to treat

abnormal pacemaker

av NODE TO TAKE OVER, SETs A JUNCTIONAL RHYTHM 40-60 BEATS/MIN

• premature contraction
• ectopic focus sets high rate
• can be from excessive caffeine or nicotine

AV node.

• few (partial) or no (total) impulses reach ventricles
• ventricles beat at intrinsic rate - too slow for life

heartbeat modified by ANS via cardiac centers in medullar oblongata

sympathetic affects SA, AV nodes, heart muscle, coronary arteries

parasympathetic inhibits SA and AV nodes via vagus nerves

• composite of all action potentials generated by nodal and contractile cells at given time.
• three waves: P wave, QRS complex, T wave

depolarization SA node > atria

ventricular depolarization and atrial repolarization

ventricular repolarization

beginning of atrial excitation to beginning of ventricular excitation

entire ventricular myocardium depolarized

beginning of ventricular depolarization through ventricular repolarization

• two sounds (lug dup) associated with closing of heart valves
• first as AV valves close, beginning of systole
• second as SL valves close, beginning of ventricular diastole
• pause indicates heart relaxation

• abnormal heart sounds
• usually indicate incompetetent or stenotic valves

• blood flow through heart during one complete heart beat. atrial systole and diastole followed by ventricular systole and diastole
• series of pressure and blood volume changes

contraction

relaxation

• ventricular filling, takes place in mid to late diastole
• AV valves are open, pressure low
• 80% of blood passively flows into ventricles
• atrial systole occurs, delivering remaining 20%
• end diastolic volume(EDV): volume of blood in each ventricle at end of ventricular diastole

• ventricular systole
• atria relax, ventricles begin to contract
• rising ventricular pressure > closing of AV valves
• isovolumetric contraction phase (all valves closed(
• in ejection phase, ventricular pressure exceeds pressure in large arteries, forcing SL valves open
• end systolic volume (ESV): volume of blood remaining in each ventricle after systole

• isovolumetric relaxation -early diastole
• ventricles relax, atria relaxed and filling
• backflow of blood in aorta and pulmonary trunk closes SL valves. causes dicrotic notch, ventricles totally closed chambers
• when atrial pressure exceeds that in ventricles, AV valves open, cycle begins again at step 1

• volume of blood pumped by each ventricle in one minute
• normal: 5.25 liters per minute

difference between resting and maximal cardiac output

• preload: degree of stretch of cardiac muscle cells before they contract
• contractility: contractile strength at given muscle length, independent of muscle stretch and EDV
• afterload: pressure ventricles must overcome to eject blood

increase heart rate

decrease heart rate

• sympathetic nervous system activated by emotional or physical stressors
• NE causes pacemaker to fire more rapidly

• parasympathetic nervous system opposes sympathetic effects
• acetylcholine hyperpolarizes pacemaker cells

atral reflex: sympathetic reflex initiated by increased venous return, hence increased atrial filling

• hormones
• epinephrine from adrenal medulla increases heart rate and contractility
• thyroxine increases heart rate, enhances effects of NE and E

• age: fetus has faster HR
• gender: females faster than males
• exercise: increases HR
• body temp: increases with increased temp

• abnormally fast heart rate (over 100 bpm)
• if persistent, may lead to fibrillation

• heart rate slower than 60 bpm
• may result in grossly inadequate blood circulation in nonathletes
• may be desirable result of endurance training