Chapter 18 – The Heart

Heart function • Serves as the pump

for the cardiovascular system

• “double pump” – Right side of the

heart – pulmonary circulation

– Left side of the heart – systemic circulation

Heart Anatomy • Located within the

mediastinum • 2/3 of heart left of

sternum • Base is most superior

portion – Angled toward right

shoulder • Apex is most inferior

portion – Angled toward left hip – Rests on diaphragm

Heart coverings • Fibrous pericardium– Tough superficial

layer • Serous pericardium – Deep to fibrous layer – Parietal layer – Visceral layer – In between parietal

and visceral layers is pericardial cavity filled with serous fluid

Heart covering abnormalities

• Pericarditis – Inflammation of pericardium • Swelling can cause friction; impedes heart activity

• Cardiac tamponade– Accumulation of fluid in pericardial cavity;

compresses heart – Excess fluid can be drained via a syringe

Layers of heart walls • Superficial

– Epicardium (visceral layer of serous pericardium)

• Middle – Myocardium – Mainly cardiac muscle – Muscle connected by

spiral/circular intercrossing connective tissue • Supports muscle; anchors in place • Thicker in high stress

• Deep – Endocardium – Simple squamous epithelium – Lines heart chambers – Continuous with endothelium of

blood vessels

Heart chambers • 4 chambers

– 2 superior atria – 2 inferior ventricles

• Left and right sides of heart are divided by septum – Interatrial and

interventricular • 2 main sulci on surface

– Coronary sulcus • Divides atria from

ventricles – Interventricular sulcus

• Separates two ventricles • Anterior and posterior

Atria (singular = atrium)• Receiving chambers of the heart • Relatively thin walled • Superficially covered by flaplike

auricles • Anterior surface of RA has ridged

walls – pectinate muscles • Interatrial septum has fossa

ovalis – Remnant of fetal circulation

• RA receives blood from 3 main vessels – Inferior and superior vena cava,

and coronary sinus • LA receives blood from lungs via

4 pulmonary veins

Ventricles • Actual pumps of the heart • RV = most of heart’s

anterior surface • Walls are thicker than atrial

walls/LV thicker than RV• Internal walls have

irregular muscle ridges – trabeculae carneae

• Domelike papillary muscles involved with AV valves

• RV pumps blood through pulmonary trunk

• LV pumps blood through aorta

Heart valves • Atrioventricular– RAV – tricuspid – LAV – bicuspid/mitral

valve– Chordae tendinae

“heartstrings”• Attaches valve cusps

to papillary muscles• Allows cusps to close

tightly, and not flap back into atria – Prohibits backflow

of blood

Heart valves • Semilunar • Aortic – junction between LV

and aorta • Pulmonary – junction

between RV and pulmonary trunk

• Both have three cusps • Open when pressure inside

ventricles is higher than pressure in blood vessels; close when pressure is less in ventricles than in blood vessels – Blood flows backwards and

closes valves

Blood vessels

• Direction of blood flow – Arteries – carry blood away from heart – Veins – retun blood back to the heart

• Respiratory gas content – Red – contains oxygen-rich/carbon dioxide-poor

blood – Blue – contains oxygen-poor/carbon dioxide-rich

blood

Pathway of blood through heart

• Pulmonary circuit– To and from lungs – RA → RV → pulmonary trunk → pulmonary

arteries → lung → pulmonary veins → LA • Systemic circuit – To and from all other body tissues – LA → LV → aorta → systemic arteries → tissues →

systemic veins → RA

Coronary circulation • Myocardium is too

thick for diffusion to occur

• Coronary arteries– Supply heart with

oxygen and nutrients – Branch from base of

aorta (ascending aorta)

• Cardiac veins – Carries carbon dioxde

and wastes – Join with cardiac sinus,

or enter RA directly

Coronary circulation abnormalities • Myocardial

infarction “heart attack”– Coronary

blockage leads to cell death • Cardiac muscle

is amitotic • Replaced by

non-functioning scar tissue

Remnants of fetal circulation

• Blood does not need to go to lungs to get oxygenated

• Fossa ovalis– Depression that was fetal foramen ovalis • allowed for blood in RA to directly enter LA

• Ligamentum arteriosum – Fetal ductus arteriosum • Connected pulmonary trunk to aorta

Cardiac muscle fibers• Cardiac muscle cells

– Striated, branched, and involuntary

• Intercalated discs– Anchoring desmosomes

• Keep cells associated with each other

– Gap junctions• Allows ions to pass

directly from cell to cell

• Large, numerous mitochondria – Fatigue resistant

Heart physiology • Intrinsic cardiac conduction

– Noncontractile cardiac cells that have the ability to initiate contraction • Located in RA in sinoatrial (SA)

node “pacemaker”• Depolarization spreads via gap

junctions allowing atria to contract

– Impulse spread to atrioventricular (AV) node• Located immediately above

tricuspid valve • Impulse is delayed to allow for

complete contraction of atria before ventricular contraction

Heart physiology • Intrinsic cardiac conduction

cont – No gap junctions between

atria and ventricles • Electrical impulse from AV node

to bundle of His/atrioventricular bundle – Located in atrioventricular

septum

– Purkinje fibers transmit impulse throughout ventricles

• Extrinsic cardiac conduction – Autonomic nervous system

can modify heartbeat

Heart physiology abnormalities

• Arrhythmia– Uncoordinated atrial and ventricular contractions

• Fibrillation – SA node not in control – out of phase contractions – Defibrillators

• Electrical shock to heart – hopefully eliminates chaotic rhythms so SA node can re-establish normal rhythm

– Tachycardia – heartbeat over 100 per minute; can cause fibrillation

– Bradycardia • Heartbeat below 60 per minute

ECG/EKG (electrocardiogram)• Graphic recording of

electrical current generated/transmitted through heart

• 3 waves – P wave (small)

• Depolarization from SA node to atria

– QRS (large/sharp)• Ventricular depolarization

(during same time, atria are re-polarizing)

– T wave• Ventricular repolarization

Heart sounds

• “lub dup” caused by closing of valves – “lub” closing of AV valves; ventricular contraction – “dup” closing of SL valves; ventricular relaxation

• Shorter, sharper sound

• Abnormalities – Heart murmurs

• Blood more turbulent due to obstruction • Leaky valves

– VSD (ventricular septal defect)• Causes blood to leak from RV into LV• Causes hissing sounds

Cardiac cycle • Systole – contraction of

chambers • Diastole – relaxation of

chambers • Cardiac cycle = one complete

heartbeat• Ventricular filling

– Mid-late diastole – AV valves open; SL valves closes – Atrial systole forces all blood

into ventricles • Ventricular systole

– AV valves close; SL valves open – Blood forced into pulmonary

trunk (from right) and aorta (from left)

Cardiac cycle cont • Ventricular diastole – early

– Backflow from pulmonary trunk and aorta causes SL valves to close

– Atria fill; increase in pressure forces AV valves to open

• Average cardiac cycle = 0.8 seconds– Approx 74 heartbeats per

minute • Cardiac output

– Amount of blood pumped out of each ventricle per minute

– ~5L per minute