Functions of the Heart

• Generaon of blood pressure • Roung of blood • Ensuring unidirecon flow of blood • Regulaon of blood supply

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CO2 O2

Pulmonary circuit

O2-poor, CO2-rich O2-rich, blood CO2-poor blood

Systemic circuit

CO2 O2

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4 5

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Le AV (bicuspid) valve

Right AV (tricuspid) valve

Fibrous skeleton Openings to coronary arteries

Aorc valve

Pulmonary valve

(a) 10 11

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10 1 Blood enters right atrium from superior and inferior venae cavae.

2 Blood in right atrium flows through right Aorta Le pulmonary AV valve into right ventricle. 11 artery 3 Contracon of right ventricle forces 5 5 pulmonary valve open.

4 Blood flows through pulmonary valve 9 Pulmonary trunk Superior into pulmonary trunk. vena cava 4 Le pulmonary 6 5 Blood is distributed by right and le veins pulmonary arteries to the lungs, where it Right 6 unloads CO and loads O . pulmonary 2 2 Le atrium veins 1 Aorc valve 6 Blood returns from lungs via pulmonary veins to le atrium. 3 7 Le AV 7 Blood in le atrium flows through le AV Right (bicuspid) valve 8 valve into le ventricle. atrium Le ventricle 2 8 Contracon of le ventricle (simultaneous with Right AV step 3 ) forces aorc valve open. (tricuspid) valve 9 Blood flows through aorc valve into Right ascending aorta. ventricle 10 Blood in aorta is distributed to every organ in Inferior 11 vena cava the body, where it unloads O2 and loads CO2.

11 Blood returns to heart via venae cavae.

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Striaons

Nucleus

Intercalated discs

(a)

Striated myofibril Glycogen Nucleus Mitochondria Intercalated discs

(b)

Intercellular space

Desmosomes

Gap juncons

(c) a: © Ed Reschke 18 19

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1 SA node fires.

2 Excitaon spreads through Right atrium 1 2 atrial myocardium. Sinoatrial node (pacemaker) Le 3 AV node fires. atrium 2 Purkinje 3 Excitaon spreads down AV Atrioventricular fibers 4 node bundle. Bundle Atrioventricular branches 5 Purkinje fibers distribute bundle 4 5 excitaon through ventricular myocardium.

Purkinje fibers

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R R

+1

PQ ST segment segment

P wave T wave

Millivolts 0

PR Q interval S

QT interval QRS interval

–1

Atria Ventricles Atria Ventricles contract contract contract contract

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Key Wave of depolarizaon R Wave of repolarizaon

P P

Q S

1 Atria begin depolarizing. 4 Ventricular depolarizaon complete.

R

P P T

Q S

2 Atrial depolarizaon complete. 5 Ventricular repolarizaon begins at apex and progresses superiorly.

R R

P P T

Q Q S

3 Ventricular depolarizaon begins at apex and 6 Ventricular repolarizaon complete; heart is progresses superiorly as atria repolarize. ready for the next cycle. 25

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Diastole Systole Diastole

120 Aorc pressure 100

80 Aorc valve Aorc valve Le closes opens 60 ventricular (dicroc notch) pressure AV 40 valve AV Pressure (mm Hg) Le atrial valve closes 20 pressure opens

0

120 End-diastolic volume 90 Ventricular

volume (mL) 60 End-systolic volume R R T P P ECG Q Q S S

Heart sounds

S2 S3 S1 S2 S3 S1

Phase of 1a 1b 1c 2 3 4 1a 1b 1c 2 cardiac cycle

0 .2 .4 .6 .8 .2 .4 Time (sec)

Ventricular filling 2 3 4 1a Rapid filling 1c Atrial systole Isovolumetric Ventricular Isovolumetric 1b Diastasis contracon ejecon relaxaon

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MAP ∝ CO × PR

CO = HR × SV € MAP is mean arterial pressure CO is cardiac output € PR is peripheral resistance HR is heart rate SV is stroke volume

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