Unit II: TransportCardiovascular System I

Chapter 18

Systemic circuit

Pulmonary circuit

O2-poor,CO2-richblood

O2CO2

O2-rich,CO2-poorblood

CO2 O2

Circulatory System: The Heart

• Circulatory system

• Cardiovascular system

Two major divisions:

• Pulmonary circuit - route to/from lungs

• Systemic circuit – route to/from organs

Position, Size, and Shape• Located in mediastinum, between

lungs

• Base -

• Apex -

• 3.5 in. wide at base, 5 in. from base to apex and 2.5 in. anterior to posterior; weighs 10 oz

Membranes Surrounding Heart

• Pericardial sac (Parietal pericardium)

– Fibrous layer

– Serous layer

• Pericardial cavity

– filled with pericardial fluid

• Visceral pericardium (a.k.a. epicardium of heart wall)

– covers heart surface

Pericardial sac

Epicardium

Myocardium

Endocardium

Epicardium

Pericardial cavityPericardialsac:

FibrouslayerSerouslayer

Myocardium

Endocardium

Epicardium

Parietal Pericardium

Dense fibrous layer

Areolar tissue

Mesothelium

Mesothelium

Areolar tissue

Connective tissues

Pericardial cavity(contains serous fluid)

Fibrous skeleton – network of collagen and elastic fibers

Cardiac muscle cells

Areolar tissue

Covers the inner surfaces ofthe heart

Endothelium

Outer surface of the heart; also calledvisceral pericardium

The outer wall of thepericardial cavity

Ventricularmusculature

Atrialmusculature

Heart Wall

Heart Surface Features

Pulmonary trunk

Left auricle

Apex of heart

Inferior vena cava

Right ventricle

Right atrium

Superior vena cava

Aortic arch

Coronary sulcus

Right auricle

Left ventricle

Branches of theright pulmonaryartery

Right pulmonaryveins

Ascendingaorta

Left pulmonaryartery

Left pulmonaryveins

Anteriorinterventricularsulcus

(a) Anterior view

Bra

chio

ceph

alic

T

runk L. S

ubcl

avia

n ar

tery

L. C

omm

on

Car

otid

art

ery

Blood Flow Through Heart

Pulmonary

Circulation

Systemic

Circulation

veins

Notes on Blood Flow

Ascending aorta

Superior vena cava

Right lung

Rightpulmonaryarteries

Rightpulmonary

veins

Inferior vena cava

Descending aorta

Aortic arch

Pulmonary trunk

Left lung

LeftpulmonaryarteriesLeftpulmonaryveins

Alveolus

Capillary

In Pulmonary Circulation:

• Deoxygenated blood is carried by arteries

• Oxygenated blood is carried by veins

Coronary Circulation

Arterial Supply• Left coronary artery (LCA)

– anterior interventricular branch• interventricular septum and anterior walls of both ventricles

– circumflex branch• left atrium and posterior wall of left ventricle

• Right coronary artery (RCA)– marginal branch

• lateral right atrium and ventricle– posterior interventricular branch

• interventricular septum and posterior walls of both ventricles

Coronary Circulation

Venous Supply

• 10% drains directly into right ventricle via anterior cardiac veins

• 90% returns to right atrium via:

– great cardiac vein

– middle cardiac vein (posterior interventricular)

– coronary sinus

Rightcoronaryartery(RCA)

Rightmarginalbranchof RCA

Left coronaryartery (LCA)Left auricle(reflected)Circumflexbranchof LCAGreat cardiacveinAnteriorinterventricularbranch of LCA

(a) Anterior view

Coronary Circulation

(b) Posterior view

Great cardiacvein

Circumflexbranch ofLCA

Coronarysinus

Left marginal branch of LCA

Left marginalvein

Right coronaryartery (RCA)Right marginalbranch of RCAPosteriorinterventricularbranch of RCAPosteriorinterventricularvein

Cardiac Muscle Cells

• Striated, branched cells, one central nucleus

• Intercalated discs join cardiocytes

– interdigitating folds

– mechanical junctions

– electrical junctions

• Metabolism

– Aerobic respiration

– Resistant to fatigue

– Autorhythmic

Cardiac Conduction SystemCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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1

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2Right atrium

Purkinje fibers

Sinoatrial node(pacemaker)

Atrioventricularnode

Atrioventricularbundle

SA node fires.

Excitation spreads throughatrial myocardium.

AV node fires.

Excitation spreads down AVbundle.

Purkinje fibers distributeexcitation throughventricular myocardium.

Leftatrium

Purkinjefibers

Bundlebranches

StartChambers are relaxed, and theventricles are partially filled with blood.

Atrial systole filling the relaxedventricles with blood. Atrial diastole

until the start of the next cardiac cycle.

As atrial systole ends, ventricular systole begins.

Ventricular systole—first phase: AV valves close isovolumetric contraction

Ventricular systole—second phase: ventricular pressure rises, semilunarvalves open, ventricularejection

Ventricular diastole—blood flows backAgainst the semilunar valves and forcesthem closed.

Blood flows into therelaxed atria but theAV valves remainclosed. This is knownas the period ofisovolumetricrelaxation.

Ventricular diastole—All chambers arerelaxed. The ventriclesfill passively to roughly70% of their finalvolume.

800msec

0msec 100

msec

370msec

Atrial

Cardiaccycle

systole

dias

tole

syst

ole

diastole

Ven

tric

ula

r

Atrial

Ven

tric

ular

Cardiac Rhythm

• Systole –

• Diastole -

• Sinus rhythm

– 60 – 100 bpm

– adult at rest is 70 to 80 bpm

• Arrhythmia –

– heart block: failure of conduction system

• Premature ventricular contraction (PVC)

– caused by hypoxia, electrolyte imbalance, stimulants, stress, etc.

• Ectopic foci -

– nodal rhythm - 40 to 50 bpm

• Fibrillation -

Abnormal Cardiac Rhythms

Electrocardiogram (ECG or EKG)

• P-wave

• QRS Complex

• T-wave

• Cardiac Cycle

ECGs, Normal and Abnormal

ECGs - Abnormal