29

Human

Anatomy

& Physiology

SEVENTH EDITION

Elaine N. Marieb

Katja Hoehn

PowerPoint® Lecture Slides

prepared by Vince Austin,

Bluegrass Technicaland Community College

C H A P T E R

TheCardiovascularSystem: TheHeart

P A R T B

Cardiac Muscle Contraction

Heart muscle:

Is stimulated by nerves and is self-excitable(automaticity)

Contracts as a unit

Has a long (250 ms) absolute refractory period

(compared to 1-2 ms in skeletal muscle)

Cardiac muscle contraction is similar to skeletalmuscle contraction

Heart Physiology: Intrinsic ConductionSystem

Autorhythmic cells:

Initiate action potentials

Have unstable resting potentials called pacemakerpotentials

http://t0.gstatic.com/images?q=tbn:ANd9GcTQedX4Zb2h1zSpbGOXw6dTOI3ChiRD-c9jU1mjdNC7Dqj6hgOGgmXgQgwj

Heart Physiology: Sequence of Excitation

Sinoatrial (SA) node generates impulses about 75times/minute

Atrioventricular (AV) node delays the impulseapproximately 0.1 second

Impulse passes from atria to ventricles via theatrioventricular bundle (bundle of His)

Heart Physiology: Sequence of Excitation

AV bundle splits into two pathways in theinterventricular septum (bundle branches)

Bundle branches carry the impulse toward the apexof the heart

Purkinje fibers carry the impulse to the heart apexand ventricular walls

Cardiac Intrinsic Conduction

Figure 18.14a

SA node generates impulse;

atrial excitation begins

Impulse delayed

at AV node

Impulse passes to

heart apex; ventricular

excitation begins

Ventricular excitation

complete

SA node

AV node

Purkinje

fibers

Bundle

branches

Figure 18.17

Heart Excitation Related to ECG

http://www.youtube.com/watch?v=MGxxRyJTmwU&feature=related

SA node generates impulse;

atrial excitation begins

SA node

Figure 18.17

Heart Excitation Related to ECG

Impulse delayed

at AV node

AV node

Figure 18.17

Heart Excitation Related to ECG

Impulse passes to

heart apex; ventricular

excitation begins

Bundle

branches

Figure 18.17

Heart Excitation Related to ECG

Ventricular excitation

complete

Purkinje

fibers

Figure 18.17

Heart Excitation Related to ECG

SA node generates impulse;

atrial excitation begins

Impulse delayed

at AV node

Impulse passes to

heart apex; ventricular

excitation begins

Ventricular excitation

complete

SA node

AV node

Purkinje

fibers

Bundle

branches

Figure 18.17

Heart Excitation Related to ECG

Extrinsic Innervation of the Heart

Heart is stimulated bythe sympatheticcardioacceleratorycenter

Heart is inhibited bythe parasympatheticcardioinhibitorycenter

Figure 18.15

Electrocardiography

Electrical activity is recorded by electrocardiogram(ECG)

P wave corresponds to depolarization of SA node

QRS complex corresponds to ventriculardepolarization

T wave corresponds to ventricular repolarization

Atrial repolarization record is masked by the largerQRS complex

PLAY

InterActive Physiology ®:

Intrinsic Conduction System, pages 3–6

Electrocardiography

Figure 18.16

ECG Tracings

Figure 18.18

Heart Sounds

Figure 18.19

Heart Sounds

Heart sounds (lub-dup) are associated with closingof heart valves

First sound occurs as AV valves close and signifiesbeginning of systole (when ventricles contract andthe atria relax)

Second sound occurs when semilunar (SL) valvesclose at the beginning of ventricular diastole(when ventricles relax)

Cardiac Cycle

Cardiac cycle refers to all events associated withblood flow through the heart

Systole – contraction of heart muscle

Diastole – relaxation of heart muscle

Phases of the Cardiac Cycle

Ventricular filling – mid-to-late diastole

Heart blood pressure is low as blood enters atriaand flows into ventricles

AV valves are open, then atrial systole occurs

Phases of the Cardiac Cycle

Ventricular systole

Atria relax

Rising ventricular pressure results in closing of AVvalves

Isovolumetric contraction phase

Ventricular ejection phase opens semilunar valves

Phases of the Cardiac Cycle

Isovolumetric relaxation – early diastole

Ventricles relax

Backflow of blood in aorta and pulmonary trunkcloses semilunar valves

Dicrotic notch – brief rise in aortic pressure causedby backflow of blood rebounding off semilunarvalves

PLAY

InterActive Physiology ®: Cardiac Cycle, pages 3–18

Figure 18.20

Blood flow through the heart is controlled bypressure changes.

Blood flows down a pressure gradient.

Cardiac Output (CO) and Reserve

CO is the amount of blood pumped by eachventricle in one minute

CO is the product of heart rate (HR) and strokevolume (SV)

HR is the number of heart beats per minute

SV is the amount of blood pumped out by aventricle with each beat

Cardiac reserve is the difference between restingand maximal CO

Cardiac Output: Example

CO (ml/min) = HR (75 beats/min) x SV (70ml/beat)

CO = 5250 ml/min (5.25 L/min)

Entire blood supply passes through each side of theheart once each minute

Cardiac output varies directly with SV and HR

Regulation of Stroke Volume

SV = end diastolic volume (EDV) minusend systolic volume (ESV)

EDV = amount of blood collected in aventricle during diastole

How long ventricular diastole lasts

Venous pressure

ESV = amount of blood remaining in aventricle after contraction

Arterial blood pressure

Force of ventricular contraction

Atrial and Ventricular diastole isovolumetric filling

Factors Affecting Stroke Volume

Preload – amount ventricles are stretched bycontained blood

Affects EDV

Contractility – cardiac cell contractile force

Affects ESV

Afterload – back pressure exerted by blood in thelarge arteries leaving the heart

Affects ESV

Regulation of Heart Rate

Positive chronotropic factors increase heart rate

Negative chronotropic factors decrease heart rate

Autonomic Nervous System

Chemical Regulation

Other Factors

Age, gender, exercise, body temperature

Sympathetic nervous system (SNS) stimulation isactivated by stress, anxiety, excitement, or exercise

Parasympathetic nervous system (PNS)stimulation is mediated by acetylcholine andopposes the SNS

PNS dominates the autonomic stimulation, slowingheart rate and causing vagal tone

Slows SA node by 25 beats/min.

Regulation of Heart Rate: Autonomic NervousSystem

Chemical Regulation of the Heart

The hormones epinephrine and thyroxine increaseheart rate

Intra- and extracellular ion concentrations must bemaintained for normal heart function

PLAY

InterActive Physiology ®: Cardiac Output, pages 3–9

Homeostatic Imbalance of Cardiac Output

Congestive heart failure (CHF) – when thepumping efficiency (CO) of the heart is so low thatblood circulation is inadequate to meet tissueneeds.

Congestive heart failure (CHF) is caused by:

Coronary atherosclerosis

Persistent high blood pressure

Multiple myocardial infarcts

Dilated cardiomyopathy (DCM)

Developmental Aspects of the Heart

Begins as two simple endothelial tubes, fuse toform one chamber.

Pumps by day 23

By day 25, four chambers are present

Developmental Aspects of the Heart

Fetal heart structures that bypass pulmonarycirculation

Foramen ovale connects the two atria

Ductus arteriosus connects pulmonary trunk andthe aorta

At or shortly after birth, these shunts close

Examples of Congenital Heart Defects

Figure 18.25

1.Lead to mixing or oxygen-poor systemic bloodwith oxygenated pulmonary blood

2.Involves narrowed valves or vessels

Age-Related Changes Affecting the Heart

Sclerosis and thickening of valve flaps

Usually mitral

Decline in cardiac reserve

Fibrosis of cardiac muscle

Atherosclerosis