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The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location –...

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The Heart Chapter 20
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Page 1: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The Heart

Chapter 20

Page 2: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Function of the Heart• Pumping the red stuff

Anatomy of the Heart• Location – mediastinum, slightly to the left

of center

• Size – about that of your fist

• Mass – 250 – 300 g

Page 3: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Organization of the

Cardiovascular System

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Location

Page 5: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Tissues of the Heart

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Coverings of the Heart: Anatomy

• Pericardium – a double-walled sac around the heart composed of:– A superficial fibrous pericardium– A deep two-layer serous pericardium

• The parietal layer lines the internal surface of the fibrous pericardium

• The visceral layer or epicardium lines the surface of the heart

• They are separated by the fluid-filled pericardial cavity

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Coverings of the Heart: Physiology

• The pericardium:– Protects and anchors the heart– Prevents overfilling of the heart with blood– Allows for the heart to work in a relatively

friction-free environment

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Serous pericardium

Page 9: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

General Anatomy

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Heart Wall

• Epicardium – visceral layer of the serous pericardium

• Myocardium – cardiac muscle layer forming the bulk of the heart

• Fibrous skeleton of the heart – crisscrossing, interlacing layer of connective tissue

• Endocardium – endothelial layer of the inner myocardial surface

Page 11: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

• Vessels returning blood to the heart include:– Superior and inferior venae cavae– Right and left pulmonary veins

• Vessels conveying blood away from the heart include:– Pulmonary trunk, which splits into right and left

pulmonary arteries– Ascending aorta (three branches) – brachiocephalic,

left common carotid, and subclavian arteries

External Heart: Major Vessels of the Heart (Anterior View)

Page 12: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

• Arteries – right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular arteries

• Veins – small cardiac, anterior cardiac, and great cardiac veins

External Heart: Vessels that Supply/Drain the Heart (Anterior View)

Page 13: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Surface features of the heart

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Page 15: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Cardiac Muscle CellsFigure 20–5

Page 16: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

• Vessels returning blood to the heart include:– Right and left pulmonary veins– Superior and inferior venae cavae

• Vessels conveying blood away from the heart include:– Aorta– Right and left pulmonary arteries

External Heart: Major Vessels of the Heart (Posterior View)

Page 17: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Posterior view

Page 18: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Atria of the Heart

• Atria are the receiving chambers of the heart

• Each atrium has a protruding auricle

• Pectinate muscles mark atrial walls

• Blood enters right atria from superior and inferior venae cavae and coronary sinus

• Blood enters left atria from pulmonary veins

Page 19: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Deep in your heart of hearts…

Page 20: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Ventricles of the Heart

• Ventricles are the discharging chambers of the heart

• Papillary muscles and trabeculae carneae muscles mark ventricular walls

• Right ventricle pumps blood into the pulmonary trunk

• Left ventricle pumps blood into the aorta

Page 21: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.
Page 22: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Note the differences in wall thickness

Page 23: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Heart Valves

• Heart valves ensure unidirectional blood flow through the heart

• Atrioventricular (AV) valves lie between the atria and the ventricles

• AV valves prevent backflow into the atria when ventricles contract

• Chordae tendineae anchor AV valves to papillary muscles

Page 24: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Heart Valves

• Aortic semilunar valve lies between the left ventricle and the aorta

• Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk

• Semilunar valves prevent backflow of blood into the ventricles

Page 25: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The heart valves

Page 26: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Function of the bicuspid valve

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Valve functions

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Page 29: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Heart Sounds

Page 30: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Where to go to listen to heart sounds

Page 31: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Some heart valve disorders• Stenosis (narrowing) – the inability of a valve to

open fully

• Insufficiency (incompetence) – failure of the valve to prevent back flow or close properly– Mitral valve prolapse – one or both of the flaps

blows back into the atrium during systole (contraction) of the ventricle allowing backflow into the atrium.

– The aortic semilunar valves can also suffer from stenosis or insufficiency, allowing backflow into the ventricle.

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Pathway of Blood Through the Heart and Lungs

• Right atrium tricuspid valve right ventricle

• Right ventricle pulmonary semilunar valve pulmonary arteries lungs

• Lungs pulmonary veins left atrium

• Left atrium bicuspid valve left ventricle

• Left ventricle aortic semilunar valve aorta

• Aorta systemic circulation

Page 33: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Systemic & pulmonary circuits

Page 34: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Blood flow

Page 35: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Coronary Circulation

• Coronary circulation is the functional blood supply to the heart muscle itself

• Collateral routes ensure blood delivery to heart even if major vessels are occluded

Page 36: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Coronary Circulation

(arterial)

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Coronary Circulation

(venous)

Page 38: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.
Page 39: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Cardiac histology & physiology• Cardiac muscle is made of short, branched

fibers

• Striated

• Uninucleate

• There is now some evidence that it has limited mitotic capability (it is likely that regeneration is from migration of stem cells from the blood)

• 99% are contractile

• 1% are “autorhythmic” or “pacemaker” cells

Page 40: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Cardiac Muscle Tissue

Page 41: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.
Page 42: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Cardiac Muscle Cells

• Intercalated discs:– interconnect cardiac muscle cells– secured by desmosomes – linked by gap junctions– convey force of contraction – propagate action potentials

Page 43: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Characteristics of Cardiac Muscle Cells

1. Small size

2. Single, central nucleus

3. Branching interconnections between cells

4. Intercalated discs

Page 44: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Cardiac Cells vs. Skeletal Fibers Table 20-1

Page 45: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The intrinsic conduction system

• Sinoatrial node: the primary pacemaker – has an intrinsic firing rate of about 100 bpm but kept at 60 – 80 by parasympathetic tone

• Generates pacemaker potentials from leakage of Ca++

• Depolarization spreads via gap junctions in intercalated disks

• Rate can be adjusted by ANS

Page 46: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Intrinsic conduction system • Signals from SA node travel to the

Atrioventricular Node via the internodal pathway

• The AV node has its own intrinsic firing rate of 40 – 60 bpm. In absence of SA node function it can establish a “junctional rhythm” that keeps the ventricles working

Page 47: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The conducting pathways

• The signal is delayed about 0.1 s and then transmitted down the …

• Bundle of His or AV bundle and the left & right bundle branches to the apex

• And from there the depolarization is distributed by the Purkinje fibers

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Fig. 20.10a

Page 49: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.
Page 50: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Contraction of cardiac muscle fibersand the cardiac cycle

Page 51: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The ElectrocardiogramFigure 20–14b

Page 52: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

NSR:Normal Sinus

Rhythm

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Prolonged contraction of cardiac muscle

Page 54: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Features of an ECG

• P wave:

– atria depolarize

• QRS complex:

– ventricles depolarize

• T wave:

– ventricles repolarize

Page 55: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Resting Potential

• Of a ventricular cell:

–about —90 mV

• Of an atrial cell:

–about —80 mV

Page 56: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

3 Steps of Cardiac Action Potential

1.Rapid depolarization:

» voltage-regulated sodium channels (fast channels) open

Page 57: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

3 Steps of Cardiac Action Potential

2. As sodium channels close:

– voltage-regulated calcium channels (slow channels) open

– balance Na+ ions pumped out

– hold membrane at 0 mV plateau

Page 58: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

3 Steps of Cardiac Action Potential

3. Repolarization:

– plateau continues

– slow calcium channels close

– slow potassium channels open

– rapid repolarization restores resting potential

Page 59: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The Refractory Periods

• Absolute refractory period:

– long

– cardiac muscle cells cannot respond

• Relative refractory period:

– short

– response depends on degree of stimulus

Page 60: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Timing of Refractory Periods

• Length of cardiac action potential in ventricular cell:– 250–300 msecs

• 30 times longer than skeletal muscle fiber• long refractory period prevents summation

and tetany

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ElectricalActivity and the Cardiac Cycle

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Calcium and Contraction

• Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils

Page 63: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

2 Steps of Calcium Ion Concentration

1. 20% of calcium ions required for a contraction:

– calcium ions enter cell membrane during plateau phase

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2 Steps of Calcium Ion Concentration

2. Arrival of extracellular Ca2+:– triggers release of calcium ion reserves from

sarcoplasmic reticulum

Page 65: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Intracellular and Extracellular Calcium

• As slow calcium channels close:– intracellular Ca2+ is absorbed by the SR– or pumped out of cell

• Cardiac muscle tissue:– very sensitive to extracellular Ca2+

concentrations

Page 66: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

The Cardiac Cycle

• CO is the amount of blood pumped by each ventricle in one minute

• CO is the product of heart rate (HR) and stroke volume (SV)

• HR is the number of heart beats per minute

• SV is the amount of blood pumped out by a ventricle with each beat

• Cardiac reserve is the difference between resting and maximal CO

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Phases of the Cardiac CycleFigure 20–16

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Cardiac output

• CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)• CO = 5250 ml/min (5.25 L/min)

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Cardiac output

• SV = end diastolic volume (EDV) minus end systolic volume (ESV)

• EDV = amount of blood collected in a ventricle during diastole

• ESV = amount of blood remaining in a ventricle after contraction

Page 70: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Pressure and

Volume in the

Cardiac Cycle

Figure 20–17

Page 71: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Factors Affecting Stroke Volume

• Preload – amount ventricles are stretched by contained blood

• Contractility – cardiac cell contractile force due to factors other than EDV

• Afterload – back pressure exerted by blood in the large arteries leaving the heart

Page 72: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Factors Affecting Stroke Volume

• Changes in EDV or ESV

Figure 20–23 (Navigator)

Page 73: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Frank-Starling Law of the Heart

• Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume

• Slow heartbeat and exercise increase venous return to the heart, increasing SV

• Blood loss and extremely rapid heartbeat decrease SV

Page 74: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Extrinsic Factors Influencing Stroke Volume

• Contractility is the increase in contractile strength, independent of stretch and EDV

• Increase in contractility comes from: – Increased sympathetic stimuli– Certain hormones– Ca2+ and some drugs

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Factors Affecting Heart Rate and Stroke Volume

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Extrinsic Factors Influencing Stroke Volume

• Agents/factors that decrease contractility include:– Acidosis– Increased extracellular K+

– Calcium channel blockers

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Contractility and Norepinephrine

• Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system

Figure 18.22

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Regulation of Heart Rate

• Positive chronotropic factors increase heart rate

• Negative chronotropic factors decrease heart rate

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• Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise

• Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS

• PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone

Regulation of Heart Rate: Autonomic Nervous System

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Autonomic Innervation

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Autonomic Pacemaker Regulation

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Autonomic Pacemaker Regulation (1 of 3)

• Sympathetic and parasympathetic stimulation:– greatest at SA node (heart rate)

• Membrane potential of pacemaker cells:– lower than other cardiac cells

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Autonomic Pacemaker Regulation (2 of 3)

• Rate of spontaneous depolarization depends on:– resting membrane potential– rate of depolarization

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Autonomic Pacemaker Regulation (3 of 3)

• ACh (parasympathetic stimulation):– slows the heart

• NE (sympathetic stimulation):– speeds the heart

Page 85: The Heart Chapter 20. Function of the Heart Pumping the red stuff Anatomy of the Heart Location – mediastinum, slightly to the left of center Size – about.

Atrial (Bainbridge) Reflex

• Atrial (Bainbridge) reflex – a sympathetic reflex initiated by increased blood in the atria– Causes stimulation of the SA node– Stimulates baroreceptors in the atria,

causing increased SNS stimulation

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CNS and ANS controls of Cardiac output

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Chemical Regulation of the Heart

• The hormones epinephrine and thyroxine increase heart rate

• Intra- and extracellular ion concentrations must be maintained for normal heart function

InterActive Physiology®: Cardiovascular System: Cardiac OutputPLAYPLAY

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Factors Involved in Regulation of Cardiac Output

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How the heart starts

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Examples of Congenital Heart Defects

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Congestive Heart Failure (CHF)

• Congestive heart failure (CHF) is caused by:– Coronary atherosclerosis– Persistent high blood pressure– Multiple myocardial infarcts– Dilated cardiomyopathy (DCM)

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Arteriosclerosis

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Fig. 20.20

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Age-Related Changes Affecting the Heart

• Sclerosis and thickening of valve flaps

• Decline in cardiac reserve

• Fibrosis of cardiac muscle

• Atherosclerosis


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