unit 5 heart

8/10/2019 Unit 5 Heart

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Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C h a p t e r

20

The Heart

PowerPoint Lecture Slidesprepared by Jason LaPres

Lone Star College - North Harris

Copyright 2009 Pearson Education, Inc.,

publishing as Pearson Benjamin Cummings


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Introduction to Cardiovascular System

The Pulmonary Circuit

Carries blood to and from gas exchange surfaces of

lungs

The Systemic Circuit

Carries blood to and from the body

Blood alternates between pulmonary circuit and

systemic circuit


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Three Types of Blood Vessels

Arteries

Carry blood away fromheart

Veins

Carry blood toheart

Capillaries

Networks betweenarteries and veins


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Capillaries

Also called exchange vessels

Exchange materials between blood and

tissues

Materials include dissolved gases, nutrients,

wastes


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Figure 201 An Overview of the Cardiovascular System.


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Four Chambers of the Heart

Right atrium

Collects blood from systemic circuit

Right ventricle

Pumps blood to pulmonary circuit

Left atrium

Collects blood from pulmonary circuit

Left ventricle

Pumps blood to systemic circuit


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Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 202c

Anatomy of the Heart

Great veins and arteries at the base

Pointed tip is apex

Surrounded by pericardial sac

Sits between two pleural cavities in the

mediastinum


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Figure 202a The Location of the Heart in the Thoracic Cavity


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Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 202c


The Pericardium

Double lining of the pericardial cavity

Parietal pericardium

Outer layer

Forms inner layer of pericardial sac

Visceral pericardium

Inner layer of pericardium


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Figure 202b The Location of the Heart in the Thoracic Cavity


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Figure 20c2 The Location of the Heart in the Thoracic Cavity


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Superficial Anatomy of the Heart

Atria

Thin-walled

Expandable outer auricle(atrial appendage)

Sulci

Coronary sulcus: divides atria and ventricles

Anterior interventricular sulcusand posterior

interventricular sulcus:

separate left and right ventricles

contain blood vessels of cardiac muscle


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Figure 203a The Superficial Anatomy of the Heart


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Figure 203c The Superficial Anatomy of the Heart


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The Heart Wall

Epicardium(outer layer)

Visceral pericardium

Covers the heart

Myocardium (middle layer)

Muscular wall of the heart

Concentric layers of cardiac muscle tissue

Atrial myocardium wraps around great vessels Two divisions of ventricular myocardium

Endocardium (inner layer)

Simple squamous epithelium


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Figure 204 The Heart Wall


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Cardiac Muscle Tissue

Intercalated discs

Interconnect cardiac muscle cells

Secured by desmosomes

Linked by gap junctions

Convey force of contraction

Propagate action potentials


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Figure 205 Cardiac Muscle Cells


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Figure 205 Cardiac Muscle Cells


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Characteristics of Cardiac Muscle Cells

Small size

Single, central nucleus

Branching interconnections between cells

Intercalated discs


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Internal Anatomy and Organization

Interatrial septum: separates atria

Interventricular septum: separates ventricles

Atrioventricular (AV) valves

Connect right atrium to right ventricle and left atrium to left

ventricle

The fibrous flaps that form bicuspid (2) and tricuspid (3)valves

Permit blood flow in one direction: atria to ventricles


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The Right Atrium

Superior vena cava

Receives blood from head, neck, upper limbs, and chest

Inferior vena cava

Receives blood from trunk, viscera, and lower limbs

Coronary sinus

Cardiac veins return blood to coronary sinus

Coronary sinus opens into right atrium


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The Right Atrium

Foramen ovale

Before birth, is an opening through interatrial

septum

Connects the two atria

Seals off at birth, forming fossa ovalis


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Figure 206a-b The Sectional Anatomy of the Heart.


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Figure 206a-b The Sectional Anatomy of the Heart.


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The Right Ventricle Free edges attach to chordae tendineae

from papillary musclesof ventricle

Prevent valve from opening backward

Right atrioventricular (AV) Valve

Also called tricuspid valve

Opening from right atrium to right ventricle Has three cusps

Prevents backflow


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The Pulmonary Circuit

Conus arteriosus(superior end of right ventricle)

leads to pulmonary trunk

Pulmonary trunk divides into left andright

pulmonary arteries

Blood flows from right ventricle to pulmonary trunkthrough pulmonary valve

Pulmonary valve has three semilunar cusps


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The Left Atrium

Blood gathers into left andright pulmonary

veins Pulmonary veins deliver to left atrium

Blood from left atrium passes to left ventricle

through left atrioventricular (AV) valve

A two-cusped bicuspid valveor mitral valve


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The Left Ventricle

Holds same volume as right ventricle

Is larger; muscle is thicker and more powerful

Systemic circulation

Blood leaves left ventricle through aortic valveinto

ascending aorta

Ascending aorta turns (aortic arch) and becomes

descending aorta


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Structural Differences between the Left

and Right Ventricles

Right ventricle wall is thinner, develops less

pressure than left ventricle

Right ventricle is pouch-shaped, left ventricle

is round


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Figure 207 Structural Differences between the Left and RightVentricles


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Figure 207 Structural Differences between the Left and RightVentricles


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The Heart Valves Two pairs of one-way valves prevent backflow

during contraction

Atrioventricular (AV) valves

Between atria and ventricles

Blood pressure closes valve cusps during ventricular

contraction

Papillary muscles tense chordae tendineae: prevent valves

from swinging into atria

Figure 208


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The Heart Valves

Semilunar valves

Pulmonary and aortic tricuspid valves

Prevent backflow from pulmonary trunk and aorta

into ventricles

Have no muscular support

Three cusps support like tripod

Figure 208


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Figure 208a Valves of the Heart


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Figure 208b Valves of the Heart


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The Blood Supply to the Heart = Coronary

Circulation

Coronary arteriesand cardiac veins

Supplies blood to muscle tissue of heart


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The Coronary Arteries

Left and right

Originate at aortic sinuses

High blood pressure,

elastic rebound

forces blood through coronary arteries between

contractions


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Two main branches of left coronary artery

Circumflex artery

Anterior interventricular artery

Arterial Anastomoses

Interconnect anterior and posterior

interventricular arteries

Stabilize blood supply to cardiac muscle


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Figure 209a Coronary Circulation


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The Conducting System

Heartbeat

A single contraction of the heart

The entire heart contracts in series

First the atria

Then the ventricles


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Two Types of Cardiac Muscle Cells

Conducting system

Controls and coordinates heartbeat

Contractile cells/ Auto rhythmic cells

Produce contractions that propel blood

99 % of the cells in the heart

C S


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Chapter 9 Cardiac Physiology

Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Circulatory System

Heart

Dual pump

Right and left sides of heart function as two

separate pumps


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Blood Flow Through and Pump Action of the Heart

Th C d ti S t


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The Cardiac Cycle

Begins with action potential at SA node

Transmitted through conducting system

Produces action potentials in cardiac muscle cells (contractile

cells)

Th C d ti S t


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Structures of the System

Sinoatrial (SA) node - wall of right atrium

Atrioventricular (AV) node - junction betweenatria and ventricles

Bundle of His through the septum

Purkinje fibres branches from His to the

ventricle walls


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S d f C di E it ti


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Spread of Cardiac Excitation

Th C d ti S t


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Prepotential

Also called pacemaker potential

Resting potential of conducting cells

Gradually depolarizes toward threshold

SA node depolarizes first, establishing heart

rate

Th C d ti S t


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Figure 2012 The Conducting System of the Heart

Th C d ti S t


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Heart Rate

SA node generates 80100 action potentials

per minute

Parasympathetic stimulation slows heart rate

AV node generates 40

60 action potentialsper minute

Th C d ti S t


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The Sinoatrial (SA) Node

In posterior wall of right atrium

Contains pacemaker cells

Connects to interartial pathway

& Connected to AV node by internodal

pathways

Begins atrial activation (Step 1)

Th C d ti S t


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Figure 2013 Impulse Conduction through the Heart

The Cond cting S stem


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The Atrioventricular (AV) Node

In floor of right atrium

Receives impulse from SA node (Step 2)

Delays impulse (Step 3)

AV nodal delay

Ensures maximum filling of ventricle before

Atrial contraction begins

In order to complete ventricular filling


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Bundle of His

In the septum

Carries impulse to left and right bundle

branches

Which conduct to Purkinje fibers (Step 4)

The signal is sent bottom then up so that the large

muscles of the ventricle contract & not just the top

half



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Purkinje Fibers

Distribute impulse through ventricles (Step 5)

Atrial contraction is completed

Ventricular contraction begins

Which forces blood up into the arteries



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Abnormal Pacemaker Function

Bradycardia: abnormally slow heart rate

Tachycardia: abnormally fast heart rate

Ectopic pacemaker

Abnormal cells

Generate high rate of action potentials

Bypass conducting system

Disrupt ventricular contractions

Electrocardiogram (ECG)


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Electrocardiogram (ECG)

Record of overall spread of electrical activity through heart

Represents Records part of electrical activity induced in body fluids by

cardiac impulse that reaches body surface

Not direct recording of actual electrical activity of heart

Records overall spread of activity throughout heart during

depolarization and repolarization

Not a recording of a single action potential in a single cell at a

single point in time

Comparisons in voltage detected by electrodes at two

different points on body surface, not the actual potential



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Features of an ECG

P wave

Atria depolarize

QRS complex

Ventricles depolarize

T wave

Ventricles repolarize



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Time Intervals Between ECG Waves

PR interval

From start of atrial depolarization To start of QRS complex

QT interval

From ventricular depolarization

To ventricular repolarization



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Figure 2014b An Electrocardiogram: An ECG Printout



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Contractile Cells

Purkinje fibers distribute the stimulus to the

contractile cells, which make up most of the

muscle cells in the heart

Resting Potential

Of a ventricular cell: about 90 mV

Of an atrial cell: about 80 mV



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Figure 2015 The Action Potential in Cardiac Muscle



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Figure 2015 The Action Potential in Skeletal and Cardiac Muscle



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Contractile Cells

Purkinje fibers distribute the stimulus to the

contractile cells, which make up most of the

muscle cells in the heart

Resting Potential

Of a ventricular cell: about 90 mV

Of an atrial cell: about 80 mV



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Figure 2015 The Action Potential in Skeletal and Cardiac Muscle



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Abnormal Pacemaker Function

Bradycardia: abnormally slow heart rate

Tachycardia: abnormally fast heart rate

Ectopic pacemaker

Abnormal cells

Generate high rate of action potentials

Bypass conducting system

Disrupt ventricular contractions



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Electrocardiogram (ECG or EKG)

A recording of electrical events in the heart

Obtained by electrodes at specific body

locations

Abnormal patterns diagnose damage



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Features of an ECG

P wave

Atria depolarize

QRS complex

Ventricles depolarize

T wave

Ventricles repolarize



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Time Intervals Between ECG Waves

PR interval

From start of atrial depolarization

To start of QRS complex

QT interval

From ventricular depolarization

To ventricular repolarization



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Figure 2014a An Electrocardiogram: Electrode Placement forRecording a Standard ECG



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Figure 2014b An Electrocardiogram: An ECG Printout



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Refractory Period

Absolute refractory period

Long

Cardiac muscle cells cannot respond

Relative refractory period

Short

Response depends on degree of stimulus



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Timing of Refractory Periods

Length of cardiac action potential in

ventricular cell

250300 msecs:

30 times longer than skeletal muscle fiber

long refractory period prevents summation and tetany



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The Role of Calcium Ions in Cardiac

Contractions

Contraction of a cardiac muscle cell is

produced by an increase in calcium ion

concentration around myofibrils



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Contractions

20% of calcium ions required for a contraction

Calcium ions enter plasma membrane during plateau phase

Arrival of extracellular Ca2+

Triggers release of calcium ion reserves from sarcoplasmic

reticulum



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Contractions

As slow calcium channelsclose Intracellular Ca2+is absorbed by the SR

Or pumped out of cell

Cardiac muscle tissue

Very sensitive to extracellular Ca2+concentrations



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The Energy for Cardiac Contractions

Aerobic energy of heart

From mitochondrial breakdown of fatty acids and

glucose

Oxygen from circulating hemoglobin

Cardiac muscles store oxygen in myoglobin

The Cardiac Cycle


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The Cardiac Cycle

Cardiac cycle = The period between the

start of one heartbeat and the beginning of

the next

Includes both contraction and relaxation

The Cardiac Cycle


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The Cardiac Cycle

Phases of the Cardiac Cycle

Within any one chamber

Systole(contraction)

Diastole(relaxation)

The Cardiac Cycle


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The Cardiac Cycle

Figure 2016 Phases of the Cardiac Cycle

The Cardiac Cycle


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y

Blood Pressure

In any chamber

Rises during systole

Falls during diastole

Blood flows from high to low pressure

Controlled by timing of contractions

Directed by one-way valves

The Cardiac Cycle


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y

Cardiac Cycle and Heart Rate

At 75 beats per minute

Cardiac cycle lasts about 800 msecs

When heart rate increases

All phases of cardiac cycle shorten, particularly

diastole

The Cardiac Cycle


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y

Eight Steps in the Cardiac Cycle1. Atrial systole

Atrial contraction begins

Right and left AV valves are open

2. Atria eject blood into ventricles

Filling ventricles

3. Atrial systole ends

AV valves close

Ventricles contain maximum blood volume

Known as end-diastolic volume (EDV)

The Cardiac Cycle


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y

Eight Steps in the Cardiac Cycle4. Ventricular systole

Isovolumetric ventricular contraction

Pressure in ventricles rises

AV valves shut

5. Ventricular ejection

Semilunar valves open

Blood flows into pulmonary and aortic trunks

Stroke volume (SV) = 60% of end-diastolic volume

The Cardiac Cycle


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y

Eight Steps in the Cardiac Cycle6. Ventricular pressure falls

Semilunar valves close

Ventricles contain end-systolic volume (ESV), about 40%of end-diastolic volume

7. Ventricular diastole

Ventricular pressure is higher than atrial pressure

All heart valves are closed

Ventricles relax (isovolumetric relaxation)

The Cardiac Cycle


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y

Eight Steps in the Cardiac Cycle

8. Atrial pressure is higher than ventricular

pressure

AV valves open

Passive atrial filling

Passive ventricular filling Cardiac cycle ends

The Cardiac Cycle


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y

Heart Sounds

S1

Loud sounds

Produced by AV valves

S2

Loud sounds

Produced by semilunar valves

S3, S4 Soft sounds

Blood flow into ventricles and atrial contraction

The Cardiac Cycle


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y

Heart Murmur

Sounds produced by regurgitation through

valves

The Cardiac Cycle


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y

Figure 2018 Heart Sounds

Cardiodynamics


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y

The movement and force generated by cardiaccontractions

End-diastolic volume (EDV)

End-systolic volume (ESV)

Stroke volume (SV)

SV = EDV ESV

Ejection fraction

The percentage of EDV represented by SV

Cardiac output (CO)

The volume pumped by left ventricle in 1 minute

Cardiodynamics


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y

Figure 2019 A Simple Model of Stroke Volume

Cardiodynamics


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y

Cardiac Output

CO = HR X SV

CO = cardiac output (mL/min)

HR = heart rate (beats/min)

SV = stroke volume (mL/beat)

Cardiodynamics


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Factors Affecting Cardiac Output

Cardiac output

Adjusted by changes in heart rate or stroke volume

Heart rate

Adjusted by autonomic nervous system or hormones

Stroke volume

Adjusted by changing EDV or ESV

Cardiodynamics


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Figure 2020 Factors Affecting Cardiac Output

Cardiodynamics


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Factors Affecting the Heart Rate Autonomic innervation

Cardiac plexuses: innervate heart

Vagus nerves (X): carry parasympathetic preganglionic fibers

to small ganglia in cardiac plexus

Cardiac centers of medulla oblongata:

cardioacceleratory centercontrols sympathetic

neurons (increases heart rate)

cardioinhibitory centercontrols parasympathetic

neurons (slows heart rate)

Cardiodynamics


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Autonomic Innervation Cardiac reflexes

Cardiac centers monitor:

blood pressure (baroreceptors)

arterial oxygen and carbon dioxide levels(chemoreceptors)

Cardiac centers adjust cardiac activity

Autonomic tone

Dual innervation maintains resting tone by

releasing ACh and NE

Fine adjustments meet needs of other systems

Cardiodynamics


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Figure 2021 Autonomic Innervation of the Heart

Cardiodynamics


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Effects on the SA Node Sympathetic and parasympathetic stimulation

Greatest at SA node (heart rate)

Membrane potential of pacemaker cells

Lower than other cardiac cells Rate of spontaneous depolarization depends on

Resting membrane potential

Rate of depolarization

ACh (parasympathetic stimulation) Slows the heart

NE (sympathetic stimulation)

Speeds the heart

Cardiodynamics


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Atrial ReflexAlso called Bainbridge reflex

Adjusts heart rate in response to venous

return

Stretch receptors in right atrium

Trigger increase in heart rate

Through increased sympathetic activity

Cardiodynamics


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Hormonal Effects on Heart Rate

Increase heart rate (by sympathetic

stimulation of SA node)

Epinephrine (E)

Norepinephrine (NE)

Thyroid hormone

Cardiodynamics


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Factors Affecting the Stroke Volume

The EDV: amount of blood a ventricle contains at the

end of diastole

Filling time:

duration of ventricular diastole

Venous return:

rate of blood flow during ventricular diastole


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Cardiodynamics


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The EDV and Stroke Volume

At rest

EDV is low

Myocardium stretches less

Stroke volume is low

With exercise

EDV increases

Myocardium stretches more

Stroke volume increases

Cardiodynamics


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The Frank

Starling Principle

As EDV increases, stroke volume increases

Physical Limits

Ventricular expansion is limited by

Myocardial connective tissue

The cardiac (fibrous) skeleton

The pericardial sac

Cardiodynamics


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End-Systolic Volume (ESV)

The amount of blood that remains in the

ventricle at the end of ventricular systole is

the ESV

Cardiodynamics


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Three Factors That Affect ESV Preload

Ventricular stretching during diastole

Contractility

Force produced during contraction, at a given preload

Afterload

Tension the ventricle produces to open the semilunar valve

and eject blood

Cardiodynamics


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Contractility

Is affected by

Autonomic activity

Hormones

Cardiodynamics


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Effects of Autonomic Activity on Contractility Sympathetic stimulation

NE released by postganglionic fibers of cardiac nerves

Epinephrine and NE released by suprarenal (adrenal)medullae

Causes ventricles to contract with more force

Increases ejection fraction and decreases ESV

Cardiodynamics


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Effects of Autonomic Activity on

Contractility

Parasympathetic activity

Acetylcholine released by vagus nerves

Reduces force of cardiac contractions

Cardiodynamics


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Hormones

Many hormones affect heart contraction

Pharmaceutical drugs mimic hormone actions

Stimulate or block beta receptors

Affect calcium ions (e.g., calcium channel

blockers)

Cardiodynamics


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Afterload

Is increased by any factor that restricts arterial

blood flow

As afterload increases, stroke volume

decreases

Cardiodynamics


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Heart Rate Control Factors

Autonomic nervous system

Sympathetic and parasympathetic

Circulating hormones

Venous return and stretch receptors

Cardiodynamics


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Stroke Volume Control Factors

EDV

Filling time

Rate of venous return

ESV

Preload

Contractility

Afterload

Cardiodynamics


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Cardiac Reserve

The difference between resting and maximal

cardiac output

Cardiodynamics


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The Heart and Cardiovascular System Cardiovascular regulation

Ensures adequate circulation to body tissues

Cardiovascular centers

Control heart and peripheral blood vessels

Cardiovascular system responds to

Changing activity patterns

Circulatory emergencies

unit 5 heart

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