The Cardiovascular System: The Heart Physiology... · The Cardiovascular System: The Heart . ... (longer than 20 min) strengthens cardiovascular system ... John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc.

Chapter 15

The Cardiovascular

System: The Heart


Location of the Heart

Thoracic cavity between two lungs ~2/3 to left of midline

surrounded by pericardium:

Fibrous pericardium - Inelastic and anchors heart in place

Inside is serous pericardium - double layer around heart Parietal layer fused to fibrous pericardium

Inner visceral layer adheres tightly to heart

Filled with pericardial fluid - reduces friction during beat.


Position of the Heart


Position of the Heart


Heart Wall

Epicardium - outer layer

Myocardium - cardiac muscle

Two separate networks via gap junctions in

intercalated discs - atrial & ventricular

Networks- contract as a unit

Endocardium - Squamous epithelium

lines inside of myocardium


Pericardium


Cardiac Muscle Fibers


Cardiac Muscle Tissue


Chambers of the Heart

4 chambers

2 upper chambers = Atria

Between is interatrial septum

Contains fossa ovalis - remnant of foramen ovalis

2 lower chambers = ventricles

Between is interventricular septum

Wall thickness depends on work load

Atria thinnest

Right ventricle pumps to lungs & thinner than left


Structure of the Heart






Great Vessels Of Heart-Right

Superior & inferior Vena Cavae

Delivers deoxygenated blood to R. atrium from body

Coronary sinus drains heart muscle veins

R. Atrium R. Ventricle

pumps through Pulmonary Trunk

R & L pulmonary arteries

lungs


Great Vessels Of Heart-Left

Pulmonary Veins from lungs

oxygenated blood

L. atrium Left ventricle

ascending aorta body

Between pulmonary trunk & aortic arch is

ligamentum arteriosum

fetal ductus arteriosum remnant


Posterior View of Heart


Anterior View of Frontal Section


Valves

Designed to prevent back flow in response to pressure changes

Atrioventricular (AV) valves

Between atria and ventricles

Right = tricuspid valve (3 cusps)

Left = bicuspid or mitral valve

Semilunar valves near origin of aorta & pulmonary trunk

Aortic & pulmonary valves respectively


Atrioventricular Valves: Bicuspid

Valves


Atrioventricular Valves: Superior

View


Blood Flow

Through

Heart


Blood Flow


Blood Supply Of Heart

Blood flow through vessels in myocardium = coronary circulation

Left & right coronary arteries

branch from aorta

branch to carry blood throughout muscle

Deoxygenated blood collected by coronary

sinus (posterior)

Empties into right atrium


Conduction System

1% of cardiac muscle generate action

potentials= Pacemaker & Conduction

system

Normally begins at sinoatrial (SA) node

Atria & atria contract

AV node - slows

AV bundle (Bundle of His)

bundle branches Purkinje fibers

apex and up- then ventricles contract


Pacemaker

Depolarize spontaneously

sinoatrial node ~100times /min

also AV node ~40-60 times/min

in ventricle ~20-35 /min

Fastest one run runs the heart = pacemaker

Normally the sinoatrial node


Frontal plane

Right atrium

Right ventricle

Left atrium

Left ventricle

Anterior view of frontal section

Frontal plane

Left atrium

Left ventricle


SINOATRIAL (SA) NODE 1

Right atrium

Right ventricle

Frontal plane

Left atrium

Left ventricle


SINOATRIAL (SA) NODE

ATRIOVENTRICULAR

(AV) NODE

1

2

Right atrium

Right ventricle

Frontal plane

Left atrium

Left ventricle



ATRIOVENTRICULAR

(AV) NODE

ATRIOVENTRICULAR (AV)

BUNDLE (BUNDLE OF HIS)

1

2

3

Right atrium

Right ventricle

Frontal plane

Left atrium

Left ventricle



ATRIOVENTRICULAR

(AV) NODE



RIGHT AND LEFT

BUNDLE BRANCHES

1

2

3

4

Right atrium

Right ventricle

Frontal plane


ATRIOVENTRICULAR

(AV) NODE

Left atrium

Left ventricle




RIGHT AND LEFT

BUNDLE BRANCHES

PURKINJE FIBERS

1

2

3

4

5

Right atrium

Right ventricle


Electrocardiogram

Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG)

P wave = atrial depolarization Contraction begins right after peak

Repolarization is masked in QRS

QRS complex = Ventricular depolarization Contraction of ventricle

T-wave = ventricular repolarization Just after ventricles relax


ECG


Cardiac Cycle

after T-wave ventricular diastole Ventricular pressure drops below atrial & AV

valves open ventricular filling occurs

After P-wave atrial systole Finishes filling ventricle (`25%)

After QRS ventricular systole Pressure pushes AV valves closed

Pushes semilunar valves open and ejection occurs

Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves


Action Potential

Review muscle

Heart has addition of External Ca2+

Creates a plateau

Prolonged depolarized period

Can not go into tetanus


Cardiac Cycle


Flow Terms

Cardiac Output (CO) = liters/min

pumped

Heart Rate (HR) = beats/minute (bpm)

Stroke volume (SV) = volume/beat

CO = HR x SV


Controls - Stroke Volume (S.V.)

Degree of stretch = Frank-Starling law

Increase diastolic Volume increases strength

of contraction increased S.V.

Increased venous return increased S.V.

increased sympathetic activity

High back pressure in artery decreased

S.V.

Slows semilunar valve opening


Controls- Heart Rate

Pacemaker adjusted by nerves

Cardiovascular center in Medulla

parasympathetic- ACh slows

Via vagus nerve

Sympathetic - norepinephrine speeds

Sensory input for control:

baroreceptors (aortic arch & carotid sinus)-

B.P.

Chemoreceptors- O2, CO2, pH


Other Controls

Hormones:

Epinephrine & norepinephrine increase H.R.

Thyroid hormones stimulate H.R.

Called tachycardia

Ions

Increased Na+ or K+ decrease H.R. & contraction force

Increased Ca2+ increases H.R. & contraction force


Autonomic Nervous System Regulation

of Heart Rate


Exercise and the Heart

Aerobic exercise (longer than 20 min)

strengthens cardiovascular system

Well trained athlete doubles maximum

C.O.

Resting C.O. about the same but resting H.R.

decreased


End of Chapter 15

Copyright 2010 John Wiley & Sons, Inc.

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The Cardiovascular System: The Heart Physiology... · The Cardiovascular System: The Heart . ... (longer than 20 min) strengthens cardiovascular system ... John Wiley & Sons, Inc.

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