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The Cardiovascular System. The Heart. Chapter 20. Location. The heart lies in the mediastinum. Pericardium and Layers of Heart Wall. Chambers and Sulci. Chambers and Sulci. Right Atrium. Right Ventricle. Left Atrium. Left Ventricle. Anterior Heart. Myocardial Thickness and Function.

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Presentation Transcript
The cardiovascular system
The Cardiovascular System

The Heart

Chapter 20


Location

The heart lies in the mediastinum.










Myocardial Thickness and Function

Thickness of myocardium varies according to the function of the chamber



Blood circulation
Blood Circulation

  • Blood flow

    • Blue: deoxygenated

    • Red: oxygenated







Conducting system
Conducting System

Autorhythmic cells – self excitable

Reduced permeability of K+, but no change in permeability to Na+.

Na+ continues to diffuse in.

Unstable resting potential – continuously depolarizes, drifting slowly toward threshold. (pacemaker potential)


Physiology of Contraction

Potentials initiated by conducting fibers stimulate contractile fibers.




Cardiac rhythm and rate
Cardiac Rhythm and Rate

Normal heart rate: 60-100 beats/min

Avg. heart beat at rest: 70-72 beats/min

Sinus tachycardia: > 100 beats/min

Sinus bradycardia: < 60 beats/min


Cardiac rhythm and rate1
Cardiac Rhythm and Rate

Arrhythmias: abnormal rhythm resulting from a defect in the heart conduction system.

Fibrillation: rapid and irregular contractions. Can be atrial or ventricular.

Defibrillation: electrical shock to depolarize myocardium.

Ectopic Focus: a region of the heart, other than the conducting system, that causes and abnormal depolarization.

Junctional rhythm: AV node becomes pacemaker

Heart block: an arrhythmiathat occurs when electrical pathway between the atria and ventricle is blocked.



Cardiac cycle
Cardiac Cycle

Systole: contraction

Diastole: relaxation


Heart sounds
Heart sounds

Lubb - AV valves close Dupp - semilunar valves close


Stroke volume sv
Stroke Volume (SV)

Volume of blood pumped out by a ventricle with each beat

Stroke volume = end diastolic volume - end systolic volume

SV = EDV - ESV

EDV = Amount of blood that collects in a ventricle during diastole

ESV = Amount of blood remaining in a ventricle after contraction

SV depends on amount of stretch produced by venous return.

Averages about 70 ml/beat

Anything that influences heart rate or blood volume influences venous return and therefore SV


Cardiac output co
Cardiac Output (CO)

amount of blood pumped by each ventricle in one minute

Cardiac output = Heart rate x Stroke volume

CO = HR x SV

HR = beats per minute

SV = volume of blood pumped out by a ventricle with each beat


Factors Affecting SV

Preload

  • Degree of stretch on the heart before it contracts

  • Greater preload increases the force of contraction

  • Frank-Starling law of the heart – the more the heart fills with blood during diastole, the greater the force of contraction during systole

    • Preload proportional to end-diastolic volume (EDV)

  • 2 factors determine EDV

    • Duration of ventricular diastole

    • Venous return – volume of blood returning to right ventricle


Factors Affecting SV

Contractility

  • Strength of contraction at any given preload

  • Positive inotropic agents increase contractility

    • Often promote Ca2+ inflow during cardiac action potential

    • Increases stroke volume

    • Epinephrine, norepinephrine, digitalis

  • Negative inotropic agents decrease contractility

    • Anoxia, acidosis, some anesthetics, and increased K+ in interstitial fluid


Factors Affecting SV

Afterload

  • Pressure that must be overcome before a semilunar valve can open

  • Increase in afterload causes stroke volume to decrease

    • Blood remains in ventricle at the end of systole

  • Hypertension and atherosclerosis increase afterload


Regulation of Heart Rate

1. Autonomic regulation

2. Chemical regulation

3. Other Factors


Cardiac Output

Change stroke volume and/or heart rate


Homeostatic imbalance of co
Homeostatic Imbalance of CO

Congestive heart failure - occurs when the pumping ability of the heart is inadequate to provide normal circulation to meet body needs.

Pulmonary congestion - left side failure

Peripheral congestion - right side failure


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