the cardiovascular system
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Myocardial Thickness and FunctionThickness of myocardium varies according to the function of the chamber
Conducting System
Autorhythmic cells – self excitableReduced 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)
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 RateArrhythmias: 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 arrhythmia that occurs when electrical pathway between the atria and ventricle is blocked.
Stroke Volume (SV)
EDV = Amount of blood that collects in a ventricle during diastole
ESV = Amount of blood remaining in a ventricle after contraction
Stroke volume = end diastolic volume - end systolic volume
SV = EDV - ESV
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
Volume of blood pumped out by a ventricle with each beat
Cardiac Output (CO)
Cardiac output = Heart rate x Stroke volume
HR = beats per minute
SV = volume of blood pumped out by a ventricle with each beat
CO = HR x SV
amount of blood pumped by each ventricle in one minute
– 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 EDV1. Duration of ventricular diastole2. Venous return – volume of blood returning to right
ventricle
Factors Affecting SVPreload
– 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
ContractilityFactors Affecting SV
– 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
Afterload
Factors Affecting SV