25 topics with concise breakdowns: definitions, key facts, and class questions.
In this section, we examine the pumping function of the body's main «engine» — cardiac physiology. You will study the basic physiological properties of the myocardium: from the mechanisms of automatism and slow diastolic depolarization to the action potential of a typical cardiomyocyte. Special attention is paid to the classic Stannius experiment, which clearly demonstrates the gradient of automatism.
The heart works in a strictly cyclical manner. We will analyze in detail all phases of the cardiac cycle: atrial activity, ventricular systole and diastole, as well as pressure changes in the cavities and the functioning of the valve apparatus. You will learn how to evaluate parameters of the pumping function and hemodynamics, and understand the nature of heart sounds and the principles of phonocardiography.
In practical classes and exams, electrocardiography (ECG) and the regulation of cardiac activity are tested most rigorously. You will need to clearly understand the origin of each wave and segment, the pathways of excitation conduction in the heart, as well as the specific features of myocardial contraction and the nature of extrasystole.
The law states: the more cardiomyocytes are stretched during ventricular filling (increasing EDV), the greater the force with which they subsequently contract, increasing stroke volume.
What is the function of the pacemaker?
The pacemaker primarily generates excitation and imposes its high rhythm on the entire heart, thereby suppressing the automatism of all downstream parts of the conduction system.
Why do the atria and ventricles stop after the first ligature is applied, while the sinus continues to beat?
The sinus is the main pacemaker. A tight ligature blocks the transmission of its impulses further down the myocardium. The ventricular arrest is associated with a pre-automatic pause: the secondary pacemaker (AV node) needs time to recover from the inhibitory influence of the fast sinus rhythm and start generating its own impulses.
Why is the heart muscle incapable of tetanic contraction?
Due to the presence of the plateau phase, the absolute refractory period of cardiomyocytes is very prolonged (about 270 ms in the ventricles). The cell remains unexcitable for almost the entire duration of its mechanical contraction, making wave summation impossible.
In which cells does slow diastolic depolarization take place?
It occurs in the pacemaker cells of the sinoatrial (sinus) node, providing their automaticity.
What is the hemodynamic significance of the atrioventricular delay?
The conduction delay in the AV node is necessary to allow the atria to contract fully and pump blood into the ventricles strictly before the onset of ventricular systole.
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