Functions of conductive system of heart

Spontaneous generation of rhythmic impulses is result of the harmonious activity of many cells of sinoatrial node which is provided with close contacts (nexuses) and electrotonic interaction of these cells. Excitation extends on conductive system on retractive a myocardium.

Feature of conductive system of heart is ability of each cell independently to generate excitation. There is a gradient of automatism, expressed in decreasing ability to automatism various sites of conductive systems.

In usual conditions automatism of all parts of conductive system is suppressed with more frequent impulses acting from sinoatrial node. Impulses will arise with frequency 40-50 in a minute.

Distinctive feature of conductive system of heart is presence in its cells of a plenty of intercellular contacts - nexuses. These contacts are a place of transition of excitation from one cell on another. The same contacts are available and between cells of conductive system and a working myocardium. Owing to presence of contacts the myocardium consisting of separate cells, works as a unit. Existence of a plenty of intercellular contacts increases reliability of carrying out of excitation in a myocardium.

Excitation extends on auricles, reaching atrioventricular node. In sinoatrial node there is some delay of carrying out of excitation. Owing to a delay excitation reaches up to sinoatrial bunch and cardiac conductive myocyte after the muscles of auricles have time to be reduced and pump over blood from auricles in ventricle.

Hence, atrioventricular delay provides necessary sequence (coordination) of reductions of auricles and ventricles.

Speed of distribution of excitation in sinoatrial bunch and in cardiac conductive myocytes reaches 4,5-5 m/sec, that in 5 times more speed of distribution of excitation on a working myocardium. Owing to it cells of a myocardium of ventricles are reduced almost at once or synchronously. Synchronism of reduction of cells raises capacity of a myocardium and efficiency force functions of ventricles.

Presence of conductive system provides a number of the important physiological features of heart: 1) rhythmic generation of impulses (potentials of action); 2) necessary consecution, (coordination) of reductions of auricles and ventricles; 3) synchronous involving in process of reduction of cells of a myocardium of ventricles (that increases efficiency of a systole).

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