• Medicine

  Physiology of human heart

  Posted by Encyclios on April 3, 2023 at 2:06 PM

  The heart can be likened to a suction and pressure pump that, in its internal cavities, receives the waste blood from the veins and pushes it into the arteries. During its physiological activity, the heart continuously changes its shape and volume, alternating between diastole (relaxation of the heart muscle) and systole (contraction of the heart muscle). If in the first phase the appearance of the heart is very similar to that already described, in systole it presents modifications, especially in the ventricles, on whose left front wall appears a kind of hump (which comes to rest against the chest wall, allowing the perception of the so-called heartbeat), while the cavities are reduced to a jagged and branched fissure.

  The myocardium contracts, as a rule, 70-75 times per minute (equivalent to about one hundred thousand times a day). During the cardiac cycle or revolution, three essential phases can be distinguished: a presystole, characterized by contraction only of the atria and ventricular relaxation (or diastole) (during which the blood passes from the atria to the ventricles); a systole proper (with ventricular contraction, during which the blood is pushed into the arterial circulation) and a perisystole, characterized by complete rest of the heart. These functions occur rhythmically and their complex allows the circulation of blood in the body. The contraction of the myocardium begins at a point (sinus node) of the terminal groove of the right atrium, spreads to the two atria and finally reaches the ventricles, filling them from the apex to the base.

  The propagation of the contraction is due to specialized muscle tissue: in the atria, the presystole is under the control of the sinus node (made up of the Keith and Flack nodes on the right and the Pace and Bruni nodes on the left); on the other hand, the Tawara node and the His bundle are responsible for the propagation of the contraction from the atria to the ventricles. These nodes and bundles are each composed of tangles and cords of contractile fibers stimulated by excitatory nerve fibers from the cardiac plexus and inhibitory fibers from the vagus nerve. The specific characteristics of the myocardium are therefore automatism (the ability to generate stimuli), excitability and, finally, contractility (the ability to contract, to perform a task).

  Encyclios replied 2 months, 1 week ago 1 Member · 0 Replies
• 0 Replies

Log In to Reply