Cardiomyocytes are cells 100-150 microns long, 10-20 microns in diameter, having an irregular cylindrical shape. The main part of the myocardium is formed by cardiomyocytes.
Using a light microscope, you can see numerous anastomoses, bundlesэ divarication of cardiomyocytes that form meshes. This is due to the irregular connection between individual cells. Each cardiomyocyte contains one or two elongated oval nuclei, which are located in the center and surrounded by myofibrils, straightforwardly located along the periphery.
At both poles of the nucleus, elongated zones of the cytoplasm are noticeable, which is devoid of myofibrils.
The contacts of two adjacent cardiomyocytes are characteristic, which have the form of dark sinuous stripes, intercalated discs, actively participating in the transfer of excitation from cell to cell.
Cardiomyocytes are connected to each other using discs. Cardiomyocytes are rich in mitochondria. Their sarcolemma, about 9 nm thick, contains many vesicles, micropinocytic invaginations.
Just as in the muscle fiber, the following functional apparatuses are distinguished: energy membrane, contractile (fibrillar), trophic. Cardiomyocytes are interconnected in chains by the bases of the cylinders. These areas are called “intercalated discs” in which desmosomes and slit contacts are allocated.
Desmosomes serve to provide mechanical adhesion that prevents cardiomyocytes from separating. Slit contacts are involved in the transmission of contractions from one cardiomyocyte to another. All types of cardiomyocytes do not contain cambial cells and are not capable of division. They are characterized only by intracellular regeneration.
Types of cardiomyocytes
The following types of cardiomyocytes are distinguished in the myocardium: working cardiomyocytes; conducting cardiomyocytes; secretory cardiomyocytes.
Working (contractile, typical) cardiomyocytes are cylindrical cells with a diameter of 10-20 microns and a length of 100-150 microns.
Conducting cardiomyocytes differ from working in smaller sizes (they are much narrower). Conducting cardiomyocytes are characterized by: poorly developed disordered myofibrillar apparatus; lower glycogen content; rich vascularization, which is 1.5-3 times higher than in the working myocardium; autonomic efferent innervation, which is 2.5-5 times higher than in the working myocardium. Conductive cardiomyocytes are capable of generating and rapidly conducting electrical impulses. They formed the nodes and bundles of the cardiac conduction system.
Secretory cardiomyocytes are mainly located in the myocardium of the right atrium. Secretory cardiomyocytes are characterized by the presence of a well-developed Golgi apparatus at the poles of the nuclei and secretory granules. Function of secretory cardiomyocytes: endocrine. Secretory cardiomyocytes produce atriopetine (a natriuretic factor that is involved in the regulation of urine output and blood pressure). Atriopetine causes loss of sodium and water in urine, dilates blood vessels, lowers blood pressure, inhibits the secretion of vasopressin, cortisol, aldosterone.