How do heart muscle cells work
Heart muscle cell
Synonym: cardiomyocyte, myocytus cardiacus
English: heart muscle cell, cardiomyocyte
Heart muscle cells or. Cardiomyocytes are cells of the myocardium. Two types of heart muscle cells can be distinguished:
- Myocardial cells of the working muscles, which in their entirety are responsible for the contraction of the heart
- Cardiac muscle cells of the conduction system, responsible for the formation and transmission of excitations of the heart
The cardiac muscle cells of the ventricular muscles of the human heart are about 10-25 µm thick and 50-100 µm long. The number of myocardial cells in the left ventricle is estimated to be around 6 billion cells, and their number continuously decreases over the course of life.
2.1 Heart muscle cells of the working muscles
Heart muscle cells of the working muscles are branched cells with one or two central cell nuclei. A heart muscle cell is connected to a large number of neighboring cells via glossy strips (Disci intercalares) or gap junctions (Nexus).
The cell structure is characterized by the longitudinally arranged myofibrils and the sarcoplasmic reticulum that runs parallel to them. T-tubules transmit excitations that hit the cell to the sarcoplasmic reticulum. The numerous mitochondria in the heart muscle cells of the working muscles are known as sarcosomes and the cytoplasm as sarcoplasm.
The cell nucleus is surrounded by a myofibril-free area, the sarcoplasmic court. The sarcoplasmic courtyard contains glycogen, fat and lipofuscin.
2.2 Cardiac muscle cells of the conduction system
The cardiac muscle cells of the conduction system have a modified structure. Under the microscope they appear lighter - possibly because of the larger glycogen reserves - and have a larger cell diameter. The number of sarcosomes is also lower than that of working muscle cells.
The sarcoplasm of the cells contains a comparatively large amount of glycogen, since glycolysis in the cardiac muscle cells of the conduction system is the most important source of energy.
Heart muscle cells are able to renew themselves. That could be based on 14C-examinations of cardiomyocyte DNA can be detected. According to this, about 1% of the heart muscle cells are replaced every year in a 25-year-old. This rate drops to 0.45% for 75 year olds. However, less than 50% of cardiac muscle cells are exchanged during a lifetime.
- Bergmann et al. Evidence for Cardiomyocyte Renewal in Humans, Science 3 April 2009: Vol. 324. no. 5923, pp. 98-102 -> Abstract
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