ULTRASTRUCTURE OF CARDIOMYOCYTES AND THEIR HISTOPHYSIOLOGICAL CHANGES UNDER HYPOXIC CONDITIONS

This article provides a systematic overview of the ultrastructural organization of cardiomyocytes (heart muscle cells), their functional characteristics related to energy and ion-calcium homeostasis, and the histological, ultrastructural, and physiological changes that occur under conditions of hypoxia and ischemia. The ultrastructure of the cardiomyocyte’s contractile apparatus (sarcomere), mitochondria, sarcoplasmic reticulum, transverse tubules (T-tubules), intercalated discs, and nuclear apparatus is analyzed. The molecular mechanisms of hypoxia (the HIF signaling pathway, the shift to anaerobic glycolysis, the disruption of Na⁺/Ca²⁺ homeostasis, and the mitochondrial permeability transition pore) are examined, along with the ultrastructural markers of reversible and irreversible injury, necrosis and apoptosis, reperfusion injury, the states of myocardial "hibernation" and "stunning," and adaptive responses to chronic hypoxia. This article is intended to serve as a theoretical foundation for advanced-level research (doctoral and post-doctoral studies)