Mitochondria are highly dynamic intracellular organelles with ultrastructural heterogeneity reflecting the behaviour and functions of the cells. The ultrastructural remodelling, performed by the counteracting active processes of mitochondrial fusion and fission, enables the organelles to respond to diverse cellular requirements and cues. It is also an important part of mechanisms underlying adaptation of mitochondria to pathophysiological conditions that challenge the cell homeostasis. However, if the stressor is constantly acting, the adaptive capacity of the cell can be exceeded and defective changes in mitochondrial morphology (indicating the insufficient functionality of mitochondria or development of mitochondrial disorders) may appear. Beside qualitative description of mitochondrial ultrastructure, stereological principles concerning the estimation of alterations in mitochondrial volume density or surface density are invaluable approaches for unbiased quantification of cells under physiological or pathophysiological conditions. In order to improve our understanding of cellular functions and dysfunctions, transmission electron microscopy (TEM) still remains a gold standard for qualitative and quantitative ultrastructural examination of mitochondria from various cell types, as well as from those experienced to different stimuli or toxicity-inducing factors. In the current study, general morphological and functional features of mitochondria, and their ultrastructural heterogeneity related to physiological and pathophysiological states of the cells are reviewed. Moreover, stereological approaches for accurate quantification of mitochondrial ultrastructure from electron micrographs taken from TEM are described in detail.

线粒体是高度动态的细胞内细胞器，具有反映细胞行为和功能的超微结构异质性。通过抵消线粒体融合和裂变的活性过程进行的超微结构重塑，使细胞器能够响应不同的细胞需求和线索。它也是线粒体适应挑战细胞稳态的病理生理条件的机制的重要组成部分。然而，如果压力源不断作用，细胞的适应能力可能会被超过，线粒体形态的缺陷变化（表明线粒体功能不足或线粒体疾病的发展）可能会出现。除了线粒体超微结构的定性描述，关于线粒体体积密度或表面密度变化估计的体视学原理是在生理或病理生理条件下对细胞进行无偏见量化的宝贵方法。为了提高我们对细胞功能和功能障碍的理解，透射电子显微镜 (TEM) 仍然是定性和定量超微结构检查各种细胞类型以及那些经历过不同刺激或毒性诱导因素的线粒体的金标准. 在目前的研究中，综述了线粒体的一般形态和功能特征，以及与细胞生理和病理生理状态相关的超微结构异质性。而且，