Page 37 - Textbook of Pathology, 6th Edition

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Cell Injury and
Chapter 3
Chapter 3
Cellular Adaptations CHAPTER 3

Cells are the basic units of tissues, which form organs and adaptations, which can be best understood in the context of
systems in the human body. Traditionally, body cells are basic knowledge of normal structure and functions of cell
divided in to two main types: epithelial and mesenchymal outlined below.
cells. In health, the cells remain in accord with each other. In
1859, Virchow first published cellular theory of disease, THE NORMAL CELL
bringing in the concept that diseases occur due to
abnormalities at the level of cells. Since then, study of Different types of cells of the body possess features which
abnormalities in structure and function of cells in disease has distinguish one type from another. However, most
remained the focus of attention in understanding of diseases. mammalian cells have a basic plan of common structure and
Thus, most forms of diseases begin with cell injury followed function, except the red blood cell which is devoid of nucleus
by consequent loss of cellular function. Cell injury is defined as and its structure is described separately on page 288. Cell Injury and Cellular Adaptations
a variety of stresses a cell encounters as a result of changes in its
internal and external environment. CELL STRUCTURE
In general, cells of the body have inbuilt mechanism to
deal with changes in environment to an extent. The cellular Under normal conditions, cells are dynamic structures
response to stress may vary and depends upon the following existing in fluid environment. A cell is enclosed by cell
variables: membrane that extends internally to enclose nucleus and
i) The type of cell and tissue involved. various subcellular organelles suspended in cytosol
ii) Extent and type of cell injury. (Fig. 3.2).
Various forms of cellular responses to cell injury may be
as follows (Fig. 3.1): Cell Membrane
1. When there is increased functional demand, the cell may Electron microscopy has shown that cell membrane or
adapt to the changes which are expressed morphologically plasma membrane has a trilaminar structure having a total
and then revert back to normal after the stress is removed thickness of about 7.5 nm and is known as unit membrane.
(cellular adaptations, see Fig. 3.39). The three layers consist of two electron-dense layers
2. When the stress is mild to moderate, the injured cell may separated by an electronlucent layer. Biochemically, the cell
recover (reversible cell injury), while when the injury is membrane is composed of complex mixture of phos-
persistent cell death may occur (irreversible cell injury). pholipids, glycolipids, cholesterol, proteins and carbo-
3. The residual effects of reversible cell injury may persist hydrates. These layers are in a gel-like arrangement and are
in the cell as evidence of cell injury at subcellular level in a constant state of flux. The outer surface of some types of
(subcellular changes), or metabolites may accumulate within cells shows a coat of mucopolysaccharide forming a fuzzy
the cell (intracellular accumulations). layer called glycocalyx. Proteins and glycoproteins of the cell
In order to learn the fundamentals of disease processes membrane may act as antigens (e.g. blood group antigens),
at cellular level, it is essential to have an understanding of or may form receptors (e.g. for viruses, bacterial products,
the causes and mechanisms of cell injury and cellular hormones, immunoglobulins and many enzymes). The cell

Figure 3.1 Cellular responses to cell injury.