Applied Basic Science for Basic Surgical Training concepts and conceptual ideas that we need
All mammalian cells strive to survive against a hostile fl uctuating environment by expending energy to maintain a tightly regulated internal and local external environment. If the environmental fl uctuations are suffi ciently large, they will change the state of the cell, which will then attempt to return to its usual condition. Cellular injury, manifest as a signifi cant disturbance of cell function and central to almost all human disease, occurs if the changes in the cell are suffi ciently large. In any particular case it may be diffi cult to tell On the whole, (b) is the least likely because cells are capable of signifi cant reparative processes, and if they survive an insult, they generally repair it; if the damage is not lethal but is very severe or persistent and beyond the capacity of the cell to regenerate, the cell may activate mechanisms that result in its own death.
Certain injurious agents (radiation, certain chemicals, viruses, and some bacterial and fungal toxins) directly damage the cell nucleus and deoxyribonucleic acid (DNA), resulting in genetic DNA mutations. Depending on the degree of damage and the portion of the DNA damaged, the damage may be reparable, resulting in a temporary cell cycle arrest but ultimately no phenotypic alteration. Severe irreparable damage triggers apoptotic pathways that culminate in cell death. An intermediate degree of DNA damage results in genetic mutations that do not directly impair cell survival and may confer a survival advantage. Successive mutations will then drive the cell down the multi-step pathway towards neoplasia. The processes involved in oncogenesis are described in Chapter 5.
Cellular injury can be caused by a variety of mechanisms, including:
• chemical; and
• biological processes.
Cell death may result in replacement by:
• a cell of the same type;
• a cell of another type; or
• non-cellular structures.
The cell is a highly-structured complex of molecules and organelles that are arranged to fulfi l routine metabolic housekeeping functions and the specialised functions that make one cell different from another. In order to carry out these functions the cell has energy needs and some transport mechanisms to facilitate the import of metabolites and the export of waste products. Injury to a cell results in relative disruption to one or more of these structures or functions.