What pathology studies: failed homeostasis and cellular change
Pathology studies the structural and functional changes disease produces in cells and tissues, and many diseases can be understood as consequences of failed homeostasis.
Remember
Many diseases can be understood as failed homeostasis, so cells change in structure and function, which is why pathology looks at cells and tissues.
The word pathology joins pathos (suffering) and logos (study), so it literally means the study of suffering. It is the disease-focused counterpart of biology (the study of life and normal cell function): pathology is about disease and what happens when normal cell function is lost.
Homeostasis means the body keeping its internal conditions, for example temperature, pH and fluid balance, within narrow limits, so that its cells can work normally. Many diseases can be understood as consequences of failed homeostasis. When cells are stressed, injured or deprived of what they need, their shape (morphology) and their function change, and these changes can be seen under the microscope.
Failed homeostasis can follow injury, infection, poor blood supply or a faulty gene. The cells then change in structure and function, for example by swelling, shrinking, dying or growing abnormally. Because organs and tissues are made of cells, the disturbance spreads to them, which is why the cell is seen as the centre of disease. A pathologist examines cells and tissues under the microscope to make a diagnosis. Diagnostic pathology is the study of how cells and tissues have changed in structure and function, with the aim of reaching a diagnosis.
The cell-centred view began with Rudolf Virchow, a German physician regarded as the first cellular pathologist. In the 19th century he showed that disease arises in cells, replacing humoral theory (the old idea that disease comes from imbalances in bodily fluids).
Pathology has several branches, including medical microbiology (the study of bacteria, viruses, fungi and parasites), chemical pathology (using biochemical tests), haematology (diseases of the blood), immunology (the immune response), and histopathology and cytopathology (the study of cells and tissues). Microbiology is one branch of pathology, far too narrow to be its central principle.
Key facts
- Word origin
- pathos means suffering and logos means study, so pathology literally means the study of suffering.
- Unifying idea
- many diseases can be understood as consequences of failed homeostasis, with changes in the shape and function of cells.
- Cell changes
- stressed or injured cells change in shape and function, for example by swelling, shrinking, dying or growing abnormally.
- Centre of disease
- the cell can be seen as being at the centre of disease, because organs and tissues are made of cells.
- Diagnosis
- a pathologist examines cells and tissues under the microscope, because symptoms alone cannot show the mechanism of disease.
- Origin of the cell-centred view
- Rudolf Virchow showed in the 19th century that disease arises in cells, replacing humoral theory.
Exam traps
- Identifying the microorganisms that cause an infection is the work of medical microbiology, one branch of pathology, and it is too narrow to be the fundamental focus, because pathology also covers non-infectious disease such as cancer, inflammation and immune disorders.
- Imbalance of bodily fluids as the cause of disease is humoral theory, which was the dominant idea until the 19th century and was discredited by Virchow, so it is not the basis of modern pathology.
- Organ-level thinking gives a description of effects, not the underlying principle, because organs are made of cells and their changes occur at cell level.
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