General Pathology

Theme 1: Introduction and Overview

1. Define the terms "aetiology", "pathogenesis", "morphology" and "pathophysiology".
2. List and discuss the broad categories of disease processes:
   • Congenital: Genetic, Non-genetic
   • Acquired: Inflammatory, ischaemic, immunologic, infections, neoplastic, metabolic and nutritional
3. Recognise the role of pathology in clinical practice

Aetiology is the cause of disease. Sometimes several causative agents may interact to result in disease. Often, we do not know the exact aetiologic factors. Almost always we do know the risk factors that would predispose a particular individual to developing a disease.

Pathogenesis is the sequence of events, ensuing at a molecular, cellular and tissue level, that will eventually result in the manifestation of the clinically recognizable disease. These pathological processes are stereotyped and few in number but they underlie all disease.

Morphology refers to the morphologic changes or structural alterations that are induced in cells and tissues by the disease.

Pathophysiology refers to the functional consequences of the morphologic changes, as observed clinically.

Congenital (present at birth)

• Genetic: Inherited or hereditary diseases due to transmission of defective genes or chromosomes from one or both parents.
• Non-genetic: Sometimes called developmental disease, this is a defect in embryonic or fetal development that may create a physiologic (functional) disorder, or a physical (structural) abnormality. A congenital defect may be genetic; may be induced by chemicals, drugs or viruses; or may be a spontaneous event.

Acquired (after birth)

• Metabolic: This is an upset in the biochemical reactions that govern the body processes, or metabolism. These are often genetic in origin but some metabolic diseases may have an origin in improper nutrition with resultant upsets in carbohydrate, fat, or protein metabolism.
• Nutritional: Malnutrition can create disease because of insufficient resources for the body. Deficient protein means a decrease in osmotic pressure, a decrease in healing or formation of new body tissue, or a decrease in antibody production. Vitamin or mineral deficiencies can lead to interference in tissue integrity or in biochemical reactions of metabolism.
• Ischaemic: Interference in blood supply, and therefore oxygen, robs cells of their fuel and causes injury or death of cells and tissues.
• Inflammatory: These are conditions in which the inflammatory response plays the major role. Within this groups, it is important to distinguish the infections because their treatment is entirely different from noninfective inflammatory disease, such as that due to autoimmune processes.
• Infections: Such disease are caused by invasion and colonization by pathogenic microorganisms. The most common pathogens are bacteria, viruses and fungi. Treatment of these conditions is aimed at eliminating the causative organism.
• Immunologic: Over-reaction by the immune system (hypersensitivity), under-reaction by the immune system (immune deficiency such as AIDS), and autoimmune disease are the 3 categories of immunologic disease. Autoimmune disease is the destruction of one's own tissues by antibodies produced by one's own immune system. When the disease is due to unwanted activity of the immune system, the treatment is often immunosuppression. It is important therefore that these conditions be distinguished from infections in which the immune system plays an appropriate protective role.
• Neoplastic: This is uncontrolled growth of abnormal cells. A neoplasm ("new growth") may be benign or malignant. Malignant neoplasia is commonly called cancer, and its fatality is related to its ability to invade the surrounding tissues and to spread (metastasize) to distant organs.

In clinical practice, pathology plays an important part in diagnosing disease.