BIOLOGY OF DISEASES

 BIOLOGY OF DISEASES

Factors and etiologic of diseases: -

-        Genes and gene products, molecular, cellular, and physiological structures and functions

-        Biological factors linked to ethnicity, age, gender, pregnancy, and body weight.

-        Endogenous biological factors or pathways involved in responses to infection or damage by external factors

-        Metastases, degenerative processes, regeneration, and repair

-        Complications, reoccurrence, and secondary conditions

-        Bioinformatics and structural studies

-        Development and characterization of models

-        Environmental or external factors associated with the cause, risk, or development of disease, conditions, or ill health, including:

-        Physical agents, occupational hazards, environmental surroundings, radiation, and pollution

-        Chemicals and nutrients infection by pathogens - bacteria, fungi, viruses, and other types of pathogens associated with social, psychological, and economic factors, including:

-        Individual or group behaviours and lifestyle

-        Cultural or religious beliefs or practices

-        Ethnicity, age, and gender differences

-        Socioeconomic factors

Proof that the causes of disease require more rigorous evidence. To identify novel factors associated with human disease, one may use a sequence-based where no aetiology can be ascertained; the disorder is said to be idiopathic.

However, proof of causation in infectious diseases is limited to individual cases that provide experimental evidence of aetiology.

Several lines of evidence together are required for causal inference for infectious cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). Sometimes, several symptoms always appear together, or more often than what could be expected, though it is known that one cannot cause the other. These situations are called syndromes.

Sometimes, there is no single cause of a disease; instead, there is a chain of causation from an initial trigger to the development of the clinical disease.

An example of all the above, which was recognized late, is that peptic ulcer disease may be induced by stress, requires the presence of acid secretion in the stomach, and has primary aetiology in Helicobacter pylori infection. Many chronic diseases of unknown cause may be studied in this framework to explain multiple epidemiological associations.

Some diseases, such as diabetes or hepatitis, are syndromic allies defined by their signs and symptoms but include different conditions with different aetiologies. These are called heterogeneous conditions.

An endotype is a subtype of a condition that is defined by a distinct functional or path biological mechanism - One example is asthma, which is considered to be a syndrome consisting of a series of endotypes.

Another example could be AIDS, where an HIV infection can produce several clinical stages.

Classifications of diseases

Classifications of diseases become extremely important in the compilation of statistics on causes of illness (morbidity) and causes of death (mortality).

It is important to know what illnesses and diseases are prevalent in an area and how these prevalence rates vary over time.

With this knowledge, a search was instituted for possible causes of this increased prevalence.

The most widely used classifications of disease are (1) topographic, by bodily region or system; (2) anatomic, by organ or tissue; (3) physiological, by function or effect; (4) pathological, by the nature of the disease process, (5) etiologic (causal), (6) juristic, by the speed of advent of death, (7) epidemiological, and (8) statistical. Any single disease may fall within several of these classifications.

In the topographic classification, diseases are subdivided into such categories as gastrointestinal disease, vascular disease, abdominal disease, and chest disease.

In the anatomic classification, the disease is categorized by the specific organ or tissue affected; hence, heart disease, liver disease, and lung disease.

The physiological classification of disease is based on the underlying functional derangement produced by a specific disorder. Included in this classification are such designations as respiratory and metabolic disease

Metabolic diseases are those in which disturbances of the body's chemical processes are a basic feature. Diabetes and gout are examples.

The pathological classification of disease considers the nature of the disease process. Neoplastic and inflammatory diseases are examples.