INTRODUCTION TO PATHOLOGY

•Pathology is the study of disease by scientific methods.

•The word pathology came from the Latin words “patho” & “logy”. ‘Patho’ means disease and ‘logy’ means study, therefore pathology is a scientific study of disease.

•Pathology gives explanations of a disease by studying the following four aspects of the disease.

–Etiology,

–Pathogenesis 发病机理(Course of disease)

–Morphologic 形态学changes and

–Functional derangements错乱 and clinical significance意义

•Etiology of a disease means the cause of the disease.

•If the cause of a disease is known it is called primary etiology. If the cause of the disease is unknown it is called idiopathic.

•There are two major classes of etiologic factors: genetic and acquired (infectious, nutritional, chemical, physical, etc).

•Pathogenesis means the mechanism through which the cause operates to produce the pathological and clinical manifestations.

•The pathogenetic mechanisms could take place in the latent 潜在的or incubation潜伏期period. Pathogenesis leads to morphologic changes.

•The morphologic changes refer to the structural alterations in cells or tissues that occur following the pathogenetic mechanisms.

•The structural changes in the organ can be seen with the naked eye or they may only be seen under the microscope.

Functional derangements and clinical significance

•The morphologic changes in the organ influence the normal function of the organ.

•By doing so, they determine the clinical features (symptoms and signs), course, and prognosis of the disease.

The causes of disease

•Diseases can be caused by either environmental factors, genetic factors or a combination of the two.

Environmental causes of disease are many and are classified into:

1.Physical agents:  

These include trauma, radiation, extremes极端的 of temperature, and electric power. These agents apply excess physical energy, in any form, to the body.

2.Chemicals: 

With the use of an ever-increasing number of chemical agents such as drugs, in industrial processes, and at home, chemically induced injury has become very common.

Their effects vary:

–Some act in a general manner, for example cyanide氰化物is toxic to all cells.

–Others act locally at the site of application, for example strong acids and caustics腐蚀性的.

–Another group exhibit a predilection for certain organs, for example – the effect of alcohol on liver. Many toxic chemicals are metabolized in liver and excreted in kidney, as a result, these organs are susceptible to chemical injury.

3.Nutritional deficiencies & excesses

•Nutritional deficiencies may arise as a result of poor supply, interference with absorption, inefficient transport within the body, or defective utilization. It may take the form of deficiency either of major classes of food, usually protein and energy, or vitamins or elements essential for specific metabolic processes, e.g. iron for haemoglobin production. Often, the deficiencies are multiple and complex.

•On the other hand, dietary excess plays an important role in diseases. Obesity has become increasingly common, with its attendant dangers of type 2 diabetes, high blood pressure and heart disease.

4.Infections 

•Viruses, bacteria, fungi, protozoa, all cause diseases. They may do so by causing cell destruction directly as in virus infections or protozoal infections (for example malaria).

5.Immunological factors

The immune process is essential for protection against micro-organisms and parasites. The immune system can be abnormal which can lead to diseases. The abnormalities of the immune system include:

A. Hypersensitivity reaction: This is exaggerated immune response to an antigen. For example, bronchial asthma can occur due to exaggerated immune response to the harmless pollen.

B. Immunodeficiency:This is due to deficiency of a component of the immune system which leads to increased susceptibility to different diseases. An example is AIDS.

C. Autoimmunity: This is an abnormal (exaggerated) immune reaction against the self antigens of the host. Therefore, autoimmunity is a hypersensitivity reaction against the self antigens. For example, type 1 diabetes is caused by autoimmune destruction of the beta cells of the islets of the pancreas.

•The mental stresses imposed by conditions of life, particularly in technologically advanced communities, are probably contributory factors in some groups of diseases.

Genetic Factors

•These are hereditary遗传 factors that are inherited genetically from parents.

Course of disease

•Exposure

•Latency period 

•Biological onset 

•Clinical onset 

•Permanent damage 

•Death

Natural history of the disease

The course of a disease in the absence of any intervention is called the natural history of the disease. Include:

Exposure to various risk factors (causative agents)

Latency, period between exposure and biological onset of disease

Biological onset of disease; this marks the initiation of the disease process, without any sign or symptom. Following biological onset of disease, it may remain asymptomatic or subclinical (i.e. without any clinical manifestations), or may lead to overt clinical disease.

The clinical onset of the disease, when the signs and symptoms of the disease become apparent. The expression of the disease may be variable in severity or in terms of range of manifestations.

The onset of permanent damage, and Death

Natural recovery, i.e. recovery without any intervention, can occur at any stage in the progression of the disease.

Following clinical onset, disease may follow any of the following trends:

A. Resolution can occur leaving no sequelae,

B. The disease can settle down, but sequelae are left, or

C. It may result in death.

•Clinical death is the reversible transmission between life and biologic death. Clinical death is defined as the period of respiratory, circulatory and brain arrest.

•Signs indicating clinical death are:

•The patient is without pulse or blood pressure and is completely unresponsive to the most painful stimulus.

•The pupils are widely dilated

•Recovery can occur with resuscitation(CPR)心脏复苏.

•Biological death (sure sign of death), which sets in after clinical death, is an irreversible state of cellular destruction.

•It manifests with irreversible cessation of circulatory and respiratory functions, or irreversible cessation of all functions of the entire brain, including brain stem.