NEET MDS Lessons
General Pathology
Pathology gives explanations of a disease by studying the following four aspects of the disease.
1. Etiology,
2. Pathogenesis,
3. Morphologic changes and
4. Functional derangements and clinical significance.
1. Etiology 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. Knowledge or discovery of the primary cause remains the backbone on which a diagnosis can be made, a disease understood, & a treatment developed. There are two major classes of etiologic factors: genetic and acquired (infectious, nutritional, chemical, physical, etc).
2. Pathogenesis 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 or incubation period. Pathogenesis leads to morphologic changes.
3. 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. Those changes that can be seen with the naked eye are called gross morphologic changes & those that are seen under the microscope are called microscopic changes. the morphologic changes will lead to functional alteration & to the clinical signs & symptoms of the disease.
4. 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.
Q Fever
An acute disease caused by Coxiella burnetii (Rickettsia burnetii) and
characterized by sudden onset of fever, headache, malaise, and interstitial
pneumonitis.
Symptoms and Signs
The incubation period varies from 9 to 28 days and averages 18 to 21 days. Onset
is abrupt, with fever, severe headache, chills, severe malaise, myalgia, and,
often, chest pains. Fever may rise to 40° C (104° F) and persist for 1 to > 3
wk. Unlike other rickettsial diseases, Q fever is not associated with a
cutaneous exanthem. A nonproductive cough and x-ray evidence of pneumonitis
often develop during the 2nd wk of illness.
In severe cases, lobar consolidation usually occurs, and the gross appearance of
the lungs may resemble that of bacterial pneumonia
About 1/3 of patients with protracted Q fever develop hepatitis, characterized
by fever, malaise, hepatomegaly with right upper abdominal pain, and possibly
jaundice. Liver biopsy specimens show diffuse granulomatous changes, and C.
burnetii may be identified by immunofluorescence.
CONGESTION
Congestion or hyperaemia means an increase in the content of blood in an organ. It may be :
A. Active - due to increased arterial flow to the organ with dilatation of micro vessels as in
- Inflammation.
- Increased metabolic activity.
- Neurogenic blushing.
B. Passive - due to decreased venous drainage resulting in pooling of blood. There is always an associated element of oedema.
DYSPLASIA
It is disturbed growth or cells in regard to their size, shape arrangement. In its mild degrees it represents a reversible reaction to chronic inflammation whereas the most severe degrees warrant a labelling of intraepithelial neoplasia. Hence it includes a wide spectrum of changes ranging from a reversible disorientation to 'carcinoma-in-situ'.
Histologically it is characterized by:
o Basal cell hyperplasia.
o Variation in size and shape of cells.
o Disorderly maturation.
o Increased mitotic activity.
o Disorientation of arrangement of cells (loss of polarity)
Dysplasia is commonly seen in:
o Squamous epithelium of cervix.
o Bronchial epithelium in habitual smokers.
o Gastric and colonic mucosa in long standing inflammation
o Oral and vulval leucoplakia
Biochemical examination
This is a method by which the metabolic disturbances of disease are investigated by assay of various normal and abnormal compounds in the blood, urine, etc.
Myocardial infarction (MI)—heart attack
A. Ischemia versus MI: Ischemia is a reversible mismatch between the supply and demand of oxygen. Infarction
is an irreversible mismatch that results in cell death caused by the lack of blood flow (oxygenation). For instance, chest pain caused by ischemia can be relieved by administering nitroglycerin (a vasodilator) to the patient. If the patient has an MI, the pain will not be relieved with nitroglycerin.
1. MIs most commonly occur when a coronary artery is occluded by a thrombus generated in an atherosclerotic artery.
2. Symptoms include:
a. Chest pain, shortness of breath.
b. Diaphoresis (sweating), clammy hands.
c. Nausea, vomiting.
3. Consequences:
a. Death (one third of patients).
b. Arrhythmias (most common immediate cause of death).
c. Congestive heart failure.
d. Myocardial rupture, which may result in death from cardiac tamponade.
e. Thrombus formation on infarcted tissue; may result in systemic embolism.
Causes of disease
The causes of disease Diseases can be caused by either environmental factors, genetic factors or a combination of the two.
A. Environmental factors
Environmental causes of disease are many and are classified into:
1. Physical agents
2. Chemicals
3. Nutritional deficiencies & excesses
4. Infections & infestations
5. Immunological factors
6. Psychogenic factors
1. Physical agents
These include trauma, radiation, extremes 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,
3. Nutritional deficiencies and 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.
4. Infections and infestations
Viruses, bacteria, fungi, protozoa, and metazoa all cause diseases. They may do so by causing cell destruction directly as in virus infections (for example poliomyelitis) or protozoal infections (for example malaria).
5. Immunological factors
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. 4
6. Psychogenic factors
The mental stresses imposed by conditions of life, particularly in technologically advanced
communities, are probably contributory factors in some groups of diseases.
B. Genetic Factors
These are hereditary factors that are inherited genetically from parents.