NEET MDS Lessons
General Pathology
Histopathological techniques
Histopathological examination studies tissues under the microscope. During this study, the pathologist looks for abnormal structures in the tissue. Tissues for histopathological examination are obtained by biopsy. Biopsy is a tissue sample from a living person to identify the disease. Biopsy can be either incisional or excisional.
Once the tissue is removed from the patient, it has to be immediately fixed by putting it into adequate amount of 10% Formaldehyde (10% formalin) before sending it to the pathologist.
The purpose of fixation is:
1. to prevent autolysis and bacterial decomposition and putrefaction
2. to coagulate the tissue to prevent loss of easily diffusible substances
3. to fortify the tissue against the deleterious effects of the various stages in the preparation of sections and tissue processing.
4. to leave the tissues in a condition which facilitates differential staining with dyes and other reagents.
Osteogenesis Imperfecta (OI) (Brittle bone diseases)
It is a group of hereditary disorders caused by gene mutations that eventuate in defective synthesis of and thus premature degradation of type I collagen. The fundamental abnormality in all forms of OI is too little bone, resulting in extreme susceptibility to fractures. The bones show marked cortical thinning and attenuation of trabeculae.
Extraskeletal manifestations also occur because type I collagen is a major component of extracellular matrix in other parts of the body. The classic finding of blue sclerae is attributable to decreased scleral collagen content; this causes a relative transparency that allows the underlying choroid to be seen. Hearing loss can be related to conduction defects in the middle and inner ear bones, and small misshapen teeth are a result of dentin deficiency
Roseola
- alias exanthem subitum; caused by Herpes virus type 6.
- children 6 months to 2 years old; spring and fall; incubation 10-15 days.
- sudden onset of a high fever with absence of physical findings; febrile convulsions are particularly common.
- fever falls by crisis on the 3rd or 4th day → 48 hours after temperature returns to normal macular or maculopapular rash starting on the trunk and spreading centrifugally.
HERPES ZOSTER (Shingles)
An infection with varicella-zoster virus primarily involving the dorsal root ganglia and characterized by vesicular eruption and neuralgic pain in the dermatome of the affected root ganglia.
caused by varicella-zoster virus
Symptoms and Signs
Pain along the site of the future eruption usually precedes the rash by 2 to 3 days. Characteristic crops of vesicles on an erythematous base then appear, following the cutaneous distribution of one or more adjacent dermatomes
Eruptions occur most often in the thoracic or lumbar region and are unilateral. Lesions usually continue to form for about 3 to 5 days
Geniculate zoster (Ramsay Hunt's syndrome) results from involvement of the geniculate ganglion. Pain in the ear and facial paralysis occur on the involved side. A vesicular eruption occurs in the external auditory canal, and taste may be lost in the anterior two thirds of the tongue
STREPTOCOCCAL INFECTIONS
Most streptococci are normal flora of oropharynx
Group A streptococci: Str. pyogenes
Group B streptococci: Str. agalactiae
Str. pneumoniae
Strep viridans group
Group D: Enterococcus (lately Strep. Fecalis and E. fecium), causes urinary tract infections,
Nephrosclerosis
Disease of the renal arteries.
Clinical manifestations:
(1) Benign (arterial) nephrosclerosis → Caused by the formation of atherosclerotic plaques in the renal artery. Results in narrowing of the arterioles.
(2) Malignant nephrosclerosis → Caused by malignant hypertension. Common signs of malignant hypertension include severe hypertension, retinal hemorrhages, and hypertrophy of the left ventricle. Results in inflammatory changes in the vascular walls, which may lead to rupture of the glomerular capillaries.
CHRONIC INFLAMMATlON
When the inflammatory reaction instead of subsiding after the acute phase (or without entering an acute phase), persists as a smouldering lesion, it is called chronic inflammation. .
Characteristics
- Predominantly mononuclear response.
- Inflamation.and..repair going on simultaneously.
- Usually results in more prominent-scarring.
Causes:
Chronicity may be due to :
- Defective defence mechanisms.
- Persistence of injurious agent.
(a) Certain organisms resist phagocytosis and destruction e.g tubercle bacillus, fungi
(b) insoluble particulate matter e.g., crystals. fibres suture materials.
(c) Constants supply of causative agent as in autoimmune disease where body reacts against its own tissues.
- Defective healing.
Granulomatous inflammation
It is a type of chronic inflammation characterised by localised collections of histiocytes.
These cells are usually accompanied by lymphocytes, fibroblasts and giant cells also.
Granulomas are characteristically seen in diseases like tuberculosis. syphilis, leprosy, sarcoidosis, fungal infections etc. In some of these, the lesion is morphologically distinct enough to point to the type of underlying disease. These are sometimes called' specific' granulomas. Granulomas can also be elicited by particulate, insoluble foreign material e.g. granuloma, suture granuloma, cholesterol granuloma (organising haemorrhages).