OVERVIEW OF PATHOLOGY

Definitions

The study of the essential nature of disease, including symptoms/signs, patho-genesis, complications, and morphologic consequences including structural and functional alterations in cells, tissues, and organs

The study of all aspects of the disease process focusing on the pathogenesis leading to classical structural changes (gross and histopathology) and molecu-lar alterations

The etiology (cause) of a disease may be genetic or environmental. The pathogen-esis of a disease defines the temporal sequence and the patterns of cellular injurythat lead to disease. Morphologic changes of the disease process include both gross changes and microscopic changes. The clinical significance of a disease relates to its signs and symptoms, disease course including complications, and prognosis.

Methods Used

Gross examination of organs on exam questions has 2 major components: identify-ing the organ and identifying the pathology. Useful gross features include consid-eration of size, shape, consistency, and color.

Microscopic examination of tissue

In light microscopic examination of tissue, hematoxylin and eosin (H&E) is considered the gold standard stain and is used routinely in the initial micro-scopic examination of pathologic specimens.

The common denominator of the features shown in Table 1-1 is that hematoxylin binds nucleic acids and calcium salts, while eosin stains the majority of proteins (both extracellular and intracellular).

·              Other histochemical stains (chemical reactions): Prussian blue (stains iron),Congo red (stains amyloid), acid fast (Ziehl-Neelsen, Fite) (stains acid-fast bacilli), periodic acid-Schiff (PAS, stains high carbohydrate content mol-ecules), Gram stain (stains bacteria), trichrome (stains cells and connective tissue), and reticulin (stains collagen type III molecules).

·              Immunohistochemical (antibody) stains include cytokeratin (stains epithe-lial cells), vimentin (stains cells of mesenchymal origin except the 3 muscle types; stains many sarcomas), desmin (stains smooth, cardiac, and skeletal myosin), prostate specific antigen, and many others.

Ancillary techniques include immunofluorescence microscopy (IFM), typicallyused for renal and autoimmune disease, and transmission electron microscopy(EM), used for renal disease, neoplasms, infections, and genetic disorders.

Molecular techniques include protein electrophoresis, Southern and Western blots,polymerase chain reaction (PCR), and cytogenetic analysis (karyotyping, in situ hybridization studies).

Summary

Pathology is the study of disease and concerns itself with the etiology, pathogenesis, morphologic changes, and clinical significance of different diseases.

Gross examination of organs involves identifying pathologic lesions by evaluating abnormalities of size, shape, consistency, and color.

Tissue sections stained with hematoxylin (nucleic acids and calcium salts) and eosin (most proteins) are used for routine light microscopic examination.

Additional techniques that pathologists use to clarify diagnoses include histochemical stains, immunohistochemical stains, immunofluorescence microscopy, transmission electron microscopy, and molecular techniques.