General Pathology Lecture 3-4 PDF

GENERAL PATH, HISTOPATH, AND CYTOPATHOLOGY Lecture Chapter 2: HISTOPATHOLOGIC TECHNIQUES BSMT-3A HISTOLOGIC / HISTOPATHOLOGIC TECHNIQUES...

GENERAL PATH, HISTOPATH, AND CYTOPATHOLOGY Lecture Chapter 2: HISTOPATHOLOGIC TECHNIQUES BSMT-3A HISTOLOGIC / HISTOPATHOLOGIC TECHNIQUES FACTORS AFFECTING FIXATION Deals with the preparation of tissues for microscopic examination through which a total or selected parts of The volume of the fixative must be 10-20 times a tissue is being submitted into a series of processes the volume of tissue to be fixed Histopathology refers to the microscopic examination of tissue in order to study the manifestations of 1. Hydrogen Ion Concentration disease pH must be within 6 and 8 ○ Hypoxia of tissue lowers the pH, so there must be 10 STEPS IN TISSUE PROCESSING buffering capacity in the fixative to prevent excessive acidity 1. Fixation 6. Trimming ○ Acidity favors the formation of formalin-heme 2. Dehydration 7. Sectioning pigment that appears as black, polarized deposits 3. Clearing 8. Staining in tissue 4. Infiltration (impregnation) 9. Mounting ○ Buffers: phosphates, bicarbonate, cacodylate, 5. Embedding 10. Labeling veronal. 2. Temperature FIXATION RT Formalin @ 60°C First and most critical step in tissue processing ○ for rapid fixation of urgent biopsy specimen Fixation prevents autolysis and putrefaction of the tissue, while preserving it in a form as close to the Formalin @ 100°C living state as possible ○ can be used to fix tissues with tuberculosis ○ Prevents autolysis by inactivating lysosomal enzymes 3. Thickness of Section ○ Stabilizes fine structure of cells, making Tissue blocks should be small, 1-2 mm² for electron macromolecules resistant to dissolution by water microscopy and 2 mm² wide for light microscopy, and other liquid and thin