define histology

study of microscopic structures of tissues

steps in making histological samples

1. specimen acquisition 2. gross examination 3. fixation 4. tissue processing 5. tissue embedding 6. tissue sectioning 7. staining 8. microscopic examination

sample acquisition

be as fresh as possible (not frozen) 1:10 tissue to fixative note for examination that cells undergo immediate change after death

fixation

preserves tissue specimens in life like state prepares tissue for clearing and staining

benefits of fixation (6)

-prevents autolysis & putrefaction of cell -prevents loss of cellular constituents -prevents shrinkage, distortion, cell swelling -kills microorganisms -hardens tissue for staining -establishes chemical sites for stain reaction

name the types of fixation (2)

physical & chemical

describe and contrast the two types of chemical fixation

- coagulant (non additive) react w/ tissue , do not add or combine w/ tissue eg ethanol - disrupts cytoplasm by causing it to be opaque & congeal into a net-like structure/transparent gel. - non coagulant (additive) binds either to a proteins' amino or carboxyl group which changes reactivity with stains eg formalin. strengthens cells structure and insures tissue preservation

name the physical types of fixation

heat (preserves overall but not internal) microwave freeze drying & freeze substitution

whats the most commonly used fixative

10% neutral buffered formalin

factors affecting fixation

buffers & pH size of sample & duration of fixation temperature osmolarity (conc. salt & solutes)

steps of tissue proccesing

dehydration (removal of water from tissue) clearing (make tissue translucent) infiltration (putting tissue in medium) embedding (solid supporting medium) sectioning (5 microns thickness) staining (haematoxylin & eosin)

common problems when sectioning

section wont form ribbons splitting in sections sections roll up