FIXATION PT1

What is the primary purpose of tissue fixation?

To alter tissue by stabilizing proteins and preserving cellular morphology.

What is the common choice of fixative used in histology?

10% neutral buffered formalin (NBF) is most often the fixative choice.

What are some considerations when choosing a fixation method?

Molecular changes, loss of components, preservation of structures, shrinkage or swelling conditions, staining effects, cost, and safety.

What is the effect of temperature on tissue fixation?

Increased temperature increases the rate of fixation but also increases the rate of autolysis.

What is the recommended minimum thickness of tissue for proper fixation?

≤3-4 mm to facilitate proper fixation and processing.

What kind of changes do additive fixatives produce in proteins?

Additive fixatives may change the protein shape and charge by forming chemical links.

What type of fixation method is heat considered?

Heat is a physical fixation method that denatures and stabilizes proteins.

What is a major drawback of using mercuric chloride as a fixative?

It is very toxic and affects the central nervous system.

What is the best fixative for preserving lipids?

Osmium tetroxide is the best fixative for preserving lipids.

What color change might indicate the formation of formalin pigment during fixation?

A dark brown crystalline pigment found if the pH drops below 6.0.

What are hallmark signs of well-fixed tissue on an H&E-stained slide?

Well-defined nuclei, no smudginess or artifacts, and well-stained cytoplasm.

What is the effect of acetone as a fixative?

Acetone causes significant shrinkage, hardening, and distortion of tissue.

What happens to cellular structures during delayed fixation?

Autolysis may occur, leading to breakdown of tissue morphology and artifacts.

What is the relationship between penetration rate and fixation effectiveness?

Faster penetration rates can improve fixation effectiveness, especially for coagulant fixatives.

What is the main issue with incomplete fixation before processing?

It can result in poor tissue morphology and smudgy nuclear staining.

What are the safety precautions when using formaldehyde?

Use in a fume hood with proper personal protective equipment (PPE) due to its carcinogenic properties.