PRELIM: CH11 IMPREGNATION AND EMBEDDING

To replace the clearing agent with a medium that fills tissue spaces and provides support

What is the primary purpose of impregnation (infiltration) in tissue processing?

An embedding medium

During impregnation, the clearing agent is replaced primarily by:

It provides firmness that allows thin sections to be cut without excessive distortion

Why is adequate impregnation important before sectioning?

Placing impregnated tissue in a mold in a precise position and allowing the medium to solidify

Embedding is best described as the process of:

Casting or blocking

Which term is also used to describe embedding?

• It should be stable.

• It should be homogeneous.

• It should be suitable for sectioning and ribboning.

Which of the following are the ideal properties of an embedding medium?

30–60°C

Ideally, an embedding medium should be molten at approximately:

Ability to flatten after ribboning

Which characteristic of an embedding medium helps produce good ribbons during sectioning?

Paraffin wax, celloidin, gelatin, and plastic

Which four materials are listed as the general types of impregnation and embedding media?

Paraffin wax

Which embedding medium is the most commonly used for routine tissue processing?

Polycrystalline mixture of solid hydrocarbons

Paraffin wax is best described as a:

Solid at room temperature

Paraffin wax is normally:

56–58°C

The most common melting point range for histological paraffin wax is approximately:

To reduce viscosity and facilitate tissue penetration

Why is paraffin wax commonly heated slightly above its melting point during infiltration?

Molecular weight of its components and ambient temperature

Wax hardness or viscosity depends partly on:

High molecular weight mixtures generally melt at higher temperatures.

Which statement about molecular weight and paraffin wax is correct?

Small, uniform-sized crystals

What type of crystal morphology generally provides better physical support for tissue?

Produce a less brittle, more homogeneous wax with better cutting characteristics

Additives may be incorporated into paraffin wax primarily to:

Thin serial sections can be cut relatively easily from most tissues.

Which is an important advantage of paraffin wax?

24 hours

A major advantage of paraffin processing is that it can generally produce sections within:

DNA and RNA may still be recovered decades after fixation.

Formalin-fixed, paraffin-embedded tissue is valuable for historical medical studies because:

Tissue brittleness

Which is a disadvantage of overheated paraffin?

Excessive shrinkage and hardening

Prolonged impregnation in paraffin may result in:

Clearing agent may be retained, causing soft and shrunken tissue.

What happens when tissue is inadequately impregnated with paraffin?

Crumble during sectioning and break apart in the water bath

A poorly impregnated paraffin block may: