TOPIC IV A: PARAFFIN SECTION

Dehydration

Fixed tissue in an Alcohol = Alcohol replaces fixative and water = Dehydrates the tissue

Clearing

Dehydrates tissue in a Xylene = Dissolves the alcohol so that the embedding wax will penetrate the tissue

Infiltration

• Cleared tissue in Paraffin = Ready for embedding

• Helps preserve tissue structure, provides support, enables precise sectioning, maintains uniformity, and preserves cellular structures

DEHYDRATION

• Second step after fixation and third step if there is decalcification process

• process wherein there is a slow substitution between water and organic solvent

• Remove fixative and free water

ALCOHOL

• Considered the best dehydrating agent and most commonly used

• Start from a lower concentration (gradual)

ACETONE

● Rapid-acting ; mostly used for reagent (urgent) biopsies

● Dehydrates in ½ to 2 hours

● Highly flammable

● Poor penetration can cause considerable shrinkage

(altho rapid-acting, it poorly penetrates :<)

● More miscible in water

● Causes brittleness - prolonged time

● NOT recommended for routine purposes

DIOXANE (Diethyl Oxide)

● Excellent dehydrating and clearing agent

● Miscible to xylene, water, alcohol and paraffin wax

● Less shrinkage compared to alcohol

● Staining properties of tissues are unaffected

● Produces poor tissue ribbons (often wrinkled and dali maguba)

● Expensive

● Extremely toxic (especially to liver)

CELLOSOLVE

● AKA Ethylene glycol monoethyl ether

● Rapid, tissues can be stored for months without distortions

● Combustible and toxic

● Expensive

TRIETHYLPHOSPHATE

● Very little distortion and hardening of tissue

● Used to dehydrate smears and sections following certain stains

● Can be used (substitute) for routine - paraffin

TETRAHYDROFURAN

● Miscible with paraffin wax

● Toxic when inhaled and ingested

• Vapors causes nausea and headache

CLEARING

● Miscible in both wax and preceding alcohol

● Dissolved lipids

● Imparts optical clarity

● Must be miscible with resins used for mounting

● Canada balsam

XYLENE

● AKA Xylol

● Used clearing both for embedding and mounting

● Works well with short term clearing

● Cost-effective

● Used as a dewaxing agent during staining

● Cleaning of tissue processors

● Toxic

TOLUENE

● More tolerant of small amounts of water than xylene

● More expensive and more toxic

BENZENE

● Penetrates and clears rapidly; ideal for urgent biopsies (Can provide clearing very well)

● Carcinogenic

○ Not commonly used nowadays

○ Its use is discouraged

CHLOROFORM

● Slower in action than xylene

● Causes less brittleness

● Tissues doesn’t become translucent

CEDARWOOD OIL

● Used to clear both paraffin and colloid in sections during embedding

● Requires TWO CHANGES to clear solutions

● Produces crystals with acetic-alcohol fixed tissues

● Recommended for

• CNS tissue = Spinal Cord, Brain stem and the lobe

• Cytological studies

INFILTRATION

● Impregnation

○ Replace clearing agent with medium

○ Fill all tissue cavities

○ Provides firm consistencies to the specimen

EMBEDDING

● Infiltrated tissue is placed into a mold

○ Tissue is positioned with the medium

● Tissue block

Paraffin Section

A method of tissue processing in which tissues are thinly cut or sliced and embedded in paraffin wax.

PARAFFIN WAX SUBSTITUTE

A petroleum-based alternative used in candle making, cosmetics, and other applications as a substitute for paraffin wax. It has a similar melting point and texture but is made from different ingredients.