Tissue Processing

Question 1

Three stages

Answer 1

Dehydration, clearing and wax impregnation
Each step involved the replacement of the fluids in the tissues by another fluid

Question 2

Factors that affect tissue processing

Answer 2

1. Viscosity
2. Agitation
3. Heat
4. Pressure

Question 3

Viscosity

Answer 3

Friction within fluids caused by adhesion between molecules
Low viscosity fluids penetrate tissues more rapidly

Question 4

Heat

Answer 4

May increase the rate of fluid exchange as fluids become less viscous
Excessive heat must be avoided as it causes shrinkage and distortion if the tissues -over 65 degrees Celsius

Question 5

Pressure

Answer 5

Newer tissue processors employ both positive and negative pressure (vacuum) to accelerate the penetration and exchange of fluids

Question 6

Dehydration

Answer 6

Complete removal of water from tissues
Dehydrating agents must be miscible with water and with the clearing agent
Most commonly used is ethyl alcohol
Treating the tissues with a series of graded alcohols can reduce shrinkage of tissues (70 percent alcohol all the way to 100 percent alcohol)

Question 7

Clearing

Answer 7

A clearing agent that is miscible with both alcohol and wax is needed
Xylene is the most commonly used, it is flammable, volatile and toxic
Removes all remaining traces of fat from tissue samples

Question 8

Wax impregnation

Answer 8

The clearing agent in the tissue is replaced by molten paraffin wax which is a relatively impure by-product. Melting point is 56-58 degrees Celsius