Histology And Tissue Journey

Question 1

Fixation- tissue staining

Answer 1

1st step
- maintain tissue morphology and stabilise proteins
- inhibits bacterial/fungal growth and inhibits degradation.

Question 2

Problems with fixation- damage

Answer 2

• damages proteins
• has to be carefully optimised for enzyme histochemistry, immunocytochemistry and electron microscopy in order to preserve antigenic sites.

Question 3

Hypertonic cells

Answer 3

Lose fluid and shrink

Question 4

Isotonic cells

Answer 4

Normal shape and size maintained

Question 5

Hypotonic cells

Answer 5

Cells swell and can rupture

Question 6

Aldehydes

Answer 6

A fixative used in histopathology. (Formalin). Cross links are formed within and between protein molecules.
Reactions between aldehydes and proteins are pH dependant (faster at higher)

Question 7

Problems with aldehydes

Answer 7

Glutaraldehyde can cause the loss of up to 30% of the alpha helical structure of a protein.
Slow, overnight usually required.

Question 8

Microwave fixation

Answer 8

Microwave energy interacts with dipolar molecules ( water and protein side chains) so that their thermal energy throughout the tissue is increased. Speeds up chemical fixation using formalin.

Question 9

Embedding

Answer 9

2nd step.
Aim is to embed the tissue in a solid medium firm enough to support the tissue and provide sufficient rigidity so it can be cut and soft enough not to damage the knife or tissue. (Mostly paraffin wax)

Question 10

Tissue processing

Answer 10

1- Dehydration: to remove the fixative and water. Replace with dehydration fluid.
2- clearing: replacing the dehydrating fluid with one thats miscible with both the embedding medium and d. fluid.
3- inpregnation: replace the clearing agent with the embedding medium.
4- embedding

Question 11

Factors affecting processing

Answer 11

• Agitation: ensure fluid exchange occurs across all tissue surfaces.
• heat: increases the rate of penetration.
  -viscosity of solutions used
• vacuum: can reduce impregnation time when used in a closed system

Question 12

Dehydration

Answer 12

The removal of aqueous fixative fluids from tissues.

Question 13

Clearing

Answer 13

Dehydration agents dont mix with paraffin wax.
When dehydration agent has been replaced by these solvents the tissue has a translucent appearance.