Session 1: Introduction to Pathology Flashcards
First problem with looking at tissue under a microscope.
Autolysis.
What is autolysis?
Tissue autolysis is self-digestion of tissue which begins when the blood supply is cut off.
It destroys cells and tissue architecture.
How is autolysis prevented?
We can block biochemical process of autolysis with fixatives which inactive tissue enzymes and denature proteins, prevent bacterial growth and harden the tissue.
What is used as fixation?
Formalin aka formaldehyde in water.
How long does it take for a tissue to be fixed?
1mm/hr so usually between 24-48 hours.
What is the next step/problem?
Cutting up the tissue and finding appropriate parts.
Why might cutting up be a problem?
Because the tissue might not be hard enough to be able to take very thin slices.
How do you go about this problem with too soft tissue?
In order to be able to cut very thin sections the tissue has to be surrounded and impregnated with a hardening agent.
What hardening agent is usually used?
Paraffin wax
Explain the process of hardening.
Have to remove water from tissue first. Dehydration using alcohol in a vacuum so that water is drawn out of the cells.
You then replace the alcohol with xylene which can mix with wax.
Xylene is then replaced with molten paraffin wax which will even be inside the cells.
Next step after hardening.
Tissue inte a piece of wax that can be cut. Tissue is taken out of the cassettes by hand and put into metal blocks. They are filled with molten paraffin wax and the body of the cassette is placed on top.
The wax is the allowed to Harden and the metal tray is removed.
How is the sections cut very thinly now?
By the use of a microtome. This is important to be able to see though them with a microscope.
Next step after thin cuts.
Staining.
Explain staining.
Haematoxylin and Eosin used to stain the.
Haematoxylin stains nucleus purple
Eosin stains cytoplasm and connective pink.
What happens after staining?
Preservation and protection of tissue via mounting.
