Histology

Question 1

What is the order of processes for preparing sections on slides?

Answer 1

Fixation, dehydration, embedding, cutting, mounting

Question 2

What is the fixation (first step) used for?

Answer 2

To maintain tissue morphology and stabilise proteins

Question 3

What do fixatives do?

Answer 3

Crosslink proteins and form gels

Question 4

What do fixatives inhibit?

Answer 4

Bacterial/fungal growth
Degradation

Question 5

What happens to soluble proteins?

Answer 5

Rendered insoluble which provides mechanical strength

Question 6

What does fixation damage?

Answer 6

Proteins

Question 7

What is the most common fixative?

Answer 7

Aldehydes

Question 8

Explain aldehydes

Answer 8

Cross links are formed with and between protein molecules (e.g. lysine-argnine)

Question 9

True or false: Reaction between protein and aldehydes is pH dependent

Answer 9

True (faster at high pH)

Question 10

What are the problems with aldehydes?

Answer 10

Protein alterations that lead to change in isoelectric points
Toxic! Slow process!

Question 11

Explain oxidising agents (fixative)

Answer 11

More detailed and higher resolution
Allows stable cross links

Question 12

Explain microwave fixation and stabilisation

Answer 12

Fixation by heat which leads to good cross linking
Microwave energy reacts with dipolar molecules

Question 13

Problems with microwave fixation and stailisation

Answer 13

Unsuitable for larger biopsies

Question 14

What are the two types of embedding?

Answer 14

Paraffin embedding and frozen sections

Question 15

Explain paraffin embedding

Answer 15

Cheap, simple and common
Lipid will be stripped out using paraffins and destroy enzyme activity and antigenic sites

Question 16

Explain frozen sections

Answer 16

Used to demonstrate subcellular location of enzymes
Lipid analysis

Question 17

Explain dehydration in tissue processing

Answer 17

Removal of aqueous fixative fluids

Question 18

What is the most used dehydration agent?

Answer 18

Industrial methylated spirit

Question 19

Explain clearing in tissue processing

Answer 19

Dehydrating agents do not generally mix with paraffin wax
Give tissue translucent appearance
Enable rapid removal of dehydrating agents

Question 20

Which clearing agent is the best?

Answer 20

Xylene

Question 21

What is the most used embedding agent?

Answer 21

Paraffin wax

Question 22

When is paraffin wax not suitable?

Answer 22

When sections need to be thinner
Heat affects tissue (e.g. pancreas)
Processing agents remove or destroy tissue components

Question 23

What are alternative embedding media?

Answer 23

Waxes - no longer used
Resins - high resolution, cut much thinner sections

Question 24

Explain tissue orientation

Answer 24

Sections are generally cut from largest area of tissue

Question 25

What are the exceptions to the general tissue orientation

Answer 25

Tubular structures
Skin and epithelial
Muscle biopsies

Question 26

True or false: A microtome can cut frozen sections

Answer 26

False: it can’t

Question 27

True or false: Sections are cut at 2-4 mM thick

Answer 27

False: cut at 2-4 um sections

Question 28

True or false: Microtomes cannot cut through paraffin very easily

Answer 28

False: Cut easily

Question 29

True or false: Citrus fruit oils mix well with alcohol

Answer 29

TRUE