Theory of Staining

Question 1

What is the term used in light microscopy to refer to the stainable substance in the nucleus?

Answer 1

Chromatin

Question 2

What does heterochromatin refer to?

Answer 2

Stainable condensed regions of chromosomes that stain intensely basophilic

Question 3

What is euchromatin characterized by?

Answer 3

Unstainable chromatin representing genetically active DNA, appearing as clear spaces

Question 4

Which staining method demonstrates intense staining in lymphocytes?

Answer 4

Hemalum Staining

Question 5

What is the primary physical factor influencing staining reactions?

Answer 5

Most reactions include physical and chemical factors, except lipid staining which is strictly physical

Question 6

What does dye adsorption refer to in the context of staining?

Answer 6

Attraction of minute particles from solution by the surface of certain tissue components

Question 7

Define capillary staining.

Answer 7

The ‘taking in’ or ‘sucking up’ of the dye into the minute tubules of tissue

Question 8

What is adsorption staining also known as?

Answer 8

Electrical theory of staining

Question 9

Fill in the blank: Selective solubility theory is based on the dye being more soluble in the substance being stained than in the _______.

Answer 9

solvent in which it is dissolved

Question 10

What does permeability/porosity refer to in staining?

Answer 10

The size of the protein mesh that captures and holds a given dye molecule

Question 11

What type of bonding occurs when dye and tissue are attracted to each other due to different charges?

Answer 11

Ionic/Electrostatic Bonding

Question 12

What characterizes covalent bonding in staining?

Answer 12

Occurs when atoms share electrons, forming strong bonds

Question 13

What is the role of hydrogen bonding in staining?

Answer 13

Occurs when covalently bonded hydrogen is attracted to electronegative atoms

Question 14

What is hydrophobic bonding in staining?

Answer 14

Holds dyes in tissues by the exclusion of water from hydrophobic groups

Question 15

What appearance do interphase nuclei typically show when stained by H&E?

Answer 15

Discrete, membrane-bound masses that stain basophilic

Question 16

What is an accentuator in staining?

Answer 16

A substance that increases the staining power of a dye without forming a link to the tissue

Question 17

What is the function of a mordant in staining?

Answer 17

Improves binding of tissue elements with the dye by forming a link

Question 18

What is ripening in the context of hematoxylin staining?

Answer 18

The oxidation product of hematoxylin called hematein during a conversion process

Question 19

True or False: Basophilic tissues attract basic dyes.

Answer 19

True

Question 20

True or False: Acidophilic tissues attract acid dyes.

Answer 20

True

Question 21

Define chromogen.

Answer 21

A compound containing a colour-bearing group or chromophore

Question 22

What is a chromophore?

Answer 22

The chemical grouping that bestows colour on a compound

Question 23

What is an auxochrome?

Answer 23

A group of atoms that enables a chromogen to form salts with tissue groups

Question 24

What distinguishes a cationic dye?

Answer 24

It has a positive charge and is often used for nuclear stains

Question 25

What characterizes anionic dyes?

Answer 25

They are negatively charged and often used to stain proteins in cytoplasm

Question 26

What is a 'lake' in staining?

Answer 26

A coloured complex formed by the union of dye and mordant

Question 27

What are the two essential qualities of every dye?

Answer 27

* It must be a coloured substance * It must attach itself to the tissue

Question 28

What factors affect dye binding?

Answer 28

* Temperature * pH * Concentration * Time * Tissue Preparation

Question 29

What is progressive staining?

Answer 29

A technique where different elements are coloured in sequence until desired intensity is reached

Question 30

What is regressive staining?

Answer 30

A technique where tissue is over-stained and then differentiated to leave only the desired element stained

Question 31

What is direct staining?

Answer 31

Staining tissues directly in a simple aqueous or alcoholic dye solution

Question 32

What is indirect staining?

Answer 32

Staining that requires a mordant before satisfactory combination with tissues takes place

Question 33

What is argyrophilic reaction in staining?

Answer 33

Reactions where certain tissue elements have a natural affinity for silver nitrate

Question 34

What is argentaffin reaction?

Answer 34

Use of phenolic groups that can reduce silver salts to stain tissue components directly

Question 35

What is the result of reducing a bound colourless silver salt like silver nitrate?

Answer 35

Forms a black, reduced silver compound ## Footnote Reduced by substances such as hydroquinone or formalin

Question 36

What are Argentaffin Reactions?

Answer 36

Use of phenolic groups capable of reducing silver salts ## Footnote Tissue elements that can reduce silver ions in solution stain it black or brown

Question 37

What characterizes argentaffin positive tissues?

Answer 37

The tissue component itself reduces the silver salt directly ## Footnote Forms visible metallic silver in the tissue without a separate reducing agent

Question 38

Give an example of an argentaffin material.

Answer 38

Melanin

Question 39

What happens to carbohydrate-containing tissues when treated with oxidants?

Answer 39

They form aldehydes that can reduce methenamine and silver nitrate ## Footnote Requires appropriate conditions of temperature and pH

Question 40

What do histochemical reactions involve?

Answer 40

Reaction between a colourless solution and a specific tissue component ## Footnote Produces a colour or opaque reaction without needing a dye

Question 41

True or False: Leuco dyes can become re-colourized by oxidation.

Answer 41

True

Question 42

What is the purpose of differentiation in regressive staining methods?

Answer 42

Removes stain from sites with less affinity while retaining strong staining in other structures

Question 43

What is acid differentiation?

Answer 43

Uses dilute solutions of inorganic acids like HCl or acetic acid in solvents ## Footnote Acts by dissolving dye that has not firmly attached

Question 44

How do basic dyes differentiate?

Answer 44

By weakly acidic solutions

Question 45

How do acid dyes differentiate?

Answer 45

By weakly alkaline solutions

Question 46

What is mordant differentiation?

Answer 46

Uses a weak solution of the mordant used in the original stain ## Footnote Allows dye to leave tissue and combine with free mordant in solution

Question 47

What must be monitored during the differentiation process?

Answer 47

Ensure structures that must be stained remain stained with a colourless background

Question 48

What is solvent differentiation?

Answer 48

A process that depends on dye binding strength, bond type, and solvent volume ## Footnote Easier to control and can be employed slowly

Question 49

What does oxidizing differentiation do?

Answer 49

Oxidizes (bleaches) the dye to a colourless substance ## Footnote Mild oxidizing agents are used for this process

Question 50

List some solutions used in oxidizing differentiation.

Answer 50

* Potassium ferricyanide * Potassium permanganate * Chromic acid * Picric acid * Potassium dichromate

Question 51

What are natural dyes?

Answer 51

Dyes obtained from natural sources like insects and plants ## Footnote Largely replaced with synthetic dyes

Question 52

What is Carmine?

Answer 52

A deep red dye extracted from the female cochineal bug ## Footnote Usually treated with alum or iron to increase its affinity for tissue

Question 53

What is Hematoxylin derived from?

Answer 53

The heartwood of the logwood tree (Hematoxylum campechianum) ## Footnote One of the most important natural dyes in biological staining

Question 54

What is Orcein?

Answer 54

A vegetable dye obtained from certain lichens ## Footnote Best known as a specific stain for elastic tissue

Question 55

What is Saffron used for?

Answer 55

Occasionally used in trichrome methods ## Footnote Limited in use due to high cost

Question 56

What topic will be covered next week?

Answer 56

Hematoxylin and Eosin Staining and troubleshooting H and E staining