4.1-EMBEDDING

Question 1

What is the process of placing infiltrated tissue into a mold containing embedding medium

Answer 1

which is allowed to solidify?

Question 2

What is the difference between infiltration and embedding?

Answer 2

Infiltration: tissue submerged in medium bucket; Embedding: tissue placed in mold to solidify

Question 3

At what temperature should embedding paraffin wax be maintained?

Answer 3

2-4°C above its melting point

Question 4

Why must the embedding medium match the tissue type in strength and hardness?

Answer 4

To ensure proper sectioning and support during microtomy

Question 5

Why must tissues be free of water during embedding?

Answer 5

Water hinders wax infiltration

Question 6

What is the process of arranging tissue in precise positions in the mold during embedding?

Answer 6

Orientation

Question 7

How should tubular tissues (e.g.

Answer 7

intestines

Question 8

How should skin samples be oriented during embedding?

Answer 8

All layers (epidermis to dermis) must be visible

Question 9

How should fragmented tissues (e.g.

Answer 9

endometrial curettings) be oriented?

Question 10

How should long tissues be positioned during embedding?

Answer 10

Diagonally to optimize sectioning

Question 11

What are examples of embedding molds?

Answer 11

Leuckhart’s molds+compound embedding units+plastic embedding rings+disposable molds (peel-away

Question 12

What is celloidin/nitrocellulose embedding used for?

Answer 12

Hard tissues (bones

Question 13

How is evaporation controlled during celloidin embedding?

Answer 13

Shallow tins/enamel pans covered with weighted glass or bell jars

Question 14

What is the process of embedding tissues first in a supporting medium (e.g.

Answer 14

agar) and then in paraffin wax?

Question 15

What types of tissues require double-embedding?

Answer 15

Large dense tissues (e.g.

Question 16

What is plastic (resin) embedding used for?

Answer 16

Hard tissues (undecalcified bone)

Question 17

What resins are used in plastic embedding?

Answer 17

Epoxy+polyester+acrylic

Question 19

Gelatin Impregnation Section

Question 20

What is the process of embedding tissues without dehydration using a water-soluble medium?

Answer 20

Gelatin impregnation

Question 21

Why is gelatin used for enzyme studies?

Answer 21

Preserves enzymes destroyed by paraffin processing

Question 22

What are the steps for gelatin impregnation?

Answer 22

1. 10% gelatin + 1% phenol (24h)→2. 20% gelatin + 1% phenol (12h)→3. Fresh 20% gelatin (cooled)→4. Harden in 10% formalin (12-24h)→5. Tissue thickness ≤2-3mm

Question 23

Why must tissues be ≤2-3mm thick in gelatin impregnation?

Answer 23

To ensure complete medium infiltration

Question 24

Why must impregnating medium volume be 25x the tissue volume?

Answer 24

To ensure complete clearing agent displacement and uniform infiltration

Question 26

Paraffin Wax Substitutes Section

Question 27

What substitutes replace paraffin wax in embedding?

Answer 27

Paraplast+Embeddol+Ester Wax+Water-soluble waxes (Carbowax)+DMSO

Question 28

What is Paraplast composed of?

Answer 28

Purified paraffin + synthetic plastic polymers

Question 29

What are Paraplast’s advantages?

Answer 29

Elastic+uniform blocks+better ribboning+no cracking

Question 30

What is Embeddol?

Answer 30

Synthetic wax (56-58°C) less brittle than Paraplast

Question 31

What is Ester Wax?

Answer 31

Hard wax (46-48°C) soluble in alcohol

Question 32

What is Carbowax?

Answer 32

Water-soluble PEG-based wax preserving lipids and enzymes

Question 33

How is Carbowax used?

Answer 33

Four ethanol changes (70%→90%→100%→100%) followed by embedding at 50°C

Question 34

What is DMSO’s role in embedding?

Answer 34

Reduces infiltration time but has a garlic-like taste

Question 36

Celloidin/Nitrocellulose Section

Question 37

What is celloidin composed of?

Answer 37

Nitrocellulose dissolved in ether/alcohol

Question 38

What are celloidin’s advantages?

Answer 38

Rubbery consistency+supports dense tissues+no heat required

Question 39

What are celloidin’s disadvantages?

Answer 39

Slow (days/weeks)+flammable vapor+difficult thin sections

Question 40

What is the wet celloidin method?

Answer 40

For bones/organs: ether/alcohol→thin→medium→thick celloidin→dessicator→70-80% alcohol storage

Question 41

What is the dry celloidin method?

Answer 41

Uses Gilson’s mixture (chloroform/cedarwood oil) for transparency

Question 42

How does nitrocellulose differ from celloidin?

Answer 42

Harder+thinner sections but more explosive

Question 43

What are the types of plastic (resin) embedding?

Answer 43

Epoxy+Acrylic

Question 44

What is epoxy resin made of?

Answer 44

A balanced mixture of epoxy plastic

Question 45

What are the three types of epoxy resins?

Answer 45

Bisphenol A (Araldite)+Glycerol (Epon)+Cyclohexene dioxide (Spurr)

Question 46

What are the characteristics of Bisphenol A (Araldite)?

Answer 46

Low infiltration rate

Question 47

What are the characteristics of Glycerol (Epon)?

Answer 47

Lower viscosity

Question 48

What are the characteristics of Cyclohexene dioxide (Spurr)?

Answer 48

Very low viscosity+fastest infiltration+polymerization at 60°C is recommended

Question 49

What are the disadvantages of epoxy resin?

Answer 49

Hydrophobic+tissue damage from peroxide oxidation+reduced antigenicity+sensitizer+toxic+carcinogenic (e.g.

Question 50

Why is epoxy resin not recommended for IHC?

Answer 50

It reduces antigenicity

Question 51

What is epoxy resin primarily used for?

Answer 51

Electron microscopy studies

Question 52

What are acrylic plastics made of?

Answer 52

Esters of acrylic or methacrylic acid

Question 53

Why are acrylic plastics preferred for high-resolution light microscopy?

Answer 53

Ease of handling+excellent staining quality

Question 54

What are the limitations of acrylic plastics in IHC?

Answer 54

The matrix may act as a physical barrier to molecules

Question 55

What is glycol methacrylate (GMA) used for?

Answer 55

Tissues for transmission electron microscopy (TEM)

Question 56

What are the advantages of glycol methacrylate (GMA)?

Answer 56

Hydrophobic nature allows many staining methods+polymerization without a hardener+does not require water-free conditions+works best with some water present+polymerization at ambient temperatures or with UV radiation to 60°C+thin sections can be cut with glass or diamond knives+resists non-specific background staining in low-acid GMA+enzyme digestion and immunological localization can be performed on thick sections without removing plastic

Question 57

What is methyl methacrylate (MMA) used for?

Answer 57

Embedding undecalcified bone for histomorphometry and bone marrow hematopathology

Question 58

Why is methyl methacrylate widely used for bone studies?

Answer 58

Hardness makes it ideal for undecalcified bone+better tissue penetration+superior staining and morphological detail+easily removable from tissue sections

Question 59

Why is methyl methacrylate not recommended for enzyme or IHC studies?

Answer 59

Complete loss of enzyme activity and protein antigenicity occurs during processing