1. What will happen if the cutting edge compresses the softer tissues?
- The sections will have a rough appearance.
2. Why will the edges become frayed if the tissue is pressed against the right or
left side of the mold?
- The tissue will be compressed and the edges will become frayed.
3. What will happen if the tissue cut is too thick?
- The mold will not sit properly in the cassette and wax will seep out.
4. What is the consequence of plastic cassettes not being placed properly into
the mold?
- One corner will be exposed to air and wax will seep out.
5. What happens if there is a prolonged delay in embedding tissue?
- The wax may snap off the cassette when the block is placed on the microtome.
6. Why is it important to press down the tissue in corners and center?
- To ensure the tissue is embedded evenly to avoid trimming issues or loss of tissue.
7. What problems can air bubbles cause during sectioning?
- They may cause wrinkling of tissue or separation of tissue from the block.
8. What is the consequence of using too little volume of wax?
- The block may break under pressure.
9. What happens if too much wax is used?
- There will be excess buildup on the chuck.
10. Why should one avoid applying too much pressure on tissue during
orientation?
- To prevent damage to fragile tissues.
11. What is the consequence of having too much wax on the bottom of the mold?
- There will be wax displacement.
12. What happens if the tissue is against the top or bottom of the mold during
embedding?
- Ribbons will not form properly.
13. What should you never do with a mold containing molten wax and tissue?
- You should never shake it.
14. What are the consequences of using over-heated paraffin during infiltration?
- It may result in block cracking, tissue shrinkage, and over-hardening.
15. What can happen if tissue blocks are not properly cooled?
- A 'dish effect' may form at the center, blocks may be pearly white or grey, or they may crack.
16. What should be done to correct improperly embedded tissue?
- The tissue block should be melted in a heated chamber of an embedding station, or it should
be restarted.
17. What is the consequence of the cutting edge compressing soft tissues?
- The sections will have a rough appearance.
18. How can the edges become frayed?
- When the tissue is pressed against the right or left side of the mold.
19. Why would the mold sit improperly in the cassette if the tissue cut is too
thick?
- The wax will seep out because the mold cannot sit properly.
20. What happens if the plastic cassettes are not placed properly into the mold?
- One corner of the cassette will be exposed to air and wax will seep out.
21. What can happen with a prolonged delay in embedding tissue?
- When the block is placed on the microtome, the wax may snap off the cassette with force.
22. What can occur if tissue is not pressed down in corners and center during
embedding?
- Parts of the tissue may be embedded deeper than the rest and cannot be trimmed, resulting
in possible loss.
23. What problems can air bubbles cause?
- They may cause wrinkling of tissue or separation of tissue from the block during sectioning.
24. What happens when too little volume of wax is used?
- The block may break under pressure.
25. What problems can excess wax cause?
- There will be excess buildup of wax on the chuck.
26. Why should too much pressure not be applied to tissue during orientation?
- Fragile tissues may be damaged.
27. What is the consequence of having too much wax on the bottom of the mold?
- The wax will displace.
28. What happens if the tissue is against the top or bottom of the mold?
- Ribbons will not form properly during embedding.
29. What should never be done to a mold containing molten wax and tissue?
- It should never be shaken.
30. What are the consequences of using over-heated paraffin?
- It may cause block cracking, tissue shrinkage, and over-hardening.
31. What problems can occur if tissue blocks are not properly cooled?
- There may be a 'dish effect' formation, blocks may be pearly white or grey, or they may crack.
32. How can improperly embedded tissue be corrected?
- The tissue block can be melted in the heated chamber of an embedding station, or the
process can be restarted.
33. What will cause the sections to have a rough appearance?
- The cutting edge compressing the softer tissues.
34. What will happen if the tissue is pressed against the right or left side of the
mold?
- The edges will become frayed.
35. What is the consequence of the mold not sitting properly in the cassette?
- Wax will seep out.
36. What can occur if the plastic cassettes are not placed properly into the mold?
- One corner of the cassette will be exposed to air and wax will seep out.
37. What is the consequence of a prolonged delay in embedding tissue?
- The wax may snap off the cassette when the block is placed on the microtome.
38. Why should tissue be pressed down in corners and center during
embedding?
- To ensure even embedding and avoid trimming or loss of tissue.
39. What problems can air bubbles cause during sectioning?
- They may cause wrinkling of tissue or separation of tissue from the block.
40. What will happen if too little volume of wax is used?
- The block may break under pressure.
41. What problems can excess wax cause?
- There will be excess buildup on the chuck.
42. Why should too much pressure not be applied to tissue during orientation?
- It may damage fragile tissues.
43. What is the consequence of having too much wax on the bottom of the mold?
- The wax will be displaced.
44. What happens if the tissue is against the top or bottom of the mold?
- Ribbons will not form properly.
45. What should never be done with a mold containing molten wax and tissue?
- It should never be shaken.
46. What are the consequences of using over-heated paraffin during infiltration?
- It may cause block cracking, tissue shrinkage, and over-hardening.
47. What can happen if tissue blocks are not properly cooled?
- There may be a 'dish effect' formation, blocks may be pearly white or grey, or they may crack.
48. How can improperly embedded tissue be corrected?
- The tissue block can be melted in the heated chamber of an embedding station, or the
process can be restarted.
49. What will cause the sections to have a rough appearance?
- The cutting edge compressing the softer tissues.
50. What will happen if the tissue is pressed against the right or left side of the
mold?
- The edges will become frayed.
51. What is the consequence of the mold not sitting properly in the cassette?
- Wax will seep out.
52. What can occur if the plastic cassettes are not placed properly into the mold?
- One corner of the cassette will be exposed to air and wax will seep out.
53. What is the consequence of a prolonged delay in embedding tissue?
- The wax may snap off the cassette when the block is placed on the microtome.
54. Why should tissue be pressed down in corners and center during
embedding?
- To ensure even embedding and avoid trimming or loss of tissue.
55. What problems can air bubbles cause during sectioning?
- They may cause wrinkling of tissue or separation of tissue from the block.
56. What will happen if too little volume of wax is used?
- The block may break under pressure.
57. What problems can excess wax cause?
- There will be excess buildup on the chuck.
58. Why should too much pressure not be applied to tissue during orientation?
- It may damage fragile tissues.
59. What is the consequence of having too much wax on the bottom of the mold?
- The wax will be displaced.
60. What happens if the tissue is against the top or bottom of the mold?
- Ribbons will not form properly.
61. What should never be done with a mold containing molten wax and tissue?
- It should never be shaken.
62. What are the consequences of using over-heated paraffin during infiltration?
- It may cause block cracking, tissue shrinkage, and over-hardening.
63. What can happen if tissue blocks are not properly cooled?
- There may be a 'dish effect' formation, blocks may be pearly white or grey, or they may crack.
64. How can improperly embedded tissue be corrected?
- The tissue block can be melted in the heated chamber of an embedding station, or the
process can be restarted.
65. What is the loss of reactivity of myelin in Weigert’s Iron Hematoxylin?
- The loss of reactivity of myelin in Weigert’s Iron Hematoxylin can cause dermatitis and
sinusitis.
66. What has been implicated in lymphoma?
- Weigert’s Iron Hematoxylin has been implicated in lymphoma.
67. What occurs in the paraffin infiltration step?
- Some tissue damage will occur in the paraffin infiltration step because proteins are not
coagulated and stabilized.
68. What does Formal Saline (FS) contain?
- Formal Saline (FS) contains formaldehyde, sodium chloride, and water.
69. What are the uses of Formal Saline?
- Formal Saline is one of the simplest compound fixatives and has a gentle denaturing effect on
tissue protein.
70. What enhances the rate of penetration in Formal Saline?
- The combination of Formal Saline with NaCl (in a compound fixative) enhances the rate of
penetration due to the action of indifferent salts.
71. Is Formal Saline a tolerant fixative?
- Yes, Formal Saline is a tolerant fixative.
72. Can tissues stored in Formal Saline be stored for long periods of time?
- Yes, tissues can be stored for long periods of time with minimum hardening in Formal Saline.
73. On average, how long does fixation in Formal Saline usually take?
- Fixation is usually complete within 24 hours in Formal Saline.
74. What are the disadvantages of Formal Saline?
- The disadvantages of Formal Saline include possible formation of formalin pigment during
long storage and the potential to cause dermatitis and sinusitis.
75. What is the process for removal of formalin pigments?
- The process for removing formalin pigments includes taking the tissue to water, immersing it
in saturated alcoholic picric acid for 30 minutes, washing in running tap water for as long as
needed, and staining the tissues as required.
76. What does Formal Calcium contain?
- Formal Calcium contains 10% formaldehyde in 1.0% CaCl2.
77. What does Formal Calcium demonstrate in lung and brain tissue?
- Formal Calcium demonstrates phospholipids in lung and brain tissue.
78. What is Formal Calcium recommended for?
- Formal Calcium is recommended for lipid histochemistry.
79. What are the disadvantages of Formal Calcium?
- The disadvantages of Formal Calcium are similar to those of NBF and FS, and it cannot be
used to demonstrate calcium, acid phosphatase, and alkaline phosphatase because it contains
CaCl2.
80. What does Buffered Formal Sucrose contain?
- Buffered Formal Sucrose contains 10% formaldehyde with 7.5% sucrose in phosphate buffer
pH 7.4.
81. What can be demonstrated with Buffered Formal Sucrose?
- Buffered Formal Sucrose can demonstrate phospholipids, fine structures, some enzymes,
mitochondria, and endoplasmic reticulum.
82. What are the disadvantages of Buffered Formal Sucrose?
- The disadvantages of Buffered Formal Sucrose include being more expensive than NBF for
routine use (due to containing sugar) and requiring cold storage at 4°C.
83. What is the stock solution for Zenkers Fluid?
- The stock solution for Zenkers Fluid includes mercuric chloride, potassium dichromate,
sodium sulphate, distilled water, and glacial acetic acid.
84. What is Zenkers Fluid used for?
- Zenkers Fluid is used as a fixative and can be combined with either acetic acid (Zenker’s
acetic) or formaldehyde (Zenker’s formal or Helly’s).
85. What is Zenker’s Acetic Fixative?
- Zenker’s Acetic Fixative is a compound fixative that consists of Zenker’s stock solution
combined with acetic acid.
86. What happens to Zenker’s Acetic Fixative after the addition of acetic acid?
- Zenker’s Acetic Fixative does not keep well after the addition of acetic acid and turns muddy
brown after 24 hours.
87. What role does mercuric chloride play in Zenker’s Acetic Fixative?
- Mercuric chloride is a simple fixative functioning as a coagulating fixing agent in Zenker’s
Acetic Fixative.
88. What role does potassium dichromate play in Zenker’s Acetic Fixative?
- Potassium dichromate is a simple fixative that functions as a non-coagulating fixing agent in
Zenker’s Acetic Fixative due to the low pH (2.6) resulting from the addition of acetic acid.
89. What does sodium sulphate do in Zenker’s Acetic Fixative?
- Sodium sulphate is an indifferent salt in Zenker’s Acetic Fixative, preserving the osmotic
environment of cells and aiding fixative penetration.
90. What is the role of acetic acid in Zenker’s Acetic Fixative?
- Acetic acid is a primary fixative and excellent nucleo protein fixative in Zenker’s Acetic
Fixative, leaving the tissue soft.
91. What are the advantages of Zenker’s Acetic Fixative?
- Zenker’s Acetic Fixative is a good routine microanatomical fixative that provides rapid and
even penetration, counteracts shrinkage, and gives good nuclear detail in tissues, making it
suitable for liver, spleen, nuclei, CT. It is also recommended for trichrome stain and subsequent
PTAH stain.
92. What are the disadvantages of Zenker’s Acetic Fixative?
- The disadvantages of Zenker’s Acetic Fixative include mercury pigment formation, the need
for washing in running water to remove dichromate (tissue turning green), the requirement of
iodine and HYPO for removing mercury pigment, the addition of acetic acid prior to use, and
tissue brittleness if fixation exceeds 24 hours.
93. What does PEL stand for?
- PEL stands for Permissible Exposure Limit.
94. How is PEL monitored?
- PEL is monitored per 8-hour shift.
95. What is TWA?
- TWA stands for Time-Weighted Average.
96. How is TWA measured?
- TWA is measured by the employee's average exposure.
97. Can shorter exposures exceed the average exposure?
- Yes, shorter exposures may exceed the average exposure.
98. What is the purpose of a STEL?
- STEL is the short-term exposure limit for any 15-minute period during the work shift.
99. How is STEL measured?
- STEL is measured during the worst 15-minute period.
100. Is STEL always higher than TWA?
- Yes, STEL is always higher than TWA.
101. What does CL stand for?
- CL stands for Ceiling Limit.
102. What is CL?
- CL is the maximum permissible instantaneous exposure to a toxic substance during any part
of the work shift.
103. What type of substances is CL monitoring reserved for?
- CL monitoring is reserved for highly dangerous substances.
104. Are there chemicals with both STEL and CL values?
- Yes, there are a few hazardous chemicals that are given both STEL and CL.
105. What values can be established for chemicals lacking CL or STEL?
- For chemicals lacking CL or STEL, values can be established by multiplying the TWA by 3 or
the CL by 5.
106. What is the TWA permissible exposure limit for formaldehyde?
- The TWA permissible exposure limit for formaldehyde is 0.75 ppm.
107. What is the action level for formaldehyde?
- The action level for formaldehyde is defined as 0.5 ppm.
108. How long is the STEL monitoring period for formaldehyde?
- The STEL monitoring period for formaldehyde is 15 minutes.
109. What is the maximum allowable STEL for formaldehyde in a 15-minute
period?
- The maximum allowable STEL for formaldehyde in a 15-minute period is 2.0 ppm.
110. When should monitoring be repeated for employees exposed to
formaldehyde?
- Monitoring should be repeated every 6 months if initial monitoring shows TWA greater than
0.5 ppm (action level).
111. When should monitoring be repeated for employees exposed to STEL?
- Monitoring should be repeated at least once per year under worst-case conditions if employee
monitoring demonstrates exposure limits at or above the STEL.
112. Under what conditions can employer discontinue monitoring for
formaldehyde?
- Employer can discontinue monitoring if two consecutive samplings collected at least 7 days
apart indicate results below the STEL and action levels.
113. When does employee monitoring for formaldehyde require change?
- Employee monitoring for formaldehyde only requires change if there are procedural changes,
conditions causing exposure changes, or if an employee presents with signs/symptoms of
exposure.
114. How soon should monitoring results be available to staff?
- Monitoring results must be available to staff within 15 days.
115. What is the purpose of a medical surveillance program?
- The purpose of a medical surveillance program is to monitor employees exposed to
formaldehyde at or above the action level or STEL, or if they show signs or symptoms of
excessive exposure.
116. What is required in areas with formaldehyde levels exceeding the TWA or
STEL?
- Warning signs must be posted at all entrances to areas known to show levels of formaldehyde
exceeding the TWA or STEL.
117. What is the employer responsible for in reducing employee exposure?
- The employer is responsible for ensuring all protocols are in place to reduce employee
exposure.
118. What can be used to control exposure if protocols cannot reduce employee
exposure?
- Approved respirators may be used to control exposure if protocols cannot reduce employee
exposure.
119. How can chemical hazards be reduced?
- Chemical hazards can be reduced through chemical inventory management, such as
monitoring expiration dates.
120. What factors should chemicals be evaluated for?
- Chemicals should be evaluated for carcinogenic potential, reproductive toxicity, and acute
toxicity.
121. What should be in place regarding specific handling requirements for
chemicals?
- A procedure manual should be in place regarding specific handling requirements for
chemicals.
122. How are reagents tagged in some facilities?
- In some facilities, reagents are tagged with specific colored labels for visual enhancement.
123. What are the health hazards mentioned in the course notes?
- The health hazards mentioned are biohazards, irritants, corrosive chemicals, sensitizers, and
carcinogens.
124. What are biohazards?
- Biohazards can be infectious agents themselves or items contaminated with infectious agents.
125. When is a substance classified as a biohazard?
- A substance is classified as a biohazard if it has the potential to cause disease in humans.
126. What is the rate of penetration of mercuric chloride fixation?
- The rate of penetration is slow, 0.7 to 0.8 mm/hr.
127. Why does the rate of penetration decrease after 5 minutes?
- The rate of penetration decreases after 5 minutes due to extreme hardening.
128. What does mercuric chloride combine with in proteins?
- Mercuric chloride combines with the acid groups of proteins (carboxyl and hydroxyl).
129. What does mercuric chloride combine with in nucleoproteins?
- Mercuric chloride combines with the phosphoric acid of nucleoproteins.
130. What happens when a protein solution is mixed with a nucleic acid solution?
- The phosphoric acid component of the nucleic acid combines with the positively charged
ammonium groups of the protein to form a protein-nucleic acid complex.
131. What is the role of mercuric chloride in inhibiting freezing?
- Mercuric chloride inhibits freezing, making frozen samples difficult to prepare.
132. What does mercuric chloride chemically add itself to in proteins?
- Mercuric chloride can chemically add itself to sulfhydryl, carboxyl, and amino acids, which are
found in proteins.
133. How does mercuric chloride alter the protein structure?
- Mercuric chloride can alter the structure and chemically combine with the protein of the
structure.
134. What happens to the acidity of solutions during fixation with mercuric
chloride?
- Solutions become more acidic during fixation with mercuric chloride.
135. What is the mordant quality of mercuric chloride?
- Mercuric chloride can facilitate the addition of dye, thus having a mordant quality.
136. What type of mucopolysaccharides can be fixed with mercuric chloride?
- Mercuric chloride is somewhat useful for fixing certain mucopolysaccharides like mucin.
137. Does mercuric chloride react with carbohydrates?
- No, mercuric chloride does not react with carbohydrates.
138. How does mercuric chloride affect glycogen in tissues?
- Glycogen is not preserved in tissues fixed with mercuric chloride and cannot be demonstrated
or stained with glycogen stains.
139. Does mercuric chloride react with lipids?
- No, mercuric chloride does not react with lipids and does not fix or destroy them.
140. What happens to lipids in tissues when exposed to organic solvents?
- Lipids are lost from the tissue when exposed to organic solvents like xylene or alcohol.
141. What are the disadvantages of mercuric chloride fixation?
- The disadvantages include excessively hardening tissues, intolerance, and extreme shrinkage.
142. What is another name for mercuric chloride?
- Mercuric chloride is also known as corrosive sublimate.
143. What is the chronic effect of mercuric chloride exposure?
- The chronic effect of mercuric chloride is mercury poisoning.
144. What are mercury pigments?
- Mercury pigments are precipitates appearing as brown granules in tissue sections.
145. How can mercury pigments be removed from tissues?
- Mercury pigments can be removed by treating tissues with metallic iodine and then using
sodium thiosulfate to remove iodine.
146. What is the procedure for mercury pigment removal?
- The procedure includes immersing the tissue in water, alcoholic iodine, running tap water, 5%
hypochlorite (HYPO) solution, and then staining as required.
147. Can mercuric chloride be used alone?
- No, mercuric chloride is never used alone and is always used with a gentler solution.
148. What are some compound fixatives used with mercuric chloride?
- Compound fixatives include formaldehyde, acetic acid, potassium dichromate, etc.
149. What staining characteristics does mercuric chloride provide?
- Mercuric chloride gives brilliant cytoplasmic staining and yields bright metachromatic staining.
150. How can the formation of mercury pigments be prevented in automated
staining procedures?
- The formation of mercury pigments can be prevented by incorporating iodine in xylene in
routine H&E automated staining procedures.
151. What is ethanol and its histological quality?
- Ethanol is a colorless liquid, a primary alcohol that is miscible with both water and xylene,
which is an important quality in histological terms.
152. What happens when protein is added to ethanol?
- The protein coagulates and forms a white cloud when added to ethanol.
153. What is the fixing property of ethanol?
- Ethanol is an intolerant fixing agent that causes severe tissue shrinkage by reacting with
protein in a non-additive manner.
154. How does ethanol react compared to other primary fixing agents?
- Ethanol reacts with protein in a non-additive manner, while all other primary fixing agents
react in an additive manner.
155. What are the disadvantages of arnoy's fluid as a fixative?
- Arnoy's fluid causes considerable shrinkage and destroys or dissolves most cytoplasmic
elements.
156. How can the degree of shrinkage be reduced when using arnoy's fluid as a
fixative?
- The degree of shrinkage may be reduced if tissue is fixed at 0° C for 18 hours.
157. Which components are dissolved by ethanol in a fixative?
- Lipids are dissolved by ethanol in a fixative.
158. What happens to RBC's when arnoy's fluid is used as a fixative?
- RBC's are lysed by acetic acid in arnoy's fluid.
159. What kinds of tissues are suitable for arnoy's fluid fixative?
- Arnoy's fluid is suitable for very small pieces of tissues.
160. What is the purpose of using ether/alcohol as a cytological fixative?
- Ether/alcohol is a cytological fixative for smears or tissue imprints.
161. Which fixative stains nuclei well and has rapid fixation time?
- Ether/alcohol fixative stains nuclei well and has rapid fixation time.
162. What are the main components of ether/alcohol fixative?
- Ether is a dimethyl ether and alcohol is usually isopropanol, methanol, or ethanol.
163. What is the purpose of histochemical fixatives?
- Histochemical fixatives preserve chemical constituents in or on cells, including enzymes and
antigens.
164. What is a disadvantage of histochemical fixatives?
- Histochemical fixatives can cause the loss of tissue architecture and cellular morphology due
to ethanol dissolving lipids and causing shrinkage.
165. What are secondary fixatives used for?
- Secondary fixatives are used to improve the preservation of tissue, continue the process of
protein denaturation, or enhance the staining of tissues.
166. What is the usual primary fixative used in tissue fixation?
- NBF (neutral buffered formalin) is generally used as a primary fixative.
167. When are secondary fixatives used?
- Secondary fixatives are used when tissues have been fixed and stored in a primary fixative.
168. What are the main components of secondary fixatives?
- Secondary fixatives usually contain mercury or picric acid.
169. What is the purpose of mercuric chloride as a secondary fixative?
- Mercuric chloride is often used as a secondary fixative and it results in tissue sections that
stain more brilliantly than formalin fixed tissue.
170. When is Bouin's fixative used?
- Bouin's fixative is used as a mordant prior to staining tissue sections with the trichrome
staining method.
171. How long does tissue usually sit in Bouin's fixative before staining?
- Tissue usually sits in Bouin's fixative for about 1 hour prior to staining.
172. What is post chromatization?
- Post chromatization is a type of secondary fixative used when tissue seems to harden
excessively.
173. What is the process of post fixation in post chromatization technique?
- In post chromatization, the tissue section is post-fixed in a solution of aqueous potassium
dichromate for 24 hours following the initial fixation, then washed thoroughly in water overnight.
174. Why is the volume of fixative important in proper tissue fixation?
- Inadequate fixative volume results in poor fixation, so the volume of fixative should be 20
times the volume of the tissue.
175. What factors can result in poor fixation of tissues?
- Poor fixation may result from fixative not penetrating tissue from all sides, inadequate fixative
volume, inadequate fixation time, or using any intolerant fixative for an extended period of time.
176. What are the key requirements for good fixation of tissues?
- Good fixation requires an adequate volume of fixative that penetrates tissue from all sides and
the use of a tolerant fixing agent.
177. What is histology?
- Histology is the study of the structure of the cells and tissues microscopically that
demonstrates disease processes and the effects on tissues.
178. What is pathology?
- Pathology is the study of disease processes and the effects on tissues.
179. What are the processes involved in tissue processing?
- Tissue processing involves dehydration, clearing, infiltration, and embedding.
180. What are corrosives?
- Corrosives are agents that cause reversible inflammatory effects at the site of contact.
181. What damage can corrosive chemicals cause?
- Corrosive chemicals can damage metals and/or tissues.
182. What are some examples of corrosive chemicals?
- Acids are corrosives and can cause irreversible damage to skin, eyes, and tissues.
183. What are sensitizers?
- Sensitizers are chemicals that cause substantial allergic reactions.
184. What are the risks associated with sensitizers?
- True sensitizers can cause life-long sensitization and worsen with every exposure.
185. What are carcinogens?
- Carcinogens are agents that can cause cancer or increase the risk of developing
malignancies.
186. Give an example of an extreme carcinogen.
- Benzene is an extreme carcinogen and increases the risk of causing leukemia.
187. Which chemical is considered a potential carcinogen?
- Formaldehyde is considered a potential carcinogen.
188. Name three universally recognized histology chemicals as carcinogenic.
- Chloroform, chromic acid, and formaldehyde are universally recognized as carcinogenic.
189. Name three other chemicals also classified as carcinogenic.
- Basic fuchsin, auramine, and ponceau 2R are also classified as carcinogenic.
190. What are the different types of physical hazards?
- The different types of physical hazards include combustibles, flammables, explosives, and
oxidizers.
191. What are combustibles?
- Combustibles have a flash point at or above a specified temperature.
192. What is the best option between combustible and flammable products?
- If possible, it is best to choose a combustible product over a flammable one.
193. What precaution must be taken with flammables?
- Vapors of flammables must be carefully controlled and special storage conditions are
mandated.
194. Are explosives commonly used in histology?
- No, explosives are rarely used in histology, but picric acid is a common explosive used.
195. Which silver solutions used in impregnation methods can become
explosive?
- Some silver solutions used in impregnation methods can become explosive with age.
196. What does the flash point of a liquid determine?
- The flash point is the lowest temperature at which sufficient vapors are produced to form an
ignitable mixture with air.
197. Why are many reagents used in histo considered fire hazards?
- Many reagents used in histo are fire hazards because they can contribute to fire or explosion.
198. What are oxidizers?
- Oxidizers can initiate or promote combustion in any other material.
199. Are oxidizers harmless by themselves?
- Oxidizers are harmless if used alone, but they present a serious risk when in contact with
suitable substances.
200. What are insidious chemical hazards?
- Insidious chemical hazards develop gradually and subtly, but in a harmful way.
201. What are some examples of insidious chemical hazards?
- Ethers like isopropyl ether, diethyl ether, tetrafurantoin, and dioxane are examples of insidious
chemical hazards.
202. What can ethers oxidize to form?
- Ethers can oxidize to form peroxides, which are shock-sensitive explosives.
203. What precautions should be taken with ethers?
- Opened containers should be discarded after 6 months, stored away from heat and sunlight,
and disposal specialists should be called for old containers with evaporated contents.
204. What are the risks associated with liquid mercury?
- Liquid mercury releases vapors at levels exceeding permissible exposure limits and
microscopic droplets can continue to release vapors.
205. How do vapors of mercury relate to surface area?
- Vapors of mercury are proportional to the surface area.
206. What are the precautions for handling picric acid?
- Substitute mercury thermometers, protect from breakage, clean spills promptly with
specialized kits, and always store wet.
207. How should containers of picric acid be inspected?
- Containers of picric acid should be inspected regularly.
208. What should never be done with dried picric acid?
- Dried picric acid should never be opened or removed.
209. How is HIV destroyed outside the host?
- HIV is destroyed within several hours outside the host.
210. What are the hazards of direct contact with HIV?
- Direct contact hazards include skin and mucous membranes.
211. How can HIV enter the skin?
- HIV can enter the skin through accidental percutaneous injuries.
212. What precautions should be taken with infected material?
- All equipment in direct contact with infected material must be considered infectious.
213. What is the incubation period of HBV?
- The incubation period of HBV is 24-180 days.
214. How can HBV be transmitted through the skin?
- HBV can be transmitted through the skin percutaneously.
215. What are the effective agents against HBV?
- 1% Bleach, Formaldehyde, 70% Ethanol, and 2% Alkalinized glutaraldehyde are effective
against HBV.
216. Why is Hepatitis B more frequently encountered among laboratory
personnel?
- Hepatitis B is 7 times greater in laboratory personnel.
217. What precautions should be followed for preventing HBV infection?
- Always follow standard precautions, wear PPE, never re-cap or break needles, and follow
SOP protocols.
218. What is Creutzfeldt-Jakob Disease (CJD) known as?
- Creutzfeldt-Jakob Disease is known as a 'prion' disease.
219. What are prions and what can they cause?
- Prions are abnormal proteins that can cause diseases and may be transmitted or inherited.
220. How does CJD affect the brain?
- CJD affects the white matter of the brain, causing spongiform encephalopathy.
221. How can CJD be transmitted?
- CJD can be transmitted via transplants or exposure to brain tissue and CSF.
222. What are the characteristics of CJD?
- CJD can be latent/asymptomatic for up to 20 years before symptoms appear.
223. What are prions resistant to?
- Prions are resistant to heat, ionizing radiation, formalin, enzymes, freezing, drying, and some
organic solvents.
224. How can prions be inactivated?
- Prions can be inactivated by autoclaving at 121°C for one hour, or increasing the temperature
to 132-134°C.
225. What are the three classifications/types of CJD?
- Sporadic, familial, and iatrogenic are three classifications/types of CJD.
226. What is Variant CJD (vCJD) associated with?
- Variant CJD is associated with eating meat from cows infected with bovine spongiform
encephalopathy (BSE).
227. What remains infectious in CJD?
- CJD remains infectious in well-fixed tissues, paraffin blocks, and stained slides.
228. How can CJD be inactivated?
- CJD can be inactivated by fixing brain tissue in NBF for > 48hrs, treating with concentrated
formic acid, and returning to fresh NBF for additional 48 hours.
229. What is the recommended fixation for CJD specimens?
- Fixing brain tissue in NBF for > 48hrs or whole brain 10-14 days in NBF is recommended for
CJD specimens.
230. What is the effect of fixation on tissue specimens?
- Fixation inactivates the prion, allowing routine processing and sectioning without adverse
effects.
231. How long should specimens be treated with sodium hypochlorite to
inactivate prions?
- Specimens should be treated with 5% sodium hypochlorite for two hours to inactivate prions.
232. How long should specimens be treated with formic acid to inactivate prions?
- Specimens should be treated with concentrated formic acid for one hour to inactivate prions.
233. How long should specimens be treated with sodium hydroxide to inactivate
prions?
- Specimens should be treated with 1N sodium hydroxide for one hour to inactivate prions.
234. What are the age characteristics of variant CJD?
- Variant CJD typically affects individuals younger than 30 years of age.
235. Why is standard fixation insufficient to kill microorganisms in CJD material?
- Standard fixation is typically sufficient, except for material from patients with CJD.
236. What is the recommended treatment for brain tissue specimens in CJD
cases?
- The recommended treatment includes fixing brain tissue in NBF for > 48hrs or whole brain
10-14 days in NBF, treating with concentrated formic acid, and returning to fresh NBF for
additional 48 hours.
237. What is the recommended method of disposal for waste formalin diluted
with 2N NaOH?
- Let it stand for 1 hour prior to disposal
238. How should steel instruments and grossing station be treated?
- Treated with 1N NaOH for one hour then washed with soap and water
239. What is the recommended method of disposal for gloves, gowns, and
aprons?
- Autoclave or incinerate them
240. What are infectious aerosols?
- Aerosols that can result in possible increased exposure to pathogens
241. When should cryogenic sprays not be used?
- On frozen sections or on poorly fixed tissue
242. What type of bags should waste tissue and materials in contact with waste
tissue be disposed of in?
- Biohazardous bags
243. How should sharps be disposed of?
- Sharps should be disposed into sharps containers, which must be labeled with biohazard
warning
244. What should be considered when establishing an SOP for returning
specimens to patients?
- Chemical and biological risks associated with both fixed and unfixed specimens
245. What are the four classifications of infectious waste?
- Pathologic material specimens, blood, microbiological or culture specimens, sharp objects
246. How should tissue waste and materials in contact with tissue be disposed
of?
- Disposed of in biohazard bags in a container labeled with a biohazard warning
247. What is the recommended method of sterilization for waste except
pathologic waste?
- Steam sterilization or incineration
248. What are examples of mechanical hazards?
- Knife blades, razors, scalpels, needles, glass, electrical hazards, pinch points
249. What are the requirements for sharps containers?
- Closable, puncture resistant, upright, and must be color-coded
250. What should be done with glassware that has cracks or chips?
- It should be disposed of
251. What should be done with non-disposable equipment like saws and
cryostats?
- They should be disinfected following the institution's established SOPs
252. What are some examples of musculoskeletal injuries in histopathology?
- Carpal tunnel, trigger finger, tendonitis
253. How can musculoskeletal injuries be prevented?
- Take mini-breaks, do stretching exercises, use the other hand, introduce automation where
possible
254. How can chemical hazards be classified?
- Physical (flammable, explosive, oxidizers) and health (carcinogens, sensitizers, toxins,
corrosives, irritants)
255. What are the potential routes of exposure to hazardous chemicals?
- Inhalation, absorption, or ingestion
256. Why is safety monitoring required for certain chemicals like formaldehyde?
- Because of the occupational exposure risk
257. What should not be done in the presence of hazardous chemicals?
- Eating, drinking, smoking, and pipetting by mouth
258. What should be worn to protect against the absorption of chemicals?
- Gloves
259. What engineering controls are required to prevent inhalation exposure in
histopathology?
- Ventilation hoods or similar mechanisms
260. What does EL stand for in relation to exposure limits?
- Permissible exposure limit
261. What is the purpose of the TWA (time weighted average) exposure limit?
- To define an action level for exposure
262. How should tissue be oriented during embedding?
- Tissue should be aligned across the long axis of the mold, side by side with the epithelial layer
facing in the same direction.
263. What is the purpose of using a tamper during orientation and initial chilling
of specimens?
- Applying light pressure using a tamper helps with orientating and chilling the tissue.
264. How should hard tissue like bone be embedded?
- Hard tissue like bone should be embedded diagonally.
265. What should the margin of paraffin surrounding the tissue be?
- There should be a relatively small margin of paraffin surrounding the tissue.
266. How many cassettes of tissue should be embedded at one time?
- Only one cassette of tissue should be embedded at one time.
267. Why is it important to wipe embedding forceps between tissue samples?
- Wiping embedding forceps between tissue samples reduces the chance of tissue
contamination and misdiagnosis.
268. What should be done to the blocks after embedding?
- The blocks should be cooled rapidly to reduce paraffin crystal size which may affect sectioning.
269. What should be done to validate the record of tissue pieces in each
cassette?
- The record of the number of tissue pieces in each cassette should be validated with the log or
on a computer tracking system.
270. What are the modules of an embedding center?
- The modules of an embedding center are a paraffin dispenser, cold plate and Peltier plate,
and a heated storage area.
271. What are the advantages of using an embedding system?
- The advantages of using an embedding system are ease of use, speed, secure attachment of
tissue and holder, immediate filing of blocks, and permanent identification.
272. What is the function of the paraffin dispenser in the Tissue Tek embedding
center?
- The paraffin dispenser combines a thermal adjustable dispenser with a thermostatically
controlled heating platform for pre-heating base molds and orienting tissues.
273. What temperature should the paraffin in the dispenser be kept at?
- The paraffin in the dispenser should be kept at a temperature 2°C to 4°C above the melting
point of wax.
274. What is the purpose of the thermal console in the paraffin dispenser?
- The thermal console stores and warms base molds and holds specimens in cassettes for
embedding in the heated area.
275. What is the function of the small cold plate in the embedding center?
- The small cold plate partially solidifies paraffin and enhances the embedding of smaller
specimens.
276. What is the benefit of cooling embedded specimens using a refrigerated
plate?
- Cooling embedded specimens on a refrigerated plate reduces crystal formation and ensures
clearer wax for sectioning.
277. What should be done before placing tissue in the mold for embedding?
- The base mold should be filled with warmed paraffin wax.
278. What should be done to ensure correct orientation of the specimen in the
mold?
- The surface of the tissue that will be cut should be placed flat against the base of the mold.
279. How can the block be secured in the mold during embedding?
- More molten wax should be dispensed to cover the tissue and a labeled cassette should be
added to the mold to make a block.
280. What is the purpose of placing the block on a cold plate?
- Placing the block on a cold plate helps it cool rapidly, leading to smaller crystal size and better
support for sectioning.
281. What should be done to ensure the specimen has not shifted during
cooling?
- The block should be checked to ensure that the specimen has not floated out of position.
282. What should be done to the base mold after removing the finished block?
- The base mold should be placed in a mold release solution to aid in its removal.
283. What are the potential sources of error in embedding?
- Issues with tissue orientation, improper cooling, or specimen shifting can be sources of error
in embedding.
284. What are the properties of chloroform?
- Chloroform is very expensive, it used to be an anaesthetic, it dessicates connective tissue.
285. Why can't chloroform be used in automated tissue processors?
- Chloroform will melt any plastic parts in automated tissue processors.
286. What problems are encountered when using chloroform in open
processors?
- Maintaining fluid levels is difficult due to its volatility.
287. What is the disposal problem associated with chloroform?
- Chloroform cannot be incinerated or burned.
288. What toxic gas may form when heating chloroform?
- Heating chloroform may produce phosgene, a very toxic gas.
289. What are the advantages of using carbon tetrachloride?
- Carbon tetrachloride clears tissues up to 5.0 mm in 8 to 15 hours and is cheaper than
chloroform.
290. What are the disadvantages of using carbon tetrachloride?
- Carbon tetrachloride is very toxic, considered narcotic, and may cause tissue damage.
291. Why is determining the endpoint of clearing difficult with carbon
tetrachloride?
- The refractive index of the tissue does not change with carbon tetrachloride.
292. What difficulties arise in removing carbon tetrachloride from wax?
- Carbon tetrachloride is difficult to remove from wax.
293. What are aliphatic hydrocarbons and their advantages?
- Aliphatic hydrocarbons are low in toxicity, comparable to xylene, and can be used on all tissue
processors and automated stainers.
294. What are the disadvantages of using aliphatic hydrocarbons?
- Aliphatic hydrocarbons are intolerant to water, incompatible with certain mounting media, and
cannot be used in areas of high humidity.
295. What are terpenes and how are they derived?
- Terpenes are naturally occurring hydrocarbons derived primarily from a wide variety of plants,
especially conifers.
296. What are essential oils and why are they used in histology?
- Essential oils are volatile oils that take on the aroma or flavor of their originating plant. They
are used in histology as xylene substitutes.
297. What are the advantages and disadvantages of using cedarwood essential
oil?
- Cedarwood essential oil is the most widely used and damages tissues less than any other
clearing agent, but it hardens tissues less, causing increased contamination of paraffin.
298. What are limonenes and their characteristics?
- Limonenes are aliphatic hydrocarbons, less toxic than xylene, clear colorless liquid, causes
nausea and prolonged use may result in sensitization.
299. What is the purpose of impregnation in histology?
- Impregnation is the infiltration of the tissue with wax after replacing the clearing agent.
300. What does the term 'intolerant' refer to in the context of fixing agents?
- The term 'intolerant' refers to the length of time tissues can be exposed to fixing agents
without harmful effects.
301. How are tissues affected when using tolerant fixative agents?
- Tissues may be exposed for a considerable length of time without adversely affecting them.
302. What happens to tissues when exposed to intolerant fixatives for more than
24 hours?
- Tissues are bleached and excessively hardened, leading to destruction of the tissue.
303. What are the two categories of fixatives based on their composition?
- The fixatives may be simple (composed of one fixing chemical) or compound (composed of
more than one fixing chemical).
304. What types of fixatives fall under the category of micro-anatomical fixatives?
- Fixatives used routinely and retain the overall tissue anatomy.
305. What do cytological fixatives target?
- Cytological fixatives target intracellular components, including nuclear and cytoplasmic
components.
306. Which type of fixative should not alter or inactivate substances that require
demonstration?
- Histochemical fixatives must not alter or inactivate substances like enzymes and antigens.
307. Which fixation method is suitable for investigating tissues requiring enzyme
activity?
- Tissues requiring enzyme activity investigation must be fresh frozen.
308. What is the purpose of microtomy in the tissue processing process?
- Microtomy is the process of cutting tissue sections.
309. What is the routine stain used for all tissue samples?
- H&E stain is the routine stain for all tissue samples.
310. What are pathologists able to do with stained slides?
- Pathologists make the final diagnosis from stained slides.
311. What are some of the hazards in histology?
- Hazards in histology include infection, needle stick injuries, cuts, carcinogenic agents,
flammable chemicals, allergenic agents, and physical hazards.
312. What precautions should be practiced in the histology department?
- Standard precautions should be practiced, treating everything as infectious, and wearing
appropriate protective gear.
313. Which disease affects nervous tissue and is resistant to destruction?
- Creutzfeldt-Jakob Disease (CJD) is a prion disease that affects nervous tissue and is resistant
to destruction.
314. What is the proper disposal method for waste tissue specimens and sharps?
- Proper disposal of waste tissue specimens and sharps is necessary.
315. What are the acute or chronic health concerns caused by chemical
hazards?
- Chemical hazards can cause acute or chronic health concerns and require safety monitoring.
316. What is the commonly used fixative with specific exposure limits?
- Formaldehyde is a commonly used fixative with specific exposure limits.
317. What is the importance of proper ergonomics in the histology department?
- Proper ergonomics in the histology department is important for maintaining a healthy work
environment.
318. What is histology?
- Histology is the study of cells and tissues.
319. How can tissue fragments be properly oriented on a glass slide for
processing?
- By dropping warm 25% gelatin on top of the tissue fragments.
320. What is the purpose of using 30% Sucrose for preparing frozen sections?
- It acts as a cryoprotectant and results in high-quality frozen sections.
321. What are the advantages of using closed systems in automated processors?
- They keep exposure to toxic vapors to a minimum and prevent tissue specimens from drying
out in case of malfunction.
322. What are the requirements for a good automated processor?
- Primary processor should be a closed system, computerized with digital readout and alarm
system, and have LIS connectivity.
323. What maintenance steps should be taken for automated processors?
- Change/rotate baths per schedule, maintain baths at topped off level, dispose of aged
reagents, and record temperatures and maintenance.
324. What is the purpose of infiltration in histopathology?
- To prepare tissue samples for embedding by replacing water with a suitable medium.
325. What are the key steps in infiltration using an open system?
- No vacuum is used during infiltration in an open system.
326. What is the process for infiltration using a closed system?
- Closed systems use both heat and vacuum for infiltration.
327. How long is the overnight process in an open system for infiltration?
- The overnight process in an open system typically takes several hours.
328. How long is the overnight process in a closed system for infiltration?
- The overnight process in a closed system typically takes several hours.
329. What is the purpose of using heat in paraffin infiltration?
- Heat is used to aid in the infiltration of paraffin into the tissue.
330. Why should heating be avoided in all reagents during processing?
- Heating in all reagents can cause overprocessing and result in microtomy and staining
artifacts.
331. What is the purpose of appropriate labels on chemical containers?
- The purpose of appropriate labels on chemical containers is to provide information about the
contents.
332. What must be available in areas where specific reagents are used?
- Signage must be available in areas where specific reagents are used.
333. What should be readily available for all chemicals used?
- Data sheets (DS) must be readily available for all chemicals used.
334. What is reproductive toxicity?
- Reproductive toxicity is the ability of a substance to cause damage to reproductive genes.
335. What does LD50 stand for?
- LD50 stands for the calculated dose of a chemical expected to cause the death of 50% of an
experimental animal population.
336. Which chemicals are examples of toxic chemicals?
- Some examples of toxic chemicals are Formaldehyde, Metallic compounds (mercury,
chromium, Ag), and Hydrocarbons (xylene and toluene).
337. What are the potential health effects of formaldehyde?
- Formaldehyde can cause irritation to mucous membranes and eyes, may cause cancer, and
can lead to difficulty breathing and pulmonary edema.
338. How should accidental inhalation of formaldehyde be handled?
- In case of accidental inhalation, the individual should be removed to fresh air and medical
attention should be sought.
339. What should be done in case of ingestion of formaldehyde?
- In case of ingestion, medical attention should be sought immediately.
340. What should be done in case of eye or skin contact with formaldehyde?
- In case of contact with eyes or skin, flush immediately with copious amounts of water for a
minimum of 15 minutes.
341. What are the potential health effects of methanol?
- Methanol can cause heart and liver damage, blindness, reproductive damage, and even death
if ingested.
342. What should be done in case of inhalation of methanol?
- Inhalation of methanol can cause sleepiness, loss of consciousness, headache, and confusion.
343. How should methanol spills be handled?
- Employees must be trained, and PPE's should be worn for small spills.
344. What are the properties of picric acid?
- Picric acid is hazardous, corrosive to skin and eyes, and can explode if allowed to dry.
345. How should picric acid be stored?
- Picric acid must be stored underwater and kept damp at all times.
346. What are the potential health effects of osmium tetroxide?
- Osmium tetroxide can cause dizziness, headaches, chest tightness, and can damage the
kidneys if ingested.
347. Is osmium tetroxide a fire or explosive hazard?
- No, osmium tetroxide is not a fire or explosive hazard.
348. What is the routine stain for every tissue sample?
- Hematoxylin and Eosin (H&E) stain.
349. What does the Hematoxylin component of H&E stain stain?
- The nucleus.
350. What does the Eosin component of H&E stain stain?
- The cytoplasm.
351. Who is responsible for grossing in pathology?
- Pathology assistants.
352. What is the role of a pathologist in stained slides?
- Makes the final diagnosis.
353. What stains are used in special staining Immunohistochemistry (IHC)?
- Numerous special stains and IHC tests looking for specific antigens.
354. What are the types of tissue samples?
- Surgical, autopsy, cytological, blood, and bone marrow.
355. Why should tissues be fixed immediately after removal from the body?
- To prevent putrefaction and autolysis.
356. What is autolysis?
- The self-destruction of tissue once it is removed from the body.
357. What are the consequences of autolysis?
- Swelling of collagen, desquamation, protein breakdown, and eventual liquefaction of the cell.
358. What is desquamation?
- The sloughing off/shedding of epithelial cells from the basement membrane.
359. What is putrefaction?
- The destruction of cellular components by microbial action.
360. What are the results of putrefaction?
- Putrid odors, liquefaction of tissue proteins, and production of ammonia and H2S gas.
361. What is tissue fixation?
- The process of mobilizing, killing, and maintaining tissue for staining and viewing under a
microscope.
362. What is the purpose of tissue fixation?
- To maintain tissues permanently in a life-like state for evaluation.
363. Why is fixation considered the most important step in histology?
- It is the foundation for all subsequent procedures.
364. What makes a good fixative?
- Rapid penetration, quick killing, minimal artifact, and preservation of tissue elements.
365. What are the subsequent processes after fixation?
- Dehydrating, clearing, impregnation, embedding, staining, and mounting.
366. What are the uses of picric acid?
- It is used as a coagulant fixative of protein picrates and has an affinity for anionic dyes.
367. Why is picric acid kept damp at all times?
- Picric acid must be kept damp because it needs to be stored under a layer of water and it
helps in weighing the reagent.
368. What is acetic acid's mode of action?
- Fixation occurs between the ionized form of acetic acid (the acetate ion) and the amine group
of the protein.
369. How does acetic acid affect tissue structure?
- Acetic acid breaks amino-carboxyl bonds in tissue structural fibers, causing tissue to swell.
370. What is the main function of acetic acid as a fixative?
- Its main function is precipitation and preservation of nucleoproteins.
371. What is glacial acetic acid?
- Concentrated acetic acid with a freezing point of 17 degrees Celsius, solidifying it.
372. What are the advantages of acetic acid as a fixative?
- It fixes nuclei well and yields a more distinct chromatin pattern.
373. What are the disadvantages of acetic acid?
- It destroys mitochondria and Golgi apparatus, lyses red cells, and can cause severe burns.
374. What is the primary use of osmium tetroxide as a fixative?
- It is used for fixing specimens for electron microscopy.
375. Why is osmium tetroxide not frequently used?
- It interferes with subsequent staining.
376. What is the effect of osmium tetroxide on tissues?
- Osmium tetroxide reacts with side chains of proteins, causing cross-linking.
377. Why must tissues fixed with osmium tetroxide be washed in a buffer
solution?
- To remove all residual osmium tetroxide prior to immersion in alcohols.
378. What happens if the clearing agent is incomplete during tissue processing?
- The blocks become soft and mushy.
379. How can you determine if dehydration has been achieved?
- If the solution is clear, dehydration has been achieved and all water has been removed.
380. What is the disadvantage of using alcohol as a clearing agent?
- Alcohol fumes may ignite.
381. Why should alcohol be used in ascending order of strength during tissue
processing?
- It slowly replaces water in the tissue, reducing shrinkage and distortion.
382. In which areas is the dehydration procedure used?
- 1) Preparation of tissue for embedding, 2) Preparation of stained tissue for mounting.
383. How do dehydrating agents remove water from tissue?
- They attract water from tissue or dilute the aqueous tissue fluids.
384. What are some common dehydrating agents?
- Ethanol, Isopropyl alcohol, Acetone.
385. What are the characteristics of ethanol as a dehydrant?
- Clear, colorless, fast acting, miscible with water and xylene, slightly toxic.
386. What are the characteristics of isopropyl alcohol as a dehydrant?
- Excellent substitute for ethanol, less shrinkage and hardening, mildly irritating to eyes, nose,
and throat.
387. What are the characteristics of acetone as a dehydrant?
- Rapid dehydrant, tissues dehydrate rapidly, more expensive than ethanol, very volatile,
flammable.
388. Name some less common dehydrating agents.
- Butanol, Dioxane, Ethylene glycol monoethyl ether.
389. What are the characteristics of butanol as a dehydrating agent?
- Low dehydrating power, causes less shrinkage and hardening than ethanol, strong odor,
causes tissue distortion.
390. What are the characteristics of dioxane as a dehydrating agent?
- Universal solvent, miscible with water, alcohol, xylene, and paraffin, faster dehydrant than
ethanol, explosive on extended storage.
391. What are the characteristics of ethylene glycol monoethyl ether as a
dehydrating agent?
- Rapid dehydrant, does not harm tissue, expensive, minimal distortion, dissolves some
intracellular components.
392. What are universal solvents in tissue processing?
- Reagents that perform both dehydrating and clearing steps, not suitable for delicate tissues.
393. Name some universal solvents.
- Butanol, Dioxane, Tetrahydrofuran.
394. What factors affect the duration of dehydration?
- Fixative used, size of tissue, type of tissue.
395. What are some of the spill kits required on site?
- Absorbent pads, neutralizers for acids and alkalis, cleaning supplies
396. How should materials used in spill clean-up be treated?
- As hazardous waste
397. What should be done in the event of a large spill?
- Evacuate the area
398. How should a spill on an employee be treated?
- Flush with copious amounts of water and seek medical attention
399. What actions should be taken for eye contact with a hazardous substance?
- Flush eyes for a minimum of 15 minutes and always seek medical attention
400. Where should flammables be stored?
- In approved containers and outside of flammable storage cabinet
401. What should be used when transporting flammable liquids?
- Safety cans
402. How should corrosives be stored?
- Separately in dry, well-ventilated areas away from sunlight and flammables
403. How should picric acid be stored?
- Damp, as it is explosive in a dry state
404. What should be done with hazardous chemicals for disposal?
- They should not be disposed of down the drain
405. How should acids and bases be disposed of?
- They must be neutralized with water
406. What chemicals should not enter the sewer system?
- Mercury, chromium, or silver
407. What should be done with organic solvents for disposal?
- They should be maintained in containers and disposed of by a contractor
408. What are the four groups of fires?
- A, B, C, D
409. What types of fires involve flammable liquids and gases?
- Class B fires
410. How can electrical fires be extinguished?
- Using nonconductive agents
411. What type of fires involve combustible and reactive agents?
- Class D fires
412. What is the significance of the 0-4 rating system in NFPA?
- It indicates hazard severity, ranging from minimal to severe
413. What do the colours blue and red represent in NFPA?
- Blue represents health hazards and red represents flammability hazards
414. What is the study of diseased tissues and conditions called?
- Pathology
415. What are the steps involved in tissue preparation techniques?
- Fixation, Accession, Grossing, Processing, Embedding, Paraffin sectioning, Frozen
sectioning, Staining
416. What is the purpose of tissue fixation?
- To stabilize proteins and make tissues resistant to further changes or damage
417. What are the two ways tissue proteins may be altered?
- Chemically and physically
418. What unique identifiers must be included in the requisition for specimen
identification?
- Patient full name, D.O.B., Patient ID #
419. What is the purpose of grossing in tissue assessment?
- Macroscopic review and inspection of tissue samples
420. Why is it important to open only one specimen container at a time during
grossing?
- To prevent sample mix-ups
421. What must be recorded prior to processing the tissue specimen?
- Sample numbers
422. What are the 5 steps involved in tissue processing?
- Fixation, Dehydration, Clearing, Infiltration, Embedding
423. What technique is used to cut tissue sections of a preset thickness?
- Microtomy
424. What is the purpose of embedding tissues into liquid paraffin?
- To allow solidifying before sectioning
425. How are sections of tissue attached to a clean slide?
- Sections are gently separated and then attached using slides that are positively charged
426. What is the last step of tissue processing before subsequent processes?
- Drying the slides in a drying oven
427. What does H & E stand for in the context of tissue staining?
- Hematoxylin and Eosin
428. What is the purpose of vacuum impregnation/infiltration?
- To speed up the process of infiltration.
429. What can be added to paraffin wax for better elasticity?
- Plastic polymers or resins.
430. What is the consequence of insufficient paraffin impregnation?
- The block will shrink.
431. Why can't paraffin be used in electron microscopy?
- Because it cannot withstand the high temperatures used in the process.
432. What additives can commercial paraffins contain?
- Beeswax, rubber, and other waxes.
433. What are the requirements for paraffin wax as an infiltration medium?
- Rapidly convert from a solid to liquid, permeate the tissue in a liquid state, and solidify upon
cooling.
434. What is the melting point range of paraffin wax?
- 40-60°C.
435. How does the melting point of paraffin wax affect its hardness?
- Higher melting points result in harder waxes.
436. Why is lower melting point paraffin preferred for immunohistochemical
procedures?
- Heat can cause inactivation of antigens.
437. What is the plastic point of paraffin?
- The lowest temperature at which permanent deformation can occur without fracturing.
438. Why is the plastic point of paraffin important?
- Large crystals pushed apart during sectioning can affect support and flattening of the section.
439. What is the most common melting point range for routine work?
- 55°C to 58°C.
440. Why should tissues remain in paraffin for the shortest time necessary?
- Prolonged heat exposure causes shrinkage and hardening.
441. What is the purpose of additives in paraffin wax?
- To provide hardness and support to the block.
442. What is the recommended quality control for infiltration baths?
- Temperature must be recorded daily and paraffin containers should be rotated frequently.
443. What are the advantages of paraffin infiltration?
- Same paraffin can be used for both infiltration and embedding, large numbers of tissue blocks
can be processed quickly, and serial sections can be easily obtained.
444. What is the purpose of embedding tissue blocks?
- To prepare the tissue for sectioning.
445. How is a ribbon formed during sectioning?
- Successive sections stick edge to edge, forming a ribbon.
446. What are the steps involved in tissue preparation techniques?
- Fixation, Accession, Grossing, Processing, Embedding, Paraffin sectioning, Frozen
sectioning, Staining
447. What is the purpose of fixation in tissue preparation?
- To maintain tissues in a life-like state and prepare them for subsequent processing
448. What happens during the accession step in tissue preparation?
- Specimens are verified, labeled, and assigned a unique histology number
449. What is the purpose of grossing in tissue preparation?
- To perform a cross examination of tissues, including specimen description
450. What are the steps involved in tissue processing?
- Dehydration, Clearing (de-alcoholization), Infiltration, Embedding
451. Why is dehydration an important step in tissue processing?
- To remove the free water from tissues and allow for infiltration with paraffin wax
452. What are the key agents used for dehydration in tissue processing?
- 70%, 80%, 90%, and 100% ethyl alcohol
453. What can happen if dehydration is done too rapidly?
- Rupture of cells may occur
454. What is the purpose of embedding in tissue preparation?
- To prepare paraffin blocks of tissue for sectioning and staining
455. What is frozen sectioning used for?
- Primarily used for STAT procedures and demonstration of lipids or in some IHC methods
456. What types of stains are used in tissue staining?
- Routine stains (e.g., H and E), special stains, IHC, impregnation techniques, histochemical
reactions, decalcification techniques
457. Why is specimen identification important in tissue processing?
- To ensure proper tracking and labeling of specimens throughout the process
458. What is the first step of tissue processing?
- Dehydration
459. How do dehydration agents remove water from tissues?
- Some are hydrophilic and attract water, while others dilute aqueous tissue fluids
460. Which tissues may require a different alcohol concentration during
dehydration?
- Fragile tissues, such as brain or blood clots, may start at 50% alcohol and work upwards
461. What does alcohol do to tissues during the dehydration process?
- It hardens the tissues
462. What should be done to minimize the hardening effects of alcohol during
dehydration?
- Agitation and heat can reduce the time tissues spend in alcohol baths
463. What is the purpose of a fixative?
- To preserve cells and tissue constituents in a life-like state.
464. What are the requirements of a fixative?
- To penetrate rapidly, not shrink or swell tissue, not distort or dissolve tissue parts, render
enzymes inactive, kill bacteria and molds, and modify tissue constituents.
465. What is the function of a fixative?
- To maintain a proper relationship between cells and extracellular substances and bring out
differences in refractive indexes.
466. What are the five major groups of fixatives?
- Aldehydes, alcohols, mercurials, oxidizing agents, and picrates.
467. What is the mode of action of aldehydes as fixatives?
- Aldehydes form cross-linkages in proteins, minimally harm proteins, and retain antigenicity.
468. What is the mode of action of alcohols as fixatives?
- Alcohols denature proteins and are harsher on tissue, causing brittleness or hardness.
469. What is the mode of action of mercurials as fixatives?
- Mercurials react with nitrogen and anion groups, yielding excellent nuclear detail.
470. What is the mode of action of oxidizing agents as fixatives?
- Oxidizing agents cross-link proteins and cause extensive denaturation.
471. What is the mode of action of picrates as fixatives?
- Picrates change the charges on ionisable side chains of proteins, disrupting electrostatic and
hydrogen bonds.
472. What are the factors that affect fixation?
- Temperature, size, volume ratio, time, fixative choice, penetration, tissue storage, pH, and
osmolality.
473. How does temperature affect fixation?
- Higher temperatures increase the rate of fixation but also speed up autolysis and putrefaction.
474. How does tissue size affect fixation?
- Thicker tissues have slower penetration of fixatives compared to porous tissues.
475. What physical barriers can affect the penetration of fixatives?
- Blood, mucous, and fibrous capsules can slow down the rate of penetration.
476. What is the advantage of using hot formalin as a fixative?
- Hot formalin fixes tissues faster and is often the first step in an automated tissue processor.
477. What effect does cold and room temperature fixation have?
- It acts slightly slower but does not accelerate autolysis and putrefaction.
478. What are the major disadvantages of mercurial fixatives?
- They have disposal issues due to their mercury content.
479. What is the purpose of infiltration?
- The purpose of infiltration is to replace tissue fluids with a supporting medium to make tissues
firm and easier to handle.
480. Why is impregnation important during tissue processing?
- Impregnation maintains the proper relationship between cells and intercellular structures,
preventing compression and distortion during sectioning.
481. What factors determine the duration of infiltration?
- The size and type of tissue, type of clearing agent used, type of processing method, and
volume of tissue affect the duration of infiltration.
482. What is vacuum infiltration?
- Vacuum infiltration is the introduction of solvents and wax under reduced pressure, which
reduces the infiltration time and allows for faster penetration of wax.
483. Which tissues benefit from vacuum infiltration?
- All tissues benefit from vacuum infiltration, especially those containing air, brain/CNS tissues,
skin/bone, dense/hard tissues, fatty tissues, and urgent biopsies.
484. What is the hazard associated with lung tissue during vacuum infiltration?
- If air is reintroduced too rapidly to the vacuum chamber, lung tissue may show artifacts by the
rupturing of alveoli. This can be prevented by slowly opening the valve leading to the vacuum
chamber to reduce pressure slowly.
485. What factors affect tissue impregnation?
- Tissue size, density, type, agitation, vacuum, and improper dehydration & clearing can affect
tissue impregnation.
486. What are the properties of paraffin wax?
- Paraffin wax is relatively inert, melts easily & hardens quickly, and will not harm tissue (unless
too hot). It is produced by cracking petroleum and typically has a melting point of 54°C to 60°C.
487. How can ribbons and serial sections be easily produced with paraffinembedded tissues?
- Paraffin-embedded tissues can be floated on a water bath, allowing for the production of
ribbons and serial sections.
488. What happens if there is carryover of clearing agents or alcohol during wax
impregnation?
- If there is carryover of clearing agents or alcohol, the wax block will harden, dry up, and
crumble.
489. What staining technique can be used to stain glycogen?
- Glycogen staining techniques can be used to stain glycogen.
490. What happens to lipids during prolonged storage in formalin?
- During prolonged storage in formalin, lipids gradually lose their insolubility and dissolve.
491. How can lipids be demonstrated in formalin-fixed tissues?
- Lipids can be demonstrated with frozen sections of formalin-fixed tissues using special stains.
492. What is the role of calcium ions in preserving lipids in formalin solutions?
- Calcium ions in formalin solutions reduce phospholipid solubility and preserve lipids.
493. Why should formaldehyde not be combined with an oxidizing agent in a
compound fixative?
- Combining formaldehyde with an oxidizing agent in a compound fixative leads to poor fixation
and the formation of precipitate.
494. Why is formaldehyde the most commonly used fixing agent?
- Formaldehyde is relatively stable, allowing for subsequent application of many staining
techniques and providing strength to the tissue structure.
495. What is the purpose of buffering formalin solutions?
- Buffering formalin solutions ensures a pH of 7.4 to 7.6 and prevents the formation of formalin
pigment.
496. What is the visual working solution of buffered formalin?
- The visual working solution of buffered formalin is a 10% neutral buffered formalin.
497. How can formalin pigment be prevented or removed?
- Formalin pigment can be prevented by maintaining a near-neutral pH and using appropriate
volume ratio of fixative. It can also be removed by soaking the tissue in alkaline solutions or
using alcoholic picric acid.
498. What are the disadvantages of formaldehyde usage?
- Formaldehyde has a strong pungent odor, can irritate mucous membranes and eyes, may
cause dermatitis and sinusitis, and is a carcinogen.
499. What is the purpose of tissue embedding?
- The purpose of tissue embedding is to orient and support tissue in a mould.
500. What is the most critical step in tissue embedding?
- The most critical step in tissue embedding is tissue orientation.
501. What should be considered during gross examination for tissue orientation?
- Orientation needs to be considered at the time of gross examination.
502. Why is tissue orientation important?
- Tissue orientation is important for the proper demonstration of morphology.
503. What should the orientation offer during sectioning?
- The orientation should offer the least resistance of the tissue against the knife during
sectioning.
504. What does improper orientation in embedding lead to?
- Improper orientation leads to diagnostic tissue elements being damaged.
505. How should large, flat sections be oriented during embedding?
- Large, flat sections should be embedded flat.
506. Which specimens require inking during embedding?
- Certain specimens may require inking.
507. What can be used for tissue inking?
- India ink or tattoo ink may be used for tissue inking.
508. Why is inking used?
- Inking may be used to indicate margins and assist with microscopic orientation.
509. What is the purpose of elongate tissue placement in embedding?
- Elongate tissues are placed diagonally across the block.
510. How are tubular and walled specimens embedded for optimal sectioning?
- Tubular and walled specimens are embedded to provide transverse sections showing all
tissue layers and the lumen.
511. How should skin, intestine, gallbladder, and other epithelial biopsies be cut
for embedding?
- Skin, intestine, gallbladder, and other epithelial biopsies should be cut at right angles to the
surface.
512. What is the preferred orientation when cutting epithelial biopsies?
- Epithelial biopsies should be oriented so that the epithelial surface is cut last to minimize
compression and distortion of the epithelial layer.
513. What are the advantages of benzene as a clearing agent?
- Rapid clearing, minimal shrinkage, easily removed from wax
514. What are the disadvantages of benzene as a clearing agent?
- Flammable, carcinogenic, toxic by inhalation and skin absorption
515. What are the advantages of cedarwood oil as a clearing agent?
- Gentle on tissues, excellent for fragile and delicate tissues, clears from alcohol
516. What are the disadvantages of cedarwood oil as a clearing agent?
- Very slow penetrating, difficult to remove from wax, expensive
517. What are the advantages of chloroform as a clearing agent?
- Readily clears from ethanol, not flammable, causes little shrinkage, suitable for large tissue
specimens
518. What are the disadvantages of chloroform as a clearing agent?
- Difficult to determine the endpoint of clearing, not transparent, toxic, requires well ventilated
room
519. Which clearing agent is highly toxic and carcinogenic?
- Benzene
520. What effect does benzene have on tissues?
- Tissues are not rendered hard or brittle, minimal shrinkage
521. What makes cedarwood oil an eco-friendly alternative to xylene?
- It is naturally occurring from cedar wood
522. Which clearing agent is known for being tolerant and causing minimal
damage to cells?
- Cedarwood oil
523. Which clearing agent is excellent for almost all tissues and penetrates
slowly?
- Chloroform
524. What are the uses of chloroform as a clearing agent?
- Better clearing agent for uterus, muscle, and tendon specimens
525. What is the recommended use of benzene as a clearing agent?
- Not recommended for use
526. What is the primary use of cedarwood oil as a clearing agent?
- Primarily used in research
527. What factors make chloroform a suitable clearing agent?
- Causes minimal shrinkage, evaporates quickly, does not alter the refractive index of tissue
528. What issue arises when using chloroform?
- Difficult to determine the endpoint of clearing
529. What is the processing schedule referred to in slide #89?
- Example of overnight process of closed system
530. What time does the processing begin?
- 1800 hours on Wednesday
531. What time will the tissues be in the last xylene bath?
- 0300 hours
532. How many baths in paraffin are there?
-3
533. What is the processing program for small biopsy specimens?
- Rapid (4 hour program)
534. What is the processing program for routine surgical or autopsy tissues?
- Routine (8 hour program)
535. What is the processing program for larger surgical or autopsy tissue
specimens?
- Routine (12 hour program)
536. What does over-dehydration in tissue processing result in?
- Chatter artifact
537. What causes poor or no nuclear staining in H&E?
- Residual water when tissue exposed to clearing agents
538. What artifact occurs when smaller tissues are placed between dry sponges?
- Sponge artifact
539. How can precipitation formation be corrected?
- Start dehydration baths at 60% to 65% alcohol
540. How can over-dehydration be prevented?
- Process biopsy samples separately and reduce time in dehydrating agents
541. How can poor processing be prevented?
- Ensure proper QC of the processor and avoid residual water exposure
542. What are the steps to prevent poor processing?
- Watch for condensation, monitor alcohol baths, inspect processor, rotate and change reagent
baths, use heat in paraffin chambers
543. What is the advantage of the microwave oven method for tissue processing?
- Increased turnaround time and elimination of xylene as clearing agent
544. How does a laboratory grade microwave differ from a household microwave?
- Controlled temperature, fume hood-like design
545. What is the first step in the microwave oven method for 1mm tissue?
- Place fresh tissue in labeled cassette and fix for 30 minutes with agitation
546. What is the temperature used in the microwave oven method for 1mm
tissue?
- 67-¤0
547. What are the two types of fixation methods?
- Chemical and heat
548. What type of fixation denatures and coagulates proteins?
- Fixation by heat
549. What type of fixation does not denature proteins?
- Fixation by freezing
550. What are coagulant fixatives?
- Fixatives that are harsher and alter protein architecture
551. What are non-coagulant fixatives?
- Fixatives that are gentler and form gel compounds with proteins
552. What is the difference between coagulating and non-coagulating fixatives?
- The degree of protein denaturation
553. Why are non-coagulant fixatives commonly used?
- They cause fewer artifacts
554. What are compound fixatives?
- Fixatives that contain both coagulant and non-coagulant properties
555. What is additive fixation?
- Fixation where the fixing agent chemically links or adds to the tissue
556. What is non-additive fixation?
- Fixation where the fixing agent does not chemically combine with tissue
557. What is the primary fixing agent that reacts like a non-additive fixative?
- Ethanol
558. What is the process of water loss in non-additive fixation?
- Dehydration
559. What does non-additive fixation result in?
- Shrinkage and tissue hardening
560. What is the tolerance of tissues?
- The ability of tissues to withstand fixation
561. What are the sources of error in tissue dehydration?
- a) Section too thick
b) Inadequate immersion time
c) Old/deteriorated solutions
d) Too much tissue
e) Insufficient volume of dehydrating agent
f) Incorrect strength
g) Tissues remaining in low concentrations less than 70%
h) Tissues remaining in high concentrations greater than 80%
i) Over-dehydration
j) Insufficient dehydration
562. What is the purpose of the clearing process?
- To remove alcohol or wax and prepare the tissue for complete wax infiltration
563. Which agent is used to remove alcohol from tissue in processing?
- Clearing agent
564. What are the effects of clearing on tissues?
- a) Tissue hardens
b) Tissues become semi-transparent
565. Which clearing agent has no effect on the refractive index?
- Chloroform
566. What factors affect the clearing process?
- a) Size of the tissue
b) Agitation
c) Clearing agent used
d) Heat
e) Ratio of reagent to tissue
f) Tissue density
567. What are the consequences of improper clearing?
- a) Moth-eaten appearance in tissue
b) Sections crumble and tend to tear out of the block
568. What indicates improper clearing of tissue?
- Shrinking of the tissue center and drying up, causing fragmentation
569. What corrective actions can be taken for improper clearing?
- a) Melt wax and put specimens back in wax
b) Work backwards through xylene to remove wax
c) Use ethanol
570. What are the commonly used clearing agents?
- a) Xylene
b) Toluene
571. What is the recommended volume ratio of fixative to tissue?
- At least 15 to 20x greater than the volume of the tissue.
572. When might you need to change fixative at regular intervals?
- To avoid fixative exhaustion.
573. What is the effect of agitation on fixation?
- It improves the speed and quantity of tissue fixation.
574. What is the recommended interval from tissue removal to fixation?
- As short as possible to prevent adverse effects like cellular organelle loss.
575. What is the consequence of inadequate exposure to fixative?
- It leads to poor tissue processing and poor staining.
576. What fixative is generally preferred?
- NBF (neutral buffered formalin).
577. What fixative is used for demonstrating muscle cross-striations?
- Zenker or Bouin fixative.
578. Why should tissue sections be cut to recommended thickness?
- To ensure adequate penetration of the fixative.
579. How should tissues suspected to require IHC staining be stored?
- In 70% alcohol to prevent cross-linking.
580. What is the optimal pH range for fixation?
- pH 6.0 to 8.0.
581. What role do buffering salts play in fixation?
- They help maintain the desired pH of the fixative solution.
582. What physical changes occur during fixation?
- Tissues undergo beneficial hardening, making it easier to dissect or slice.
583. What is the function of fixatives in the fixation of tissue specimens?
- They denature proteins and coagulate or precipitate them.
584. What is the purpose of primary fixatives?
- Primary fixatives are used to coagulate or precipitate proteins in tissue specimens.
585. Why are primary fixatives almost never used alone?
- Primary fixatives are usually combined in compound fixatives.
586. What are the 8 common primary fixatives?
- 1) Formaldehyde, 2) Potassium dichromate, 3) Mercuric chloride, 4) Ethanol, 5) Picric acid, 6)
Acetic acid, 7) Osmium tetroxide, 8) Glutaraldehyde.
587. What is the formula and solubility of formaldehyde?
- CH2O; it is a gas but can be dissolved in water to form a 37-40% weight-by-volume solution.
588. What is the correct terminology for formalin?
- Formalin is a 40% solution of formaldehyde gas.
589. What is the purpose of buffering formalin to pH 7?
- Buffering formalin to pH 7 allows for the greatest binding of formaldehyde with tissue groups.
590. What is the main reaction site of formaldehyde?
- The main reaction site of formaldehyde is the amino group found on the side chains of amino
acids.
591. What type of reaction does formaldehyde undergo with tissue groups?
- Formaldehyde forms cross-links with amino acids, creating a Methylene bridge that links
protein chains together.
592. How does formaldehyde react with sulfhydryl groups?
- Formaldehyde reacts with sulfhydryl groups to form cross-links with the amino acid cysteine.
593. How does formaldehyde preserve glycogen in tissue specimens?
- Formaldehyde denatures proteins, forming a meshwork that traps glycogen within it.
594. What is the appearance of glycogen when fixed with formaldehyde?
- Glycogen appears polarized or streaming in the direction of the fixative penetration, known as
the 'streaming artifact'.
595. What is the preferred fixative for immunoperoxidase staining of paraffinembedded tissue?
- B-5 fixative
596. What is the function of formalin added to B-5 fixative?
- To prevent deterioration of the fixative
597. Why must excess fixative of B-5 fixative be treated to remove mercury
pigment?
- To avoid staining issues in subsequent processes
598. How should tissues fixed with B-5 fixative be stored?
- In 70% alcohol
599. What are the disadvantages of B-5 fixative?
- Extreme hardening, tissue brittleness, difficulty in cutting tissue ribbons, unstable fluid
600. Which fixative is non-corrosive and can be used with metal objects?
- Z-5 fixative
601. What is the main advantage of Z-5 fixative over B-5 fixative?
- Less tissue distortion
602. What is the composition of Carnoy's fixative?
- Absolute ethanol, chloroform, glacial acetic acid
603. How quickly does Carnoy's fixative penetrate the tissue?
- Rapidly for the first 2mm, then the penetration rate decreases
604. Which fixative is recommended for urgent diagnosis due to its rapid fixation?
- Carnoy's fixative
605. What type of fixative is Carnoy's fixative classified as?
- Cytological fixative
606. What is the function of chloroform in Carnoy's fixative?
- Controversial, but it potentially acts as an adjuvant to enhance effectiveness
607. What are water-soluble waxes used for?
- Water-soluble waxes are used for special projects.
608. What is the advantage of using polyethylene glycol over paraffin wax?
- The advantage of using polyethylene glycol over paraffin wax is minimal shrinkage.
609. What is the disadvantage of using polyethylene waxes?
- The disadvantage of using polyethylene waxes is solubility.
610. Which type of plastic is commonly used for infiltration and impregnation?
- Glycol Methacrylate is commonly used.
611. What is the purpose of a transitional fluid in epoxy resins?
- A transitional fluid is used to clear the tissue and make it miscible with the embedding medium.
612. What are some commonly used epoxy resins?
- Some commonly used epoxy resins are Araldite, Epon, Spurr, and Maraglas.
613. What are the advantages of using epoxy resins?
- Epoxy resins are primarily used in electron microscopy and produce very thin sections.
614. What is the disadvantage of using epoxy resins?
- Epoxy resins have a highly viscous mixture and offer poor penetration.
615. How can agar and gelatin be used for embedding tissue?
- Agar and gelatin can be used to produce a single block of friable tissue or multiple fragments
for cutting frozen sections.
616. What is the process of embedding tissue in gelatin?
- The tissue is washed, impregnated with gelatin solutions, embedded in gelatin, and further
hardened in formalin.
617. What is ethanol classified as?
- A cytolgical fixative.
618. What happens to the cell fibres when ethanol is used as a fixative?
- They become shrunken and distorted.
619. Why is ethanol not a good fixing agent for demonstrating the microanatomy
of tissue?
- Because it causes extreme shrinkage.
620. What is ethanol's reaction with carbohydrates?
- Ethanol is the best fixative for preserving glycogen.
621. What process occurs with ethanol fixation?
- Streaming or polarization.
622. What does ethanol do to lipids?
- Dehydrates them.
623. What is the disadvantage of ethanol as a fixative?
- It causes extreme shrinkage.
624. In what form is picric acid commonly found?
- As a saturated aqueous solution.
625. What does picric acid coagulate?
- Nucleoprotein.
626. Is picric acid a hardening agent for tissue?
- No.
627. What is the main reaction that occurs with picric acid fixation?
- Between the negatively charged, ionized radical of picric acid and positively charged amine
groups on protein chains.
628. How should tissue fixed in picric acid be processed to avoid loss of picrates?
- It should be transferred directly to dehydrating alcohols.
629. What does picric acid fix indirectly?
- Glycogen.
630. What are the disadvantages of glutaraldehyde as a fixative?
- Slow penetration, instability, false positive PAS reaction, toxic
631. What are the uses of glutaraldehyde as a fixative?
- Best fixative for electron microscopy, preserves cellular organelles, conserves esterase and
phosphatase
632. What is glyoxal used for?
- Industrial applications, replacing glutaraldehyde and formaldehyde, stains well with fewer
artifacts
633. What are compound fixatives?
- Fixatives that combine primary fixing agents to balance their effects and include coagulating/
non-coagulating fixing agents
634. What is the role of acetate in a compound fixative?
- Counteracts tissue shrinkage caused by coagulating fixing agents
635. What are the three categories of compound fixatives?
- Microanatomical, cytological, histochemical
636. What is neutral buffered formalin (NBF) used for?
- Primary fixative, preservation of tissues for prolonged time without excessive hardening,
inexpensive
637. What are the disadvantages of NBF?
- Gradual loss of basophilic staining, can form formalin pigment
638. What are the components of NBF?
- Formaldehyde, phosphate buffer, water
639. What is the pH of NBF?
- pH 7.0