Podcast
Questions and Answers
What is the primary focus of histology?
What is the primary focus of histology?
Which of the following represents the correct definition of cytology?
Which of the following represents the correct definition of cytology?
Which group of tissues is considered one of the four basic types?
Which group of tissues is considered one of the four basic types?
What term describes a group of organs with related functions?
What term describes a group of organs with related functions?
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Which of the following microscopes is not used in histological studies?
Which of the following microscopes is not used in histological studies?
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How are tissues primarily defined?
How are tissues primarily defined?
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Histology can be described as a branch of which broader scientific field?
Histology can be described as a branch of which broader scientific field?
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What language do the roots of the word histology derive from?
What language do the roots of the word histology derive from?
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What is the primary role of fixation in tissue processing?
What is the primary role of fixation in tissue processing?
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Which step in tissue processing involves the use of increasing concentrations of alcohol?
Which step in tissue processing involves the use of increasing concentrations of alcohol?
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What is the most common fixative used in tissue processing?
What is the most common fixative used in tissue processing?
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How many jars of xylene are included in an automated tissue processor?
How many jars of xylene are included in an automated tissue processor?
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Which of the following steps is NOT part of the tissue processing sequence?
Which of the following steps is NOT part of the tissue processing sequence?
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What effect does fixation have on tissues during the processing?
What effect does fixation have on tissues during the processing?
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What is the duration of treatment in 90% alcohol during the dehydration process?
What is the duration of treatment in 90% alcohol during the dehydration process?
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How many total stations are there in an automated tissue processor?
How many total stations are there in an automated tissue processor?
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What is the primary purpose of dehydration in tissue preparation?
What is the primary purpose of dehydration in tissue preparation?
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Which agent is most commonly used for the clearing process in tissue preparation?
Which agent is most commonly used for the clearing process in tissue preparation?
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What happens to the tissue during the infiltration step?
What happens to the tissue during the infiltration step?
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What is the function of a microtome in histology?
What is the function of a microtome in histology?
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What color does haematoxylin typically stain the nucleus?
What color does haematoxylin typically stain the nucleus?
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Which of the following statements about eosin is true?
Which of the following statements about eosin is true?
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What are the typical melting points for the paraffin wax used in tissue preparation?
What are the typical melting points for the paraffin wax used in tissue preparation?
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Why is the clearing step named as such in tissue preparation?
Why is the clearing step named as such in tissue preparation?
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Study Notes
Tissue Processing
- Haematoxylin and Eosin (H&E)-stained sections of formalin-fixed tissue are most commonly examined for histologic studies with a light microscope.
- There are 10 steps in tissue processing: receipt and identification, labeling, fixation, dehydration, clearing, infiltration, embedding, sectioning, staining, and mounting.
Automated Tissue Processor
- An automated tissue processor contains 12 stations.
- These stations include 1 jar of formalin, 7 jars with grades of alcohol, 2 jars of xylene, and 2 jars of molten paraffin wax.
### Fixation
- Fixation prevents tissue decomposition by terminating cell metabolism, preventing enzymatic degradation, killing microorganisms, and hardening the tissue.
- The most common fixative is formalin, a 37% aqueous solution of formaldehyde.
### Dehydration
- Involves removing water from tissue by passing it through increasing concentrations of alcohol.
- The process takes 7 hours, with 1 hour in each of the following solutions: 50% alcohol, 60% alcohol, 70% alcohol, 80% alcohol, 90% alcohol, absolute alcohol, and absolute alcohol.
- Dehydration ensures the paraffin wax used for infiltration can easily mix with the tissue as it is not miscible with water.
Clearing
- This process removes the alcohol from the tissue and replaces it with a fluid that mixes with paraffin.
- Clearing agents penetrate the tissue, make it transparent, and harden it.
- Xylene is the most commonly used clearing agent.
Infiltration and Embedding
- Once clearing agents are removed, molten paraffin wax is used to fill the empty spaces in the tissue for 6-8 hours.
- The paraffin wax hardens the tissue and makes it easier to section.
- The tissue embedded in wax is transferred to a mould filled with molten wax, allowed to solidify, and then sectioned to obtain ribbons.
Sectioning
- Sectioning involves cutting the wax blocks into thin strips of varying thickness using a microtome.
Routine Staining (H&E)
- Staining highlights specific tissue details.
- The most commonly used stain is Haematoxylin and Eosin (H&E).
- Haematoxylin stains nuclei blue as it is a basic dye that stains acidic structures.
- Eosin stains cytoplasm pink as it is an acidic dye that stains basic structures.
Histology
- Histology is the study of tissues and organs using a microscope.
- It is often referred to as microscopic anatomy and involves the study of the detailed structure of tissues and organs using a light microscope or electron microscope (EM) (Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM)).
- The word "histology" comes from the Greek words "histos" (tissue) and "logia" (science).
Cytology
- Cytology is the study of the structure and function of the cell.
Levels of Organization
- Cells are the smallest living units of the levels of organization.
- Tissues are comprised of many cells and an extracellular ground substance.
- The four basic types of tissues are: epithelial, connective, muscular, and nervous.
- Organs are made up of different tissues and have a specific shape, structure, and function.
- Systems are groups of organs that perform related functions.
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Description
Test your knowledge on tissue processing and histology techniques, including the role of fixation, dehydration, and the automated tissue processor. Explore the critical steps involved in preparing tissue samples for microscopic examination. Understand the importance of various reagents like formalin and alcohol in the preservation of biological specimens.
