Histology I - Introduction and Tissue Preparation

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Questions and Answers

What is the primary purpose of fixation in tissue preparation?

To remove excess fluids from the tissue samples

To freeze the tissue for long-term storage

To preserve tissue structure and prevent degradation (correct)

To enhance the color of the tissue for visualization

Why are tissues usually cut into small fragments before fixation?

To increase the weight of the samples for handling

To facilitate preparation for staining procedures

To minimize the surface area exposed to fixatives

To allow fixatives to diffuse fully through the tissues (correct)

What role does vascular perfusion play in the fixation process?

It allows for rapid fixation throughout the tissues (correct)

It helps in the staining of specific tissues

It removes contaminants from the tissue samples

It aids in freezing the samples before fixation

Which of the following fixatives is commonly used for light microscopy?

Formalin Signup and view all the answers

How does glutaraldehyde function as a fixative?

It reacts with amine groups of proteins and cross-links them Signup and view all the answers

What is the primary purpose of fixation in microscopy?

To preserve cellular lipids and proteins Signup and view all the answers

Which chemical is typically used to dehydrate fixed tissue?

Ethanol Signup and view all the answers

What does the term 'clearing' refer to in the tissue preparation process?

Replacing ethanol with an organic solvent Signup and view all the answers

What materials are commonly used for embedding tissues?

Paraffin and plastic resins Signup and view all the answers

What is the main characteristic of fixed tissue after infiltration?

It becomes firm for thin sectioning Signup and view all the answers

What is the primary focus of histology?

The arrangement of tissues in organs Signup and view all the answers

Which of the following statements about tissue preparation is correct?

Thin sections allow light to pass through for microscopic examination. Signup and view all the answers

Why are advances in various fields essential for histology?

They facilitate better knowledge of tissue biology. Signup and view all the answers

What is a common challenge in preparing microscopic tissue slides?

Preventing distortion of cell structure Signup and view all the answers

What tools are essential for histology studies?

Microscopes and molecular methods Signup and view all the answers

Which characteristic is ideal for a microscopic tissue preparation?

The tissue displays the same structural features as in the body Signup and view all the answers

Which process is NOT typically involved in the preparation of histological samples?

Generating 3D imaging of organs Signup and view all the answers

What is a significant reason for the dependence on microscopes in histology?

Most tissues are small and structured at a cellular level. Signup and view all the answers

Study Notes

Histology I - Introduction

Histology is the study of body tissues and their arrangement into organs.
It encompasses all aspects of tissue biology, focusing on how cell structure and arrangement optimise organ functions.
Histology relies on microscopes and molecular methods due to the small size of cells and matrix components.
Advances in biochemistry, molecular biology, immunology, and pathology are vital for a deeper understanding of tissue biology.
Understanding the tools and methods used within any scientific field is crucial for a comprehensive understanding of the subject.

Histology I - Tissue Preparation for Study

Tissue slices, or sections, are prepared for visual examination with transmitted light.
Tissues are usually too thick for light to pass through, so thin sections are cut and placed on slides for examination of internal structures.
Ideal tissue preparations preserve the same structural features as the tissue in the body.
Unfortunately, the preparation process can remove cellular lipids and slightly distort cell structure.

Histology I - Tissue Preparation Steps

The basic steps of tissue preparation for light microscopy are shown in Figure 1-1(a).
- Fixation: Placing tissue in chemicals to cross-link proteins and inactivate enzymes.
- Dehydration: Transferring tissue through solutions of increasing alcohol concentration, ending in 100% ethanol.
- Clearing: Removing alcohol using organic solvents, making the tissue translucent.
- Infiltration: Immersing tissue in melted paraffin until it is completely infiltrated.
- Embedding: Placing the infiltrated tissue in a mold with paraffin and allowing it to harden.
- Trimming: Trimming the paraffin block to expose tissue for sectioning.
Similar steps are used for transmission electron microscopy (TEM), but using different fixatives and dehydrating solutions, and embedding in epoxy resins.
Tissue samples for TEM are smaller and require very thin sectioning.

Histology I - Fixation

Fixation is important because it preserves tissue structure and prevents degradation by enzymes released from cells or microorganisms.
Tissue samples are placed in fixatives (stabilizing/cross-linking compounds), as soon as possible after removal from the body.
For large organs, fixatives are introduced via blood vessels (vascular perfusion) for rapid penetration.
Common fixatives for light microscopy include formalin (buffered solution of 37% formaldehyde).
Glutaraldehyde is also used as a fixative for electron microscopy because it reacts with proteins, preventing their degradation and reinforcing cell and ECM structures.
For electron microscopy, tissue is often immersed in buffered osmium tetroxide

Histology I - Dehydration

The fixed tissue is dehydrated gradually by passing it through a series of increasing concentrations of ethanol solutions, ending in 100% ethanol.

Histology I - Clearing

Ethanol is replaced by an organic solvent miscible with both alcohol and the embedding medium, a process called clearing.
This step results in tissue becoming translucent.
The reagents used in this stage contribute to the translucent appearance.

Histology I - Infiltration and Embedding

To allow thin sectioning, fixed tissues are infiltrated and embedded in a medium that gives a firm consistency to the tissue preparation.
Common embedding media include paraffin for light microscopy and plastic resins for both light and electron microscopy.

Histology I - Sectioning

The hardened block with embedded tissue is trimmed and placed on a microtome for sectioning.
Paraffin sections are typically 3-10 µm thick for light microscopy (LM).
Electron microscopy (EM) requires sections thinner than 1 µm.

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Description

This quiz covers the fundamentals of histology, focusing on the study of body tissues and their arrangement into organs. It also explores the essential methods and tools used for tissue preparation and examination, crucial for understanding tissue biology and its applications in various fields. Prepare to test your knowledge on these foundational concepts.