Histology Concepts and Tissue Processing

• Human Histology Lecture MT120225
• Unit 1 is an Introduction to Histology
• UST General Santos - School of Health Sciences
• Department of Medical Technology, Second Semester A.Y. 2024-2025.

Unit Intended Learning Outcomes

• Understand the fundamental concepts of human histology and its relevance to the Medical Technology profession.
• Describe the various methods involved in tissue processing.

Introduction to Human Histology

• Histology is the study of tissues + science

Significance of Histology to MedTech Profession

• In The Philippines Registered Medical Technologists (RMTs) assist pathologists in the laboratory and prepare and process tissue samples.
• In the United States one can be a histotechnician HT(ASCP) or Histotechnologist HTL(ASCP)
• Histotechnicians prepare and process tissue samples for routine histologic techniques (fixation, processing, embedding, microtomy, staining)
• Histotechnologists perform both routine and complex histologic techniques (enzyme histochemistry, immunohistochemistry, in-situ hybridization, immunofluorescence)

Requirements to be a histotechnician HT(ASCP) or Histotechnologist HTL(ASCP)

• Education: Includes obtaining an associate's or bachelor's degree or completing an accredited histologic technician program
• Certification: Includes a certification form ASCP

Levels of Organization in the Human Body

• Chemical
• Cells
• Tissues
• Organs
• Organ system
• Organism

Tissue Processing

• The steps are: Fixation, Dehydration, Clearing, Infiltration, Embedding, Trimming, Sectioning, Water Bath, Staining and Mounting

Fixation

• Small pieces of tissue are placed in solutions of chemical that cross-link proteins and inactivate degradative enzymes.
• This preserves cell and tissue structure
• The aim of fixation is to preserve the tissue nearest to its living state
• A commonly used fixative is formalin

Dehydration

• The tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100% alcohol, which removes all water.
• The aim is to remove water molecules from the tissue
• A commonly used dehydrating agent is ethanol

Clearing

• The dehydrating agent is removed and replaced by an organic solvent to facilitate the transition of dehydration and infiltration stage
• The aim is to remove the dehydrating agent, make the tissue clear and improve the microscopic exam
• A Commonly used clearing agent is Xylene

Infiltration

• The tissue is then placed in melted medium until it becomes completely infiltrated.
• The aim is to provide support to the tissue and permit thin sectioning
• A commonly used medium is paraffin wax

Embedding

• The infiltrated tissue is placed in a small mold with melted media and allowed to harden.
• The aim is to provide support to the tissue and permit thin sectioning
• A commonly used medium is Paraffin wax

Trimming

• The resulting paraffin block is trimmed to expose the tissue for sectioning on a microtome.

Sectioning

• A microtome is used to cut tissue specimens into a thin paraffin ribbon that can be placed on a slide for microscopy.

Water Bath

• The tissue ribbon is floated on a water bath to flatten it
• It is then fished onto a microscope slide coated with Meyer's egg albumin as an adhesive.

Staining

• The tissue is stained to visualize different tissue components.
• Commonly used stains are Hematoxylin and Eosin

Mounting

• A mounting agent is added to the specimen
• A thin glass coverslip is placed over the specimen to secure it and prevent damage
• A commonly used agent is Canada balsam

Examination of a Histological Slide in Light Microscope

• Slides can be sectioned as longitudinal, transverse, or oblique

Artifacts

• Errors can occur during the preparation process

These questions cover key aspects of studying histology, its importance for Medical Technology students, and skills improvement. It emphasizes methods in tissue processing and examination of histologic slides. Focus on expressing understanding of histology concepts.