MDSC 1401 Environment & Health: Histology

MDSC 1401 Environment & Health

• Course is offered by the Anatomy Unit, Department of Pre-clinical Sciences, Faculty of Medical Sciences, The University of the West Indies.

Introduction to Histology and Microscopy

• The study covers histology and microscopy.
• The course includes sessions in the Anatomy Laboratory.

What is Histology?

• Histology is the study of the microscopic anatomy of cells, tissues and organs.
• Histopathology involves the study of tissues affected by disease.

How are histological slides produced?

• Steps involved:
  • Obtain fresh specimen.
  • Fixation: used to preserve tissue structure and prevent microbial growth, common fixatives include formaldehyde, acetone, and Bouin's fluid.
  • Dehydration: tissues are progressively dehydrated using increasing concentrations of alcohol before transferring to an organic solvent (like xylene).
  • Clearing: the tissue is immersed in an organic solvent (xylene) to prepare it for wax infiltration.
  • Wax Infiltration: the xylene is replaced with molten paraffin wax, which infiltrates the tissue.
  • Embedding: tissues are immersed in molten paraffin wax, enclosed in a mould, and allowed to solidify.
  • Sectioning: Tissues are cut into thin sections (3-5 μm) using a microtome. Alternatively, cryostat cuts sections from deep-frozen blocks, often of unfixed tissues.

Staining Techniques & Mounting of Slides

• Most cells and tissues are transparent so require staining.
• Haematoxylin and eosin (H&E) staining is frequently used: nuclei stain blue, cytoplasm and extracellular matrix stain varying shades of pink.
• Slides are dehydrated with a series of alcohols, passed through xylene, and covered by a coverslip for preservation.

Microscopy

• Histology departments use light microscopes that use transmitted light, where light passes through the specimen to the objective lens.
• Light from a lamp is focused onto the specimen by the substage condenser in the microscope.
• The objective lens collects and focuses light to create an image within the microscope's barrel, which is then viewed through an eye-piece as if it is a projection.
• Microscopes have various parts, including the ocular lens (eyepiece), diopter adjustment, nose piece, objective lens, stage clip, diaphragm, condenser, illuminator (light source), head, arm (carrying handle), mechanical stage, coarse adjustment, fine adjustment, stage controls, base, brightness adjustment, and light switch.
• Procedure for using a light microscope includes switching on the power supply, cleaning the slide, placing it onto the microscope's slide holder, centering, using the coarse adjustment to move the stage, turning the objective lens to lowest magnification (typically x4), using the fine adjustment. Then switching to higher magnification (like x10) and adjusting again with the fine adjustment.