Introduction to HistologyTissue processing and Microscope

Dr Abubakr H MossaAnatomy Department

8 & 11/9/2011Lab 1

Outlines: Definition of Histology Basic organization of human body Tissue processing:

o Fixation o Dehydration o Clearing o Embedding o Sectioning o Staining

Light microscope: parts and how to use

Definition of histology:

Histology is the study of the tissues of the body and how these tissues are arranged to constitute organs.

The Greek root histo can be translated as either "tissue" or "web“.

Histology involves all aspects of tissue biology, to correlate the tissue structure with its function.

Basic organization of human body

Tissue processing

To be able to study the microscopic features of the tissue, it should undergo several steps. Each step is done for a certain reason.

Here, we are going to talk about these steps briefly.

Tissue processing

Tissue processing

Fixation: o The most commonly used

substance is formalin.• Aqueous solution (hydrophilic)• Used to preserve the tissue by:

• Terminating cell metabolism,• Preventing autolysis,• Sterilizing the tissue, • Hardening the tissue.

Tissue processing

Embedding: o After hardening (fixing) the tissue, we have to put

the small pieces of the tissue in a block of paraffin (embedding) to facilitate the next step (sectioning).

o But we can not embed the tissue in paraffin without:• Washing the tissue from formalin,• Then drying it (dehydration) by using alcohol,• Finally removing the alcohol (clearing) by organic solvents.

o The tissue, then, is immersed in hot paraffin and left to cool to obtain the tissue blocks.

Tissue processing Sectioning :

o This is done by a machine called microtome.o The blocks are sliced in the range of 5 to 15

µm (1 µm = 1/1000mm)o The slices then are fixed on the slides.

µµ

Sectioning

Tissue processing Staining:

o If the slide is examined under the microscope without staining we can see only vague shadows of the tissue.

o So to visualize the tissue and the cellular components we have to use dyes which stain the different components according to their chemical composition.

Tissue processing Staining; Different dyes or stains are used to display the

cellular components. Hematoxylin and eosin (H & E) are the stains

used in most of the slides we are going to study in our course.o Eosin is an acidic dye and stains the basic cellular

organelles in blue.o Hematoxylin acts like basic dye and stains the acidic

components in different degrees of red color.

H & E stain

Other stains

Other stains

Other stains

Tissue processing

Rough endoplasmic reticulum

Parts of microscope

Thanks