Histology is the study of tissues at the microscopic level. It involves preparing tissue samples using various techniques like fixation, processing, embedding, sectioning, and staining. This allows tissues to be viewed under light or electron microscopes. There are four basic tissue types - epithelial, connective, muscular and nervous. Special stains are used to highlight structures and make tissues distinguishable. Histology provides information about normal and pathological cellular structure and organization.

1. Dr Sani Ismaila MD/MBBS, DVM

2. Histo-Tissue Logia-study of/knowledge
Histology is the study of the
microscopic anatomy (microanatomy)
of cells and tissues of plants and animals.
It is commonly performed by examining
cells and tissues under a light
microscope or electron microscope,
the specimen having been sectioned (cut
into a thin cross section with
a microtome), stained, and mounted on
a microscope slide.

3. In the 19th century, histology was
an academic discipline in its own
right.
The 1906 Nobel Prize in Physiology
or Medicine was awarded to
histologists Camillo Golgi and
Santiago Ramon y Cajal.They had
dueling interpretations of the
neural structure of the brain based
in differing interpretations of the
same images.
HISTORY OF HISTOLOGY

4. Cell: smallest unit of structure and function of body
↓
tissue: group of cell+extracellular ground substance
four basic tissue:
---epithelium
↓ ---connective tissue
---muscular tissue
---nervous tissue
organ: made up of tissue, have special shape, structure
and function
↓
system: organs Which have related function get together.

5. There are four basic types of human
tissues:
1. muscle tissue,
2. nervous tissue,
3. connective tissue,
4. epithelial tissue.
All tissue types are subtypes of these
four basic tissue types (for example,
blood is classified as connective
tissue, since the blood cells are
suspended in an extracellular matrix,
the plasma)

6. Micro-techniques for tissue preparation -
Using Light or Electron Microscope.
Basic sample preparation techniques
1.Fixing
2.Processing - dehydration, clearing, and
infiltration
3.Embedding
4.Sectioning
5.Mounting
6.Staining

7. 1- Fixation:- -
Buffered formol saline - 10%formalin - Suza,
Bouin, Zenker solution - Formaldehyde or
Glutradhyde - Osmium tetraoxide - Potassium
permanganate
2-Processing:
Dehydration: Gradual removal of water from
the tissue using ascending grads of ethyl
alcohol to prevent tissue shrinking.
Clearing: Replacement of alcohol in tissue by
clearing fluid like xylem, benzene, or acetone
Tissue preparation stages

8. 3.Embedding: -Tissues are impregnated in paraffin -Tissues
are impregnated in Epon in gelatin capsule
4- Sectioning/Cutting: - Paraffin block are cut by microtome
using metal knife, into thin sections ~ 6µ. - Capsules are cut
by ultra-microtome, using glass or diamond knife, into ultra
thin sections 50-100nm.
5- Mounting: - Sections spread on the hot plate and
mounted on glass slides. - Sections mounted on metal grids.
6- Staining: -Variable stains are used for specific tissues. -
Stained by heavy metals like lead nitrate and uranyl
acetate.
Tissue preparation stages

9. Stains - Special dyes used to stain
the histological sections and
make them ready for microscope
examination. - Heamatoxylin and
Eosin are most common used.
Types of stains / Reaction of stain:
1. Acidic Eosin stain
2. Basic Heamatoxylin stain
3.Neutral Leishman stain
HISTOLOGICAL STAINS

10. Physical stain: stain dissolve in tissue without any
chemical reaction such as : SUDAN III for fatty tissues.
Vital stain: Staining living tissue inside the body. ----
Trypan blue stain.
Supra-vital stain: Staining living tissues outside the
body. ---Brilliant cresyl blue.
Metachromatic stain: Staining the tissues with a color
different from the original color of stain. ---Toluidin blue
staining for Mast cells.
HISTOLOGICAL STAINS

11. Polychromatic stain: Staining the tissues with multiple
colors in spite of using a single stain. ---Geimsa stain for
blood.
Orthocromatic stain: Staining the tissues with the same
color of the stain, such as H&E.
Histo-chemical stain: Staining the different chemical
components of the cell.
Immuno-histo-chemical stain: Localization and staining
specific proteins by the antigen antibody reaction.

12. SPECIALTECHNIQUES USED FOR HISTOLOGICAL DIAGNOSIS
1.Histchemistry
2.Immunohistochemistry
3.Tissue / Cell Culture
4.Cell Fractionation
5. ExfoliativeCytology
6.Cytogenetics and Molecular Cytogenetics
7. Bone Marrow smear / Blood film
8.Fine needle aspiration / biopsy
9.Flowcytometry
10.Autoradiography