INTRODUCTION TO HISTOLOGY Dr Sani Ismaila MD/MBBS, DVM

INTRODUCTION 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.

HISTORY OF HISTOLOGY 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.

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.

There are four basic types of human tissues:  muscle tissue,  nervous tissue,  connective tissue, 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)

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

Tissue preparation stages 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 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.

HISTOLOGICAL STAINS 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 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.

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.

SPECIAL TECHNIQUES USED FOR HISTOLOGICAL DIAGNOSIS Histchemistry Immunohistochemistry Tissue / Cell Culture Cell Fractionation Exfoliative Cytology Cytogenetics and Molecular Cytogenetics Bone Marrow smear / Blood film Fine needle aspiration / biopsy Flowcytometry Autoradiography

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