Introduction to Histology PDF

Introduction to Histology  What is Histology?  Basic elements of the body.  The Four Basic Tissues of the body  Tools of studying Histology.  Preparation of Histological Sections.  Types of Stains.  What is Histology? Histology is the science that deals with studying ti...

Introduction to Histology  What is Histology?  Basic elements of the body.  The Four Basic Tissues of the body  Tools of studying Histology.  Preparation of Histological Sections.  Types of Stains.  What is Histology? Histology is the science that deals with studying tissues and cells of the body. Basic elements of the body. Cell: is structural & functional unit of any living organism Tissue: is formed of Cells & Extracellular matrix Organ: is formed of different tissue types System (organ system) Living organism  The Four Basic Tissues of the Body Epithelial Connective Muscular Nervous Tissue Tissue Tissue Tissue Tools of studying Histology (Microscopy)  Light Microscope (L.M.)  Electron Microscope (E.M.): (a) Transmission electron microscope (TEM) visualizes the internal structure of the cell (b) Scanning electron microscope (SEM) visualizes the surface ultrastructure  Magnification power of microscope: Magnification power of objective lens X magnification power of ocular lens Maximum magnification power of light microscope is 1500x Maximum magnification power of electron microscope is 300000x or more  Resolution (a measure of clarity): The smallest distance between two adjacent particles at which they still be seen as separate objects The maximum resolving power of light microscope is 0.2 μm The maximum resolving power of electron microscope is 0.2 nm E  Units of measurements micrometer (μm) = 1/1000 of a millimeter nanometer (nm) = 1/1000 of a micrometer  Light Microscope (L.M.)  Idea: Used to examine stained sections by using natural / electric light as a source of illumination.  Components: Light source Stage Objective lens, Ocular lens  The resulting image: colored  Electron Microscope (E.M.)  Idea: Used to study fine structures with high resolution by using a beam of electrons  Components: Electromagnetic lenses that detect the beam of electrons  The resulting image is always greyscale or black (electron-dense) & white (electron-lucent)  Preparation of Histological Sections Paraffin sections Two main steps Preparation of sections Staining of sections  Preparation of paraffin sections 1.Obtain the tissue 2.Fixation 3.Dehydration 4.Clearing 5.Impregnation with soft paraffin 6.Embedding in hard paraffin 7.Sectioning 8.Mounting  Fixation: The aim: is to preserve cells and tissue components in a “life- like state” by preventing autolysis or putrefaction. The standard solution is 10% neutral buffered formalin  Dehydration: The aim: is to remove water from tissues gradually The tissue sample is placed in ascending grades of alcohol (from 50 percent 70% 90% to 100% alcohol). Clearing: The aim: is to replace alcohol with agent miscible with paraffin. The tissue sample is treated with clearing agents (xylol) After treatment with xylol the tissue becomes transparent (clear).  Impregnation: The aim: is to replaces xylol with melted soft paraffin and infiltrates the tissue with it. tissue is placed in melted soft paraffin in an oven at 50 to 55 C.  Embedding: The aim: to form hard paraffin block. The specimen is transferred into a cast which is filled with melted hard paraffin and is left to cool  Sectioning: The aim is to get thin sections (5 to 8 μm) from the paraffin block Using microtome  Mounting: Sections are mounted on glass slides and left to dry.  Staining of sections  Main stain: Hematoxylin & Eosin (H&E) stain 1- Xylol 2- Absolute alcohol 3- Bring sections down to water (grades of alcohol) 4- Stain in Hematoxylin 5- Blue in tap water 6- Eosin staining 7- Wash in water 8- Dehydrate 9- Clearing in Xylol then Mounting  Types of Stains Main stain: Hematoxylin & Eosin (H&E) stain  Hematoxylin: Basic Stain, blue in color It stains structures acidic in reaction (DNA&RNA) Those structures called basophilic structures  Eosin: Acidic Stain, pink in color It stains structures basic in reaction Those structures called acidophilic structures  Other types o stains Special stain Histo-chemical stain Immuno-histo-chemical stain Vital stain Supravital stain Metachromatic stain