Histology And Its Method Of Study PDF

HISTOLOGY AND ITS METHOD OF STUDY ERYL AIRA D. MUAN, RMT, MD WHAT IS HISTOLOGY? The study of the microscopic structure of tissues. “Histo” – Greek root means “tissue” or “web” Provides insight into how tissues and organs function and relate to diseases Basic Concepts in Histology Level...

HISTOLOGY AND ITS METHOD OF STUDY ERYL AIRA D. MUAN, RMT, MD WHAT IS HISTOLOGY? The study of the microscopic structure of tissues. “Histo” – Greek root means “tissue” or “web” Provides insight into how tissues and organs function and relate to diseases Basic Concepts in Histology Level of structural organization: Chemical – Cells – Tissues – Organs – Organ System – Organism Basic Concepts in Histology Tissue is a group of cells that performs a specific function Four main types of tissue make up the human body Basic Concepts in Histology Epithelial Tissue – form coverings, linings and glands Connective Tissue – protection and support Muscle Tissue – provides movement Nervous Tissue – allows communication Preparing Tissues for Examination Tissues must be carefully prepared for examination Multiple factors influence the appearance of a tissue Plane of section Stain used during preparation Planes Influence Appearance Same structure may appear differently depending on the plane of the section Sagittal plane Transverse plane Oblique plane Basic Steps used in tissue preparation for Histology Fixation Small pieces of tissue are placed in chemical solutions (fixatives) that preserve cell and tissue structure by cross-linking proteins and inactivating degradative enzymes. Formalin: one of the best fixatives Dehydration Tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100%, which removes all water. Clearing Alcohol is removed in organic solvents in which both alcohol and paraffin are miscible. Infiltration Tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance. In an oven with temperature of 52-60 C Embedding Paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden NOTE Similar steps are used in preparing tissue for transmission electron microscopy, except special fixatives and dehydrating solutions are used with smaller tissue samples and embedding involves epoxy resins which become harder than paraffin to allow very thin sectioning. Basic Steps used in tissue preparation for Histology Trimming Resulting paraffin block is trimmed to expose the tissue for sectioning (slicing) on a microtome for light microscopy. Tissues Placed on Slides Thin slices of tissue are placed on slides Tissues are Stained for Examination Many tissues are stained prior to examination Common Stains and Their Uses Hematoxylin: stains nuclei blue Eosin: stains cytoplasm and extracellular matrix pink Special stains: Periodic acid-shiff (PAS), Masson’s Trichome, etc Results of Various Stains Tissues may have different appearances and colors depending on the stain used MICROSCOPE “to see small” First primitive microscope was created in 1595 Light Microscopy Bright-field Microscopy: stained preparations are examined by means of ordinary light that passes through the specimen. Microscope is composed of mechanical and optical parts. Bright-field Microscopy Optical system has 3 sets of lenses: Condenser: collects & focuses light, producing a cone of light that illuminates the tissue slide on the stage Objective lenses: enlarge and project the illuminated image of the object in the direction of the eyepiece. Eyepiece/s: further magnify the image to another X10 and projects onto viewer’s retina This Photo by Unknown Author is licensed under CC BY-SA-NC Bright-field Microscopy Objectives have three different magnifications: X4 : low magnification of large area X10: medium magnification of smaller field X40: high magnification of more detailed areas Light Microscopy Fluorescence Microscopy: tissue sections are usually irradiated with UV light; Acridine orange (stain) Phase-Contrast Microscopy: uses a lens system that produces visible images from transparent objects Differential Interference Microscopy: produces image with a more apparent 3D aspect Polarizing Microscopy: allows recognition of structures made of highly organized molecules. Confocal Microscopy: uses small point of high intensity light provided by a laser Electron Microscopy Transmission Electron Microscopy: provides high- resolution images of internal cell structures Scanning Electron Microscopy: shows detailed 3D images of cell surfaces Clinical Applications of Histology Histochemistry: uses chemical reactions to visualize cell components Biopsy: removal of tissue for microscopic examination; detect cancer Cytology: study of individual cells from tissues; Pap smear LABORATORY EXERCISE NO. 1: The Microscope I. Parts of the microscope and function II. Magnification III.Inversion Phenomenon – “e” IV.Caring for the Microscope