Lecture 1 (H) PDF (Histology and Tissue Classification)

Unified Lecture 1 Introduction to Histology and Classification of Tissue HIHD-211 TERM-3 Basic Science Department COSHP, KSAU-HS, KSA Learning Outcomes By the end of this lecture the student must be able to: 1. Define histology and its importance in medicine. 2. Recognize some historical notes about...

Unified Lecture 1 Introduction to Histology and Classification of Tissue HIHD-211 TERM-3 Basic Science Department COSHP, KSAU-HS, KSA Learning Outcomes By the end of this lecture the student must be able to: 1. Define histology and its importance in medicine. 2. Recognize some historical notes about light microscope and their functions in histology. 3. Explain methods for tissue processing and staining. 4. Classify the tissues of the human body. Define histology & its importance in medicine ▪ ▪ ▪ ▪ ▪ Histology is scientific study of the microscopic structures (Tissues) of animals and plants. Histology includes both procedures used to prepare the tissues for observation and the actual process of examining the tissues under the microscope. Knowing the normal histological features of different tissues is necessary for the recognition of diseases which manifest themselves at the cellular level. Study of abnormal (diseased) tissues and cells is called histopathology. Information from histopathology can be understood and used only if the normal histological features of cells and tissues are well understood. LO-1 Recognize some historical notes about light microscope and their functions in histology ▪ The use of single convex lens for magnification of objects has been known for centuries. This type of microscopy (where only one lens is used) is called simple microscope. ▪ Using two lenses in a tube with certain distance between them can magnify the objects much more than a single lens. This type of microscopy was called a compound microscope. ▪ Compound microscope is a light microscope that has two converging lens systems: the objective lens and the eyepiece lens. LO-2 Simple microscope Compound microscope Recognize some historical notes about light microscope and their functions in histology ▪ A light microscopes include almost all compound microscopes ▪ Monocular Microscope is a light (compound) microscope with single optical lens ▪ Binocular microscope is a light (compound) microscope with two optical lenses adapted to the use of both eyes LO-2 Monocular Binocular Units used in histology LO-2 ▪ One millimeter has 1000 micrometer ▪ One micrometer has 1000 nanometer ▪ One nanometer has 1000 picometer Magnification and resolution ▪ The magnification of a microscope is not the only factor which is important when examining cells. The details (resolution) that can be seen are also important. So, what are the differences between magnification and resolution? Magnification: ▪ Magnification is the ability to view an object as larger ▪ When your image is magnified by 40x diameters, this means that both width and length of the specimen image is magnified by 40 times. LO-2 Magnification and resolution Resolution: ▪ It is the ability to recognize two very close bodies as separate bodies ▪ It is the capacity of an optical system to reveal the details in a specimen ▪ Resolving power is the ability to measure the separation of images that are close together ▪ A lens system with resolving power 1.0 µm is better than a lens system with resolving power of 2.0 µm ▪ Resolution power of human eye is 0.2 mm (200 µm) ▪ Resolution power of light microscope is 0.2 µm (200nm) ▪ Resolution power of Transmission electron microscope is 1.0 nm LO-2 A light microscope is composed of: 9 LO-2 Methods of light microscopy ▪ The specimen is set on the stage ▪ Light shines up through the specimen from a bulb (source) beneath the stage ▪ Condenser of the microscope focus the light from the source on the specimen where it is modified ▪ The modified light pass to objective lens ▪ An image is formed in the focal plane of objective lens ▪ The eye piece lens magnifies the image that is seen by eyes LO-2 Permanent histology tissue slide ▪ ▪ ▪ ▪ ▪ Permanent histology slide is an extremely thin (5-15 um) slice of tissue, laid flat on, adhered to a glass slide, stained, and covered with mounting medium and cover slip (same refractive index) A permanent histology tissue slide could be used/preserved for long time Most common stain used for the preparation of the histology slides is Hematoxylin and Eosin (H&E) Hematoxylin is a basic dye with purple color, it has affinity for acidic structures like DNA and RNA Eosin is an acidic dye with pink color, it has affinity for basic structures like cytoplasmic components and extracellular fibers. LO-3 Steps in making permanent histology slides LO-3 1. Isolation of tissue 2. Fixation 3. Embedding 4. Cutting/sectioning 5. Staining Fixation Fixation is procedure in which cells and tissue constituents are preserved or stabilized in a condition identical to that existing during life The fixation: ▪ terminate cell metabolism ▪ prevent enzymatic degradation of cells and tissues by autolysis (self-digestion) ▪ kill pathogenic microorganisms such as bacteria, fungi, and viruses ▪ harden the tissue as a result of either cross-linking or denaturing protein molecules ▪ Commonly used fixatives are formalin, formaldehyde, glutaraldehyde, alcohol etcetera LO-3 Embedding ▪ ▪ ▪ ▪ The tissue specimen is infiltrated with embedding medium that allows for easy sectioning and preserve morphology Before embedding, water is removed from the fixed tissue by a process called dehydration. It is achieved by immersing tissues in ascending series of alcohol like 70%, 95%, 100%, 100% To remove the alcohol and to make the specimen transparent, it is immersed in organic solvent like xylene which is miscible with paraffin. This step is called clearing Following clearing, the specimen is infiltrated with melted paraffin and embedded in blocks of appropriated size and shape LO-3 Tissue embedding unit Sectioning ▪ ▪ The paraffin embedded block of a specimen is mounted on a specially designed machine, the microtome, and is cut in to slices of 5- 15 um thickness To flatten, the tissue sections are allowed to float in hot water bath and taken on gelatin coated glass slides LO-3 Staining ▪ ▪ The tissue sections are stained to study the details of the cell/tissue/organ The staining is done to: ▪ ▪ ▪ ▪ ▪ LO-3 Increases visibility of specimen Accentuate specific morphological features Preserves specimens Most common stain used in the light microscopy is the Hematoxylin & Eosin (H&E) Special stains are used to identify certain chemical substance or characteristic features Artifacts in histologic slides ▪ During histologic slide preparation an artifact (an error in the preparation process) may be introduced ▪ In general, artifacts that appear on the finished glass slide are linked to methodology, equipment, or reagents used during preparation ▪ It is important for students to recognize that not every slide in their slide collection is perfect and that they should be familiar with the most common artifacts found on their slides 17 LO-3 What is a tissue? A group of cells which are similar in functions It consists of three components: 1. Cells (fibrocysts, chondrocytes, etc.) 2. Extracellular substances (collagen, calcium salts) 3. Tissue fluid (Important for nourishment and waste disposal) LO-4 18 Classification of tissues There are 4 basic tissues in the body: 1. Epithelium covering the surface of body and lining the cavities and forming the parenchyma (functionally specialized cells) of the glands 2. Connective Tissue supports, connects, separates different types of tissues and organs of the body and act as a vehicle 3. Muscle is type of contractile tissue and by the virtue of contraction it brings about the movements 4. Nerve tissue Is a type of excitable tissue and conducts the electrical impulses LO-4 Thank you 20