Histology Lecture 1 (PMS 2022-2023) PDF

HISTOLOGY AND ITS METHODS OF STUDY Lecture 1 In Block PMS-102 Ass. Prof. Dr. Safaa Said Department of Histology &Cell Biology Assuit University  After this lecture, students sho...

HISTOLOGY AND ITS METHODS OF STUDY Lecture 1 In Block PMS-102 Ass. Prof. Dr. Safaa Said Department of Histology &Cell Biology Assuit University  After this lecture, students should be able to: ▪ Define histology ▪ Identify the methods of studying cells and tissues. Learning objectives ▪ Recognize the light and electron microscopes.. ▪ Know the cell and tissue culture.  *Tissues have two interacting components: cells and extracellular matrix (ECM). Histology is the study of the microscopic structure of cells, Cytology is the science which deals with the tissues and organs of the body, with the focus on how cells' structure, function and molecular construction of structure and arrangement optimize functions specific to the cell with the use of microscopes and various each organ. techniques. CYTOLOGY CYTOLOGY  Methods of Studying Cells and Tissues *The small size of cells and ECM components makes histology dependent on the use of microscopes. *Because most tissues and organs are too thick for light to pass through, it is difficult to study tissues directly by the microscope. *Thin tissue sections must be prepared for light microscopic examination (L.M.) of the tissue. Basic steps of tissue preparation for microscopy  Examples of tissue sections prepared for microscopic examination: A) Paraffin sections: The fixed tissue is embedded in melted paraffin wax (52ͦ -60ͦ). This makes the tissue hard enough to be cut into thin sections. This is the most common type of tissue sections for L.M. However, in this procedure, the tissue is exposed to high temperature which dissolves cell lipids and inactivates most sensitive tissue enzymes. ) Frozen sections: It is a much more rapid processing method for L.M. Frozen sections are effective in histochemical The tissue is rapidly frozen in liquid studies of very sensitive enzymes or lipids nitrogen (-195ͦ C), preserving cell because freezing preserves cell enzymes and structures and hardening the tissue. lipids.  C) Plastic sections: It is used to prepare very thin plastic-embedded tissue sections for electron microscopic examination  Most cells and ECM components are colorless and to be studied microscopically, tissue sections Staining must be stained. Staining methods make various tissue components from one another when examined by the microscope  *The types of staining methods : 1.General histological methods: one dye may stain various structures; e. g. haematoxylin stains the nucleus and other structures in the cytoplasm. -Hematoxylin is a basic dye which stains acidic cell components such as nucleic acids (DNA & RNA). The cell components which have an affinity for basic dyes are termed basophilic. -Eosin is an acidic dye which stains basic cell components such as most cytoplasm proteins (e.g. mitochondria). The cell components which have an affinity for acidic dyes are termed acidophilic..Specific (special) histological methods: one dye stains only one structure or substance e.g., orcein stains only elastic fibers. 3.Vital staining methods: are those which enter cells either by diffusion or by phagocytosis and stain cellular components without harming the cell. This makes it possible to study living cells. 4.Histochemical and cytochemical methods: a definite substance such as fat or enzyme is identified and localized in cells or tissues by using either physical or chemical procedures on histological sections (usually frozen sections) a) Chemical methods e.g. identification of glycogen by using the periodic acid schiff (P.A.S) b) Physical methods due to certain physical properties of these substances e.g., fluorescent substances (vitamin A) can be seen directly.  Microscopes *The microscope is an instrument having magnifying lenses for inspecting objects too small to be seen by the human eyes. Any microscope serves two main functions, namely resolution and magnification.  Resolution :. It is the power of the microscope to distinguish fine details. -The limit of resolution (or the resolving power) It is defined as the smallest diameter of an object below which it cannot be seen at all with the microscope. The limit of resolution of the human eye is 0.1 mm. The limit of resolution of the light microscope is 0.2 um The limit of resolution of the electron microscope is 0.2 nm 1mm Magnification : It is the increase in the linear dimensions of an object without resulting in any optical defects. *Ordinary L.M. is based on the passage of light through stained tissue sections. The maximal resolving power of L.M. is approximately 0.2 µm which allows clear images magnified 1000 times.  Electron microscopes Transmission electron microscope (a Electron microscopes (E.M.) type of E.M.) has resolving power as are based on the passage of little as 0.2 nm which allows clear beams of electrons through images magnified as much as 100, the tissue to study fine tissue 000 times. structures. Types of electron microscopes : 1. Ordinary transmission electron microscope (T E M). - High voltage E. M. (HVEM) is a subtype of transmission electron microscope with the following advantages: a) It is useful in examining thick sections (5 microns). In TEM much thinner sections 50 nanometer (nm) must be used. b) Studying living cells and objects. 2. Scanning electron microscope (SEM): it shows a three dimensional image. It is useful in studying details of surfaces (as cilia).  *Definition: is the maintenance and study of live cells and tissues outside the body in culture (in vitro). Cell and Tissue *Uses: 1. Cell culture allows the direct observation of living cells. Culture 2. Experiments which are technically impossible to perform in the body (invivo) can be accomplished in culture (in vitro). 3. In research on cell structure and function. 4. For genetic or chromosomal analyses. 5. To study molecular changes that occur in cancer. References: INTEGRATED SYSTEMS (PP. 55 Elsevier's Integrated &56), THE NERVOUS SYSTEM (PP. Histology (2007) 1st 32-36), Edition. BASIC HISTOLOGY (PP. 161-170).  Choose the correct answer Choose the correct answer: 1. ……………… is based on the passage of electron beams through the tissue: a- Light microscope. QUIZ b- Electron microscope. c- Acidic stains. d- Cell culture. 2. To study chromosomal analyses, we use: a- Periodic acid-Schiff reaction. b- In vivo studies. c- Cell culture. d- Sudan black stain.