Review Questions Histology

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14301056040 Review Questions Slide 1 (Due 15-09-08)

Q1. How is the H&E staining method applied in study of histology? A1. The H&E staining method is used as a research method in studying cells. The H stands for hematoxylin, while the E stains for eosin. In order to study the cells, tissues must be prepared by staining because most cells and extracellular material are completely colorless. Staining methods help to make the tissue components conspicuous and also allow us to see the distinctions between different types of components. Hematoxylin is an example of a basic dye, while eosin is an example of an acidic dye. Dyes stain tissue components selectively. Cell components that have a net negative charge/anionic stain more readily with basic dyes, thus are called basophilic. On the other hand, cell components that have a net positive charge/cationic stain more readily with acidic dyes, thus are called acidophilic. Hematoxylin produces a dark blue or purple color, while eosin produces a reddish/pink color. Basophilic components: nucleic acids (e.g. nucleus, RNA rich portion of the cytoplasm, matrix of the cartilage) Acidophilic components: cytoplasmic components and collagen Q2. What are the features of electron microscopy? How to apply it? A2. Electron microscopy utilizes the interaction of tissue components with beams of electrons. Since the wavelength in the electron beam is much shorter than that of the light beam, the resolution of the image seen is greater. There are two types of electron microscopy: (1) Transmission Electron Microscopy (TEM) and (2) Scanning Electron Microscopy (SEM). Transmission Electron Microscopy or TEM is used for observing the details of cells, tissues, and organs – mainly the organelles. Scanning Electron Microscopy (SEM) is used for observing the pseudo 3D views of the surface of cells, tissues, and organs. Examples include bulges, microvillum, cilium, secretion and phagocytosis of cells. In order to view cells using electron microscopy, prepare the tissues in steps similar to how you would prepare tissues view under light microscopy. Note that differences exist in the type of fixatives, dehydrating solutions and embedding used to allow thin sectioning.

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14301056040 Review Questions Slide 2 (Due 15-09-08)

Q1. What are the common features of epithelial tissue? A1. Common features of epithelial tissue include: - Sheet-like structure surrounding free surfaces of body or cavity - Polar: apical, basal, lateral - More cells bound tightly together structurally and functionally with little ECM - Rest on basement membrane underlying CT - No blood vessels, rich nerve endings - Functions: protecting surfaces* (main function), absorption or transcytosis, secretion, contractility, sensory Q2. How to classify the various types of epithelia? A2. The various types of epithelia are divided arbitrarily into two groups: covering (or lining) epithelia and secretory (glandular) epithelia. It is important to note that some lining epithelia also secrete and that some glandular cells are located amongst the lining cells. The principles of the classification of the lining epithelia are based on the number of layers or thickness and the shape or height of the cells.  Layer/thickness o One layer: simple o More than one: stratified  Shape/height o Flattened: squamous o Cube: cuboidal o Tall pillar shape: columnar Classification: Simple o Squamous o Cuboidal o Columnar Pseudo stratified - all cells rest on the cell basement membrane (difference between 2 and 3) Stratified o Squamous (very thick)  keratinised (dry)  non-keratinised (moist) o Transitional (vary in thickness) Q3. Why is it called endothelia or mesothelia? A3. Both endothelium and mesothelium are tissues composed of simple squamous epithelial cells. The difference in the terminology is due to the place the cells are in. Endothelium is a simple squamous epithelial tissue that lines blood vessels. Mesothelium is a simple squamous epithelial tissue that surrounds the outside of our visceral organs.

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14301056040

Q4. How many specializations have you learned? What are the features in structure and function? A4. The different polarization surfaces of the epithelium allows for different specialized projecting structures. Apical membrane: for absorption and secretion  Microvilli/stereocillia (extremely long microvilli): o Increase surface area of absorption o Contains microfilament that aids in movement of microvilli for efficiency  Cilia/flagellum: o Rapid back and forth movements Basal membrane: for adhesion to tissue beneath and transport  Hemidesmosomes o Adhesive structures o Resemble half of a desmosome o Contain abundant integrins rather than cadherins  Basement membrane/basal lamina o For movement and differentiation of epithelium o Made from collage and glycoprotein o Lies between the epithelium and connective tissue o Has three layers: clear layer, dense layer and reticular lamina  Plasma membrane infoldings o Infoldings of the basal membrane o Mitochondria are more longitudinal to assist active transport of water and electrolytes across basal membrane Lateral membrane  Lateral interdigitations  Types: o Seals:  Tight junction/zonula occluden:  To ensure transcellular (through) movement of materials rather than paracellular (between).  Most apical  Sealing strands are transmembrane proteins known as claudin and occludin o Adhesion:  Zonula adherens:  Firmly adhering the cells to its neighbors by cadherins and Ca2+  Located below the zonula occludens  Macula densa/desmosomes  Firm adhesion  A single spot weld and has no belt formed around the cell

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14301056040 o Cell Communication:  Gap junction  For communication between cells  Circular patched formed by a complex transmembrane protein known as connexons  Each connexon is made up of 6 connexins  Present almost everywhere

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