Histology Lecture Notes PDF

 What is Histology? The name "Histology" is derived from Greek: "Histos“: tissue "logos" : the study of Histology: the study of tissues Histology ???! Examining a thin slice (section) of tissue under a light microscope or electron microscope...

 What is Histology? The name "Histology" is derived from Greek: "Histos“: tissue "logos" : the study of Histology: the study of tissues Histology ???! Examining a thin slice (section) of tissue under a light microscope or electron microscope Enhanced by using different histological stains System  Cytosol  Organelles  Inclusions  Cytoskeleton A group of similar cells that are specialized to perform a specific function (Covering/lining) (support) (movement) (conducting nerve impulses) Primary tissue types  Light Microscopy With a maximum Electron Microscopy With a maximum magnification power of magnification power of x 1000 times x 1000000 times Microtechniques Definition : preparation of the tissue for microscopic study. Methods: 1- paraffin method 2- freezing Basic Preparation Techniques of histological sections Fixation Processing (fixation, dehydration, clearing, and infiltration) Embedding Cutting/sectioning Staining Mounting Fixation Aim – to preserve tissues in a “life-like state’’ and prevent autolysis and putrefaction. Simple : formaldehyde, alcohol, acetic acid, osmic acid, picric acid Complex : Bouin’s fluid, Zenker’s fluid, special mixtures 10 % formaldehyde is the cheapest and easiest fixative Dehydration Aim :to remove water from the sample to allow paraffin impregnation Done by passing tissue sample through gradually increasing concentrations of alcohol to avoid tissue shrinkage 50% 70% 80% 90% Absolute  Clearing Aim – to take the alcohol out of the sample to allow paraffin to impregnate the tissue The tissue is immersed in xylene (xylol) that is miscible both in the dehydrating and the embedding agent The name of the process come from the clear appearance the sample gets Infiltration (impregnation with soft paraffin) Aim – to immerse the sample in a material that allow easy cutting The melted paraffin is allowed to penetrate the tissue and to replace the xylol 15 min in the oven Embedding in hard paraffin The tissue with the melted paraffin is placed into mould then cooled down to harden. The result is hard block of paraffin wax containing the tissue. Sectioning Aim – to cut the sample in thin slices (4 and 10 µm) by the microtome for microscopic examination. The section is transferred to a glass slide Microtome Staining Aim – to add color to the structures of the sample in order to differentiate them There are several types of staining Every stain has a different procedure Most common, easiest to use & cheapest stain is hematoxylin and eosin (H and E)  Hematoxylin and Eosin (H & E) Routine H & E stains are universally used for routine histological examination of tissue sections. stain Hematoxylin is a basic dye that stains acidic components of cells a blue (basophilia) Stains the nuclei& ribosomes of cells Eosin is an acidic dye that stains the basic components of cells reddish-pink (acidophilia) Most of cytoplasm of cells is stained by eosin  Periodic acid-Schiff (PAS) stains polysaccharides (Glycogen) Masson's Trichrome stains Collagen Sudan black and Oil Red stains lipids Mounting Aim – to put the final sample in a medium where it is protected and can also be observed under the microscope The sample is dehydrated again A drop of mounting agent with a similar refractive index to that of glass is placed on the glass slide, and covered with a glass coverslip is added 1-Which embedding medium is the most common? A. Agar B. Resin C. Gelatin D. Paraffin 2-How thick are usually slices of the sample which are being glued on the underlying slide? (note: Assume light microscopy only.) A. 1 - 30 nm B. 1 - 20 μm C. 50 - 100 μm D. 4 - 10 μm 3-Electron Microscope can give a magnification up to ___________ a) 50 X b) 100X c) 500X d) 1000,000X 4. What is the usual magnification of the light microscope? a. 1X b. 10X c. 50X d. 1000X 5- What is “simple microscope"? A. Microscope with a single lens B. Microscope with two lenses C. Microscope with three lenses D. None of the above 6. In histology, using of xylene makes the tissue A. Clear B. Dehydrated C. Fixed D. Degenerated 7. All are compound fixatives except A. Formalin B. Bouin’s fluid, C. Zenker’s fluid D. None of the above 8- Which basic (routine) staining technique is used the most often? A. PAS B. Sudan blue C. Masson's trichrome D. Hematoxylin - eosin 9- Dyes of Sudan group are usually used as a staining for: A. Polysacharides B. Nucleid acids C. Proteins D. Lipids 10-What does it mean mounting of the slide? A. Final gluing of the covering slide B. Dehydration C. Embedding in paraffin D. Clearing 11-Which is common color of nuclei after staining with H&E? A. Grey B. Pink C. Green D. Blue 12-Which structure is the best example of a basophilic structure? A. Ribosomes B. Mitochondria C. Lipid droplets D. Golgi apparatus 13. Why is embedding of fixed sample important? A. increases hardness without fragility B. increases sample durability C. samples can be easily stored D. All of the above 14. How is removed the water out of tissues during common histological processing A. with xylene B. with acetone C. with benzene D. with ethanol 15-The common color of nuclei after staining with H&E is red. 16- PAS is a routine stain 17- H&E is used “routinely” with all tissue specimens 18-Xylene is used in the histology lab as a clearing agent 19- Formaldehyde is the cheapest and commonest among the known fixatives 20-Ethanol is used to remove the water out of tissues during common histological processing