General Introduction Flashcards
(19 cards)
What is histology?
Histology is the study of the tissues of the body and how they are arranged to constitute organs
What are the two interacting components of tissues?
Cells and extra cellular matrix
What is extra cellular matrix?
Extra-cellular matrix (ECM) is the area between two cells
What are the functions of the ECM?
- Surrounds the cell
- Provides mechanical support
- Controls the flow of nutrients and signals to the cells
What is the ECM composed of?
Fibrous: collagen, elastin, fibronectin, laminin and non-fibrous: proteoglycans and polysaccharides
Why is histology dependent on the use of microscopes and other molecular methods of study?
Because of the small size of the cells and matrix components
Why are tissues sliced?
Because most tissues and organs are too thick for light to pass through them, so they must be sliced to obtain thin, translucent sections that are attached to glass slides for microscopic examination
What is the name of the instrument used to slice tissues?
A microtome
What are the steps of tissue preparation?
- Fixation: small pieces of tissue are placed in solutions of chemicals that preserve by cross-linking proteins and inactivating degradative enzymes
- Dehydration: the tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in 100%, which removes all the water
- Clearing: alcohol is removed in toluene or other agents in which both alcohol and paraffin are miscible
- Infiltration: the tissue is then placed in melted paraffin until it becomes completely infiltrated with this substance
- Embedding: the paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden
What are the fixatives used in tissue preparation?
- Formalin- buffered isotonic solution of 37% formaldehyde
- formaldehyde
- glutaraldehyde
- osmium tetroxide (preserve lipid and proteins)
What cell components are stained with basic dyes and why?
Anionic components such as nucleic acids are stained more readily with basic dyes because they have a net negative charge. They are called basophilic
What cell components are stained with acidic dyes and why?
Cationic components such as proteins with many iodized amino groups. They are termed acidophilic
What are some examples of basic dyes?
Toluidine blue, alcian blue, methylene blue and hematoxylin
What are some examples of acidic dyes?
Eosin, orange G and acid fuchsin
What are some of the organelles stained by basic dyes?
DNA, RNA and glycosaminoglycans
What are some of the organelles stained by acidic dyes?
Mitochondria, secretory granules and collagen
What is the most common stain in histology?
Hematoxylin and Eosin (H&E) stain. Hematoxylin stains acidic structures dark blue or purple and eosin stains basic structures a pink or red color.
What are some special stains in histology?
PAS (Periodic Acid Schiff Stain) which stains DNA, glycogen, glycoproteins, glycosaminoglycans, proteoglycans and colloids a pink color.
Alcian blue stain which stains glycosaminoglycans and polysaccharides a blue color.
Prussian blue stain which identifies iron storage diseases, hemochromatosis and hemosiderosis.
What is a biopsy?
A biopsy is a tissue sample that is removed during surgery or routine medical procedures. They are fixed in vials of formalin for later processing and microscopic analysis in a pathological lab.
If the results of the analyses are needed before the procedure is over, a more rapid process involving freezing the biopsy with liquid nitrogen is used.
