Introduction To Histotechnology

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Introduction

Histology is the study of the tissues of the body and how these tissues are arranged to constitute organs. This subject involves all aspects of tissue biology, with the focus on how cells’ structure and arrangement optimize functions specific to each organ. 

Histology means the science of the tissues.

histos is greek for web or tissue

logia is greek for branch of learning 

Histotechnology is a medical laboratory specialty that is important in the detection, diagnosis,and treatment of diseases. The histotechnologist uses specific knowledge and technical skill to prepare human and animal tissues for microscopic examination by a pathologist. They work quickly with precision and accuracy to perform the necessary and complex procedures to process, embed,and then cut tissues sections. These thin sections are mounted on slides and stained for microscopic evaluation by pathologists.

Histotechnologists also help select,implement,and evaluate new procedures and instruments in the laboratory and performance maintenance on the equipment. 

Histopathology means the study of diseased tissue. The division of medical laboratory science was once referred to as morbid anatomy. At present, many workers prefer to call it “Cellular Pathology”. The Pathologist responsible for the diagnosis of diseased tissues is dependent On the technical skill of histotechnologist, who prepares microscopic slides of the specimen. Histopathology laboratory prepares tissue sections for establishing a histopathologic diagnosis.

Histopathology studies have proved to be one of the most effective means in diagnosing tissue abnormalities such as malignant and benign conditions. 

Cytology : Is the study of cells, is an integral part of histopathology, and in most histological Preparation, the components of individual cells are studied.

Exfoliative cytology: It is concerned with the detection of cancer. In which cells are shed (Exfoliated) spontaneously from the epithelial surfaces of the body The malignant cells diffuse into the Body fluids and secretions. The various specimens used for exfoliative cytology are sputum, vaginal Cervical and urine. The histopathological specimens are mostly collected by a surgeon in an operation theatre. 

Biopsy Means removal of tissue fragments from a living person.

Autopsy means "see for yourself". It is a special operation performed by physicians on the dead body. Its purpose is to learn the truth about the person's health during tides, and how the person really died. 

Fixation : After death or removal from the body, cell and tissue begin to undergo changes, which result in their breakdown and destruction. These are due to autolysis and Putrefaction. To event autolysis and Putrefaction immediately add into a fixative. Formaldehyde is a commonly used preservative.

Putrefaction means the breakdown of tissue by bacterial action, often with the formation of gas.

Autolysis in the lysis of cells by enzymes liberated as a result of rupture of the lysosome. Both the autolysis and Putrefaction follow rapidly upon death of the cell after removal from the body. 

Decalcification : Means removal of calcium from bone and other mineralized hard tissue in order to fulfill the process of cutting thin sections. Decalcification is done after fixation and before dehydration and paraffin infiltration. Most commonly decalcified fluids are formic acid, nitric acid. 

Dehydration: In this technique, water is completely removed from fixed tissue. The common. procedure is to treat the tissue with an increasing gradient of alcohol. e.g. 80%, 90% and 100%.

Clearning: Means removal of alcohol from the tissue. It is done with xylene. Since xylene is miscible in both paraffin wax and alcohol. It helps to replace alcohol and makes room for the paraffin during infiltration and impregnation. 

Impregnation : In this process xylene is eliminated from the tissue by diffusion in the surrounding molten wax. This procedure is carried out in the paraffin oven for 2-3 hours at 50 C to 56°C temperature.

Embedding : Embedding means casting or blocking. In embedding the impregnated tissue is placed in warm liquid paraffin, which forms a block after cooling 

Microtome : An instrument used for preparing thin slices of tissue, This instrument is designed to cut to 60 u thin section. The most common types are rocking microtome and rotary microtome.

Honing: Honing is done to remove all the nicks and to sharp the edges of the knife.

Stropping: Stropping is done for polishing the knife edss, The strop is usually made up of leather

Microtomy : It is a processing of section cutting. 

Adhesion: The process of placing the section on the slides so that it is not washed away during dehydration, staining. The most popular adhesive is egg albumin.

Mountants : Histological sections which need to be examined for any length of time or to be stored, must be mounted under a coverslip. The most commonly mounting media is DPX. 

Freezing Microtome: Is used for cutting frozen sections of a tissue. Unembedded soft specimens are generally cut in the frozen state, since the frozen condition of the specimen gives the necessary rigidity for cutting the section, in freezing microtome we use liquid carbon dioxide.

Cryostat: The best method of preparing sections from unfixed or fixed tissue is by use of a cryostat. This consists of a deep freeze cabinet, maintained at a temperature of approximately -15°C to-30°C, 

Mountants : Histological sections which need to be examined for any length of time or to be stored, must be mounted under a coverslip. The most commonly mounting media is DPX.

Laboratory Equipment for Histology and Cytology

● Microscope,

● Microtome knife and knife sharpener, 

● Constant temperature water bath,

● Flotation bath, 

● Paraffin bath 

● Timer,

● Oven,

● Bunsen burner, 

● Forceps,

● Scalpel,

● Dissecting set containers (bottles) for holding specimens.

Equipment for embedding and vacuum infiltration

● General glassware as any other laboratory (pipettes, beáker etc.) 

● Coplin staining dish

● Staining jar: vertical and horizontal, 

● Balsam bottle.

Accessories

● Labels

● Diamond pencil for marking glass slides

● Coverslips,

● Leukhart embedding boxes or "LS".

Reagents: A great number of histological procedures uses a variety of chemicals and reagents. These include fixatives, decalcifying solutions, embedding materials, stains, solvents clearing reagents, mounting media and a large number of miscellaneous solutions. All reagents and stains should be tested for proper reactivity before being put into regular use. In preparing various reagents, one should first read the label on the bottle for care and storage instructions and precisely follow the directions given in the method of their preparation. The boiling point of the solvents is important if certain limits are stated.

Reagents

1. Embedding material : Paraffin wax (melting point 50°d to 55°C)

2. Fixative: Formaldehyde,

3. Clearing Agent: Xylene

4. Mounting Medium : Permount and Canada Balsam

5. Decalcifiers : Formic acid, Nitric acid, Hydrochloric acid.

6. Stains : Haematoxylin, eosin, fast green FCF, light green, Sudan III, Malachite green. 

Reference

● Text Book Of Medical Laboratory Technology, P.B. Godkar and D.B. Godkar. Part-B, Page no. 991-996.

●      https://slideplayer.com/slide/17349189/

● https://www.slideshare.net/alubajessabeth/introduction-to-histology-59922568 

https://www.coursehero.com/file/68112157/HISTOPATHOLOGYdocx/

https://nios.ac.in/media/documents/dmlt/HC/Lesson-01.pdf

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