Histology known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visible without a microscope. Although one may divide microscopic anatomy into organology, the study of organs, the study of tissues, cytology, the study of cells, modern usage places these topics under the field of histology. In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue. In the field of paleontology, the term paleohistology refers to the histology of fossil organisms. There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, epithelial tissue. All animal tissues are considered to be subtypes of these four principal tissue types. For plants, the study of their tissues falls under the field of plant anatomy, with the following four main types: Dermal tissue Vascular tissue Ground tissue Meristematic tissue Histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue.
It is an important part of anatomical pathology and surgical pathology, as accurate diagnosis of cancer and other diseases requires histopathological examination of tissue samples. Trained physicians licensed pathologists, perform histopathological examination and provide diagnostic information based on their observations; the field of histology that includes the preparation of tissues for microscopic examination is known as histotechnology. Job titles for the trained personnel who prepare histological specimens for examination are numerous and include histotechnicians, histotechnologists, histology technicians and technologists, medical laboratory technicians, biomedical scientists. Most histological samples need preparation before microscopic observation. Chemical fixatives are used to maintain the structure of tissues and cells. Fixatives preserve tissues by irreversibly cross-linking proteins; the most used fixative for light microscopy is 10% neutral buffered formalin, or NBF. For electron microscopy, the most used fixative is glutaraldehyde as a 2.5% solution in phosphate buffered saline.
Other fixatives used for electron microscopy are uranyl acetate. The main action of these aldehyde fixatives is to cross-link amino groups in proteins through the formation of methylene bridges, in the case of formaldehyde, or by C5H10 cross-links in the case of glutaraldehyde; this process, while preserving the structural integrity of the cells and tissue can damage the biological functionality of proteins enzymes. Formalin fixation leads to degradation of mRNA, miRNA, DNA as well as denaturation and modification of proteins in tissues; however and analysis of nucleic acids and proteins from formalin-fixed, paraffin-embedded tissues is possible using appropriate protocols. Selection is the choice of relevant tissue in cases where it is not necessary to put the entire original tissue mass through further processing; the remainder may remain fixated in case it needs to be examined at a time. Trimming is the cutting of tissue samples in order to expose the relevant surfaces for sectioning, it creates tissue samples of appropriate size to fit into cassettes.
Tissues are embedded in a harder medium both as a support and to allow the cutting of thin tissue slices. In general, water must first be removed from tissues and replaced with a medium that either solidifies directly, or with an intermediary fluid, miscible with the embedding media. For light microscopy, paraffin wax is the most used embedding material. Paraffin is immiscible with water, the main constituent of biological tissue, so it must first be removed in a series of dehydration steps. Samples are transferred through a series of progressively more concentrated ethanol baths, up to 100% ethanol to remove remaining traces of water. Dehydration is followed by a clearing agent which removes the alcohol and is miscible with the wax melted paraffin wax is added to replace the xylene and infiltrate the tissue. In most histology, or histopathology laboratories the dehydration and wax infiltration are carried out in tissue processors which automate this process. Once infiltrated in paraffin, tissues are oriented in molds.
Paraffin wax does not always provide a sufficiently hard matrix for cutting thin sections. Paraffin wax may be too soft in relation to the tissue, the heat of the melted wax may alter the tissue in undesirable ways, or the dehydrating or clearing chemicals may harm the tissue. Alternatives to paraffin wax include, acrylic, gelatin and other types of waxes. In electron microscopy epoxy resins are the most employed embedding media, but acrylic resins are used where immunohistochemistry is required. For tissues to be cut in a frozen state, tissues are placed in a water-based embedding medium. Pre-frozen tissues are placed into molds with the liquid embedding material a water-
Tiffany Scott is an American figure skater. Scott was born in Massachusetts, she skated with Philip Dulebohn until 2005. They competed at the 2002 Olympic Games and won the pairs title at the 2003 U. S. Championships. In 2005, Dulebohn retired from competition and Scott teamed up with Rusty Fein. Dulebohn was one of the pair's coaches during their brief partnership. Scott and Fein finished 4th at their first and only U. S. Figure Skating Championships in 2006. Away from the ice, Scott married Brian Pryor in 2005. In May 2006, Scott announced her retirement from competitive skating. In March 2012, the couple had a son. In the 2007 film "Blades of Glory", Scott served. Tiffany Scott / Philip Dulebohn at the International Skating Union
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