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BASIC HISTO 10-1

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Published on January 20, 2009

Author: lalballer08

Source: authorstream.com

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HISTOLOGY : HISTOLOGY Slide 5: The building blocks of life are cells. Cells form tissues, tissues form organs, organs form organ-systems, and organ-systems form an entire living and breathing organism. Slide 6: Cells are structural units that make up plants, animals and single cell organisms. The cells of single cell organisms are called prokaryotic cells (prokaryotes). A prokaryotic cell does not have a membrane around its nuclear region (for example a bacterium). It has a cell wall, plasma membrane, nucleoid (region of DNA), and cytoplasm with ribosomes. Slide 7: Cells that make up plants and animals are called eukaryotic cells (eukaryotes). This type of cell contains cell organelles. The parts that make up a eukaryotic cell are Golgi bodies (secretory systems), endoplasmic reticulum (transport system within the cell), nucleus, nucleolus, microtubule organizing centers (MTOC), mitochondria (the cell's powerhouses), ribosomes (small organelles that synthesize proteins), and a cell membrane. Slide 8: Tissues are groups of cells that lie together to accomplish a common function. They are the basic building blocks of organs. Tissues are divided into four groups (epithelial tissue, connective tissue, muscle tissue, and nervous tissue). These groups are further subdivided into many subgroups. As an example, the epithelial tissue is subdivided into covering and lining epithelia (outer layer of skin, inner surface of heart and blood vessels, inner surface of respiratory cavities, etc.) and glandular epithelia (most of the glands in the body). Slide 9: Histology is the study of tissue sectioned as a thin slice, using a microtome. It can be described as microscopic anatomy. Histology is an essential tool of biology. Slide 10: Histopathology, the microscopic study of diseased tissue, is an important tool of anatomical pathology since accurate diagnosis of cancer and other diseases usually requires histopathological examination of samples. Slide 11: Histochemistry refers to the science of using chemical reactions between laboratory chemicals and components within tissue. antibodies are used to specifically visualise proteins, carbohydrates and lipids: this is called immunohistochemistry. Technical procedure : Technical procedure Fixation Embedding Sectioning Staining Alternative techniques Slide 13: Fixation The tissues are mechanically and biochemically stabilized in a fixative. The most common fixative is buffered isotonic solution of 4% formaldehyde and glutaraldehyde. In case of double fixation osmium tetraoxide is used. Slide 14: Embedding Paraffin is used for light microscopy and resins are used for both light and elctron microscopy. Dehydration and clearing. The most common technique is wax embedding. The samples are immersed in multiple baths of progressively more concentrated ethanol to dehydrate the tissue, followed by a clearing agent such as, xylene or Histoclear, and finally hot molten paraffin wax (impregnation). Slide 15: During this 12 to 16 hour process, paraffin wax will replace the water: soft, moist tissues are turned into a hard paraffin block, which is then placed in a mould containing more molten wax (embedded) and allowed to cool and harden. Embedding can also be accomplished using frozen, non-fixed tissue in a freezing medium. This freezing medium is liquid at room temperature but when cooled will solidify. Slide 16: Sectioning The tissue is then sectioned into very thin (2 - 8 micrometer) sections using a microtome. These slices, usually thinner than the average cell, are then placed on a glass slide for staining. Frozen tissue embedded in a freezing medium is cut on a microtome in a cooled machine called a cryostat. Slide 17: Alternative techniques Alternative techniques include cryosection. The tissue is frozen and cut using a cryostat. Tissue staining methods are similar to those of wax sections. Plastic embedding is commonly used in the preparation of material for electron microscopy. Tissues are embedded in epoxy resin. Very thin sections (less than 0.1 micrometers) are cut using diamond or glass knives. The sections are stained with electron dense stains (uranium and lead) so that they can be seen with the electron microscope. Slide 18: Staining To see the tissue under a microscope, the sections are stained with one or more pigments. This is done to give contrast to the tissue being examined, as without staining it is very difficult to see differences in cell morphology. Hematoxylin and eosin (abbreviated H&E) are the most commonly used stains in histology and histopathology. Hematoxylin colors nuclei blue, eosin colors the cytoplasm pink. Other compounds used to color tissue sections include safranin, oil red, congo red, fast green FCF, silver salts and numerous natural and artificial dyes. Artifacts : Artifacts Artifacts are structures or features in tissue that interfere with normal histological examination. These are not always present in normal tissue and can come from outside sources. artifacts interfere with histology by changing the tissues appearance and hiding structures. These can be divided into two categories: Slide 20: Pre-histology These are features and structures that have being introduced prior to the collection of the tissues. A common example of these include: ink from tattoos and freckles (melanin) in skin samples. Post-histology Artifacts can result from tissue processing. Processing commonly lead to changes like shrinkage, color changes in different tissues types and alterations of the structures in the tissue. Because these are caused in a laboratory the majority of post histology artifacts can be avoided or removed after being discovered. A common example is mercury pigment left behind after using Bouin's fixative to fix a section. Histological classification of animal tissues : Histological classification of animal tissues There are four basic types of tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue. All tissue types are subtypes of these four basic tissue types (for example blood cells are classified as connective tissue since they generally originate inside bone marrow). Slide 22: Epithelium: the lining of glands, bowel, skin and some organs like the liver, lung, kidney, Endothelium: the lining of blood and lymphatic vessels, Mesothelium: the lining of pleural, peritoneal and pericardial spaces, Mesenchyme: the cells filling the spaces between the organs, including fat, muscle, bone, cartilage and tendon cells, Blood cells: the red and white blood cells, including those found in lymph nodes and spleen, Slide 23: Neurons: any of the conducting cells of the nervous system, Germ cells: reproductive cells, spermatozoa in men, oocytes in women, Placenta: an organ characteristic of true mammals during pregnancy, joining mother and offspring, providing endocrine secretion and selective exchange of soluble, but not particulate, blood borne substances through an apposition of uterine and trophoblastic vascularised parts, and Stem cells: cells able to turn into one or several of the above types. Microtome : Microtome A microtome is a mechanical instrument used to cut biological specimens into very thin segments for microscopic examination. Slide 26: tissues are hardened by replacing water with paraffin. The tissue is then cut in the microtome at thicknesses varying from 2 to 25 micrometers thick. From there the tissue can be mounted on a microscope slide, stained and examined using a light microscope laser microtome : laser microtome A recent development is the laser microtome, which cuts with a laser instead of a mechanical knife. This method is contact-free and does not require sample preparation techniques. The laser microtome has the ability to slice almost every tissue in its native state. Depending on the material, being processed, slice thicknesses of 10 to 100 µm are feasible.

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