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HISTOLOGY: DON'T SWITCH OFF! Histology is a central biological and medical science Histology is the study of the structure of the biological material and the ways in which individual components are structurally and functionally related.

It is central to the biological and medical sciences since it stands at the crossroads between biochemistry, molecular biology and physiology on the one side, and disease processes and their effects on the other.

Samples can be obtained from areas of the body in quick, safe and painless techniques.

Histology was once empirical The study of histology began with the development of simple microscopes and techniques for preparing thin slices of biological material to make them suitable for examination. Despire their simple equipment, early histologists learnt a surprising amount about the structure of biological material.

Cellulare theory of the structure of living organisms that established the cell as the basic building block of most biological material.

Histology was developed on light microscopic analysis of cells accompanied by a limited understand of cell physiology and function. Collections of cells having similar morphological characteristis were described as forming tissues and these were subdivided into: epithelial tissues describe cells that cover surfaces, muscular tissues describe cells with contractile properties, nervous tissues describe cells forming the brain, spinal cord and nerves and connective tissue which describes cells that produce extracellular matrix and serv to link or support other specialized tissues by forming tendons, bones or fatty tissue.

Modern Histology is a Precise Science Techniques have revolutionized our understanding of cells. The techniques of protein sequencing, molecular genetics and cloning of cells have given insight into the working of cells.

Cells vary considerably. Molecular biology has shown that cells are diverse, mophological appearance can be grouped together because of common functional attributes of interactions. Some cells are adaptable.

Cells are now classified according to function.

Groupings involve: ephithelial cells, supporting cells, contractile cells, nerve cells, germ cells, blood cells, immune cells and hormone secreting cells.

It is important to recognize that a cell may have several functions and be a member of more than one cell class. For example: Many of the hormone producing cells, are also epithelial in type. Many immune cells are also blood cells. Some support cells are also contractile.

Tissues are functional arrangements of cells.

A tissue is an assembly of cells that are arranged in a regular formation. Simple and compound tissues are useful in descriptive histology.

Support cells, not connective tissue "Connective tissue" is used historically to describe a wide range of living material containing cells associated with a dominant extracellular matrix component, who the oretical function was to act as a supporting stroma service more highly specialized cell types. The concept of support cells is used to emphasize the importance of interactions between extracellular matrix and cells.

Cells form organs and systems An organ is an anatomically distinct group of tissues, usually of several types which perform specific functions. The term system has two uses: describing cells with similar function but widely distributed in several anatomical sites. (example: specialized hormone producing cells scattered in the gut and lung) System also describes a group of organs which have similar or related functional roles. (example: the tongue) Cell histology is aligned to cell biology A clear understanding of the fine structure and molecular organization of cells greatly improves comprehension of biochemical and physiological processes. The overlap between structure, physiology and biochemistry is now called cell biology.

Systems Histology is aligned to anatomy Histology is essential for understanding pathology Pathology accounts for nearly half of the study required by medical practitioners irrespective of their specialization. Pathology is taught at a later stage than histology.

Techniques used in histology and cell biology Light microscopy uses thin sections of tissue to study cell morphology.

Tissue is immersed into a preservative solution (fixative). The tissue is then embedded into a firm medium for cutting into thing sections. The tissue is then cut into sections with a microtome. To see cellular details, sections are placed in dyes that stain the structure.

Transmission electron microscopy Use of an electron beam instead of light allows resolution of structures as small as 1 nm in well prepared tissues.

Scanning Electron microscopy This uses solid pieces of tissue rather than sections and allows the perception of three-dimensional views of the surface of cells or tissues. A small piece of tissue is dried and coated in gold. An electron beam then scans the specimen and electrons produced from the surface are used to reconstruct a fine 3D representation of the surface.

Histochemistry Certain dyes have affinity for specific chemical groups in molecules and these are used to localize substances in histological preparations.

Autoradiography If tissues are provided with radioactively labelled metabolites, cells which take up the metabolite can be detected by dipping sections in a photographic emulsion and allowing the radioactivity to create silver grains in the emulsion.

Immunocytochemistry This uses antibodies to specific cell molecules to detect their presence in tissue sections.

Cell culture Cells may be grown in artificial media and this has facilitated analysis of structural and functional attributes of cells, particularly analysis of cell metabolism.

Cell fractionation This technique allows whole cells to be disrupted in a controlled manner. The different particles which result are then separated for functional or structural analysis.