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Structural Organization of the Human Body notes.doc

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Anatomy and Physiology
Jacqueline Carnegie

Structural Organization of the Human Bodytissues groups of cells that are similar in structure and perform a common or related function different types of tissue allow for specialization and specific functions allow for organization and efficiency in the body cell specialization allows the body to function in sophisticated ways and allows for division of labour division of labor has its hazards when a particular group of cells is indispensable its loss or injury can severely disable or even destroy the body there are 4 main types of tissueepithelial for coveringconnective for supportmuscle for movementnervous for control and regulationusually all 4 tissues make up an organ at least 2 tissue types are required but organs with 4 types of tissue are most common histology the study of tissues their organization appearance etc1 Epithelial Tissuealso called epithelium plural epitheliaa sheet of cells that covers a body surface or lines a body cavityepithe laid on covering it occurs in the body as covering and lining epithelium or glandular epitheliumcovering and lining epithelium creates boundaries forms the outer layer of the skin dips into and lines the open cavities of the cardiovascular digestive and respiratory systems and covers the walls and organs of the closed ventral body cavity eg outer walls of stomachkidneylumen etc glandular epithelium fashions the glands of the body involved in secretion eg salivary glands pancreas etc Functions of Epithelia1 Protection creates a physical boundary ie skin allows for mechanical chemical and infectious protectionchemical secretions protect body from invaders the immune system is integrated with epithelium 2 Absorption involved with the breakdown of products and movement into the bloodstream ie GI tract 3 Filtration allows for a barrier between fluidblood and waste products ie kidneys 4 Excretion5 Secretion6 Sensory Reception taste budsolfactory membranes are modified epithelial cells Special Characteristics of Epithelium 1 Cellularity epithelium is very celldense unlike connective tissues CT is fibrous and spacious 2 Specialized Contacts epithelial cells fit close together to form continuous sheets adjacent cells are bound together at many points by lateral contacts tight junctions and desmosomes tight junctions individual cell membranes fused tightly together helps keep proteins and apical regions of the plasma membrane from diffusing into the basal region and thus help to maintain epithelial polarity desmosomes connects 2 cells strongly together and contains intermediate filaments to strengthen layer ie in the esophagus 3 Polarity epithelia have apical surfaces and basal surfaces and all epithelia exhibit apicalbasal polarity where cell regions near the apical surface different from those near the basal surface in both structure and function and is maintained by the highly ordered cytoskeleton of epithelial cells apical surface an upper free surface exposed to the body exterior or the cavity of an internal organ apical surfaces are often specialized and this may include cilia hairlike projections that propel substances along their free surface can be found in respiratory passages and used to push mucous or microvilli fingerlike projections that increase exposed surface area for increased absorptiondense areas of microvilli usually found in epithelia that absorb or secret substances intestines and kidney tubules have a fuzzy appearance called a brush border basal lamina thin sheet that lies adjacent to the basal surface of an epithelium this noncellular adhesive sheet consists largely of glycoproteins secreted by the epithelial cells and find collagen fibres and acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter the epithelium also acts as a scaffolding along which epithelial cells can migrate to repair a wound provides attachment site for epithelial cells and allows for organization attachment and filtration 4 Supported by Connective Tissue all epithelial sheets rest upon and are supported by connective tissue the reticular lamina lies beneath the basal lamina and consists of a layer
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