glandularepithelium

glandularepithelium - Glandular Epithelium Definition of...

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Glandular Epithelium Definition of Epithelium - 1) Epithelia is avascular tissue comprised of cells that cover the exterior surfaces of the body and line both the internal closed cavities and those body tubes that communicate with the exterior (the alimentary, respiratory, and gastrointestinal tract). 2) Epithelia also form the receptors of certain sensory organs. 3) Epithelia form the secretory portions (or parenchyma) of glands and their ducts (a.k.a. glandular epithelium or exocrine glands). Function of Epithelium: Examples: 1) Mechanical protection - skin or in body tubes (stratified squamous) 2) Permeability barrier - cells lining the GI tract regulates what enters BVs (selective) (simple columnar cells of small intestine) 3) Absorption - small intestine (simple columnar) 4) Filtration - epithelium of renal corpuscle (simple squamous) 5) Secretion - glandular epithelium (simple cuboidal in ducts) 6) Diffusion of gases or fluids - lung alveoli or blood vessels (simple squamous) 7) Surface transport over epithelium - respiratory tract (pseudostratified columnar ciliated) or oviduct (simple columnar ciliated) 8) Sensory - epithelium often specialized among sense organs Major Types of Glands: The two types are based on the mechanism of their secretion. 1) Exocrine Glands – Glands that secrete their products onto the apical (or epithelia) surface directly OR via epithelial ducts or tubes that are connected to the apical surface. These exocrine glands are composed of highly specialized epithelial cells and thus are classified as glandular epithelia .
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2) Endocrine Glands - Glands that release their products basally, so the secretion goes through the basal lamina, moves into the underlying connective tissue, and enters the vascular system. Endocrine glands lack a duct system. a) Paracrine Glands – These glands are similar to endocrine glands, but their secretions reach target cells by diffusion through the extracellular space or immediately subjacent connective tissue. These secretory products are not delivered to their target tissue via ducts or the bloodstream. We will discuss endocrine and paracrine glands, later this semester with endocrine glands covered in great detail. Classification of Glandular Epithelia : This classification system is based on five different morphological criteria. 1) Number of secretory cells a) Unicellular glands – Mucus-secreting goblet cells are the only example of these single-celled glands in humans. These goblet cells secrete mucus and are easily visualized in slides of the small intestine. In routine (H&E) preparations, the cytoplasmic mucin is not preserved (and therefore, not stained) giving the cells an empty appearance. The mucus is not preserved The unicellular Goblet cells are best seen in Periodic Acid Schiff (PAS) staining. b)
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glandularepithelium - Glandular Epithelium Definition of...

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