A&P Epithelial Tissue and Glands
A&P Epithelial Tissue and Glands BIOL 221
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This 6 page Class Notes was uploaded by Amber Zurn on Wednesday February 10, 2016. The Class Notes belongs to BIOL 221 at Towson University taught by Stella A. Evans in Spring 2016. Since its upload, it has received 26 views. For similar materials see Human Anatomy & Physiology in Biology at Towson University.
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Date Created: 02/10/16
1 BIOL 221 Epithelium and Glands Histology: The study of the microscopic structure of tissues. What is a tissue? Groups of cells similar in structure and function. Tissue classes: pithelial: Composed almost entirely of cells; they form continuous sheets held together by tight junctions and desmosomes. Epithelial tissues also have apical and basal surfaces, both supported by connective tissue. onnective: This is the tissue that connects, supports, binds, or separates other tissues or organs. M uscle: Muscle tissue, also composed of cells and/or fibers, allows a contraction in which produces movement in the body, usually a particular movement. ervous The main component of the two parts of the nervous system; the brain and spinal cord which is part of the central nervous system (CNS) and the peripheral nerves of the peripheral nervous system (PNS); which regulates and controls bodily functions and activity. Epithelial Tissue: Functions Protection: Cover body surfaces and line body cavities. Protects skin. Produce secretion s: Sweat glands. Absorption, E xcretion and F iltration: Intestinal mucosa. Sensation: Epithelium (skin) covering our body surface allows us to sense smells, sounds, and sights from the external world. Characteristics of pithelial issue: olarity: pical urfac : Surface of epithelial cell that is exposed to the body exterior or to the cavity of an internal organ. “Free surface.” Has microvilli. (Microvilli helps increase surface area in epithelial tissue). Can also have cilia. 2 ateral urfac : Three factors act to bind the epithelial cells to each other; Adhesion proteins in the plasma membranes of the adjacent cells link together in the narrow extracellular space. The wavy contours of the membranes of adjacent cells join in a tongue and groove fashion. Special cell junctions. asal urface : Surface of epithelial tissue in contact with the structure that the epithelial tissue is covering or lining. Within basal surface is basement membrane. asal amina : A supporting sheet at the border between the epithelium and the connective tissue. Thin, noncellular sheet that consists of proteins secreted by the epithelial cells. Acts as a selective filter, determining which molecules from the capillaries in the underlying connective tissue are allowed to enter the epithelium. Also acts as a scaffolding along which regenerating epithelial cells can migrate. A layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. ttachment : Basal surface is bound to a thin basal lamina. Epithelium attaches to basal laminae; reticular laminae gives strength to epithelium. vascularity: Does not contain blood vessels, obtain nutrients by diffusion/absorption through the apical and basal membranes. egeneration: Continually recycled with new cells being created by mitotic activity while old cells are sloughed off. ellularity: Cell junctions Tight junction : Or “Zonula Occludens”, is a beltlike junction. It extends around the periphery of the apical region in most epithelial tissues. Some proteins can be fused in the plasma membrane due to the adjacent cells being so close together, which forms a seal that closes off the extracellular space; preventing molecules from passing between the cells of the epithelial tissue. Gap junction : Or “Nexus”, is a tunnellike junction that can occur anywhere alone the lateral membranes of adjacent cells. Function in Intercellular communication by allowing small molecules to move directly between neighboring cells. 3 The adjacent plasma membranes are very close and the cells are connected by hollow cylinders of protein (connexons). Button esmosone : Holds muscles together. Hemidesmosome : Are very small structures located on the inner basal surface of keratinocytes in the epidermis of skin. Classification of epithelial cells : imple : One layer. tratifi Multiple layers. Has no cilia. Simple squamous: Is a single layer of flat cells in contact with the basal lamina of the epithelium. Often permeable and occurs where small molecules pass quickly through membranes via filtration or diffusion. Stratified squamous: Consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Does not have cilia. Simple cuboidal: Is a type of epithelium that consists of a single layer of cuboidal (cubelike) cells. Have large, spherical and central nuclei. 4 Stratified cuboidal: Type of epithelial tissue composed of multiple layers of cubeshaped cells. Only the most superficial layer is made up of cuboidal cells, other layers can be made up of other types of cells. Does not have cilia. Simple columnar: Is a columnar epithelium that is unilayered. Lines most organs of the digestive tract including the stomach, small intestine, and the large intestine. Pseudostratified columnar: Is a type of epithelium that has its cell nuclei positioned in a manner suggestive of a stratified epithelia; so it appears to be more than one layer, however, is only one layer. Functions in secretion or absorption. Found in palms and bottom of the feet. Has cilia. Transitional: Glandular epithelium Endocrine glands: (endo=inside), ductless glands Secrete their products, hormones, directly into the blood stream rather than through a duct. Exocrine glands: (exo=outside), connected by ducts Secrete their products into ducts. i.e. sweat glands, salivary glands, mammary glands, and many glands in the digestive system. Exocrine glands : Gland structure: Glandular epithelial tissues arranged in single or multilayered sheets. Gland tissue does not have blood vessels running through it. Nourished by vessels in the connective tissue. nicellular glands: Singlecelled secretory cells. Ex.; goblet and mucous cells. ulticellular glands: All other exocrine glands. Function is the mode of secretion. ranched or unbranched? imple gland : Single unbranched duct (glands of large intestine). ompound gland: Branches duct (salivary glands). Shape of S ecretory Units: ubular (alveolar): Sweat glands. Acinar: Shaped like a grape (salivary glands). 5 Modes of secretion : erocrine glands: Product released by exocytosis (most sweat glands). The most common type of secretion. pocrine glands: Involves the loss of apical cytoplasm. Inclusions, secretory vesicles, and other cytoplasmic components are shed in the process. The gland cell then grows and repairs itself before it releases addition secretions. These glands are mostly merocrine. olocrine glands: The cell has everything packaged, and then the cell burst open and releases everything. The (dead) cell than is replaced by a new cell. Whole cell ruptures during release of product. Types of secretions erous: Type of watery secretion that often contains enzymes. ucous: Type of secretion which contains glycoprotein, and is not watery, by viscid. ixed exocrine: Contains both serous and mucous secretory units. Review questions from your book: 1. Distinguish between simple and stratified epithelia, and explain why pseudostratified columnar epithelium belongs in the former category. Simple is a single layer while stratified epithelia is multiple layers, pseudostratifies columnar belongs in the former category because it appears as though it is multiple layers, but it is only one. 2. Explain how to distinguish a stratified squamous epithelium from a transitional epithelium. Transitional epithelium has multiple layers that can contract and expand, while stratified squamous epithelium consists of squamous which is flat layers arranged in the basal membrane. . How do the epithelia of the esophagus and stomach differ? How does this relate to their respective functions? Esophagus: Stratifies squamous lines it to provide physical protection. Stomach: Simple columnar lines it for protection, secretion, and absorption. . Compare the structure of tight junctions and gap junctions. Relate their structural differences to their functional differences. 6 Tight junctions are beltlike and allow for very little molecules from passing through the epithelial tissue, while gap junctions are “tunnellike” functions in intercellular communication so allows some molecules to come through. . Distinguish between a simple gland and a compound gland, and give an example of each. What about a tubular gland and an acinar gland? A simple gland is a single unbranched duct while a compound gland has a branched ducts. A tubular gland has a duct and secretary portion are of uniform diameter, the acinar gland has secretory cells that form a dilated sac. . Contrast the merocrine and holocrine methods of secretion, and name a gland product produced by each method. Merocrine is within a cell and secrets out, in holocrine the cell bursts and secrets its product and then is a dead cell. . Describe the differences between a mucous and a serous membrane. Serous membrane: Lines a body cavity that does not open to the exterior. Mucous membrane: Lines a body cavity that does open to the exterior.
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