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Canada (162,411)
ANP1105 (101)
Chapter 4

ANP1105 Chapter 4 (p. 118-139) - Epithelial Tissue and Connective Tissue

11 Pages
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Department
Anatomy and Physiology
Course Code
ANP1105
Professor
Jacqueline Carnegie

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Description
(Chapter 4) Tissue: groups of cells that are similar in structure and perform a common or related function Four tissue types: epithelial, connective, nervous, and muscle tissue Microscopy: allows us to study tissue structure. Specimen is preserved, then cut into sections, and then stained to enhance contrast. Epithelial tissue • Covers a body surface or lines a body cavity • Two forms: covering and lining; forms the outer layer of the skin, and glandular; fashions the glands of the body • Forms boundaries between environments • Ex: skin- chemical and physical protection • Accomplishes 6 functions: (1) protection, (2) absorption, (3) filtration, (4) excretion, (5) secretion, and (6) sensory reception • Special characteristics of epithelium: 5 distinguishing characteristics o Polarity: apical surface (surface exposed to the body exterior or cavity of internal organ) and a basal surface. Both differ in structure and function therefore it is called apical-basal polarity.Apical surfaces have microvilli. In epithelia that absorb or secrete, microvilli are dense (ex: lining the intestine), and some epithelia have cilia (ex: trachea).Adjacent to the basal surface is the basal lamina. It is non-cellular, consists of glycoproteins, and acts as a selective filter through which molecules diffusing into the epithelium. It also acts as scaffolding which epithelial cells can migrate on to repair a wound. *Basal lamina and reticular lamina form basement membrane. o Specialized contact: except for glandular epithelia, epithelia fit closely together to form continuous sheets. Contacts such as desmosomes and tight junctions bind cells together. Subject to wear and tear. o Supported by CT: rest upon and supported by CT. Just below the basal lamina is the reticular lamina (a layer of extracellular material containing a network of collagen fibers. The two form the basement membrane which reinforces the epithelial sheet, helps it from tearing, and defines boundary. o Avascular but innervated: contains no blood (gets O2 through diffusion) and nerves penetrate BM o Regeneration: high regenerative capacity. Epithelia are exposed to friction and their surface cells rub off. Can replace themselves through cell division. Need to replace quickly so there aren’t gaps in the layers. Lining or covering epithelia: • Each has two names: the first is the number of layers present and the second describes the shape • Number of cell layers: Simple and stratified • Three shapes of cells- squamous, cuboidal and columnar Simple: • Most concerned with absorption, secretion and filtration • Single cell layer, very thin, not used for protection o Simple squamous: flattened, thin and permeable, found where rapid diffusion is crucial (ex: kidneys). o Simple cuboidal: single layer of cells in cube shape, used for absorption and secretion (ex: kidney tubules) o Simple columnar: single layer of tall, closely packed cells. Lines digestive tract, and associated with absorption and secretion. Some have cilia on their free surfaces. Nucleus near BM o Pseudostratified columnar: vary in height, all cells rest on basement membrane and tallest reach free surface, nuclei lie at different levels so it gives false impression of several cell layers. Used for absorption and secretion, and shorter cells are unspecialized Stratified: • Two or more cell layers • Regenerate from below: basal cells divide and push apically to replace older cells • More durable than simple with protection as major role o Stratified squamous: most widespread, thick, and well suited for protection. Free cells are squamous and deeper layers are columnar or cuboidal. Found in areas subjected to wear and tear (surface cells are constantly being rubbed away). Because it depends on nutrients from deep CT, apical cells are more flattened. Forms external part of skin. o Stratified cuboidal and columnar: rare, found in ducts of larger glands, typically has two layers of cuboidal cells.Apical layer of cells are columnar (columnar). o Transitional: forms lining of hollow urinary organs. Cells of basal layers are cuboidal or columnar and apical cells vary upon stretching of the organ (the more stretched the organ the less layers of cells and more squamous they become) Glandular: • Gland: one or more cells that make and secrete a substance • Secretion is an active process- obtain substances from blood • Glands are classified by: where they release their product (exocrine and endocrine), and their relative cell number (unicellular or multicellular) • Most have ducts Endocrine: • Ductless • Secrete directly into bloodstream- long distance • Produce hormones (messenger proteins which they secrete through exocytosis into the bloodstream) • Structurally diverse Exocrine: • Secrete into ducts that provide a pathway- short distance • Diverse with similar products (ex: mucus, sweat and saliva) o Unicellular: mucous cells and goblet cells, found in intestinal and respiratory tracts. Glands produce mucin which dissolves into mucus. o Multicellular: structurally more complex with two parts: a duct and a secretory unit. Classified by structure and type of secretion. Structural (simple or compound): simple- unbranched duct, compound- branched duct. Further classified by secretory units: (1) tubular- secretory cells form tubes, (2) alveolar- secretory cells form sacs, and (3) tubuloalveolar- both types of secretory units Secretion (merocrine, holocrine, or apocrine): merocrine- majority, secrete by exocytosis (ex: pancreas); holocrine- accumulate products until they rupture (replaced by division of underlying cells); and apocrine- accumulate products, and pinch off, ex: mammary glands. Connective Tissue • Most abundant of primary tissues • Four classes of CT: (1) CT proper, (2) cartilage, (3) bone, and (4) blood • Major functions: binding and supporting, protecting, insulating, storing, and transporting substances throughout the body Common characteristics: • Common origin: all arise from mesenchyme (embryonic tissue) • Degrees of vascularity: Some are vascular, some aren’t • Extracellular matrix: composed of nonliving, extracellular matrix, which separates living cells from the tissue. Because of its EM it can bear weight, withstand tension, and endure abuses (ex: physical trauma) Structural elements of CT: • Three main elements: ground substance, fibers, and cells • Ground substance and fibers make up the matrix • Matrix can be soft to form a packing around organ or can from tendons and ligaments • All CT has similar plan: areolar connective tissue Ground substance: • Fills the space between cells and contains fibers • Composed of interstitial fluid, cell adhesion proteins, and proteoglycans • Cell adhesion proteins serves as CT glue that allows CT to attach to the matrix • Proteoglycans consist of a protein core in which GAG’s attach (large, negatively-charged polysaccharides that stick out of protein). Proteoglycans form masses in which GAG’s attach and trap water • The higher the GAG content, the more viscous the ground substance • Consists of large amounts of fluid, and functions as a medium in which dissolved substances diffuse between blood capillaries and cells CT fibers: • Provide support • Three types of fibers are found in CT matrix: collagen, elastic, and reticular Collagen: • Strongest and most abundant of fibers • Constructed of collagen protein • Collagen fibers are secreted into the EM where they assemble into cross-linked fibrils (makes them tough and able to provide high tensile strength) Elastic: • Long, thin fibers forming
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