Chapter 4 – The Tissue Level of Organization

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Vocabulary flashcards summarizing key terms and definitions from Chapter 4: The Tissue Level of Organization.

exam 2

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86 Terms

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Tissue

A collection of specialized cells working together to perform a specific function.

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Histology

The study of the microscopic structure of tissues.

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Epithelial tissue

Tissue that covers exposed surfaces, lines internal passageways, and forms glands.

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Connective tissue

Tissue that fills internal spaces, supports other tissues, transports materials, and stores energy.

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Muscle tissue

Tissue specialized for contraction and movement.

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Nervous tissue

Tissue that propagates electrical impulses to carry information throughout the body.

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Polarity (epithelium)

Structural and functional differences between the apical (exposed) and basal (attached) surfaces of epithelial cells.

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Apical surface

The exposed surface of an epithelial cell that faces the exterior or a lumen; may bear microvilli or cilia.

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Basolateral surface

The basal and lateral surfaces of an epithelial cell that attach to neighbors and the basement membrane.

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Cellularity (epithelium)

Characteristic of epithelium in which cells are tightly packed and connected by junctions and CAMs.

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Basement membrane

Non-cellular layer that anchors epithelium to underlying connective tissue.

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Avascularity (epithelium)

Lack of blood vessels within epithelial tissue; nutrients diffuse from underlying tissues.

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Regeneration (epithelium)

Rapid replacement of epithelial cells through stem-cell divisions.

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Microvilli

Microscopic extensions of the plasma membrane that increase surface area for absorption or secretion.

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Cilia

Hair-like projections on a ciliated epithelium that move fluids across the cell surface.

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Cell adhesion molecules (CAMs)

Transmembrane proteins that bind epithelial cells to each other and to the basement membrane.

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Tight junction

Intercellular junction where adjacent plasma membranes fuse, preventing passage of water and solutes between cells.

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Gap junction

Intercellular junction formed by connexons that permits passage of ions and small molecules between cells.

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Desmosome

Strong intercellular junction that ties adjacent cells together via dense areas linked to cytoskeleton.

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Hemidesmosome

Half-desmosome that anchors a cell to the basement membrane.

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Spot desmosome

Small circular desmosome that stabilizes the shape of adjoining epithelial cells.

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Simple epithelium

Single layer of epithelial cells; specialized for absorption, diffusion, or secretion.

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Stratified epithelium

Multiple layers of epithelial cells; provides protection against abrasion and stress.

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Squamous cells

Thin, flat, irregularly shaped epithelial cells.

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Cuboidal cells

Box-shaped epithelial cells with a central nucleus.

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Columnar cells

Tall, slender epithelial cells with nuclei near the basal surface.

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Mesothelium

Simple squamous epithelium lining body cavities (pleura, peritoneum, pericardium).

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Endothelium

Simple squamous epithelium lining the heart and blood vessels.

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Pseudostratified columnar epithelium

Single layer of columnar cells of varying height that appears stratified; often ciliated.

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Transitional epithelium

Stratified epithelium that stretches; cells appear cuboidal when relaxed and squamous when stretched.

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Keratinized stratified squamous epithelium

Protective epithelium whose surface cells are filled with keratin; forms the epidermis of skin.

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Endocrine gland

Gland that releases hormones directly into the bloodstream; lacks ducts.

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Exocrine gland

Gland that releases secretions onto an epithelial surface through ducts.

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Goblet cell

Unicellular exocrine gland that secretes mucin to form mucus.

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Simple gland

Exocrine gland with an undivided (unbranched) duct.

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Compound gland

Exocrine gland whose duct is branched.

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Merocrine secretion

Secretory method where product is released by exocytosis without loss of cytoplasm.

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Apocrine secretion

Secretory method in which apical cytoplasm containing product is shed from the cell.

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Holocrine secretion

Secretory method in which the entire cell bursts to release its product; cell is replaced by stem cell divisions.

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Extracellular matrix (connective)

Combination of protein fibers and ground substance that surrounds connective tissue cells.

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Ground substance

Clear, viscous fluid in connective tissue that fills spaces and slows pathogen movement.

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Collagen fibers

Thick, unbranched protein fibers that provide tensile strength to connective tissues.

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Reticular fibers

Thin, branching fibers forming a supportive network (stroma) that resists forces in many directions.

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Elastic fibers

Branched, wavy fibers containing elastin that return to original length after stretching.

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Connective tissue proper

Connective tissue with a viscous matrix rich in protein fibers; includes loose and dense varieties.

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Loose connective tissue

Connective tissue with an open framework of fibers and cells; cushions organs and supports epithelia.

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Areolar tissue

Most common loose connective tissue; loosely organized fibers, abundant ground substance.

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Adipose tissue

Loose connective tissue dominated by adipocytes that store fat, insulate, and absorb shock.

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Reticular tissue

Loose connective tissue rich in reticular fibers that forms supporting stroma of organs like spleen and liver.

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Dense regular connective tissue

Connective tissue with parallel collagen fibers; forms tendons and ligaments.

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Dense irregular connective tissue

Connective tissue with interwoven collagen fibers in multiple directions; forms dermis and organ capsules.

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Elastic tissue (dense)

Dense connective tissue dominated by elastic fibers and some collagen; found in large arteries and elastic ligaments.

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Fascia

Sheets or ribbons of connective tissue that support and surround organs.

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Superficial fascia

Subcutaneous areolar and adipose layer separating skin from underlying tissues.

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Deep fascia

Dense regular connective tissue forming strong, fibrous internal framework around muscles and organs.

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Subserous fascia

Areolar tissue layer between deep fascia and serous membranes lining body cavities.

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Fluid connective tissues

Connective tissues with a watery matrix—blood and lymph.

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Plasma

Fluid matrix of blood that suspends formed elements.

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Red blood cells (erythrocytes)

Formed elements that transport oxygen and carbon dioxide in the blood.

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White blood cells (leukocytes)

Formed elements that defend the body against infection and disease.

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Platelets

Cell fragments in blood essential for clotting.

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Lymph

Fluid that forms from interstitial fluid entering lymphatic vessels; returns to bloodstream.

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Supporting connective tissues

Connective tissues with a solid or semi-solid matrix—cartilage and bone.

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Cartilage

Avascular supporting connective tissue with a firm gel matrix and chondrocytes in lacunae.

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Chondrocyte

Cartilage cell that occupies a lacuna within the matrix.

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Hyaline cartilage

Cartilage with closely packed collagen fibers; tough yet flexible; in nose, synovial joints, airways.

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Elastic cartilage

Cartilage with abundant elastic fibers; very flexible; in external ear and epiglottis.

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Fibrocartilage

Very durable cartilage with dense collagen bundles; resists compression; in intervertebral discs and pubic symphysis.

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Bone (osseous tissue)

Supporting connective tissue with a calcified matrix containing collagen fibers.

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Osteocyte

Mature bone cell that maintains the bone matrix and lives in a lacuna.

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Canaliculi

Microscopic channels through bone matrix that connect osteocytes for nutrient and waste exchange.

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Periosteum

Fibrous and cellular membrane that covers bone surfaces.

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Mucous membrane

Epithelial membrane that lines cavities opening to the exterior and produces mucus for protection.

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Serous membrane

Mesothelial membrane lining sealed body cavities; secretes serous fluid to reduce friction.

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Cutaneous membrane

Skin; thick, waterproof, keratinized stratified squamous epithelium over areolar and dense connective tissue.

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Synovial membrane

Areolar tissue with incomplete epithelium lining joint cavities; produces lubricating synovial fluid.

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Chondroitin sulfate

Polysaccharide derivative that, with proteins, forms the firm gel matrix of cartilage.

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Mesenchymal cell

Stem cell in connective tissue that differentiates into fibroblasts, macrophages, and other cell types after injury.

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Macrophage

Large phagocytic immune cell that engulfs pathogens and debris; may be fixed or free.

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Mast cell

Immune cell that releases histamine and heparin to initiate inflammation.

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Lymphocyte

Migratory immune cell; some differentiate into antibody-producing plasma cells.

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Microphage

Phagocytic leukocyte such as neutrophil or eosinophil attracted to sites of infection.

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Fibroblast

Most abundant fixed cell in connective tissue proper; secretes fibers and ground substance components.

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Fibrocyte

Second-most abundant fixed cell; maintains existing connective tissue fibers.

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Adipocyte

Fat cell storing a single large lipid droplet.

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Melanocyte

Pigment cell that synthesizes and stores melanin in skin and eyes.