Chapter 4 – The Tissue Level of Organization

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

Tissue

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

Histology

The study of the microscopic structure of tissues.

Epithelial tissue

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

Connective tissue

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

Muscle tissue

Tissue specialized for contraction and movement.

Nervous tissue

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

Polarity (epithelium)

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

Apical surface

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

Basolateral surface

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

Cellularity (epithelium)

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

Basement membrane

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

Avascularity (epithelium)

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

Regeneration (epithelium)

Rapid replacement of epithelial cells through stem-cell divisions.

Microvilli

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

Cilia

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

Cell adhesion molecules (CAMs)

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

Tight junction

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

Gap junction

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

Desmosome

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

Hemidesmosome

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

Spot desmosome

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

Simple epithelium

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

Stratified epithelium

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

Squamous cells

Thin, flat, irregularly shaped epithelial cells.

Cuboidal cells

Box-shaped epithelial cells with a central nucleus.

Columnar cells

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

Mesothelium

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

Endothelium

Simple squamous epithelium lining the heart and blood vessels.

Pseudostratified columnar epithelium

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

Transitional epithelium

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

Keratinized stratified squamous epithelium

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

Endocrine gland

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

Exocrine gland

Gland that releases secretions onto an epithelial surface through ducts.

Goblet cell

Unicellular exocrine gland that secretes mucin to form mucus.

Simple gland

Exocrine gland with an undivided (unbranched) duct.

Compound gland

Exocrine gland whose duct is branched.

Merocrine secretion

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

Apocrine secretion

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

Holocrine secretion

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

Extracellular matrix (connective)

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

Ground substance

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

Collagen fibers

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

Reticular fibers

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

Elastic fibers

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

Connective tissue proper

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

Loose connective tissue

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

Areolar tissue

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

Adipose tissue

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

Reticular tissue

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

Dense regular connective tissue

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

Dense irregular connective tissue

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

Elastic tissue (dense)

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

Fascia

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

Superficial fascia

Subcutaneous areolar and adipose layer separating skin from underlying tissues.

Deep fascia

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

Subserous fascia

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

Fluid connective tissues

Connective tissues with a watery matrix—blood and lymph.

Plasma

Fluid matrix of blood that suspends formed elements.

Red blood cells (erythrocytes)

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

White blood cells (leukocytes)

Formed elements that defend the body against infection and disease.

Platelets

Cell fragments in blood essential for clotting.

Lymph

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

Supporting connective tissues

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

Cartilage

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

Chondrocyte

Cartilage cell that occupies a lacuna within the matrix.

Hyaline cartilage

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

Elastic cartilage

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

Fibrocartilage

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

Bone (osseous tissue)

Supporting connective tissue with a calcified matrix containing collagen fibers.

Osteocyte

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

Canaliculi

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

Periosteum

Fibrous and cellular membrane that covers bone surfaces.

Mucous membrane

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

Serous membrane

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

Cutaneous membrane

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

Synovial membrane

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

Chondroitin sulfate

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

Mesenchymal cell

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

Macrophage

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

Mast cell

Immune cell that releases histamine and heparin to initiate inflammation.

Lymphocyte

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

Microphage

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

Fibroblast

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

Fibrocyte

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

Adipocyte

Fat cell storing a single large lipid droplet.

Melanocyte

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