Chapter 5: The Human Tissues

Comprehensive vocabulary flashcards covering human tissue types, histological sectioning, embryonic origins, epithelia, connective tissues, cell junctions, glands, membranes, repair, and tissue death.

Organ

A structure with discrete boundaries that is composed of two or more tissue types.

Histology

The study of tissues and how they are arranged into organs; also known as microscopic anatomy.

Tissue

A group of similar cells and cell products working together to perform a specific role in an organ.

Extracellular Matrix (ECM)

Extracellular material composed of fibrous proteins and a clear gel known as ground substance, tissue fluid, ECF, or interstitial fluid.

Ectoderm

The outer primary germ layer of an embryo that gives rise to the epidermis and the nervous system.

Endoderm

The inner primary germ layer of an embryo that gives rise to the mucous membrane lining the digestive and respiratory tracts, digestive glands, and other structures.

Mesoderm

The middle primary germ layer of an embryo that becomes gelatinous mesenchyme and gives rise to cartilage, bone, and blood.

Longitudinal Section (l.s.)

A tissue cut along its long axis.

Cross Section (c.s.)

A tissue cut perpendicular to the long axis of an organ; also called a transverse section (t.s.).

Oblique Section

A tissue cut at an angle between a cross section and a longitudinal section.

Smear

A tissue preparation in which the tissue is rubbed or spread across a slide, such as with blood or soft tissues like the spinal cord.

Spread

A tissue preparation in which tissues are laid out flat on a slide, such as membranes or cobwebby tissues like areolar tissue.

Epithelial Tissue

An avascular sheet of closely adhering cells, one or more cells thick, that covers body surfaces, lines body cavities, and constitutes most glands.

Basement Membrane

A layer between an epithelium and underlying connective tissue composed of collagen, glycoproteins, and protein-carbohydrate complexes that anchors the epithelium.

Simple Squamous Epithelium

A single row of thin, scaly cells that permits rapid diffusion or transport of substances and secretes serous fluid; found in alveoli, glomeruli, endothelium, and serosa.

Simple Cuboidal Epithelium

A single layer of square or round cells specialized for absorption, secretion, and mucus movement; found in liver, thyroid, mammary glands, salivary glands, bronchioles, and kidney tubules.

Simple Columnar Epithelium

A single row of tall, narrow cells with oval nuclei in the basal half, often featuring a brush border of microvilli or cilia; functions in absorption and mucus secretion in the GI tract, uterus, and uterine tubes.

Pseudostratified Columnar Epithelium

An epithelium that appears multilayered because nuclei are at different levels, but in which all cells touch the basement membrane; secretes and propels mucus in the respiratory tract.

Goblet Cells

Wineglass-shaped, mucus-secreting cells found interspersed in simple columnar and pseudostratified columnar epithelia.

Exfoliation (Desquamation)

The flaking off and dying of mature surface epithelial cells in stratified squamous epithelium.

Keratinized Stratified Squamous Epithelium

A multilayered epithelium whose surface is covered with compact, dead, flat cells packed with keratin; resists abrasion, retards water loss, and is heavily present on the palms and soles.

Nonkeratinized Stratified Squamous Epithelium

A multilayered, abrasion-resistant epithelium lacking a surface layer of dead cells; lines internal moist spaces including the tongue, oral mucosa, esophagus, and vagina.

Stratified Cuboidal Epithelium

An epithelium composed of two or more cell layers with surface cells being square or round; secretes sweat, produces sperm, and produces ovarian hormones.

Urothelium

A multilayered epithelium unique to the urinary tract (ureter and bladder) whose surface cells transition from round to flat when stretched, accommodating bladder filling.

Fibroblasts

Large connective tissue cells that produce the collagen and elastic fibers as well as the ground substance of the matrix.

Macrophages

Large phagocytic connective tissue cells that engulf foreign materials, destroy tissue debris, and activate the immune system.

Mast Cells

Connective tissue cells that secrete heparin to inhibit blood clotting and histamine to dilate blood vessels.

Collagenous Fibers

Tough, flexible, and stretch-resistant protein fibers found abundantly in tendons, ligaments, and the deep layer of the skin.

Reticular Fibers

Thin collagen fibers coated with glycoprotein that form the delicate structural framework of organs such as the spleen and lymph nodes.

Elastic Fibers

Connective tissue fibers composed of the protein elastin that allow structures to stretch and recoil.

Areolar Tissue

A loose connective tissue featuring loosely organized fibers, abundant blood vessels, and all six fibrous connective tissue cell types; underlies epithelia and surrounds blood vessels and nerves.

Reticular Tissue

A loose connective tissue consisting of a meshwork of reticular fibers and fibroblasts that forms the supportive stroma of lymphatic organs.

Dense Regular Connective Tissue

A dense connective tissue characterized by densely packed, parallel collagen fibers and flattened, compressed fibroblast nuclei; forms tendons and ligaments.

Dense Irregular Connective Tissue

A dense connective tissue composed of thick, randomly oriented bundles of collagen fibers capable of withstanding unpredictable stresses; located in the dermis and organ capsules.

White Adipose Tissue

The predominant type of fat in adults, characterized by cells with large central lipid inclusions that provide thermal insulation, cushioning, and energy storage.

Brown Adipose Tissue

A specialized heat-generating adipose tissue found primarily in fetuses, infants, and children, colored by dense vascularity, mitochondria, and oxidative enzymes.

Chondrocytes

Mature cartilage cells that occupy tiny enclosed cavities within the matrix called lacunae.

Perichondrium

A sheath of dense irregular connective tissue that surrounds elastic cartilage and most hyaline cartilage.

Hyaline Cartilage

A stiff connective tissue with an invisible collagen framework giving it a clear, glassy appearance; eases joint movement and holds open the trachea and bronchi.

Elastic Cartilage

A type of cartilage containing rich webs of elastic fibers surrounded by a perichondrium; provides flexible support to the external ear and epiglottis.

Fibrocartilage

A tough cartilage with coarse bundles of parallel collagen fibers that absorbs shock and resists compression in the pubic symphysis, menisci, and intervertebral discs.

Osteon

The basic structural unit of compact bone, consisting of a central canal surrounded by concentric lamellae of calcified matrix.

Canaliculi

Hairlike microscopic canals radiating from lacunae that connect osteocytes to each other and to the central canal in bone.

Formed Elements

The cellular components of blood suspended in liquid plasma, including erythrocytes, leukocytes, and platelets.

Excitable Tissues

Nervous and muscular tissues that possess the ability to respond to external stimuli by altering their electrical membrane potential.

Neuroglia

Glial cells that outnumber neurons, serving as supportive, protective, and housekeeping cells for the nervous system.

Skeletal Muscle

Voluntary, striated muscle tissue consisting of long, multinucleated, parallel cylindrical fibers attached mostly to bones.

Cardiac Muscle

Involuntary, striated muscle tissue restricted to the heart, composed of short, branched cardiomyocytes joined end to end by intercalated discs.

Smooth Muscle

Non-striated, involuntary muscle tissue composed of short, fusiform cells with a single central nucleus; forms the muscular walls of hollow visceral organs.

Tight Junction

A continuous, zipperlike seam formed by cell-adhesion proteins that circles epithelial cells near their apical surface, preventing molecules from passing between cells.

Desmosome

A patch-like intercellular junction with intermediate filaments that anchors cells together and prevents mechanical separation under stress.

Hemidesmosome

A half-desmosome junction that anchors the basal surface of epithelial cells to the underlying basement membrane.

Gap Junction

A communicating junction formed by six transmembrane proteins creating a pore-like connexon, allowing ions and small solutes to pass directly from cell to cell.

Exocrine Gland

A gland that delivers secretions to an internal or external surface via an epithelial-lined duct.

Endocrine Gland

A ductless gland with extensive capillary networks that secretes hormones directly into the bloodstream.

Parenchyma

The functional epithelial cells of an exocrine gland that carry out synthesis and secretion.

Stroma

The connective tissue framework of a gland, consisting of the capsule, septa, and trabeculae that support the glandular tissue.

Eccrine (Merocrine) Secretion

A secretory mechanism in which vesicles release their products across the apical plasma membrane via exocytosis without cell damage.

Apocrine Secretion

A mode of secretion in which a droplet of product enclosed by plasma membrane and cytoplasm buds off from the cell surface, as seen in milk fat secretion.

Holocrine Secretion

A mode of secretion in which gland cells accumulate products until the entire cell disintegrates, producing oily secretions mixed with cell fragments.

Cutaneous Membrane

The skin; the largest membrane of the body, consisting of a keratinized stratified squamous epithelium (epidermis) supported by a connective tissue dermis.

Mucous Membrane (Mucosa)

A membrane lining tracts that open to the exterior, composed of an epithelium, a lamina propria of areolar tissue, and a muscularis mucosae smooth muscle layer.

Serous Membrane (Serosa)

A membrane lining closed internal body cavities, consisting of simple squamous mesothelium on areolar tissue that secretes watery lubricating serous fluid.

Hyperplasia

Tissue growth through an increase in the number of cells via cell division.

Hypertrophy

Tissue growth through the enlargement of preexisting cells rather than an increase in cell number.

Metaplasia

A transformation in which one mature tissue type changes into another mature tissue type, such as ciliated respiratory epithelium transforming into stratified squamous in smokers.

Developmental Plasticity

The capacity of an undifferentiated stem cell to give rise to a variety of specialized mature cell types.

Totipotent Stem Cells

Early embryonic stem cells that possess unlimited developmental plasticity, able to form any cell type of the embryo and pregnancy structures.

Pluripotent Stem Cells

Stem cells derived from the embryoblast (inner cell mass) that can give rise to any tissue of the embryo proper, but not accessory pregnancy tissues.

Regeneration

The replacement of damaged or dead tissue by the exact same functional cell type, fully restoring original physiological function.

Fibrosis

The replacement of damaged tissue with nonfunctional collagenous scar tissue.

Granulation Tissue

A delicate, highly vascular healing tissue composed of infiltrating capillary sprouts and fibroblasts depositing new collagen during wound repair.

Atrophy

The shrinkage of a tissue resulting from a loss of cell size or cell number, often due to aging or disuse.

Infarction

The sudden death of tissue caused by the abrupt cessation or interruption of its blood supply.

Gangrene

Tissue necrosis caused by an inadequate blood supply, frequently accompanied by infection.

Apoptosis

Programmed, non-pathological cell death in which cells that have completed their function disassemble neatly and are phagocytized without eliciting inflammation.