Chapter 4: The Tissue Level of Organization

Vocabulary practice flashcards generated from lecture notes on Chapter 4: The Tissue Level of Organization.

Tissues

Groups of cells similar in structure and function that perform specialized duties in the body.

Epithelial Tissue

A tissue type characterized by cellularity, distribution along free surfaces, distinct apical and basal polarity, lack of blood vessels (avascularity), and high regenerative capacity.

Basement Membrane (BM)

A extracellular layer that anchors epithelium to underlying connective tissue via cell adhesion molecules (CAMs) and hemidesmosomes, regulates permeability, binds growth factors, and prevents microbe invasion.

Simple Squamous Epithelium

A single layer of thin cells that permits rapid diffusion and filtration, secretes serous fluid, and lines alveoli, blood vessels, endothelium, and kidney glomeruli.

Simple Cuboidal Epithelium

A single layer of square or round cells with spherical central nuclei, functioning in absorption and secretion in the liver, thyroid, mammary glands, salivary glands, bronchioles, and kidney tubules.

Simple Columnar Epithelium

A single layer of tall, narrow cells with oval nuclei located in the basal half; contains a brush border of microvilli ($1\,\mu m$) or cilia ($10\,\mu m$) for absorption and secretion.

Pseudostratified Columnar Epithelium

A single layer of columnar cells that appears multilayered because nuclei are at different levels, though all cells touch the basement membrane; typically ciliated and secretes/propels mucus in upper respiratory passages.

Goblet Cell

A unicellular gland specialized for synthesizing and secreting mucin/mucus within epithelial membranes.

Primary Cilium

A nonmotile hair-like projection present on nearly every human cell that functions as a sensory antenna to monitor local external conditions.

Keratinized Stratified Squamous Epithelium

Multiple cell layers featuring flat, scaly surface cells packed with keratin; protects against mechanical abrasion, limits water loss, and blocks pathogen penetration in the epidermis.

Nonkeratinized Stratified Squamous Epithelium

Multilayered flat epithelial tissue lacking a surface layer of dead cells, maintaining a moist surface while resisting abrasion and pathogen penetration in the tongue, oral mucosa, esophagus, and vagina.

Stratified Cuboidal Epithelium

Epithelial tissue with two or more layers of square or round surface cells, functioning in protection and secretion within ducts of sweat, salivary, and mammary glands.

Stratified Columnar Epithelium

A rare tissue with multiple layers where surface cells are tall and narrow; found in transition zones of the pharynx, larynx, anal canal, and male urethra.

Transitional Epithelium

A multilayered epithelium with rounded surface cells that flatten when distended, allowing expansion and stretching in the ureters, urinary bladder, urethra, and umbilical cord.

Tight Junction

A cell junction that seals off extracellular space between neighboring plasma membranes using transmembrane cell adhesion molecules (CAMs) to prevent passage of substances.

Gap Junction

A cell junction formed by six transmembrane proteins called a connexon that creates a central pore, permitting ion and fluid transport directly between adjacent cells.

Desmosome

A cell junction featuring a thick protein plaque, intermediate filaments of the cytoskeleton, and CAMs that mechanically binds adjacent cells to resist physical stress.

Hemidesmosome

An anchoring cell junction that binds the basal surface of an epithelial cell to the underlying basement membrane using integrins.

Exocrine Gland

A gland that maintains contact with body surfaces or cavities by discharging secretions through an epithelial tube called a duct.

Endocrine Gland

A ductless gland that secretes regulatory chemical messengers (hormones) directly into extracellular fluid and blood.

Merocrine Secretion

A mode of glandular secretion where secretory products are released purely by exocytosis, leaving the gland cell completely intact.

Apocrine Secretion

A mode of glandular secretion in which the apical portion of the secretory cell pinches off to release its product while the nucleus and cell body remain intact.

Holocrine Secretion

A mode of glandular secretion where the cell accumulates product until it ruptures and disintegrates entirely, so that the cell body itself becomes part of the secretion.

Collagenous Fibers

Tough, flexible white fibers composed of collagen (making up 25% of total body protein) that provide strong tensile strength with little elastic recoil.

Reticular Fibers

Thin, branching collagen fibers coated with glycoprotein that form a supportive stroma or framework in soft organs like the spleen, lymph nodes, and basement membranes.

Elastic Fibers

Branching yellow fibers composed of elastin protein that stretch easily and recoil back to their original dimensions.

Glycosaminoglycans (GAGs)

Long polysaccharides composed of amino sugars and uronic acid that attract, absorb, and hold water within connective tissue ground substance.

Chondroitin Sulfate

The most abundant glycosaminoglycan (GAG), providing structural rigidity and hydration in cartilage, bone, and blood vessels.

Hyaluronic Acid

A viscous glycosaminoglycan that serves as a gel-like lubricant in joint fluid, bursae, and the vitreous body of the eyeball.

Proteoglycan

A huge macromolecule made of a core protein bonded to multiple GAGs that creates thick colloidal gels to hold tissues and extracellular matrix together.

Areolar Connective Tissue

A loose connective tissue with loosely woven collagenous, elastic, and reticular fibers and abundant open space that underlies all epithelia and cushions internal organs.

Reticular Connective Tissue

A loose connective tissue consisting of a delicate network of reticular fibers and fibroblasts that forms the internal stroma of lymphatic organs.

Dense Regular Elastic Connective Tissue

A dense connective tissue dominated by parallel, branching elastic fibers that form wavy sheets in large arterial walls, vocal cords, and ligaments of the spine.

Dense Regular Connective Tissue (DRCT)

A connective tissue packed with parallel collagen fibers and flattened fibroblast nuclei, providing high unidirectional tensile strength (~18,000+ lb/in2) in tendons and ligaments.

Dense Irregular Connective Tissue (DICT)

A tissue containing densely packed collagen fibers arranged randomly in multiple directions, enabling it to withstand multidirectional stress in the dermis, submucosa, and organ capsules.

Adipose Connective Tissue

A connective tissue dominated by lipid-storing adipocytes with peripheral nuclei, functioning in energy storage, thermal insulation, and mechanical cushioning.

Chondrocytes

Mature cartilage cells that reside within small fluid-filled cavities in the matrix called lacunae.

Perichondrium

A dense irregular connective tissue layer surrounding elastic cartilage and most hyaline cartilage.

Hyaline Cartilage

A smooth cartilage with fine collagen fibers that provides low-friction surfaces for joint movement, keeps airways open, and forms the embryonic skeleton.

Elastic Cartilage

Cartilage filled with a web of elastic fibers surrounded by a perichondrium, offering resilient, flexible structural support to the external ear and epiglottis.

Fibrocartilage

A tough cartilage packed with coarse, parallel bundles of collagen fibers that lacks a perichondrium and absorbs compressive shock in intervertebral discs, menisci, and the pubic symphysis.

Osseous Connective Tissue

Hard connective tissue where approximately 1/2 of tissue volume consists of organic osteoid (collagen and GAGs) for tensile strength and 1/2 consists of mineral deposits for compressive strength.

Blood Connective Tissue

A fluid connective tissue consisting of a liquid ground substance called plasma and formed elements including erythrocytes, leukocytes, and cell fragments called platelets.

Nervous Tissue

A tissue type specialized for rapid electrochemical signal communication, composed of 10% signal-conducting neurons and 90% supportive neuroglial cells.

Skeletal Muscle Tissue

Voluntary muscle tissue consisting of long, threadlike multinucleated muscle fibers marked by alternating dark (A) and light (I) striations.

Cardiac Muscle Tissue

Involuntary striated muscle found only in the heart, composed of short branched cells (cardiac myocytes) with central single nuclei connected end-to-end by intercalated discs.

Smooth Muscle Tissue

Involuntary, non-striated muscle composed of spindle-shaped (fusiform) cells with single central nuclei, located in the walls of visceral organs and blood vessels.