Chapter 4: Tissues - Structure and Function

Comprehensive practice flashcards defining primary tissue types, cell junctions, epithelial classifications, glandular modes of secretion, connective tissue varieties, cartilage growth mechanisms, body membranes, neural components, and tissue repair processes.

Gametes

The reproductive sex cells (eggs and sperm) produced through the specialized cell division mechanism called meiosis.

Somatic Cells

Body cells comprising approximately $200$ different types in the human body, all produced by mitosis.

Epithelial Tissue

One of the four primary tissue types that forms surface coverings (such as the skin), lines internal cavities and tubes, and forms glandular tissue.

Apical Surface

The exposed, free surface of an epithelial cell or tissue layer that faces the exterior of the body or an internal space/lumen.

Basement Membrane

A sticky, gel-like, non-cellular foundation made of glycoproteins and polysaccharides that anchors epithelia to underlying connective tissue; composed of a clear layer (lamina lucida) and a dense layer (lamina densa).

Microvilli

Small apical membrane projections that specialize in absorption and increase the surface area of the epithelial cell by $20\times$.

Cilia

Hair-like motile membrane projections (averaging about $250\text{ cilia/cell}$) whose coordinated beating sweeps mucus and trapped debris along epithelial surfaces.

Cell Adhesion Molecules (CAMs)

Transmembrane proteins (such as cadherin and integrin) that bind cells to one another and to extracellular materials.

Occluding Junction

A tight junction where lipid portions of two adjacent plasma membranes are tightly held together by interlocking transmembrane proteins, preventing water and solute passage between cells.

Adhesion Belt

A continuous band encircling epithelial cells that binds them to their neighbors via transmembrane glycoproteins (cadherin) anchored intracellularly to actin microfilaments of the terminal web.

Gap Junction

A communicating junction formed by interlocking channel proteins (connexons) that allows ions and small molecules to travel directly between cells for chemical and electrical coordination.

Spot Desmosome

A localized cell-to-cell junction containing cell adhesion molecules (CAMs) and intermediate filaments (keratin) that stabilizes cell shape and enhances resistance to mechanical stress.

Hemidesmosome

A specialized half-desmosome junction that anchors the deepest layer of epithelial cells to the extracellular filaments of the underlying basal lamina.

Simple Squamous Epithelium

A single layer of delicate, flat cells specialized for filtration and rapid diffusion; found lining blood vessels (endothelium), lung alveoli, and forming serous membranes (mesothelium).

Keratinized Stratified Squamous Epithelium

A multilayered tissue where superficial cells are flattened and packed with the tough, water-resistant protein keratin, providing physical protection against abrasion, dehydration, and pathogens on the skin surface.

Simple Cuboidal Epithelium

A single layer of cube-shaped cells with central spherical nuclei specialized for secretion and absorption, found in kidney tubules, ducts, and the thyroid gland.

Stratified Cuboidal Epithelium

A rare multi-layered epithelial tissue specialized for protection, secretion, and absorption, located in the lining of certain sweat gland ducts.

Transitional Epithelium

A stratified epithelium characterized by cells that can change shape between cuboidal and flattened squamous, tolerating repeated stretching and recoil in the urinary bladder, ureters, and renal pelvis.

Simple Columnar Epithelium

A single layer of rectangular cells specialized for absorption and secretion, commonly equipped with microvilli and interspersed with mucus-producing goblet cells along the stomach-to-anus digestive tract.

Pseudostratified Ciliated Columnar Epithelium

An epithelium where all cells contact the basement membrane but varying cell heights and staggered nuclei give a stratified appearance; features surface cilia to propel debris-laden mucus in the respiratory tract.

Merocrine Secretion

A mode of exocrine secretion where secretory products packaged into vesicles are discharged from the cell intact via exocytosis without damaging the plasma membrane.

Apocrine Secretion

A mode of exocrine secretion in which the apical portion of the cytoplasm becomes packed with secretory vesicles and is shed, after which the cell regrows and repairs itself.

Holocrine Secretion

A mode of exocrine secretion where the entire glandular cell becomes packed with secretory products and bursts, releasing its contents and destroying the cell, which is subsequently replaced by stem cell division.

Goblet Cell

A specialized, solitary mucus-secreting exocrine gland cell scattered among the absorptive columnar cells of mucous membranes.

Connective Tissue Proper

A category of connective tissue containing diverse cell populations and extracellular protein fibers suspended in a viscous, syrupy ground substance; subdivided into loose and dense tissues.

Fibroblasts

Abundant, stationary fixed cells in connective tissue proper that synthesize extracellular fibers and the ground substance.

Mesenchymal Cells

Mobile multipotent stem cells residing in connective tissue that divide to produce daughter cells that differentiate into fibroblasts, macrophages, or other specialized connective tissue cells.

Areolar Tissue

A loose connective tissue featuring an open framework of loosely arranged collagen and elastic fibers; cushions organs, supports epithelia, and swells with interstitial fluid during edema.

Adipose Tissue

A loose connective tissue dominated by adipocytes that store lipid reserves in large intracellular vesicles, serving to cushion shocks, insulate the body, and store energy.

Reticular Tissue

A loose connective tissue containing a complex three-dimensional network of reticular fibers that creates the supporting stroma for organs such as the liver, spleen, lymph nodes, and bone marrow.

Dense Regular Connective Tissue

A connective tissue packed with parallel bundles of collagen fibers aligned with the lines of stress, forming tendons, ligaments, and aponeuroses.

Dense Irregular Connective Tissue

A connective tissue composed of interwoven networks of collagen fibers that provides tensile strength to resist multidirectional stresses; forms the dermis, organ capsules, periosteum, and perichondrium.

Hyaline Cartilage

The most common supporting cartilage, containing chondrocytes in lacunae embedded in a glassy, gel-like matrix; found at synovial joint surfaces, connecting ribs to the sternum, and supporting the trachea and larynx.

Elastic Cartilage

A resilient supporting connective tissue packed with elastic fibers in its matrix, allowing it to tolerate substantial distortion and return to its original shape; found in the auricle of the external ear and epiglottis.

Fibrous Cartilage (Fibrocartilage)

A tough supporting connective tissue with densely packed collagen fibers that resists compression, absorbs shock, and prevents bone-to-bone contact in intervertebral discs and the pubic symphysis.

Perichondrium

A protective covering around the outer boundary of hyaline and elastic cartilage consisting of an outer fibrous layer of dense irregular connective tissue and an inner cellular layer of chondrogenic stem cells.

Interstitial Growth

Cartilage growth from within, where chondrocytes inside lacunae divide and secrete new matrix, pushing daughter cells apart.

Appositional Growth

Cartilage growth at the surface, wherein stem cells of the inner cellular perichondrium differentiate into chondroblasts, secrete matrix, and mature into chondrocytes.

Osseous Tissue

A supporting connective tissue with a solid, crystalline matrix consisting of two-thirds calcium salts (principally calcium phosphate) and one-third collagen fibers, with osteocytes residing inside lacunae.

Mucous Membrane

A composite tissue membrane lined with an epithelium and an underlying areolar connective tissue layer (lamina propria) that lines cavities and tubes open to the external environment.

Serous Membrane

A membrane lining sealed ventral body cavities that consists of a simple squamous mesothelium supported by areolar tissue, producing a watery transudate to reduce internal friction.

Cutaneous Membrane

The skin, consisting of a keratinized stratified squamous epithelium (epidermis) supported by underlying areolar and dense irregular connective tissue (dermis).

Synovial Membrane

A membrane lining joint cavities that produces synovial fluid for lubrication, lacking a true basement membrane and continuous epithelial sheet.

Superficial Fascia

A layer of areolar and adipose tissue (also called the hypodermis or subcutaneous layer) situated between the skin and underlying deep organs.

Deep Fascia

A tough, dense irregular connective tissue layer organized in sheets like plywood that binds to muscle capsules, tendons, and ligaments to resist forces from multiple directions.

Neuroglia

Supporting non-neuronal cells of neural tissue that maintain physical structure, repair tissue frameworks, perform phagocytosis, provide nutrients, and regulate interstitial fluid composition.

Skeletal Muscle Tissue

A voluntary, striated muscle tissue composed of extremely long, cylindrical, multinucleated cells (muscle fibers) bundled by connective tissue sheaths.

Cardiac Muscle Tissue

An involuntary, striated muscle tissue found exclusively in the heart, consisting of short, branching, typically uninucleated cells connected by intercalated discs that contain up to $35\%$ mitochondria.

Smooth Muscle Tissue

A non-striated, involuntary muscle tissue containing spindle-shaped, uninucleated cells located within the walls of hollow organs, capable of slow sustained contractions such as peristalsis.

Intercalated Discs

Specialized junctional complexes between adjacent cardiac muscle cells containing desmosomes and gap junctions that allow electrical synchronization and synchronized muscle contraction.

Inflammation

A localized non-specific tissue response to injury triggered by the release of prostaglandins, proteins, and potassium ('3Ps') from damaged cells, leading to mast cell activation, vasodilation, increased capillary permeability, pain, and increased phagocyte activity.

Decubitus Ulcers

Bedsores or pressure ulcers caused by continuous pressure applied to the skin, soft tissue, and muscle in excess of the capillary filling pressure ($32\text{ mmHg}$), leading to localized circulatory restriction and tissue damage.