Chapter 4: Body Tissues

Comprehensive vocabulary flashcards covering Chapter 4 on human body tissues, including epithelial types and junctions, connective tissue classifications, membranes, muscle tissues, neural components, and injury responses.

Somatic Cells

The approximately 200 different non-gamete cell types in the human body that divide and reproduce via mitosis.

Gametes (Sex Cells)

Specialized reproductive cells (eggs and sperm) that are produced through the cell division mechanism of meiosis.

Epithelial Tissue

A cellular, avascular tissue that covers exposed body surfaces, lines internal cavities and passageways, and forms glandular structures.

Exocrine Glands

Glands derived from epithelia that discharge secretions onto external surfaces or into ducts connecting to the exterior.

Endocrine Glands

Ductless glands derived from epithelia that release hormones or hormonal precursors directly into interstitial fluid for distribution via the bloodstream.

Microvilli

Non-motile projections on the apical surface of epithelial cells that increase surface area by approximately $20\times$ to facilitate absorption.

Cilia

Motile apical cell extensions (roughly 250 per cell) whose synchronized beating sweeps mucus and trapped particulates across the epithelial surface.

Cell Adhesion Molecules (CAMs)

Transmembrane proteins (such as cadherins and integrins) that bind opposing cell membranes to each other or anchor them to extracellular materials.

Tight (Occluding) Junction

A junction where the lipid portions of adjacent plasma membranes are bound firmly by interlocking transmembrane proteins, preventing water and solutes from passing between cells.

Adhesion Belt

A continuous adhesion band encircling epithelial cells that attaches them to neighboring cells via transmembrane glycoproteins (cadherins) anchored to actin microfilaments.

Gap Junction

A cell junction composed of interlocking channel proteins called connexons that allows direct movement of ions and small molecules between adjacent cells.

Connexons

Protein complexes composed of 6 connexin proteins that form the central aqueous pore of a gap junction.

Spot Desmosome

A button-like intercellular junction reinforced by intermediate filaments (keratin) and CAMs that resists mechanical shear and stress.

Hemidesmosome

A specialized anchoring junction that attaches the basal surface of epithelial cells to extracellular protein filaments of the underlying basal lamina.

Basement Membrane

A non-cellular, gel-like anchoring structure between epithelia and connective tissue consisting of a superficial clear layer (lamina lucida) and a deep dense layer (lamina densa).

Simple Squamous Epithelium

A single layer of delicate, flattened cells specialized for absorption, diffusion, and reducing friction; forms mesothelia, endothelia, and pulmonary alveoli.

Stratified Squamous Epithelium

A multi-layered tissue whose apical cells are flattened, specialized to provide physical protection against abrasion, pathogens, and chemical attack (e.g., skin, mouth, esophagus).

Simple Cuboidal Epithelium

A single layer of cube-shaped cells providing limited protection and specialized for secretion and absorption in kidney tubules, ducts, and the thyroid gland.

Stratified Cuboidal Epithelium

A rare multi-layered cuboidal tissue found lining the ducts of sweat glands that functions in protection, secretion, and absorption.

Transitional Epithelium

A specialized stratified epithelium lining the urinary bladder, ureters, and renal pelvis that tolerates repeated stretching and recoiling.

Simple Columnar Epithelium

A single layer of tall rectangular cells lining the stomach and intestines that functions in secretion and absorption, frequently containing goblet cells.

Pseudostratified Ciliated Columnar Epithelium

An epithelium that appears layered because cell nuclei are positioned at varying heights, though all cells contact the basement membrane; lines the nasal cavity, trachea, and bronchi.

Paracellular Transport

The passive transfer of substances across an epithelial barrier through the narrow intercellular spaces located between adjacent cells.

Transcellular Transport

The active or passive transport of substances directly through an epithelial cell, entering one surface, crossing the cytoplasm, and exiting the opposite surface.

Merocrine Secretion

A mode of exocrine secretion where products are packaged into secretory vesicles and discharged by exocytosis without loss of cytoplasm (e.g., salivary and eccrine sweat glands).

Apocrine Secretion

A mode of exocrine secretion where the apical portion of the cytoplasm is packed with secretory vesicles and pinched off, followed by cellular regeneration (e.g., mammary glands).

Holocrine Secretion

A mode of exocrine secretion in which the entire secretory cell bursts and is destroyed to release its cytoplasmic contents (e.g., sebaceous glands).

Connective Tissue Proper

Connective tissues consisting of a syrupy ground substance containing extracellular fibers and diverse cell populations, categorized as either loose or dense.

Areolar Tissue

A loose connective tissue with an open framework of collagen and elastic fibers that cushions organs, supports epithelia, and swells during edema.

Adipose Tissue

A loose connective tissue composed primarily of adipocytes that provides padding, absorbs shock, insulates against heat loss, and stores lipid energy reserves.

Reticular Tissue

A loose connective tissue featuring a network of branched reticular fibers that creates a supporting framework (stroma) in the liver, spleen, lymph nodes, and bone marrow.

Dense Regular Connective Tissue

A dense connective tissue of parallel, densely packed collagen fiber bundles that provides unidirectional tensile strength in tendons, ligaments, and deep fasciae.

Dense Irregular Connective Tissue

A dense connective tissue containing randomly interwoven bundles of collagen fibers that resists mechanical forces from multiple directions, found in the dermis and organ capsules.

Elastic Tissue

A dense connective tissue dominated by elastic fibers that permits expansion and recoil in elastic ligaments between vertebrae and the walls of large blood vessels.

Hyaline Cartilage

A supporting connective tissue with a translucent matrix of closely packed collagen fibers; reduces joint friction and supports the airway, costal cartilages, and nasal septum.

Elastic Cartilage

A flexible supporting connective tissue rich in elastic fibers that tolerates distortion without permanent damage in the external ear (auricle) and epiglottis.

Perichondrium

A connective tissue sheath surrounding hyaline and elastic cartilage comprising an outer fibrous layer of dense irregular connective tissue and an inner cellular layer.

Appositional Growth

A mechanism of cartilage growth in which stem cells in the perichondrium differentiate into chondroblasts and deposit new matrix onto the external surface.

Interstitial Growth

A mechanism of cartilage growth in which chondrocytes within lacunae divide and secrete new matrix internally, expanding the tissue from within.

Bone (Osseous Tissue)

A supporting connective tissue with a hard, crystalline matrix of calcium salts (calcium phosphate) reinforced with collagen fibers, containing osteocytes housed in lacunae.

Mucous Membrane (Mucosa)

A membrane lining cavities and tubes that open to the body exterior, composed of an epithelium resting upon a layer of areolar connective tissue called the lamina propria.

Serous Membrane (Serosa)

A membrane lining sealed ventral body cavities, composed of a simple squamous mesothelium over areolar tissue that secretes watery transudate to reduce friction.

Cutaneous Membrane

The skin; a waterproof membrane consisting of a keratinized stratified squamous epithelium (epidermis) supported by underlying dense irregular connective tissue (dermis).

Synovial Membrane

A membrane lining joint cavities that lacks a true epithelium and secretes synovial fluid to lubricate and cushion articular surfaces.

Fasciae

Connective tissue layers and wrappings that support, insulate, and surround muscles and organs, categorized into superficial, deep, and subserous types.

Skeletal Muscle Tissue

A voluntary, striated muscle tissue composed of long, cylindrical, multinucleated fibers responsible for body movement and heat production.

Cardiac Muscle Tissue

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

Smooth Muscle Tissue

An involuntary, non-striated muscle tissue of spindle-shaped, uninucleated cells that regulates organ and blood vessel diameter and propels luminal contents via peristalsis.

Neuroglia

Supportive accessory cells of nervous tissue that maintain structural integrity, phagocytose debris, supply nutrients, and regulate interstitial fluid surrounding neurons.

Mast Cells

Connective tissue cells that activate during tissue injury to release histamine, heparin, and prostaglandins, initiating the inflammatory response.

Decubitus Ulcer

A pressure sore that develops when sustained pressure applied to skin and deeper tissues exceeds the normal capillary filling pressure of $32\,\text{mmHg}$, leading to necrosis.