Tissues and the Integumentary System

Vocabulary practice flashcards covering tissue types, epithelial classifications, connective tissue matrices, muscle and nervous tissues, tissue repair, skin layers, glands, skin pigments, cancers, burns, and integumentary conditions.

Tissue

A group of similar cells that perform a common or related function.

Histology

The study of the microscopic structure of tissues.

Four primary tissues

Epithelial, connective, muscle, and nervous tissue.

Epithelial tissue

A sheet of cells that covers body surfaces or cavities, including covering and lining epithelia and glandular epithelia.

Connective tissue

The most abundant and widely distributed primary tissue; it binds, supports, protects, insulates, stores reserve fuel, and transports substances.

Muscle tissue

Highly vascular tissue that produces movement through actin and myosin myofilaments.

Nervous tissue

Tissue of the brain, spinal cord, and nerves that regulates and controls body functions.

Polarity (epithelial)

Epithelial characteristic where the apical surface is free and exposed to a surface or cavity, while the basal surface is attached and faces inward toward the body.

Specialized contacts

Cellular structures such as tight junctions and desmosomes that bind epithelial cells into continuous sheets.

Avascular but innervated

Epithelial characteristic indicating that the tissue contains no blood vessels but is supplied by nerve connections.

Simple epithelium

Epithelium consisting of a single cell layer.

Stratified epithelium

Epithelium consisting of two or more cell layers, where protection is a primary role.

Squamous cells

Flattened and scale-like epithelial cells.

Cuboidal cells

Box-like or cube-shaped epithelial cells.

Columnar cells

Tall and column-like epithelial cells.

Simple squamous epithelium

One thin layer of flattened cells prioritized for rapid diffusion; lines kidney tubules, lung alveoli, blood vessels (endothelium), and serous membranes (mesothelium).

Simple cuboidal epithelium

One layer of cube-shaped cells active in secretion and absorption; located in smallest gland ducts and many kidney tubules.

Simple columnar epithelium

One layer of tall, close-packed cells specialized for absorption and secretion of mucus and enzymes; lines the gastrointestinal tract.

Stratified squamous epithelium

Multiple cell layers with flattened apical cells that protect high-wear areas; keratinized in skin and nonkeratinized in moist body linings.

Pseudostratified columnar epithelium

Single cell layer that appears multilayered due to varying cell heights and nuclear levels, though every cell touches the basement membrane; secretes and moves mucus in upper respiratory pathways.

Transitional epithelium

Epithelium whose cells change shape when stretched, increasing urine flow and storage capacity; lines the urinary bladder, ureters, and urethra.

Endocrine gland

Ductless gland that secretes hormones by exocytosis into interstitial fluid to be carried by blood or lymph to target organs.

Exocrine gland

Gland that secretes its products through ducts onto body surfaces or into body cavities (e.g., mucous, sweat, oil, and salivary glands).

Goblet cell

Unicellular exocrine gland in intestinal and respiratory linings that produces mucin, which dissolves in water to form protective, lubricating mucus.

Merocrine secretion

Mode of secretion where products are secreted by exocytosis as they are produced (e.g., sweat glands, pancreas, salivary glands).

Apocrine secretion

Mode of secretion where product accumulates within the cell and only the cell apex ruptures.

Holocrine secretion

Mode of secretion where whole cells accumulate product and then rupture, requiring replacement by underlying cell division (e.g., sebaceous glands).

Extracellular matrix

Protein-sugar mesh surrounding cells in connective tissue that enables tissue to bear weight, resist tension, and endure trauma.

Ground substance

Gel-like material between connective tissue cells composed of interstitial fluid, cell-adhesion proteins, proteoglycans, and trapped water through which solutes diffuse.

Collagen fibers

The strongest and most abundant connective tissue fibers, providing high tensile strength.

Elastic fibers

Long, thin fibers made of elastin that stretch and recoil.

Reticular fibers

Short, fine, highly branched collagenous fibers that form supportive networks (stroma) with more give.

Blast cells

Immature, active connective tissue cells that secrete ground substance and fibers (e.g., fibroblasts, chondroblasts, osteoblasts).

Cyte cells

Mature, less active connective tissue cells responsible for maintaining the matrix (e.g., fibrocytes, chondrocytes, osteocytes).

Mast cells

Connective tissue cells that trigger local inflammation against microorganisms using heparin, histamine, proteases, and other enzymes.

Macrophages

Phagocytic cells that ingest dead cells and microorganisms in connective tissue.

Areolar connective tissue

Most widely distributed loose connective tissue; features loose collagen fibers and abundant ground substance serving as packing material and a water reservoir.

Adipose tissue

Connective tissue rich in adipocytes with scant matrix; white fat stores energy, cushions, and insulates, while brown fat heats blood.

Dense regular connective tissue

Connective tissue composed of parallel, closely packed collagen bundles with high tensile strength in one direction; forms tendons and ligaments.

Dense irregular connective tissue

Connective tissue composed of thick collagen bundles arranged irregularly in sheets to resist tension from multiple directions; found in dermis and joint capsules.

Hyaline cartilage

Most abundant cartilage in the body, presenting a shiny bluish gristle appearance; covers ends of long bones and forms nose, trachea, larynx, and ribs.

Fibrocartilage

Very strong cartilage with properties between hyaline cartilage and dense regular connective tissue; found in intervertebral discs and knees.

Bone tissue

Richly vascularized connective tissue composed of collagen and inorganic calcium salts organized into structural units called osteons.

Skeletal muscle

Voluntary, striated muscle attached to bones containing long, multinucleate muscle fibers.

Cardiac muscle

Involuntary, striated muscle found only in the heart wall, featuring branching cells, single nuclei, and intercalated discs.

Smooth muscle

Involuntary, nonstriated muscle composed of spindle-shaped cells with one nucleus; found in walls of hollow organs other than the heart.

Cutaneous membrane

Dry membrane exposed to air consisting of keratinized stratified squamous epidermis attached to a thick dermal connective tissue layer (the skin).

Mucous membrane

Moist membrane lining cavities open to the exterior (digestive, respiratory, urogenital tracts) where epithelium lies on loose connective tissue called lamina propria.

Serous membrane

Double-layered membrane composed of simple squamous mesothelium on thin areolar connective tissue lining closed ventral body cavities (pleurae, pericardium, peritoneum).

Regeneration vs Fibrosis

Regeneration replaces destroyed tissue with the same tissue type to restore function, whereas fibrosis replaces destroyed tissue with scar tissue (connective tissue), losing original function.

Germ layer origins

Ectoderm produces nervous tissue; mesoderm produces muscle and connective tissue; all three germ layers produce epithelial tissue.

Epidermis

Superficial, avascular skin layer composed mostly of keratinized stratified squamous epithelium.

Dermis

Vascular skin layer under the epidermis, composed of loose areolar connective tissue superficially and dense irregular connective tissue deeply.

Hypodermis

Subcutaneous tissue beneath the skin (superficial fascia) consisting mostly of adipose tissue that anchors skin, absorbs shock, and insulates.

Keratinocyte

Most common epidermal cell; produces protective keratin and connects to adjacent cells via desmosomes.

Melanocyte

Spider-shaped cell in the deepest epidermal layer that synthesizes melanin and transfers it in melanosomes to keratinocytes to protect DNA from UV damage.

Dendritic cell (Langerhans cell)

Star-shaped macrophage in the deep epidermis that phagocytizes foreign material and activates the immune system.

Tactile cell (Merkel cell)

Touch receptor cell located at the epidermal-dermal junction.

Stratum basale

Deepest epidermal layer (stratum germinativum) attached to dermis; consists of a single row of mitotic stem cells, melanocytes, and Merkel cells.

Stratum granulosum

Epidermal layer of $4$ to $6$ cell rows where keratinization begins, containing keratohyaline granules and water-resistant glycolipid-releasing lamellar granules.

Stratum lucidum

Clear layer of flat, dead keratinocytes found only in thick skin (palms and soles) for extra protection in high-abrasion areas.

Stratum corneum

Outermost epidermal layer consisting of $20$ to $30$ rows of flat, anucleated, dead keratinized cells that account for three-fourths of epidermal thickness.

Papillary layer

Superficial dermal layer composed of loose areolar connective tissue containing dermal papillae with capillary loops, free nerve endings, and Meissner corpuscles.

Reticular layer

Deep dermal layer accounting for about $80\%$ of dermal thickness, composed of dense irregular connective tissue containing the cutaneous plexus and cleavage lines.

Melanin

Only pigment made in skin, synthesized by tyrosinase from tyrosine; local accumulations form freckles and moles.

Cyanosis

Blue skin coloration resulting from low oxygenation of hemoglobin, typically signaling respiratory or cardiovascular problems.

Erythema

Skin redness resulting from embarrassment, fever, hypertension, inflammation, or allergic reactions.

Jaundice

Yellow skin cast primarily associated with liver disorders.

Eccrine sweat gland

Most numerous sweat gland, under sympathetic control, secreting hypotonic sweat ($99\%$ water, salts, vitamin C, antibodies, wastes) for thermoregulation.

Apocrine sweat gland

Large sweat gland in axillary and anogenital regions opening into hair follicles; secretes viscous, protein- and lipid-rich fluid that produces body odor upon bacterial action.

Sebaceous gland

Androgen-stimulated holocrine gland absent from palms and soles that secretes oily, bactericidal sebum into hair follicles to soften skin and hair.

Basal cell carcinoma

Most common and least malignant skin cancer, originating from stratum basale cells and invading slowly.

Melanoma

Most dangerous skin cancer, originating from melanocytes; highly metastatic and resistant to chemotherapy.

Third-degree burn

Full-thickness burn affecting full skin thickness; appears gray-white, cherry red, or blackened and is painless due to destroyed nerve endings.

Rule of Nines

Clinical estimation tool dividing the body into eleven $9\%$ sections plus $1\%$ for genitals to calculate fluid loss in burn patients.

Alopecia

Hair thinning occurring in both sexes after age $40$ when hair shedding exceeds replacement rate.

Telogen effluvium

Abrupt hair thinning caused when numerous hair follicles prematurely enter the resting phase simultaneously.

Vernix caseosa

Fatty sebaceous gland secretion that coats and protects fetal skin from amniotic fluid.