Connective Tissue & Epithelium – Key Vocabulary

Vocabulary flashcards covering epithelial types, apical modifications, cell junctions, glands, connective tissue components, skin layers, epidermal cells, pigment biology, specialized skin structures, sensory receptors, and key molecular terms.

Epithelium

Avascular, polarized tissue composed of closely packed cells that line surfaces, tubes and cavities.

Simple Squamous Epithelium

Single layer of flat cells; lines blood vessel lumens (endothelium) and body cavities (mesothelium).

Simple Cuboidal Epithelium

Single layer of cube-shaped cells; forms ducts such as apocrine sweat-gland walls.

Simple Columnar Epithelium

Single layer of tall cells; can be ciliated (uterine tubes) or have microvilli (intestines).

Pseudostratified Columnar Epithelium

Columnar epithelium in which all cells touch the basement membrane but nuclei are at different heights; often ciliated (respiratory tract).

Transitional Epithelium

Stratified epithelium unique to lower urinary tract; umbrella cells allow distention.

Stratified Squamous Keratinized

Multilayered epithelium with surface dead cells full of keratin; forms skin epidermis.

Stratified Squamous Non-keratinized

Multilayered epithelium without surface keratin; lines mouth, esophagus, vagina.

Stratified Cuboidal Epithelium

Two or more layers of cube cells; seen in eccrine sweat-gland ducts.

Stratified Columnar Epithelium

Rare, multilayered columnar cells; present in large salivary-gland ducts.

Microvilli

Actin-based, microscopic projections that increase apical surface for absorption; appear as a brush border.

Terminal Web

Actin network anchoring the cores of microvilli to the apical cytoplasm.

Cilia

Microtubule-based (9×2 or 9×0) apical projections that move fluid or serve sensory roles.

Motile Cilia

9×2 microtubule arrangement; beat in waves to move material (e.g., oviduct).

Primary (Non-Motile) Cilium

9×0 microtubule core; bends passively, functions in chemical sensation.

Stereocilia

Very long actin-based projections; passive movement, found in epididymis and inner ear.

Tight Junction (Occluding Junction)

Most apical lateral junction; claudin & occludin seal adjacent cells, linking actin.

Adherens Junction (Zonula Adherens)

Cadherin-based belt below tight junction; connects actin filaments of neighboring cells.

Desmosome (Macula Adherens)

Spot welds using cadherins that link intermediate filaments between cells.

Gap Junction

Connexon channels (connexin ×6) that allow ions and small molecules to pass between cells.

Hemidesmosome

Integrin-based junction anchoring intermediate filaments to the basement membrane.

Focal Adhesion

Integrin-based complex linking actin filaments to the basement membrane; senses mechanical stress.

Exocrine Gland

Secretes product onto a surface directly or via ducts (e.g., sweat, salivary glands).

Endocrine Gland

Secretes hormones into connective tissue to enter bloodstream; lacks duct and basal lamina can be absent.

Merocrine Secretion

Exocytosis of membrane-bound vesicles; most common (salivary glands, eccrine sweat).

Apocrine Secretion

Product released with thin rim of cytoplasm and plasma membrane (mammary gland, axillary sweat).

Holocrine Secretion

Entire cell ruptures to release accumulated product (sebaceous glands).

Goblet Cell

Unicellular exocrine gland that secretes mucin in GI and respiratory epithelium.

Fibroblast

Most common CT cell; synthesizes collagen, elastin and ground substance.

Mast Cell

Granulocyte in CT; releases histamine & cytokines during immune responses.

Adipocyte

Fat cell for energy storage and hormone synthesis; nucleus pushed to side.

Collagen Fiber

Thick bundles of collagen type I or II; strong, inelastic, stain pink with H&E.

Reticular Fiber

Thin type III collagen fibers forming meshwork; visible with silver stain.

Elastic Fiber

Elastin-based fibers capable of stretch and recoil; difficult to see in H&E.

Ground Substance

Amorphous CT matrix of proteoglycans, GAGs, glycoproteins; can be liquid, gel, or solid.

Loose (Areolar) Connective Tissue

Few fibers, abundant ground substance; underlies epithelia and surrounds organs.

Dense Regular Connective Tissue

Parallel collagen bundles with trapped fibroblast nuclei; forms tendons & ligaments.

Dense Irregular Connective Tissue

Collagen bundles arranged haphazardly; resists stress in many directions; dermis reticular layer.

Hyaline Cartilage

Glassy cartilage with type II collagen; at articular ends and respiratory passages.

Elastic Cartilage

Cartilage with abundant elastic fibers; ear, epiglottis, auditory tube.

Fibrocartilage

Mixture of dense CT and hyaline; thick type I collagen bundles; intervertebral discs, pubic symphysis.

Osteocyte

Mature bone cell residing in lacuna; maintains bone matrix.

Osteoblast

Bone-forming cell that secretes osteoid; precursor to osteocyte.

Osteoclast

Multinucleated bone-resorbing cell derived from monocytes.

Epidermis

Stratified squamous keratinized epithelium forming skin surface.

Dermis

CT layer below epidermis; papillary (loose) and reticular (dense irregular) layers.

Hypodermis

Subcutaneous layer of adipose and loose CT; cushions and insulates.

Stratum Basale

Deepest epidermal layer; mitotic stem cells, melanocytes, Merkel cells.

Stratum Spinosum

Layer with desmosome-linked keratinocytes; contains Langerhans cells.

Stratum Granulosum

Cells with keratohyaline granules and lamellar bodies; start waterproof barrier.

Stratum Lucidum

Clear layer present only in thick skin; sublayer of stratum corneum.

Stratum Corneum

Surface layer of dead, flattened, anucleate corneocytes rich in keratin.

Keratinocyte

Primary epidermal cell; produces keratin; undergoes differentiation and desquamation.

Keratohyaline Granule

Stratum granulosum granules containing proteins that aggregate keratin filaments.

Lamellar Body

Lipid-rich vesicle secreted by granular cells; forms water barrier.

Desquamation

Shedding of corneocytes from stratum corneum via proteolytic loss of desmosomes.

Psoriasis

Autoimmune hyperproliferative skin disease with rapid turnover (3-10 days) and thick plaques.

Melanocyte

Neural-crest derived cell in stratum basale that synthesizes melanin pigment.

Melanosome

Organelle in melanocytes where melanin is synthesized and packaged.

Eumelanin

Brown-black pigment responsible for dark hair and skin tones.

Pheomelanin

Red-pink pigment; mixes with eumelanin to give red hair and lighter skin areas.

Langerhans Cell

Antigen-presenting dendritic cell in stratum spinosum; initiates immune response.

Merkel Cell

Mechanoreceptor cell in stratum basale associated with light-touch sensation.

Hair Follicle

Epidermal invagination producing hair; contains bulb with matrix cells and melanocytes.

Arrector Pili Muscle

Smooth muscle causing hair to stand (goose bumps); autonomic innervation.

Sebaceous Gland

Holocrine gland associated with hair follicle; secretes lipid-rich sebum.

Eccrine Sweat Gland

Widely distributed merocrine gland; narrow lumen, stratified cuboidal ducts; thermoregulation.

Apocrine Sweat Gland

Large-lumen gland in axilla & groin; secretes pheromone-rich sweat along hair follicle; functional at puberty.

Free Nerve Ending

Unencapsulated sensory fiber ending in epidermis; detects pain, temperature, light touch.

Meissner’s Corpuscle

Encapsulated mechanoreceptor in dermal papillae; senses light touch.

Pacinian Corpuscle

Large onion-like receptor deep in dermis/hypodermis; detects pressure & vibration.

Ruffini Corpuscle

Spindle-shaped dermal receptor that detects stretch.

Krause End Bulb

Encapsulated receptor in reticular dermis; function possibly cold or vibration sensing.

Vitamin D3 Synthesis

Photochemical conversion in stratum basale under UVB, leading to calcitriol production.

Fitzpatrick Phototype

System classifying skin by melanogenic response to UV exposure.

Tight Junction Proteins

Claudin and occludin—seal paracellular pathway in epithelia.

Cadherin

Calcium-dependent adhesion protein in adherens junctions and desmosomes.

Integrin

Transmembrane receptor linking cytoskeleton to ECM in hemidesmosomes and focal adhesions.

Connexon

Hexameric assembly of connexins forming a gap-junction channel.

Hydroxyapatite

Calcium phosphate crystal that forms bone’s solid ground substance.

Basement Membrane

Basal lamina plus reticular lamina; anchors epithelium to CT.