AUDIO Histology of Connective Tissue, Epithelium, and Skin

Vocabulary flashcards covering major terms from the lecture on connective tissue, epithelium, and skin histology.

Epithelial Tissue

Avascular sheets of tightly packed cells derived from ectoderm or endoderm that line surfaces, cavities, and glands.

Connective Tissue

Mesoderm-derived tissue with widely spaced cells, abundant extracellular matrix (fibers + ground substance), and rich vascularity (except cartilage).

Simple Epithelium

Single cell layer lining surfaces; all cells contact the basement membrane.

Stratified Epithelium

Two or more cell layers; only basal layer contacts the basement membrane.

Squamous Cell

Flat, thin epithelial cell wider than it is tall.

Cuboidal Cell

Epithelial cell approximately equal in height and width; cube-shaped.

Columnar Cell

Tall epithelial cell whose height exceeds width.

Pseudostratified Epithelium

Single layer of columnar cells with nuclei at different levels giving a false multilayered appearance; all cells rest on basement membrane.

Transitional Epithelium

Stratified epithelium of urinary tract capable of stretching; surface umbrella cells change from cuboidal to squamous.

Microvilli

Short actin-filled apical projections that increase absorptive surface area; form a brush border.

Cilia

Motile or non-motile microtubule-based apical projections (9+2 or 9+0) responsible for fluid movement or sensation.

Stereocilia

Very long, actin-based, non-motile apical projections found in epididymis and inner ear for absorption or mechanosensation.

Tight (Occluding) Junction

Most apical intercellular junction sealing adjacent cells via claudins/occludins to prevent paracellular leakage.

Adherens Junction

Actin-linked belt of cadherins just basal to tight junctions that strengthens cell–cell adhesion.

Desmosome

Spot-weld junction using cadherins that links intermediate filaments of neighboring cells.

Gap Junction

Connexin-built channels allowing ions and small molecules to pass between adjacent cells for communication.

Hemidesmosome

Half-desmosome anchoring epithelial basal plasma membrane to basement membrane via integrins and intermediate filaments.

Basement Membrane

Specialized extracellular matrix (basal lamina + reticular lamina) separating epithelium from underlying connective tissue.

Endocrine Gland

Ductless glandular epithelium releasing hormones into blood or connective tissue.

Exocrine Gland

Gland that secretes products onto a surface directly or through ducts.

Merocrine Secretion

Exocytosis of membrane-bound vesicles; most common glandular mode (e.g., salivary gland).

Apocrine Secretion

Release of product enveloped by a thin rim of apical cytoplasm and plasma membrane (e.g., mammary gland).

Holocrine Secretion

Entire secretory cell undergoes lysis to release contents (e.g., sebaceous gland).

Collagen Fiber

Thick, strong, inelastic bundles of type I or II collagen providing tensile strength.

Elastic Fiber

Thin elastin-containing fibers capable of stretch and recoil like rubber bands.

Reticular Fiber

Thin type III collagen fibrils forming delicate branching networks that support organs.

Ground Substance

Amorphous extracellular material of proteoglycans, GAGs, and glycoproteins filling space between cells and fibers.

Loose (Areolar) Connective Tissue

Connective tissue with few fibers, many cells, and abundant ground substance; supports epithelia and organs.

Dense Regular Connective Tissue

Parallel bundles of collagen with fibroblasts aligned between; forms tendons and ligaments.

Dense Irregular Connective Tissue

Collagen bundles arranged haphazardly; resists stress in multiple directions (e.g., dermis reticular layer).

Fibroblast

Principal connective-tissue cell synthesizing fibers and ground substance.

Adipocyte

Fat cell specialized for lipid storage, hormone production, and thermoregulation.

Mast Cell

Granulocyte in connective tissue releasing histamine and cytokines during immune responses.

Osteocyte

Mature bone cell residing in lacunae that maintains bone matrix.

Chondrocyte

Cartilage cell located in lacunae that maintains cartilage matrix.

Hyaline Cartilage

Glassy cartilage with type II collagen, found on articular bone surfaces and respiratory passages.

Elastic Cartilage

Cartilage rich in elastic fibers, giving flexibility (external ear, epiglottis).

Fibrocartilage

Cartilage with abundant type I collagen bundles providing strength (intervertebral discs, pubic symphysis).

Bone

Rigid connective tissue with hydroxyapatite matrix, collagen, and osteocytes; supports and protects.

Blood

Fluid connective tissue of plasma (liquid ground substance) and formed elements (RBCs, WBCs, platelets).

Epidermis

Superficial layer of skin; stratified squamous keratinized epithelium.

Dermis

Connective-tissue layer beneath epidermis; papillary (loose) and reticular (dense irregular) regions.

Hypodermis

Subcutaneous layer of adipose and loose connective tissue anchoring skin to underlying structures.

Stratum Basale

Deepest epidermal layer of stem cells, melanocytes, and Merkel cells resting on basement membrane.

Stratum Spinosum

Layer of living keratinocytes with spine-like desmosomal processes; contains Langerhans cells.

Stratum Granulosum

Dark granular layer where keratinocytes accumulate keratohyalin granules and form water barrier.

Stratum Lucidum

Clear layer present only in thick skin (palms/soles) between granulosum and corneum.

Stratum Corneum

Outermost layer of dead, flattened, keratin-filled corneocytes that are continually shed.

Keratinocyte

Primary epidermal cell producing keratin; undergoes differentiation from basale to corneum.

Melanocyte

Neural-crest–derived cell in stratum basale producing melanin pigment transferred to keratinocytes.

Langerhans Cell

Bone-marrow–derived antigen-presenting dendritic cell in stratum spinosum initiating immune responses.

Merkel Cell

Mechanoreceptor cell in stratum basale associated with nerve endings for light touch.

Lamellar Body

Lipid-filled organelle in granular keratinocytes that forms epidermal water barrier.

Melanosome

Organelle within melanocytes that synthesizes, stores, and transports melanin.

Eccrine Sweat Gland

Widely distributed merocrine gland with stratified cuboidal duct secreting watery sweat for thermoregulation.

Apocrine Sweat Gland

Large gland associated with hair follicles in axilla/groin; wide lumen; becomes active at puberty.

Sebaceous Gland

Holocrine gland releasing sebum into hair follicles to lubricate skin and hair.

Arrector Pili Muscle

Smooth muscle that elevates hair follicle causing goosebumps; autonomically innervated.

Hair Follicle

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

Dermal Papillae (Skin)

Finger-like projections of dermis into epidermis increasing surface area for attachment and nourishment.

Pacinian Corpuscle

Large onion-like mechanoreceptor in deep dermis/hypodermis sensing pressure and vibration.

Meissner's Corpuscle

Touch receptor in dermal papillae detecting light discriminative touch.

Ruffini Corpuscle

Dermal mechanoreceptor responsive to skin stretch.

Krause End Bulb

Encapsulated receptor in dermis, abundant in genitals; likely senses cold or vibration.

Free Nerve Ending

Unencapsulated nerve ending in epidermis/dermis sensing pain, temperature, and crude touch.

Psoriasis

Autoimmune hyper-proliferative skin disease with accelerated keratinocyte turnover (3–10 days).

Eczema

Inflammatory skin condition (genetic + environmental) featuring rapid epidermal turnover and itching.

Vitamin D3 (Cholecalciferol)

Compound synthesized in skin from 7-dehydrocholesterol upon UVB exposure; activated in liver and kidney.

Melanocyte-Stimulating Hormone (MSH)

Pituitary hormone that binds melanocytes to regulate melanin production; sensitivity varies among skin tones.