definition

Receptor

Plasma membrane protein binding extracellular chemical messengers (e.g., hormones).

Enzyme (Membrane)

Plasma membrane protein with catalytic active site facing ECF or ICF.

Ion Channel

Transmembrane protein forming a aqueous pore for specific ions.

Gated lon Channel

Channel protein opening/closing in response to specific stimuli (voltage, ligand, mechanical).

Cell-Identity Marker

Glycoprotein carrying unique carbohydrate chains.

Cell-Adhesion Molecule (CAM)

Transmembrane protein binding to CAMs of adjacent cells.

Facilitated Diffusion

Carrier/channel-mediated passive transport down concentration gradient.

Simple Diffusion

Direct unassisted movement of solutes across lipid bilayer.

Filtration

Passive movement of fluid and small dissolved solutes across tissue layer driven by hydrostatic pressure.

Specificity (Carrier Transport)

Receptor site on transport protein binds only specific ligand(s).

Transport Maximum (Tm)

Solute transport rate when all carrier proteins are fully saturated.

Hyperplasia

Normal tissue growth via cell multiplication (mitosis).

Hypertrophy

Tissue growth via enlargement of pre-existing cells.

Neoplasia

Abnormal development of a tumor composed of dysfunctional tissue.

Cell Differentiation

stem/precursor cells turn into specialized mature cell types.

Metaplasia

Transformation of one mature tissue type into another mature tissue type.

Ectoderm

Outer primary germ layer of embryo.

Endoderm

Inner primary germ layer of embryo.

Mesoderm

Middle primary germ layer of embryo forming gelatinous mesenchyme.

Basal Lamina (Basement Membrane)

Protein sheet attached to basal surface of epithelial tissue.

Tight Junctions (Occluding Junctions)

Continuous region where plasma membranes of adjacent cells are fused by adhesion proteins.

Desmosomes (Anchoring Junctions)

Protein patch/plaque holding cells together via J-shaped transmembrane proteins and intermediate filaments.

Hemidesmosomes

structures on basal surface of epithelial cells to anchor them

Gap Junctions (Communicating Junctions)

Ring-like connexon protein complexes forming water-filled intercellular pores.

Simple Squamous ET

Single layer of thin, flat, plate-like cells.

Simple Cuboidal ET

Single layer of squarish or rounded cube-like cells.

Simple Columnar ET

Single layer of tall, narrow, stalk-like cells with apical microvilli and goblet cells.

Goblet Cells

Bulbous, wineglass-shaped clear cells interspersed within columnar/pseudostratified ET.

Pseudostratified Ciliated Columnar ET (PSCCE)

Single layer of cells appearing multi-layered; all cells touch basement membrane; ciliated apical surface with goblet cells.

Keratinized Stratified Squamous ET

Multi-layered ET with dead, flat, keratin-packed scaly surface cells lacking nuclei.

Non-Keratinized Stratified Squamous ET

Multi-layered ET lacking dead keratin surface layer; surface cells remain living and nucleated.

Transitional ET

Multi-layered ET with rounded dome surface cells that flatten upon distension.

Exocrine Glands

Glands maintaining contact with body surfaces via an epithelial duct.

Endocrine Glands

Ductless glands releasing secretions directly into bloodstream/ECF.

Merocrine (Eccrine) Secretion

Exocrine secretion via vesicular exocytosis into a duct or space.

Apocrine Secretion

"Decapitation secretion" where apical membrane portion fragments off into duct.

Holocrine Secretion

"Suicide secretion" where entire disintegrating cell becomes the secretory product.

Fibroblasts

Most abundant cell type in CT proper.

Macrophages

Large phagocytic immune cells resident in CT derived from blood monocytes.

Mast Cells

Resident immune cells located along blood vessels in CT.

Type I Collagenous Fibers

Thick, tough, stretch-resistant, flexible collagen protein fibers.

Elastic Fibers

Thin, branching fibers made of elastin protein.

Reticular Fibers

Thin, branching network of Type III collagen coated with glycoproteins.

Glycosaminoglycans (GAGs)

Long negatively charged polysaccharides of amino sugars (e.g., chondroitin, hyaluronic acid).

Proteoglycans (PGs)

Massive macromolecular complexes incorporating GAGs bound to protein cores.

Dense Regular CT

Parallely arranged, packed Type I collagen fibers with few fibroblasts and little ground substance.

Dense Irregular CT

Randomly interwoven thick bundles of Type I collagen fibers.

Loose Areolar CT

Loosely arranged Type I collagen & elastic fibers, abundant ground substance, rich microvasculature.

Reticular CT

Meshwork of Type III reticular collagen fibers populated by lymphocytes.

Adipose Tissue

CT dominated by clusters of adipocytes with thin collagen framework.

Chondroblasts

Immature cartilage cells.

Chondrocytes

Mature cartilage cells housed within small matrix cavities called lacunae.

Perichondrium

Sheath of dense irregular CT surrounding most hyaline and elastic cartilage.

Hyaline Cartilage

Flexible cartilage with smooth, glassy matrix containing fine Type II collagen fibers.

Elastic Cartilage

Modified hyaline cartilage with dense network of elastic fibers.

Fibrocartilage

Extremely tough cartilage containing coarse, thick bundles of Type I collagen fibers.

Cutaneous Membrane

The skin; largest membrane.

Mucous Membrane (Mucosa)

Membrane lining hollow internal organs that open to external environment.

Serous Membrane (Serosa)

Membrane lining closed internal body cavities and covering resident organs.

Keratin

Tough, durable fibrous protein produced by keratinocytes.

Acid Mantle

Low pH (acidic) film on skin surface composed of sebum and sweat.

Epidermis

Superficial layer of skin composed of keratinized stratified squamous ET; avascular.

Dermis

Deep connective tissue layer of skin composed of papillary (areolar) and reticular (dense irregular) layers.

Hypodermis (Subcutaneous Layer)

Layer deep to dermis composed predominantly of adipose tissue and rich vasculature.

Thick Skin

Specialized skin featuring ~5x thicker epidermis with stratum lucidum and distinct ridges.

Thin Skin

Skin covering rest of body with thinner epidermis.

Stratum Basale

Deepest single row of columnar/cuboidal basal cells resting on basal lamina.

Stratum Spinosum

Thickest living epidermal stratum; contains several layers of keratinocytes and dendritic cells.

Stratum Granulosum

3-5 rows of flattened living keratinocytes containing dark basophilic keratohyalin granules.

Stratum Lucidum

Thin, translucent zone of pale dead keratinocytes containing eleidin protein.

Stratum Corneum

Most superficial layer consisting of up to 30 rows of dead, scaly, cornified, fully keratinized corneocytes.

Keratinocytes

Majority (~90-95%) of epidermal cells.

Melanocytes

Specialized cells residing exclusively in stratum basale with long branching processes.

Tactile (Merkel) Cells

Basal cells in stratum basale associated with sensory nerve endings.

Dendritic (Langerhans) Cells

Macrophage-like immune surveillance cells resident in stratum spinosum.

Papillary Layer (Dermis)

Superficial 20% of dermis composed of loose areolar CT.

Reticular Layer (Dermis)

Deeper 80% of dermis composed of thick, wavy dense irregular CT.

Tactile (Meissner's) Corpuscles

Encapsulated nerve endings located within dermal papillae.

Pacinian (Lamellar) Corpuscles

Large layered encapsulated sensory receptors in deep reticular dermis/hypodermis.

Hair Follicle

Epidermal invagination of stratum basale extending into dermis/hypodermis.

Hair Matrix

Mitotically active layer of living cells immediately above hair dermal papilla in bulb.

Arrector Pili (Piloerector) Muscle

Smooth muscle ribbon extending from dermal collagen to hair follicle root sheath.

Merocrine (Eccrine) Sweat Glands

Abundant simple coiled tubular glands with ducts opening directly onto skin pores.

Apocrine Sweat Glands

Large coiled tubular glands with ducts opening into hair follicles.

Sebaceous Glands

Flask-shaped holocrine glands opening into hair follicles.

Ceruminous Glands

Coiled tubular apocrine glands located in external auditory canal.

Mammary Glands

Milk-producing apocrine glands developing during pregnancy/lactation in female breasts.

Osteology

Scientific study of bone structure and osseous tissue.

Diaphysis

Shaft of a long bone composed of thick compact bone surrounding medullary cavity.

Epiphysis

Expanded head at end of long bone; filled with spongy bone containing bone marrow.

Epiphyseal Plate

Layer of hyaline cartilage in metaphysis between epiphysis and diaphysis in children/adolescents.

Epiphyseal Line

Bony scar remaining in adult bone after epiphyseal plate cartilage is fully ossified.

Periosteum

Dual-layered fibrous sheath covering outer surface of bone (except at articular cartilages).

Perforating (Sharpey's) Fibers

Collagen fibers of outer periosteum penetrating directly into bone matrix.

Endosteum

Thin layer of reticular CT lining internal marrow cavities, central canals, and spicules of spongy bone.

Nutrient Foramina

Minute holes on surface of bone allowing blood vessels and nerves to enter.

Osteogenic (Osteoprogenitor) Cells

Stem cells derived from embryonic mesenchyme located in endosteum and inner periosteum.

Osteoblasts

Non-mitotic bone-forming cells lining inner periosteum and endosteum.

Osteocytes

Former osteoblasts trapped in calcified matrix within micro-cavities called lacunae.

Canaliculi

Tiny microscopic canals radiating between lacunae in bone matrix.