Histology: Tissues and Epithelial Structures

Vocabulary practice flashcards covering primary tissue types, extracellular matrix components, cell junctions, epithelial classifications, and exocrine gland structures.

Histology

The study of the normal structure of tissues.

Tissue

Groups of cells, similar in structure, that cooperate to perform a function, embedded in an extracellular matrix of ground substance and fibrous proteins.

Epithelial Tissue

A primary tissue class characterized by sheets of tightly packed cells with little visible extracellular matrix, forming coverings, linings, or glands.

Connective Tissue

A primary tissue class consisting of loosely scattered cells where the extracellular matrix is the most prominent structural component; binds, supports, protects, and connects parts of the body.

Muscular Tissue

A primary tissue class composed of long, cylindrical or spindle-shaped contractile cells with little visible extracellular matrix that generate force.

Nervous Tissue

A primary tissue class featuring cells with numerous processes embedded in a mostly fluid extracellular matrix that process and transmit information.

Extracellular Matrix (ECM)

The substance secreted and maintained by cells, composed of ground substance (extracellular fluid, gel, or solid) and fibrous proteins.

Glycosaminoglycans (GAGs)

Charged macromolecules in ground substance (such as chondroitin sulfate, heparin, and hyaluronic acid) that attract water molecules.

Proteoglycans

"Bottle brush"-like ground substance complexes composed of carbohydrates and proteins that slow pathogens and connect the extracellular matrix to cell membranes.

Glycoproteins

Molecules in the ground substance that bind plasma membranes to extracellular collagen and proteoglycans.

Collagenous Fibers

Tough fibrous proteins that resist stretching and comprise approximately $25\%$ of total body protein.

Reticular Fibers

Thin collagen fibers coated with glycoproteins that form sponge-like supportive frameworks for organs such as the spleen and lymph nodes.

Elastic Fibers

Fibrous proteins composed of elastin, a coiled protein capable of stretching and recoiling.

Tight Junctions

Intercellular junctions formed by integral membrane proteins of adjacent cells locking together to create an impermeable seal.

Desmosomes

Mechanical stress-resisting junctions where integral membrane proteins interweave between adjacent cells and attach to intermediate filaments inside the cells.

Gap Junctions

Intercellular junctions formed by interlinked protein pores that allow direct passage of substances between cells.

Basement Membrane

A supporting layer anchoring epithelial cells to underlying connective tissue, composed of the basal lamina and the reticular lamina.

Simple Squamous Epithelium

A single layer of thin, flat, scaly cells bound by tight junctions that permits rapid diffusion or transport and secretes lubricating serous fluid; located in lung alveoli, kidney glomeruli, endothelium, and serosa.

Simple Cuboidal Epithelium

A single layer of square or round cells performing absorption and secretory functions; found in the liver, thyroid, mammary glands, salivary glands, kidney tubules, and bronchioles.

Simple Columnar Epithelium

A single layer of tall, narrow cells often featuring a brush border of microvilli and goblet cells for absorption and secretion; lines the GI tract, uterus, kidneys, and uterine tubes.

Pseudostratified Columnar Epithelium

An epithelium where all cells touch the basement membrane but vary in height, typically possessing cilia and goblet cells to secrete and propel mucus; located in the upper respiratory tract and parts of the male urethra.

Goblet Cells

Wineglass-shaped unicellular glands found within columnar epithelia that synthesize and secrete mucus.

Transcellular Transport

Movement of substances directly across and through epithelial cells via osmosis, simple diffusion, facilitated diffusion, active transport, or vesicular transport.

Paracellular Transport

Movement of substances across an epithelial sheet through the spaces between adjacent cells; restricted by the presence of tight junctions.

Keratinized Stratified Squamous Epithelium

A multi-layered epithelium covered with flat, scaly, dead cell layers packed with keratin; resists abrasion and retards water loss in the epidermis, palms, and soles.

Non-Keratinized Stratified Squamous Epithelium

A multi-layered epithelium lacking dead cell layers and keratin that resists abrasion on moist internal surfaces like the tongue, oral mucosa, esophagus, and vagina.

Stratified Cuboidal Epithelium

An epithelium containing two or more layers of cuboidal or round cells that functions in sweat secretion, ovarian hormone production, and sperm production; found in sweat gland ducts, ovarian follicles, and seminiferous tubules.

Transitional Epithelium

A multilayered epithelium whose cells shift from rounded to flattened when stretched, featuring an apical surface with a protective lipid layer; found in the ureter and urinary bladder.

Exocrine Glands

Glands that maintain contact with epithelial surfaces by releasing their secretions through ducts.

Endocrine Glands

Ductless glands that secrete chemical messengers directly into the bloodstream.

Stroma

The supportive connective tissue framework of a multicellular exocrine gland, comprising the external capsule and internal septa (trabeculae).

Parenchyma

The functional secretory cells (typically cuboidal) of a gland that synthesize and secrete products.

Merocrine (Eccrine) Secretion

A mode of exocrine secretion where products are released inside vesicles via exocytosis without cellular destruction (e.g., tear glands, pancreas, gastric glands, sweat glands).

Apocrine Secretion

An exocrine secretion mode in which vesicles and a portion of apical cytoplasm pinch off from the cell to release product (e.g., mammary glands).

Holocrine Secretion

A mode of exocrine secretion in which cells accumulate product and subsequently disintegrate entirely to release it (e.g., sebaceous glands of the scalp).