Histology: Tissue Types, Extracellular Matrix, Epithelia, and Glands

Vocabulary practice flashcards covering primary tissue classes, extracellular matrix components, intercellular junctions, epithelial classification and transport, and exocrine and endocrine 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 that form 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.

Nervous Tissue

A primary tissue class composed of cells exhibiting numerous processes within a mostly fluid extracellular matrix, specialized to process and transmit information.

Muscular Tissue

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

Extracellular Matrix (ECM)

Substance secreted and maintained by cells, composed of ground substance and fibrous proteins.

Ground Substance

A gelatinous to rubbery extracellular fluid, gel, or solid containing water, ions, nutrients, glycosaminoglycans, proteoglycans, and glycoproteins.

Glycosaminoglycans (GAGs)

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

Proteoglycans

Bottle-brush-like structures in ground substance that slow pathogens and connect the extracellular matrix to cell membranes.

Glycoproteins

Molecules that bind cell plasma membranes to extracellular collagen and proteoglycans.

Collagenous Fibers

Tough fibers that make up $25\%$ of the body's protein and resist stretching and tension.

Reticular Fibers

Thin collagen fibers coated with glycoproteins that provide support and form spongelike frameworks for the spleen and lymph nodes.

Elastic Fibers

Extracellular fibers made of elastin, a coiled protein with the ability to recoil (elasticity).

Tight Junctions

Intercellular connections formed when integral membrane proteins of adjacent cells lock together to establish an impermeable seal.

Desmosomes

Intercellular junctions where integral membrane proteins interweave between cells and connect to intracellular intermediate filaments to resist mechanical stress.

Gap Junctions

Interlinked protein pores that form channels allowing substances to pass directly between adjacent cells.

Apical Surface

The epithelial cell surface that is oriented toward and associated with the external environment or an internal organ cavity.

Basal Surface

The epithelial surface associated with the basal lamina (a non-cellular filter between tissue types).

Basement Membrane

A supporting structure composed of the basal lamina and reticular lamina that anchors the epithelium to underlying connective tissue and provides structural strength.

Simple Epithelia

Epithelial tissues consisting of a single layer of cells, where every cell contacts the basement membrane.

Stratified Epithelia

Epithelial tissues consisting of 2 to 20 layers of cells, where only the deepest layer contacts the basal membrane.

Goblet Cells

Wineglass-shaped cells located amongst columnar epithelium that synthesize and secrete mucous.

Simple Squamous Epithelium

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

Simple Cuboidal Epithelium

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

Simple Columnar Epithelium

A single row of tall, narrow cells that often possess microvilli and goblet cells, functioning in absorption and secretion; found in the GI tract lining, uterus, kidneys, and uterine tubes.

Pseudostratified Columnar Epithelium

An epithelium containing cells of unequal heights that all contact the basement membrane, typically possessing cilia and goblet cells to secrete and propel mucous; found in the upper respiratory tract and portions of the male urethra.

Transcellular Transport

Movement of substances directly across an epithelial cell via osmosis, simple diffusion, facilitated diffusion, active transport, or vesicular transport.

Paracellular Transport

Movement of substances between adjacent epithelial cells, which is less common due to the presence of tight junctions.

Keratinized Stratified Squamous Epithelium

A multilayered epithelium characterized by flat, scaly, dead cell layers at the surface packed with keratin that resists abrasion and retards water loss; found in the epidermis, palms, and soles.

Non-keratinized Stratified Squamous Epithelium

A multilayered, abrasion-resistant epithelium that lacks keratin and dead cell layers at its surface; found in the tongue, oral mucosa, esophagus, and vagina.

Stratified Cuboidal Epithelium

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

Transitional Epithelium

A multilayered epithelium whose apical cells shift from round to flattened shape when stretched, featuring a protective flexible lipid layer; found in the ureter and bladder.

Exocrine Glands

Glands that maintain contact with the body surface or cavities via ducts to release secretions such as sweat, milk, or saliva.

Endocrine Glands

Ductless glands that secrete products (such as hormones) directly into the bloodstream.

Capsule

A connective tissue covering that encapsulates a multicellular exocrine gland.

Septa (Trabeculae)

Connective tissue partitions extending from the capsule that compartmentalize the interior of a gland.

Stroma

The supportive connective tissue framework of a gland consisting of the capsule and septa.

Parenchyma

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

Merocrine (Eccrine) Secretion

A secretion mode in which secretory products are packaged into vesicles and released via exocytosis without loss of cytoplasm (e.g., tear glands, pancreas, gastric glands, sweat).

Apocrine Secretion

A secretion mode in which secretory vesicles along with a portion of the apical cytoplasm break off and detach from the cell (e.g., mammary glands).

Holocrine Secretion

A secretion mode in which cells accumulate secretory product throughout their cytoplasm and then completely rupture to release it (e.g., sebaceous glands on the scalp).