4. Tissues

Comprehensive vocabulary flashcards covering the primary tissues of the body: epithelial, connective, and muscular tissues, including their structural classifications, cellular specializations, and microscopic histology identification.

Epithelial Tissue

A primary tissue class that covers body surfaces, lines the cavities and insides of hollow organs, forms glands, and is characterized by tightly packed avascular cells.

Connective Tissue

The most widely distributed tissue class in the body that supports and binds organs together, provides immunity, and consists of cells, extracellular fibers, and ground substance.

Muscle Tissue

A tissue class composed of excitable cells containing collagen fibers that performs mechanical movements and generates force.

Nervous Tissue

A tissue class that initiates and transmits nerve impulses to coordinate normal body activities.

Apical Surface

The surface of an epithelial tissue that faces the lumen, the interior of an organ, or the external environment; also referred to as the luminal surface.

Basal Surface

The surface of an epithelial tissue that is attached to the basement membrane.

Simple Epithelium

An epithelial layer arrangement consisting of a single layer of cells extending from the basal surface to the apical surface.

Stratified Epithelium

An epithelial layer arrangement composed of more than one layer of cells, classified and named according to the shape of the cells in the most apical layer.

Pseudostratified Epithelium

A singular epithelial layer where every cell contacts the basal surface but not all reach the apical surface, giving the false visual appearance of stratification; occurs mostly with columnar cells.

Squamous Cells

Thin, flat epithelial cells arranged like tiles that resemble corn flakes; their reduced thickness allows rapid diffusion or osmosis across membranes.

Cuboidal Cells

Cube-shaped or hexagonal epithelial cells with centrally placed spherical nuclei that function primarily in secretion and absorption.

Columnar Cells

Tall, cylindrical epithelial cells that protect underlying structures and frequently feature apical surface specializations such as cilia or microvilli.

Transitional Epithelium

A stratified epithelial tissue featuring flexible, conventionally rounded/spherical apical cells that allows expansion in urinary structures like the bladder, ureters, and urethra.

Keratin

A tough protein produced by keratinocytes that hardens cells, making them rigid and partially waterproof for protection; keratinized cells are technically dead without nuclei or organelles.

Cilia

Motile hair-like apical cell projections found on columnar cells that propel fluids or particles along passageways such as the respiratory tract and female reproductive system.

Microvilli

Extremely uniform, dense apical projections forming a brush-like border on intestinal epithelial cells to increase surface area for absorption.

Endothelium

The specialized simple squamous epithelium that lines the lumen of blood vessels, lymphatic vessels, and the heart.

Mesothelium

The specialized simple squamous epithelium that lines serous membranes including the pleura, peritoneum, and pericardium.

Goblet Cell

A specialized mucus-secreting unicellular gland formed by a modified columnar cell found in the respiratory, digestive, and urinary tracts.

Extracellular Matrix

The material in connective tissue consisting of ground substance combined with protein fibers (collagen, elastic, and/or reticular).

Fibroblast

The typical spindle-shaped cell responsible for producing the fibers and ground substance in most connective tissues.

Chondrocyte

A mature cartilage cell that resides encased inside a hollow fluid-filled capsule called a lacuna.

Collagen Fiber

The strongest fiber type in the human body, composed of collagen; tough yet flexible and typically stains pink in histological preparations.

Elastic Fiber

A connective tissue fiber smaller than collagen that provides high elasticity and flexibility, typically staining dark pink, light purple, or black.

Reticular Fiber

A thin connective tissue fiber that forms non-uniform branching networks resembling spider webs or dead trees; stains dark purple to black.

Areolar Tissue

A loose connective tissue with a non-uniform mesh arrangement containing all three fiber types that provides structural strength and support to skin, organs, and mucous membranes.

Adipose Tissue

A loose connective tissue made of adipocytes specialized for triglyceride storage, serving functions in thermal insulation, energy storage, and mechanical cushioning.

Reticular Tissue

A loose connective tissue containing only reticular fibers organized into a delicate meshwork that provides structural framework and filtering in the spleen, liver, and muscle tissue.

Dense Regular Connective Tissue (DRCT)

A dense connective tissue with parallel, uniformly oriented collagen fibers and interspersed fibroblasts designed to withstand tensile pull in a single direction (e.g., tendons and ligaments).

Dense Irregular Connective Tissue (DICT)

A dense connective tissue containing non-uniformly arranged collagen bundles that resist mechanical pull in multiple directions (e.g., in the dermis and surrounding organs).

Elastic Tissue

A dense connective tissue characterized by wavy, spring-like elastic fibers alongside collagen that provides elasticity to the aorta, lungs, and sclera.

Hyaline Cartilage

A rigid cartilage featuring chondrocytes embedded within a solid pink-or-purple matrix containing collagen fibers that are invisible under light microscopy; found in the ribs, trachea, and joints.

Elastic Cartilage

A flexible cartilage containing dense networks of dark purple/black elastic fibers along with collagen and prominent chondrocytes; located in the pinna of the ear, epiglottis, and nasal tissue.

Fibrocartilage

A rigid, highly compressive cartilage with minimal flexibility that resembles dense regular connective tissue with small chondrocytes in lacunae; found in symphyses and menisci.

Osteon

The basic structural and functional unit of compact bone tissue, consisting of concentric lamellae arranged around a central canal.

Haversian Canal

The central vascular and nervous passage running through the center of an osteon in compact bone.

Compact Bone

The dense, hard calcified connective tissue that forms the outer protective shell and shaft of long bones.

Spongy Bone

The cancellous, porous bone tissue found at the ends (epiphyses) of long bones.

Skeletal Muscle

Striated, voluntarily controlled muscle tissue made of large parallel collagen-bound fibers with peripheral nuclei, attached to bones to execute movement.

Smooth Muscle

Non-striated, involuntarily controlled muscle tissue composed of spindle-shaped cells located in walls of hollow organs, blood vessels, and the gastrointestinal tract.

Cardiac Muscle

Involuntary striated muscle tissue found exclusively in the heart wall, characterized by branching fibers and specialized junctional complexes known as intercalated discs.