Tissue Organization and Histology

This set of vocabulary flashcards covers tissue organization, including characteristics, classifications, and components of epithelial, connective, muscle, and nervous tissues, as well as body membranes.

Histology

The study of tissues.

Tissues

Groups of similar cells and extracellular material that perform a common function, such as providing protection.

Epithelial Tissue

Tissue composed of one or more layers of closely packed cells with little to no extracellular matrix; it covers body surfaces, lines cavities, and forms the majority of glands.

Apical Surface

The surface of epithelial tissue that is exposed to the external environment or an internal body space, which may contain microvilli or cilia.

Basal Surface

The surface of epithelial tissue where the epithelium is attached to the underlying connective tissue.

Basement Membrane

A barrier between the epithelium and connective tissue composed of three layers: lamina lucida, lamina densa, and reticular lamina.

Avascularity

A characteristic of epithelial tissue meaning it lacks blood vessels; nutrients are obtained across the apical or basal surfaces.

Simple Epithelium

A type of epithelium consisting of one cell layer where all cells are in direct contact with the basement membrane; primary functions include filtration, absorption, or secretion.

Stratified Epithelium

Tissue consisting of two or more layers of cells where only the basal layer is in contact with the basement membrane; designed to resist mechanical stress.

Pseudostratified Epithelium

A type of simple epithelium that appears layered because cell nuclei are distributed at different levels, though all cells remain attached to the basement membrane.

Squamous Cells

Epithelial cells that are flat, wide, and irregular in shape, arranged like floor tiles with a flat nucleus.

Cuboidal Cells

Cells that are about as tall as they are wide, featuring rounded edges and a spherical nucleus located in the center.

Columnar Cells

Slender cells that are taller than they are wide, featuring an oval nucleus oriented lengthwise in the basal region.

Transitional Cells

Cells located in the urinary tract that change shape from polyhedral (relaxed) to flat (stretched) depending on the stretch of the epithelium.

Endocrine Glands

Glands that lack ducts and secrete hormones directly into the blood to influence cell activity elsewhere.

Exocrine Glands

Glands that maintain a connection to the epithelial surface via a duct, which is an epithelium-lined tube used for secretion.

Connective Tissue

The most diverse and abundant tissue type, consisting of cells, protein fibers, and ground substance; it supports, protects, and binds organs.

Fibroblasts

The most abundant resident cells in connective tissue proper; they are flat cells with tapered ends that produce fibers and ground substance.

Adipocytes

Also known as fat cells, these resident cells appear in small clusters in connective tissue proper or large clusters in adipose connective tissue.

Mesenchymal Cells

Embryonic stem cells within connective tissue that divide to replace damaged cells.

Fixed Macrophages

Large, irregular cells derived from monocytes that reside in the matrix to phagocytize pathogens and stimulate the immune system.

Mast Cells

Small, mobile wandering cells found near blood vessels that secrete heparin to inhibit clotting and histamine to dilate blood vessels.

Plasma Cells

Cells formed from activated B-lymphocytes that produce antibodies to immobilize foreign material.

Collagen Fibers

Unbranched, strong, and flexible 'cable-like' protein fibers that are resistant to stretching and appear white in fresh tissue.

Reticular Fibers

Thin, branching protein fibers that form an interwoven framework (stroma) in organs such as the lymph nodes, spleen, and liver.

Elastic Fibers

Wavy protein fibers containing elastin that stretch and recoil easily, helping structures return to their normal shape.

Ground Substance

The noncellular material produced by connective tissue cells that, when combined with protein fibers, forms the extracellular matrix.

Glycosaminoglycans (GAGs)

Large, negatively charged carbohydrate molecules in ground substance that attract cations like $Na^+$ and water; examples include chondroitin sulfate and hyaluronic acid.

Proteoglycans

Structures formed by a GAG linked to a protein, composed of approximately $90\%$ carbohydrate.

Mesenchyme

The first type of embryonic connective tissue and the source of all other connective tissue types.

Areolar Connective Tissue

A type of loose connective tissue found in the papillary layer of the dermis and surrounding organs, nerves, and blood vessels.

Dense Regular Connective Tissue

Tissue containing densely packed, parallel arrays of collagen fibers; found in tendons and ligaments to resist stress in one direction.

Chondrocytes

Mature cartilage cells that occupy small spaces in the extracellular matrix called lacunae.

Perichondrium

A dense irregular connective tissue covering that surrounds cartilage, consisting of an outer fibrous layer and an inner cellular layer.

Osteocytes

Mature bone cells housed within lacunae in the extracellular matrix.

Osteons

Cylindrical structures in compact bone that display concentric rings of bone connective tissue called lamellae.

Plasma

The liquid ground substance of blood containing dissolved proteins, which transports nutrients, wastes, and hormones.

Neurons

Nervous tissue cells responsible for receiving, transmitting, and processing nerve impulses.

Glial Cells

Nervous tissue cells that do not transmit nerve impulses but instead provide protection, nourishment, and support to neurons.

Mucous Membrane

Also called mucosa, this membrane lines compartments open to the external environment and performs absorptive, protective, and secretory functions.

Serous Membrane

A membrane composed of mesothelium that lines body cavities not open to the environment and produces a thin, watery fluid to reduce friction.

Synovial Membrane

A membrane lining joints composed of areolar connective tissue; it secretes fluid to reduce friction and distribute nutrients to cartilage.