Tissues and the Tissue Level of Organization

Flashcards covering the classification, types, functions, and locations of tissues, including epithelial cell shapes, germ layers, and modes of glandular secretion.

Tissues

Collections of specialized cells and cell products that perform a limited number of functions.

Histology

The study of tissues.

Differentiation

The process by which unspecialized cells, such as stem cells, develop into specialized cells with distinct structures and functions.

Epithelial Tissue

A tissue type that covers body surfaces, lines cavities and tubular structures, and forms glands.

Avascular

A characteristic of epithelial tissue meaning it lacks blood vessels.

Keratinized Epithelia

Epithelial cells filled with the protein keratin, making them hard, waterproof, and dead; found in the epidermis.

Non-keratinized Epithelia

Surface cells that are living and provide moist coverings for body parts such as the vagina, mouth, and internal organs.

Simple Squamous Epithelium

A single layer of thin, flat cells used for diffusion and filtration; found in air sacs of lungs and capillaries.

Simple Cuboidal Epithelium

A single layer of cube-shaped cells with a large round nucleus in the center that secretes and absorbs; found in kidney tubules and thyroid glands.

Simple Columnar Epithelium

A single layer of rectangular cells with nuclei near the base; it absorbs and secretes and is found in the stomach and intestines.

Stratified Squamous Epithelium

Multiple layers of cells that provide protection against abrasion; found in the skin (keratinized) and esophagus or vagina (non-keratinized).

Pseudostratified Columnar Epithelium

A tissue that appears layered due to varying nuclei positions but is only one cell layer thick; it often contains cilia and goblet cells and lines the trachea.

Transitional Epithelium

A form of stratified epithelium that allows urinary organs like the bladder and ureters to expand and stretch.

Microvilli

Extensions that increase surface area for absorption; often found on simple columnar epithelium.

Goblet Cells

Specialized cells found in pseudostratified and columnar epithelia that secrete mucus.

Ectoderm

The germ layer that gives rise to the epidermis, glands on skin, nervous system, and the mouth between cheek and gums.

Mesoderm

The germ layer that gives rise to connective tissues proper, bone, cartilage, blood, muscle, and the lining of gonads.

Endoderm

The germ layer that gives rise to the lining of airways and the digestive system, as well as glands like the thyroid and pancreas.

Synovial Membranes

Connective tissue membranes that line freely moving joint cavities and produce viscous synovial fluid for lubrication.

Mucous Membranes (Mucosae)

Epithelial membranes that line passageways open to the exterior, such as the digestive, respiratory, urinary, and reproductive tracts.

Serous Membranes

Epithelial membranes that line cavities not open to the outside, consisting of a simple epithelium supported by areolar tissue.

Parietal Lining

The portion of a serous membrane that lines the inner surface of a body cavity.

Visceral (Serosa)

The portion of a serous membrane that covers the outer surface of organs within a body cavity.

Endocrine Gland

A ductless gland that releases secretions directly into surrounding tissues and fluids.

Exocrine Gland

A gland whose secretions leave through a duct that opens directly or indirectly to the external environment.

Merocrine Secretion

The most common mode of exocrine secretion where product is released from secretory vesicles by exocytosis, such as in salivary glands.

Apocrine Secretion

A mode of secretion where secretory vesicles are packed into the outer portion of cytoplasm and released by shedding that cytoplasm; found in mammary glands.

Holocrine Secretion

A mode of secretion where the entire cell becomes packed with vesicles and bursts, releasing the secretion and killing the cell; found in sebaceous glands.

Tight Junctions

Cell junctions that form a zipper-like closure and impermeable barrier between cells, preventing leaks in organs like the bladder.

Gap Junctions

Intercellular passageways between adjacent cell membranes that allow for communication, such as sharing electrical currents in heart muscle cells.

Anchoring Junctions

Junctions such as desmosomes that provide strong and flexible connections in tissues prone to mechanical stress, like the skin.