Tissues of the Body: Epithelium and Connective Tissues

A comprehensive set of vocabulary flashcards based on lecture notes covering Epithelium and Connective Tissue, including cell types, fiber synthesis, and histological characteristics.

Four Primary Tissue Types

The four fundamental tissue types found in every organ: Epithelial Tissue (covering/lining), Connective Tissue (support), Muscle Tissue (contraction), and Nervous Tissue (communication).

Ectoderm Epithelial Origins

The germ layer that gives rise to the epidermis and its appendages, the epithelium of the oral cavity, the distal anal canal, and the corneal epithelium.

Mesoderm Epithelial Origins

The germ layer that gives rise to the endothelium of blood and lymphatic vessels, the mesothelium of serous cavities, and the renal tubular epithelium.

Endoderm Epithelial Origins

The germ layer that gives rise to the epithelium of most of the gastrointestinal and respiratory tracts, as well as the epithelial components of the liver and pancreas.

Basement Membrane

A structural layer composed of Type IV collagen that anchors the basal surface of the epithelium and separates it from the underlying connective tissue.

Avascularity of Epithelium

A defining characteristic meaning epithelium has no direct blood supply; nutrients must diffuse from the underlying connective tissue.

Microvilli

Short, finger-like membrane projections containing a cytoskeleton of actin filaments that increase surface area for absorption and secretion, commonly found in the small intestine.

Motile Cilia

Microtubule-based projections ($9 + 2$ axoneme arrangement) anchored to basal bodies that move fluid or material across epithelial surfaces, such as in the respiratory tract.

Stereocilia

Very long microvillus-like projections containing actin filaments that are non-motile and function in absorption (epididymis) or mechanosensation (inner-ear hair cells).

Axoneme

The microtubule core of a cilium consisting of a $9 + 2$ subunits arrangement (nine doublets and two central singlets), where each doublet has Subunit A with two dynein arms and Subunit B.

Endothelium

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

Mesothelium

The simple squamous epithelium that lines serous cavities.

Transitional Epithelium (Urothelium)

A specialized stratified epithelium containing basal, intermediate, and superficial umbrella cells, adapted for distension and protection in the urinary tract.

Umbrella Cells

Large, dome-shaped superficial cells of the urothelium that may be binucleate and possess apical uroplakin plaques to create a permeability barrier.

Goblet Cells

Unicellular mucous-secreting glands found in respiratory and intestinal epithelia that use merocrine secretion to release mucin granules via exocytosis.

Haematoxylin

A histological stain that carries a positive charge and binds to acidic structures, staining the nucleus blue or purple.

Eosin

An acidic histological stain that binds to basic structures, staining the cytoplasm and proteins pink or red.

Ground Substance

The aqueous, gel-like component of the extracellular matrix rich in glycoproteins and proteoglycans (such as Aggrecan) that regulates the diffusion of solutes.

Collagen Fibers

White fibers that occur in bundles and provide high tensile strength (stronger than steel) to tissues; they are the most abundant fiber type in connective tissue.

Tropocollagen

A triple helix molecule consisting of two $\alpha I$ polypeptide chains and one $\alpha II$ polypeptide chain, which self-assembles into collagen fibrils.

Scurvy

A clinical condition caused by Vitamin C deficiency, which is a required cofactor for the hydroxylation of proline and lysine residues during collagen synthesis.

Lysyl Oxidase

A copper-dependent enzyme that creates covalent cross-links between collagen molecules during extracellular fibril assembly.

Elastic Fibers

Branched structures composed of elastin and microfibrils (containing fibrillin) that provide elasticity and recoil to tissues like the aorta and ligamentum flavum.

Reticular Fibers

Thin, branching fibers composed primarily of Type III collagen that are argyrophilic (silver-staining) and form a delicate supporting framework in the liver and lymphoid organs.

Fibroblast

The most abundant resident cell in connective tissue proper, responsible for synthesizing collagen, elastic and reticular fibers, and ground substance.

Myofibroblast

An activated fibroblast-like cell characterized by the presence of $\alpha$-smooth-muscle actin, specialized for wound contraction and tissue repair.

Mast Cell

A granulated immune cell that expresses high-affinity $IgE$ receptors and releases inflammatory mediators like histamine (vasodilator) and heparin (anticoagulant).

Metachromasia

The property exhibited by mast cells where their secretory granules change the color of certain basic dyes, such as appearing pink or purple when stained with toluidine blue.

Macrophages (Histiocytes)

Professional phagocytes derived from monocytes that function in antigen presentation and cytokine secretion; examples include Kupffer cells (liver) and Microglia (CNS).

Plasma Cells

Connective tissue cells derived from B-lymphocytes characterized by a "clock-face" nucleus and well-developed rER for the synthesis of antibodies ($IgG$, $IgE$, etc.).

White Adipose Tissue

Tissue composed of unilocular adipocytes (one large lipid droplet) used for triglyceride storage, energy reserve, and thermal insulation.

Brown Adipose Tissue

Tissue composed of multilocular adipocytes that are rich in mitochondria and use $UCP1$ (thermogenin) for non-shivering thermogenesis, primarily in newborns.

Chondrocyte

A mature cartilage cell located within a lacuna that is responsible for synthesizing and maintaining the cartilage extracellular matrix.

Osteocyte

A mature bone cell located in a lacuna that maintains the bone matrix and acts as a mechanosensor to coordinate bone remodeling.

Dense Regular Connective Tissue

A type of connective tissue characterized by closely packed, parallel collagen bundles, found in tendons and ligaments.

Loose (Areolar) Connective Tissue

The most abundant connective tissue type, containing loosely arranged collagen fibers and abundant ground substance, typically found beneath epithelia.

Cromolyn Sodium

A mast-cell stabilizing drug used prophylactically to reduce the release of inflammatory mediators in allergic disorders and asthma.