Reticular fibers (ruh-TIK-yuh-ler FY-bers): Fine, highly branched fibers composed of Type III collagen that form a delicate, supportive meshwork (stroma) for cells in soft organs (e.g., bone marrow, spleen, lymph nodes); they are typically stained black by silver impregnation.
Elastic fiber (ih-LAS-tik FY-ber): Thin, branching protein fibers composed primarily of elastin; they provide elasticity and recoil to tissues, allowing them to stretch and return to their original shape (e.g., in the lungs, aorta, and elastic cartilage).
Macrophage (MAK-roh-fayj): A large, phagocytic immune cell found in connective tissue, derived from blood monocytes; its function is to engulf cellular debris, foreign substances, and pathogens, playing a key role in defense and tissue cleanup.
Lymphocyte (LIM-fuh-syt): A small, round immune cell with a large, dark nucleus and very little cytoplasm; these are the primary cells of the adaptive immune system, mediating specific defense reactions.
Collagen fibers (KOL-uh-jen FY-bers): The most abundant protein fibers in the body, composed mainly of Type I collagen (in dense tissues); they are thick, wavy, and provide tremendous tensile strength and resistance to stretching.
Mast cell (mast sell): A resident immune cell found throughout connective tissue; it is characterized by a cytoplasm packed with large granules containing inflammatory mediators (like histamine) that are released in response to injury or allergens.
Fibroblast (FY-broh-blast): The principal cell of connective tissue; it is a spindle-shaped, elongated cell responsible for synthesizing the various collagen fibers, elastic fibers, and the ground substance that makes up the extracellular matrix.
Adipocyte (Fat cell) (AD-ih-poh-syt): A specialized connective tissue cell adapted for the storage of fat (triglycerides); it typically appears as a large cell with a single, massive fat droplet that displaces the nucleus and cytoplasm to the periphery. This fat droplet is removed during normal processing for histology and so these cells appear as acidophilic rings, with a peripheral elongated basophilic nucleus and a large spherical hole (where the fat droplet used to exist).
Mesenchymal cell (mez-un-KY-mul sell): An undifferentiated, star-shaped stem cell found primarily in embryonic connective tissue (mesenchyme); in adults, these cells are retained in some locations and can differentiate into various connective tissue cells (e.g., fibroblasts, adipocytes, chondroblasts, osteoblasts).
Collagen fiber bundle (KOL-uh-jen FY-ber BUN-dul): A large aggregation of intertwined collagen fibers; these bundles are the main structural component of dense connective tissue, providing great strength. Typically found in dense connective tissue types.
Loose connective tissue (Areolar tissue) (looss kuh-NEK-tiv TISH-oo): A common type of connective tissue characterized by abundant ground substance, a wide variety of cell types (e.g., fibroblasts, macrophages, mast cells), and loosely arranged protein fibers; it is found beneath most epithelia.
Dense Regular Connective Tissue (dens REG-yuh-ler kuh-NEK-tiv TISH-oo): Connective tissue characterized by thick collagen fiber bundles arranged in parallel, orderly arrays; this arrangement provides maximum tensile strength in one direction, found in tendons and ligaments.
Dense Irregular Connective Tissue (dens ih-REG-yuh-ler kuh-NEK-tiv TISH-oo): Connective tissue characterized by thick collagen fiber bundles woven into a seemingly random, irregular network; this arrangement provides resistance to stress and tension from multiple directions, found in the dermis and organ capsules.
Fat droplet (fat DROP-let): The large, central lipid inclusion found within an adipocyte; it is the storage form of triglycerides and is not membrane-bound, but rather bound with a single layer of phospholipids.
Cell membrane (sell MEM-brayn): The plasma membrane of the adipocyte; in white fat, it is stretched thin around the periphery of the single, large fat droplet, enclosing the flattened nucleus and sparse cytoplasm.
Adipose tissue (Fat tissue) (AD-ih-pohz TISH-oo): A specialized type of connective tissue composed predominantly of closely packed adipocytes; its functions include energy storage, thermal insulation, and physical cushioning. Due to the removal of fats during processing for histology, adipose tissue appears like a net or chicken-wire in appearance.