by dbui89


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Connective Tissue characteristics
Large amounts of ECM with relatively few cells. Provides structural support for the body, storage of metabolites, plays a role in defense and protection by mediating inflammatory and allergic response, repair of other tissue (fibrous scar)
Collagen fibers
Flexible with high tensile strength
Three polypeptide chains that form a triple helical structure called tropocollagen. Can be polymerized head-to-tail and laterally to form collagen fibrils. Assembled into collagen or reticular fibers.  Collagen fibers can be further assembled into collagen bundles (Type I only).
Elastic fibers
Allow tissues to respond to stretch and distension. Thinner than collagen, arranged in branching pattern to form a network. Formed from Elastin and Fibrillin.
Ground substance
Fills in spaces between fibers in the ECM. Composed of glucosaminoglycans (GAG's), proteoglycans, and multiadhesive proteins.
Resident cells
Type of connective tissue cell, undergoes mitosis within the connective tissue.
Fibroblasts
Principal resident cell of the connective tissue. Produces ECM components. Will appear different than other connective tissue types. Usually close to collagen fibers. Four types of fibroblasts:
Active, actively growing, abundant RER and Golgi appratus. Oval-shaped, pale, euchromatic, found in loose connective tissue
Inactive, found in dense connective tissue that are not growing, limited cytoplasm, less RER and Golgi. Heterochromatic, darker, more elongated.
Myofibroblast, mix between fibroblasts and smooth muscle cells, Has RER and Golgi, but also contain actin filament bundles and dense bodies like smooth muscle cells. Can contract, important for wound closure.
Mesenchymal cells, found in embryonic connective tissue and superficially resemble active fibroblasts, Pluripotent, gives rise to fibroblasts, chondroblasts, osteoblasts, and adipocytes.
Adipocyte
Specialized connective tissue cell,  stores fat and produces hormones. There are unilocular adipocytes and multilocular adipocytes.
Unilocular adipocytes are found in loose connective tissue or aggregate to form white adipose tissue, contains a single large lipid droplet
Multilocular adipocytes rare in adult humans, found in brown adipose tissue, multiple small fat droplets and large number of mitochondrial give it its brown colo. Used to generate heat (important for babies immediately after birth).
Macrophage
Phagocytic cells derived from monocytes that migrated to connective tissue from bone marrow. Can be identified through presence of ingested material in cytoplasm and kidney-shaped nucleus. Provides important defense mechanism (phagocytosis of bateria, antigen presentation, cytokine production)
Widely distributed and can appear different in different parts of cell, histiocytes in connective tissue, alveolar macrophages in lungs, Kupffer cells in liver, osteoclasts in bone, Langerhans cells in skin, dendritic cells in lymphoid organs.
Mast cells
Originate in bone barrow, migrated to connective tissue where it proliferates and differentiates. Very large cells, oval in shape with a centrally placed spherical nucleus. Has large granules in cytoplasm. Has IgE on surface.
Mediates inflammatory and allergic responses. 
Common in connective tissue of skin/mucous membranes, absent from CNS. 
How are mast cells activated?
First exposure to antigen, mast cell produces large amount of IgE for the antigen. Second exposure, antigens cause IgE's to crosslink, clumping them up in the cytoplasmic side, causing degranulation. HIstamine released, causing vasodilation, increased vascular permeability, emigration of white blood cells into connective tissue.
Transient cells
Derived from precursors in the bone marrow, involved with immune response. Do not divide in the connective tissue, two main groups are white blood cells and plasma cells.
Plasma cells
Antibody-producing cells derived from B-lymphocytes. Present everywhere, but most numberous found in areas of inflammation and entry by foreign substances. Prominent RER and Golgi, dark heterochromatin alternates with pale euchromatin to create a clock-face pattern in nucleus.
Lymphocyte
A white blood cell, has round, dark heterochromatic nucleus. Function is production of antibodies, regulation of immune response.
Monocyte
A white blood cell, phagocytic, precursors to macrophages, has kidney-shaped nucleus.
Neutrophil
A white blood cell, phagocytic, aimed at bacteria, has elongated, segmented multi-lobed nucleus (3 lobes).
Eosinophil
A white blood cell, involved in reaction to parasitic infestations. Has intensely staining eosinophilic granules in cytoplasm and bilobed nucleus.
Basophil
A white blood cell, rare in blood and connective tissue, involved in alergic response, bilobed nucleus and large number of basophilic granules in the cytoplasm.
Loose connective tissue
Class of connective tissue that is highly cellular, has very thin sparse collage type I fibers, do not normally bundle. Abundant ground substance, fibroblasts are mostly active in this tissue, large number of transient cells
Found beneath epithlia that cover internal surfaces of the body and acts as a "filter-tissue". Surrounds blood and lymphatic vessels and nerves.
Dense connective tissue
Class of connective tissue, large number of collagen type I fibers, bundles present. Little ground substance, fewer cells than loose connective tissue. Subdivided into irregular and regular.
Dense irregular connective tissue oriented in various directions, form a meshwork resisting stress from all directions. Almost no transient cells. Fibroblasts are mostly inactive. Found in dermis of skin and capsules of internal organs (spleen and testis).
Dense regular connective tissue have collagen bundles oriented in the same direction to resist tensile forces. Very little space for ground substance or cell. Very thin sheet-like inactive fibroblasts present. Forms tendons, ligaments, and aponeuroses.
Specialized connective tissue
Responsible for specific functions such as storage of nutrients or support, such as adipose tissue which stores energy (triglycerides).
Reticular connective tissue
Loose connective tissue found in the stroma of the organs of the lymphoid system, such as lymph nodes, spleen, and bone marrow. Supported by a network of reticular fibers that form thin, branching, interconnected threads.
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