Connective Tissue

  Different types of connective tissues maintain form of the body by providing the matrix which connects and bind cells and organs of the body.   Connective tissue consists of: Cells Fibers Ground substance   Wide variety of connective tissue types reflects variation in the composition and the amount of the three components

Cells of the Connective Tissue

Fibroblast   Most dominant cell type of connective tissue   Synthesis of extracellular matrix components   Synthesis of fiber proteins   Production of growth factors   Fibroblast features   Fibrocyte features

Macrophage  Ultrastructural features  Derived from monocyte  They form the Mononuclear Phagocyte System  Kupffer cell, Microglia, Osteoclast, Langerhans cell, dendritic cell, Langerhans cell, dendritic cell,  Multinuclear giant cell, Epitheloid cell  Functions

Mast Cell  Ultrastructural features  Secretory granules and content  Metachromasia  Function  Types Connective tissue mast cell Mucosal mast cell

Plasma Cell  Ultrastructural features  Origin  Function

Adipocytes and Leukocytes   Will be described later.   Adipocytes is a connective tissue cell specialized in fat storage and heat production   Leukocytes leave the blood stream by Diapedesis. They release chemical mediators of inflammation.

Fibers of the Connective Tissue Connective Tissue

Collagen Fibers   Made of collagen protein which constitutes 30% of human body   They form a family of >25 produced by different types of cells   Classifications: Collagen forming long fibrils I, II, III, V, XI Fibril-associated collagen IX, XII, XIV Collagen forming anchoring fibrils VII Collagen forming network IV   Made mainly of glycine and proline

Reticular Fibers   Made of collagen type III   They are very thin and form an extensive net work in certain organs   They contain 6-12% hexose sugars   They are found in parenchymatous organs e.g. liver and spleen   Argyrophilia, PAS +

Elastic Fibers   A system consists of Oxytalan, Elaunin, and Elastic fibers.   Oxytalan fibers are not elastic but resistant to pulling e.g. zonular ligament and dermis. Consists of fibromodulin and fibrillin   Elaunin fibers: elastin start to deposit between oxytalan fibers e.g. around sweat glands and dermis   Elastic fibers: rich in elastin surrounded by a sheath of microfibrils of oxytalan   Made of, in addition to glycine and prolin, desmosine and isodesmosine

Ground Substance   Consists of hydrated, colorless, transparent mixture of macromolecules.   It acts as a lubricant and a barrier   Composed of: Glycoseaminoglycans Proteoglycans Glycoproteins

Glycoseaminoglycans   Composed of linear polysaccharides formed of repeating disaccharides units made of uronic acid and hexosamine   They are intensely hydrophilic and basophilic and acts as polyanion due to OH,COO, and SH groups

Types and distribution   Hyaluronic Acid   Chondroitin sulfate   Dermatin sulfate   keratin sulfate

Proteoglycans   Consists of a core protein to which different types of glycosaminoglycan are attached except hyaluronic acid   Some are free in the ground substance e.g. Aggrecan and others are attached to cell membrane e.g. Syndecan Fibroglycan

Glycoproteins   Made dominantly of protein to which attached abranched carbohydrates   Plays a role in the interaction between adult and embryonic cells and adhesion of cells into their sustrate   Examples Fibronectin Laminin

Types of Connective Tissue  Connective tissue proper Loose connective tissue Dense connective tissue RegularIrregular

Connective Tissue with Special Properties   Adipose Tissue   Elastic Tissue   Hematopoietic Tissue   Mucus Tissue   Reticular tissue

Adipose Tissue   A special type of connective tissue in which adipocytes predominate   It serves as energy depot   It shapes the body   Act as a shock absorber   Thermal insulation   Keeps some organs in place e.g. Kidney

Unilocular (Yellow) adipose Tissue   It is white to yellow because of carotenoids   Most common in adult   Almost found everywhere in the body   Distribution is affected by age and sex   Adipose tissue is divided into incomplete lobules by connective tissue   It is richly vascularized   Leptin is produced by fat cell to regulate amount of adipose tissue in the body   Ultrastructure of the adipose cell

Multilocular (Brown) Adipose Tissue   It is brown because of richness of capillaries and numerous mitochondria containing colored cytochromes   It has a localized distribution   Ultrastructure of adipose cell   Cells are directly innervated by sympathetic nerves

Clinical Applications   Immediate hypersensitivity reaction and Anaphylactic shock   Progressive systemic sclerosis and keloid   Marfan syndrome and fibrillin gene mutation   Ehlers-Danlos IV, VI, VII, Scurvy, Osteogenesis imperfecta