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Connective Tissue

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Connective Tissue Dr. Sami Zaqout Faculty of Medicine IUG Contents 1 Functions of Connective Tissue 2 Components of Connective Tissue 3 Cells of the Connective Tissue 4 Fibers of the Connective Tissue 5 Ground Substance of the Connective Tissue 6 Types of Connective Tissue Dr. Sami Zaqout Faculty of Medicine IUG Functions of Connective Tissue Providing structural support Serving as a medium for exchange Aiding in the defense and protection of the body Forming a site for storage of fat Dr. Sami Zaqout Faculty of Medicine IUG Components of Connective Tissue 1. Cells. 2. Extracellular matrix. – Fibers (collagen, reticular, and elastic) – Ground substance. • The major constituent of connective tissue is the extracellular matrix. Dr. Sami Zaqout Faculty of Medicine IUG Origin of Connective Tissues • The connective tissues originate from the mesenchyme, an embryonic tissue formed by elongated cells, the mesenchymal cells . • These cells are characterized by an oval nucleus with prominent nucleoli and fine chromatin. • They possess many thin cytoplasmic processes and are immersed in an abundant and viscous extracellular substance containing few fibers. • The mesenchyme develops mainly from the mesoderm. Dr. Sami Zaqout Faculty of Medicine IUG Cells of the Connective Tissue Dr. Sami Zaqout Faculty of Medicine IUG Fibroblasts • Fibroblasts are the most common cells in connective tissue. • Responsible for the synthesis of extracellular matrix components. • Fibroblasts synthesize: – Collagen – Elastin – Glycosaminoglycans – Proteoglycans – Multiadhesive glycoproteins Dr. Sami Zaqout Faculty of Medicine IUG Active Fibroblasts • Has an abundant and irregularly branched cytoplasm. • Its nucleus is ovoid, large, and pale staining, with fine chromatin and a prominent nucleolus. • The cytoplasm is rich in rough endoplasmic reticulum, and the Golgi complex is well developed. Dr. Sami Zaqout Faculty of Medicine IUG Quiescent Fibroblasts • Smaller than the active fibroblast and tends to be spindle shaped. • It has fewer processes • It has smaller, darker, elongated nucleus. • Acidophilic cytoplasm; and a small amount of rough endoplasmic reticulum. Dr. Sami Zaqout Faculty of Medicine IUG Myofibroblast • A cell with features of both fibroblasts and smooth muscle, • Observed during wound healing. • Their activity is responsible for wound closure after tissue injury, a process called wound contraction. Dr. Sami Zaqout Faculty of Medicine IUG Macrophages & the Mononuclear Phagocyte System • They are characterized by an irregular surface with protrusions and indentations. • They generally have a well- developed Golgi complex, many lysosomes, and a prominent rough endoplasmic reticulum. Dr. Sami Zaqout Faculty of Medicine IUG Macrophages & the Mononuclear Phagocyte System • Macrophages derive from bone marrow precursor cells that divide producing monocytes that circulate in the blood. • These cells cross the wall of venules and capillaries to penetrate the connective tissue, where they mature and acquire morphological features of macrophages . Dr. Sami Zaqout Faculty of Medicine IUG Macrophages & the Mononuclear Phagocyte System • The process of monocyte-to- macrophage transformation results in an increase in protein synthesis and cell size. • Increases in the Golgi complex and in the number of lysosomes, microtubules, and microfilaments are also apparent. • Macrophages measure between 10 and 30 µm and usually have an oval or kidney-shaped nucleus located eccentrically . Dr. Sami Zaqout Faculty of Medicine IUG Macrophages & the Mononuclear Phagocyte System • Macrophages are present in most organs and constitute the mononuclear phagocyte system. • They are long-living cells and may survive for months in the tissues . Dr. Sami Zaqout Faculty of Medicine IUG Macrophages & the Mononuclear Phagocyte System • When adequately stimulated, macrophages may increase in size and are arranged in clusters forming epithelioid cells. • Or several may fuse to form multinuclear giant cells . • Both cell types are usually found only in pathological conditions. Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • Mast cells are oval to round connective tissue cells. • 10–13 µm in diameter. • Cytoplasm is filled with basophilic secretory granules. • Small spherical nucleus is centrally situated, frequently obscured by the cytoplasmic granules Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • The principal function of mast cells is the storage of chemical mediators of the inflammatory response. • The secretory granules are 0.3– 2.0 µm in diameter. • Their interior is heterogeneous in appearance (scroll-like). • They contain preformed mediators such as: – Histamine – Heparin – Neutral proteases – Eosinophil chemotactic factor of anaphylaxis (ECF-A) Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • Metachromasia is a property of certain molecules in mast cells that changes the color of some basic aniline dyes (eg, toluidine blue). • Mast cells also release leukotrienes C4, D4, E4 • But these substances are synthesized from membrane phospholipids and immediately released to the extracellular microenvironment upon appropriate stimulation. • The molecules produced by mast cells act locally in paracrine secretion . Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • There are at least two populations of mast cells in connective tissues. Connective tissue mast cell: – Found in the skin and peritoneal cavity. – Measure 10–12 µm in diameter. – Their granules contain the anticoagulant heparin. Mucosal mast cell: – Present in the connective tissue of the intestinal mucosa and in the lungs. – Smaller (only 5–10 µm) than the connective tissue mast cells. – Their granules contain chondroitin sulfate instead of heparin . Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • The surface of mast cells contains specific receptors for immunoglobulin E (IgE) • Most IgE molecules are bound to the surface of mast cells and blood basophils. Dr. Sami Zaqout Faculty of Medicine IUG Mast Cells • Release of the chemical mediators stored in mast cells promotes the allergic reactions known as immediate hypersensitivity reactions. • There are many examples of immediate hypersensitivity reaction; a dramatic one is anaphylactic shock ,a potentially fatal condition . Dr. Sami Zaqout Faculty of Medicine IUG Plasma Cells • Plasma cells are large, ovoid cells that have a basophilic cytoplasm due to their richness in rough endoplasmic reticulum • The juxtanuclear Golgi complex and the centrioles occupy a region that appears pale in regular histological preparations. Dr. Sami Zaqout Faculty of Medicine IUG Plasma Cells • The nucleus of the plasma cell is spherical and eccentrically placed, containing compact, coarse heterochromatin alternating with lighter areas of approximately equal size. • This configuration resembles the face of a clock. • There are few plasma cells in most connective tissues. • Their average life is short, 10– 20 days. Dr. Sami Zaqout Faculty of Medicine IUG Plasma Cells • Plasma cells are derived from B lymphocytes and are responsible for the synthesis of antibodies. • Antibodies are immunoglobulins produced in response to penetration by antigens. • Each antibody is specific for the one antigen that gave rise to its production and reacts specifically with molecules possessing similar epitopes. Dr. Sami Zaqout Faculty of Medicine IUG Adipose Cells • Adipose cells are connective tissue cells that have become specialized for: – Storage of neutral fats – Production of heat Dr. Sami Zaqout Faculty of Medicine IUG Leukocytes • Leukocytes are the wandering cells of the connective tissue. • They migrate through the walls of capillaries and postcapillary venules from the blood to connective tissues by a process called diapedesis . • This process increases greatly during inflammation. Dr. Sami Zaqout Faculty of Medicine IUG Fibers • The connective tissue fibers are formed by proteins that polymerize into elongated structures. • In many cases, the predominant fiber type is responsible for conferring specific properties on the tissue. • There are two systems of fibers: – The collagen system: • Collagen fibers • Reticular fibers, – The Elastic system • Elastic • Elaunin • Oxytalan fibers. Dr. Sami Zaqout Faculty of Medicine IUG Collagen Fibers • Collagen is the most abundant protein in the human body, representing 30% of its dry weight. • Collagen contains two amino acids that are characteristic of this protein: – hydroxyproline – hydroxylysine • The collagens of vertebrates comprise a family of more than 25 members that are produced by several cell types. Dr. Sami Zaqout Faculty of Medicine IUG Collagens That Form Long Fibrils • The molecules of long fibril–forming collagens aggregate to form fibrils clearly visible in the electron microscope. Dr. Sami Zaqout Faculty of Medicine IUG Collagens That Form Long Fibrils • These are collagen types I, II, III, V, and XI. • It occurs in tissues as structures that are classically designated as collagen fibers and that form structures such as bones, dentin, tendons, organ capsules, and dermis. Dr. Sami Zaqout Faculty of Medicine IUG Collagens That Form Long Fibrils • Collagen type I is the most abundant and has a widespread distribution. • Each molecule (tropocollagen) is composed of two α1 and one α2 peptide chains, each with a molecular mass of approximately 100 kDa, intertwined in a right-handed helix and held together by hydrogen bonds and hydrophobic interactions. Dr. Sami Zaqout Faculty of Medicine IUG Collagens That Form Long Fibrils • Collagen fibrils
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