Connective tissue cells surrounded by an extracellular matrix Constituents: collagen & elastic fibers ground substance = tissue fluid (blood ultrafiltrate) & several types of large carbohydrate-containing molecules Connetive tissue cells

Functions Connective Tissue 1. Binding other tissues to each other 2. Serving as a support and padding e.g. support for epithelium e.g. support for epithelium resists compression resists compression 3. Pathway for nerves and blood vessels 4. Fluid circulation nutrients to diffuse from capillaries to cells nutrients to diffuse from capillaries to cells of various tissues of various tissues diffusion of hormones & metabolites (to cells) diffusion of hormones & metabolites (to cells) or of waste products (to capillaries). or of waste products (to capillaries). 5. Cellular response to injury and infection inflamation inflamation diffusion immune surveillance diffusion immune surveillance 6. Energy storage (heat generation)

 COLLAGEN FIBERS Collagen = 30% body protein Collagen = 30% body protein Triple helical molecules = composed of one or two genetically unique polypeptide alpha chains Triple helical molecules = composed of one or two genetically unique polypeptide alpha chains At least 21 types of collagens with genetically unique alpha chains At least 21 types of collagens with genetically unique alpha chains Many but not all collagen types are fibrillar Many but not all collagen types are fibrillar Collagen fibrils and fibers can also be heterotypic (i.e. two types of collagens present in same fibril or fiber) Collagen fibrils and fibers can also be heterotypic (i.e. two types of collagens present in same fibril or fiber)

WHICH CELLS SYNTHESIZE COLLAGENS?  Cells derived from mesenchyme  In connective tissue, most collagen from fibroblasts In other tissues, collagen from other cells of mesenchymal origin such as chondroblasts, endothelial cells and smooth muscle cells In other tissues, collagen from other cells of mesenchymal origin such as chondroblasts, endothelial cells and smooth muscle cells  Cells not of mesodermal origin e.g. surface epithelial cells of GI tract and trache e.g. surface epithelial cells of GI tract and trache DOES ONE CELL TYPE MAKE ONLY ONE TYPE OF COLLAGEN? Some cells at some locations can make more than one type of collagen simultaneously Some cells at some locations can make more than one type of collagen simultaneously

PROCOLLAGEN AND HYDROXYPROLINE Hydroxyproline (amino acid almost unique to collagen) is formed from proline in an intracellular posttranslational step of protein synthesis and is essential for the stability of the procollagen triple helix (forms hydrogen bonds) Scurvy ( deficiency in hydroxyproline formation) is proof of the importance of this amino acid

ELASTIC FIBERS  Composed of: Elastin Elastin microfibrillar proteins (including fibrillin) microfibrillar proteins (including fibrillin)  Components made by: Fibroblasts Fibroblasts In blood vessels most by smooth muscle In blood vessels most by smooth muscle In other tissues by cells of mesenchymal origin such as chondroblasts In other tissues by cells of mesenchymal origin such as chondroblasts  Elastin precursor secreted: Tropoelastin Tropoelastin  Function: Confers elasticity (allows recoil after stretching e.g.important in blood vessels) Confers elasticity (allows recoil after stretching e.g.important in blood vessels)

CONNECTIVE TISSUE GROUND SUBSTANCE  Tissue fluid Blood ultrafilrate  Large Carbohydrate-containing molecules Glycoproteins = carbohydrate covalently linked to protein (protein >carbohydrate Glycosaminoglycans (GAGs) = all carbohydrate - GAGs = linear polymer with repeating disaccharide units (usually a hexuronic acid (= negative charge) and and a hexosamine). - All GAGs except hyaluronic acid also have sulfate groups as negative charge) Proteoglycans = GAGs covalent link to protein (carbohydrate > protein) All GAGs (except hyaluronic acid) covalently linked to protein

ADULT CONNECTIVE TISSUES LOOSE CONNECTIVE TISSUES LOOSE CONNECTIVE TISSUES areolar areolar adipose adipose reticular reticular DENSE CONNECTIVE TISSUES dense irregular dense regular (includes elastic)

Functions of Areolar Loose Connective Tissue 1. Binding other tissues to each other 2. Serving as a support and padding e.g. support for epithelium e.g. support for epithelium gel-like extracellular ground substance gel-like extracellular ground substance resists compression resists compression 3. Pathway for nerves and blood vessels 4. Fluid circulation nutrients to diffuse from capillaries to cells nutrients to diffuse from capillaries to cells of various tissues of various tissues diffusion of hormones & metabolites (to cells) diffusion of hormones & metabolites (to cells) or of waste products (to capillaries). or of waste products (to capillaries). 5. Cellular response to injury and infection

CELLS OF AREOLAR LOOSE CONNECTIVE TISSUE Resident Immigrant Resident Immigrant Fibroblast Lymphocyte Myofibroblast Neutrophil * Adipose Cell Eosinophil Plasma Cell Basophil Plasma Cell Basophil Mast Cell Monocyte Mast Cell Monocyte Macrophage Macrophage * not motile yellow:derived from immigrant cells * not motile yellow:derived from immigrant cells

FIBROBLAST Derived from fibroblast mitosis and also from primitive mesenchymal precursor cell differentiation Derived from fibroblast mitosis and also from primitive mesenchymal precursor cell differentiation Secretes collagen, all elastic fiber components,hyaluronic acid, proteoglycans etc. (i.e. most of the extracellular matrix) Secretes collagen, all elastic fiber components,hyaluronic acid, proteoglycans etc. (i.e. most of the extracellular matrix)

PLASMA CELLS Not normally found in plasma Not normally found in plasma Derived from Type B lymphocytes that enter connective tissue Derived from Type B lymphocytes that enter connective tissue Synthesize and secrete by exocytosis specific antibodies (immunoglobulins) that bind to specific antigens (i.e. the molecules that provoked the plasma cell formation from B lymphocyte) Synthesize and secrete by exocytosis specific antibodies (immunoglobulins) that bind to specific antigens (i.e. the molecules that provoked the plasma cell formation from B lymphocyte) Antigen/antibody complex stimulate destruction of antigen (e.g. by stimulating phagocytosis or lysis of foreign cell source of that antigen) Antigen/antibody complex stimulate destruction of antigen (e.g. by stimulating phagocytosis or lysis of foreign cell source of that antigen) Some plasma cells may be exception to definition of resident cell as being long-lived since some only live 2 weeks but evidently plasma cells can also live longer Some plasma cells may be exception to definition of resident cell as being long-lived since some only live 2 weeks but evidently plasma cells can also live longer

Macrophage, a long-lived defense cell Derived from monocyte Derived from monocyteFunctions: Phagocytosis Phagocytosis Pinocytosis Pinocytosis Bacterial killing Bacterial killing Viruses only sometimes killed by macrophage but usually they stimulate macrophage to secrete lymphocye activators (e.g. interferons) that result in viral destruction but macrophages can become viral reservoirs (e.g. HIV) Viruses only sometimes killed by macrophage but usually they stimulate macrophage to secrete lymphocye activators (e.g. interferons) that result in viral destruction but macrophages can become viral reservoirs (e.g. HIV) Antigen-presenting cell (i.e process & present to lymphocytes to stimulate lymphocyte function) Antigen-presenting cell (i.e process & present to lymphocytes to stimulate lymphocyte function)

MAST CELLS Secretory cells rich in large secrtory granules Secretory cells rich in large secrtory granules Derived from bone marrow precursors Derived from bone marrow precursors Synthesize and secrete by exocytosis a variety of substances stored in large secretory granules Synthesize and secrete by exocytosis a variety of substances stored in large secretory granules Involved in inflammatory response Involved in inflammatory response Secrete (in response to IgE) Secrete (in response to IgE) Histamine (blood vessel permiablilty, smooth muscle Histamine (blood vessel permiablilty, smooth muscle constriction); heparin; proteases; chemotactic factor for eosinophils.