BIOL 302 – Connective Tissue

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BIOL 302 – Histology – Connective Tissue Connective Tissue: a kind of tissue, usually of mesoblastic origin, that connects, supports, or surrounds other tissues and organs, including tendons, bone, cartilage, and fatty tissue. It always sits under an epithelium. Connective tissue can be broadly subdivided into connective tissue proper, special connective tissue, and series of other, less classifiable types of connective tissues. Connective tissue proper consists of loose connective tissue and dense connective tissue (which is further subdivided into dense regular and dense irregular connective tissues.) Special connective tissue consists of reticular connective tissue, adipose tissue, cartilage, bone, and blood. Other kinds of connective tissues include fibrous, elastic, and lymphoid connective tissues. Connective Tissue Special Connective Tissue Connective Tissue Proper Reticular Adipose Cartilage Bone Blood Loose Dense Regular Irregular Functions  Maintain boundaries  Structural support: Why don’t broken bones fall off? Connective tissues can heal quickly.  Cell adhesion and movement: Leukocytes travel through connective tissue to get to point of invader.  Protection  Molecular exchange: vascularized with capillaries; beds of capillaries allow for exchange of materials. Connective Tissue Composition  Fibers: o Reticular o Elastic o Collagen  Ground substance: o Space  Cells: o Macrophage o Lymphocyte o Plasma cell o Neutrophil a) Fibres i. Collagen Appearance  Easy to see  Large, bundled  No distinct pattern  Can be curved or straight Composition  Molecules: 30% glycine, 20% proline; self assembling triple helix  Fibril: self assembling bundles of triple helices  Fiber: bundles of fibrils  Tissue: bundles of fibers; tendon Characteristics  Inelastic- tensile strength  Heavy – about 50% of body weight Function  Stores strain energy  Cross-linked for energy Types  Collagen Type I: collagen fibrils, bones, tendons, skin, ligaments  Collagen Type II: cartilage  Collagen Type III: reticular fibres (fine collagen fibres)  Collagen Type IV: non-fibrillar, attach to basement membrane Mutations  “Elastic skin man” – a hydroxylation mutation causes skin, when heated, to stretch out because it cannot form triple helices ii. Elastin Appearance  Branched, at sharp angles  Fenestrated sheets  Arteries present Composition  Elastin  Microfibrils (elastin and glycoproteins) Function  For stretch and flexibility  So tissue will recoil after stretch b) Ground Substance Appearance  White spaces between fibres  Does not have fibres Composition  Non-fibrous components of ECM  Glycosaminoglycans (GAG) – hyaluronan  Proteoglycans (protein + GAG chains)  Glycoproteins (carbohydrate + protein) Function  Support for cells  Place for molecular exchange between capillaries and ground substance – nutrients, wastes; cartilage does not have capillary network  Hydrating molecules – attach to water molecules, permit diffusion of water- soluble molecules. The more there are, the looser it is.  Cell movement: plasma cells and mast cells of the immune system use capillary network to travel around the body. Once they find a spot where they are needed, they migrate into the tissue to fight off invaders. c) Cells  Fibroblasts: o Active version (inactive is called fibrocyte) o Synthesizes ECM and collagen o Important in wound healing – make scars o Can be seen as elongated, thin, dark spots (inactive) o If it has a large pale nucleus, it is active o Embryonic tissue has a lot of fibroblasts because tissues are constantly remodeling  Macrophages: o In blood: monocyte o In tissue: macrophage o Endocytosis: ingest particles  Mast cell: o Involved in primary immune response o Full of granules that release histamine in allergy response; evokes an inflammatory response o Large cells with red granules  Plasma cells: o Also called B-lymphocyte or B-cells; released in blood o Secrete antibodies from Golgi o Large lymphocytes with considerable nucleus-to-cytoplasm ratio o Nucleus with heterochromatin in a clock face formation  Leukocytes o White blood cells; involved in immune response, defending against infectious disease and foreign materials. o Neutrophil: deal with fungal and bacterial infection; first responders, death in large numbers forms pus, polymorphonuclear (PMNs),