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Biological Sciences
Connie Soros

Lecture 4 Foundations: Connective Tissues (Chapter 3) Connective Tissues Tissues that connect or form structures Most diverse, abundant, widely distributed and microscopically variable All derived from mesoderm Examples: bone, cartilage, blood, connective tissue proper – ligament, tendon, fibrous tissue, loose connective tissue, dense connective tissue, fat Functions of Connective Tissue Physical protection – bones of cranium, sternum, vertebral column, thoracic cavity, fat surrounding organs Support and structural framework of the body – bones provide framework and support soft tissues; cartilage supports body structures such as trachea, bronchi, nose and ears; sheets of connective tissue form capsules to support such organs as spleen and kidneys Transporting fluid and dissolved materials – blood carries nutrients, gases, hormones, wastes and blood cells between different regions of the body Connecting other tissues – ligaments bind bone to bone; tendons bind muscle to bone; dense irregular tissue (fascia) binds skin to underlying muscle and bone Storing energy – fat is major energy reserve in the body, bones are a large reservoir for calcium and phosphorus Immune protection – much connective tissue contains white blood cells (leukocytes) which protect the body against disease and mount an immune response against foreign material; the viscous nature of the extracellular matrix interferes with the movement and spread of disease causing organisms Elements of Connective Tissues • Cells spaced far apart (unlike epithelium) • Lots of extracellular matrix (ECM) between cells Matrix is the collective term for the extracellular component of any connective tissue that is made of protein fibers and the ground substance  ECM is secreted from cells of connective tissue by proteins in fibrous tissues called fibroblasts TERMINOLOGY - ______cyte – a generic cell type (eg. osteocyte in bone, adipocyte in fat) -_______blast – produces something,lays down some foundation (eg. osteoblast is a cell that lays down (makes) bone matrix, fibroblasts in connective tissue proper) -______clast – reabsorbs/breaks down something (eg. osteoclast breaks down bone)  ECM composed of: o Ground substances – sugary water and protein and carbohydrate molecules (gelatin-like), proteins help to keep water in o Fibers:  C OLLAGEN – for tensile strength and stretch resistant  ELASTIC –which are flexible and resistant  RETICULAR – which form an interwoven network Classification of Connective Tissues: based on type of extracellular matrix: Connective tissue proper - has a matrix of fibers (loose and dense) in a syrupy ground substance (kind of like “jello” with fruit in it • Different types have different numbers of cell types and different relative proportions of fibers and ground substance (examples include: adipose (fat), ligaments, tendons) Fluid connective tissue - has a matrix of watery liquid than contains dissolved proteins (examples are: blood and lymph) Supporting connective tissue - has a matrix consisting of a gel (densely packed fibers), cartilage or a solid (matrix is calcified of mineral deposits of predominantly calcium), bone Connective Tissue Proper Types with Loose fibers: Areolar tissue, Adipose tissue, Reticular tissue Types with Dense fibers: Dense regular, Dense irregular, Elastic Different Types of Connective Tissue Proper contain various types of FIXED and WANDERING cells Fixed Cells: Fibroblasts – produce connective tissue fibers Fibrocytes – maintain connective tissue fibers and matrix Fixed macrophages – phagocytize pathogens and damaged cells Adipocytes – store lipid reserves Mesenchymal cells – connective tissue stem cells that can differentiate into other cell types Melanocytes – synthesize melanin Wandering Cells: Free Macrophages – mobile/travelling phagocytic cells (derived from monocytes of the blood) Mast Cells – stimulate local inflammation Lymphocytes – participate in immune response – can develop into plasmocytes which produce antibodies (proteins involved in defending the body against disease) Neutrophils and Eosinophils – small phagocytic blood cells that mobilize during infection or tissue injury Loose Connective Tissue Areolar Tissue Location - deep to the dermis, covered by epithelial lining, between muscles, around blood vessels, nerves and around joints Function - connects skin to muscle, cushions organs, provides support but with movement Matrix – abundant collagen fibers, thin irregularly arranged elastic fibers, small fibroblast cells and abundant gel-like ground substance Adipose Tissue Location – hypodermis, buttocks, breasts, around eyes, surrounds organs Function – provides padding and cushions shocks, insulates and stores energy Matrix – predominantly adipocytes, inside each cell is drop of fat surrounded by plasma membrane, pushed nucleus and organelles to the side, absence of fibers Reticular Tissue Location - liver, spleen, kidney, lymph nodes, tonsils, appendix, bone marrow Function - supporting framework Matrix – predominantly reticular fibers Dense Connective Tissue Dense Regular Connective Tissue • The collagen fibers are packed tightly and aligned parallel to applied force (like a group of cables), able to withstand stress in ONE direction, almost no ground substance and fibroblast nuclei are squeezed between layers of fibers Location and Function tendons – cords of dense regular connective tissue attach muscles to bone and cartilage aponeuroses - cartilaginous sheets that resemble broad tendons, may cover muscles or attach muscle to muscle or another structure  elastic tissue – large number of elastic fibers, tissue is springy and allows some stretch, found in elastic walls of arteries, trachea, bronchial tubes, vocal cords and suspensory ligaments of the penis ligaments - between bones or stabilizing positions of organs, stabilizes the vertebrae Dense Irregular Connective Tissue Location - nerve and muscle sheaths, capsules of visceral organs, joint capsule of synovial joint, dermis, periosteum covering bones Function - provides strength and can withstand stress in multiple directions Matrix – unorganized fibers Fluid Connective Tissue Blood Location: circulatory system Erythrocytes (erythro = red) - transport oxygen and carbon dioxide Leukocytes (leuko = white) - fight infections (monocytes, eosinophils, neutrophils, basophils, lymphocytes) Platelets - blood clotting Matrix - liquid (plasma) Lymph Location - lymphoid system (lymphatic vessels that run alongside the cardiovascular system) Cells – Lymphocytes - develop into T cells and B cells (for example) Functi
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