2 General Characteristics of Connective Tissue Most abundant type of tissue by weight.Bind structures, provide support and protection, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infections, and help repair tissue damage.Can be rigid or flexible.Usually have a good blood supply (for nutrients).
3 General Structure of Connective Tissue Cells are farther apart than cells in epithelial tissueHave an abundance of extracellular matrixExtracellular matrix consists of fibers and a ground substance that varies from fluid to solidThe ground substance binds, supports, and provides a medium through which substances can be transferred between blood and cells in the tissue
4 Major Cell Types in Connective Tissue Cells in connective tissue are divided into fixed cells and wandering cells.Fixed cells are those that reside in the connective tissue for an extended period of time.Wandering cells are those that move through and appear in connective tissue temporarily…usually in response to an injury or infection.
5 Major Cell Types in Connective Tissue Fixed cells include:FibroblastsMost common kind of fixed cell in connective tissuesLarge and star-shapedProduce fibers by secreting proteins into the extracellular matrixMast cellsUsually located near blood vessels in connective tissuesWidely distributedRelease heparin (a compound that prevents blood clotting) and histamine (a substance that promotes reactions associated with inflammation and allergies)
8 Major Cell Types in Connective Tissue Wandering cells include:Macrophages (or histiocytes)Originate as white blood cellsUsually attached to fibers but can also detach and move aboutSpecialized for phagocytosis and so are important in immunity and defense against infection
10 Connective Tissue Fibers 3 types of tissues are produced by fibroblasts:Collagenous fibersElastic fibersReticular fibers (least abundant)
11 Connective Tissue Fibers Collagenous fibersComposed of thick threads of the protein collagen (which is the major structural protein of the body)Grouped in long, parallel bundlesFlexible but only slightly elasticHave really good tensile strength (resistance to a pulling force)Important component of body parts that hold structures together such as ligaments and tendonsTissue with lots of collagenous fibers is termed dense connective tissue and appears whiteTissue with very few collagenous fibers is termed loose connective tissue
12 Connective Tissue Fibers Elastic FibersComposed of the spring-like protein elastinFibers branch and form complex networksFibers are weaker than collagenous fibers but are very elastic (easily retain their shape after being stretched and deformed)Normally found in body parts that are stretched such as vocal cords and the air passages of the respiratory systemSometimes called yellow fibers as this is the color of tissues that have lots of elastic fibers
18 Connective Tissue Proper Loose connective tissue (or areolar tissue)Forms delicate thin membranes throughout the bodyCells are mainly fibroblasts and are spread far apart with a gel-like ground substance between themThe ground substance contains many collagenous and elastic fibers that are secreted by the fibroblastsBinds the skin to underlying organs, fills spaces between muscles, and lies beneath most layers of epithelium (remember, connective tissue provides the nutrient source for epithelial tissue)
20 Connective Tissue Proper Adipose TissueOr…fatHas cells called adipocytes that store fat in droplets within their cytoplasmEvery person is born with a certain number of adipocytesAt first these cells resemble fibroblastsAs the cells get bigger (through accumulation of fat) their nuclei get pushed to one sideWhen groups of these cell become so large that they crowd out other types of cells, adipose tissue is formedIf a person goes through a period if fasting, the cells may loose fat and shrink, resembling fibroblasts againLies beneath the skin (for insulation and energy storage), in spaces between muscles, around the kidneys and certain joints (for cushioning), behind the eyeballs, in certain abdominal membranes, and on the surface of the heart
22 Connective Tissue Proper Reticular Connective TissueComposed of thin, collagenous fibers in a 3-D network (called reticular fibers)Help provide the framework for specific internal organs, such as the spleen, liver, and lymphatic organs
24 Connective Tissue Proper Dense Connective TissueComposed of many closely packed, thick collagenous fibers, a fine network of elastic fibers and a few cells (which are mostly fibroblasts)May be classified as regular or irregular depending on how the fibers are organizedRegular dense connective tissue has collagenous fibers that are very strong, which allows the tissue to withstand pulling forcesAbundant in tendons and ligamentsBlood supply is poor which slows the time for tissue repair (such as in a sprained joint)Irregular dense connective tissue has fibers that are thicker, interwoven, and more randomly organized, allowing the tissue to sustain tension exerted from many different directionsFound in the dermis (inner layer of the skin)
26 Connective Tissue Proper Elastic Connective TissueComposed mainly of yellow, elastic fibers in parallel strands or in branching networks with collagenous fibers and fibroblasts in betweenFound in the attachments between bones of the spinal column (ligamenta flava) and in layers within the walls of certain hollow internal organs (including the larger arteries), some portions of the heart, and the larger airways
28 Specialized Connective Tissue CartilageProvides support, frameworks and attachments, protects underlying tissues, and forms structural models for many developing bonesHas abundant extracellular matrix composed largely of collagenous fibers embedded in a gel-like ground substance that is rich in a protein-polysaccharide complex (chondromucoprotein) and contains a large volume of waterCartilage cells, called chondrocytes, occupy small chambers called lacunae that lie completely within this matrixBecause cartilage tissue lacks a direct blood supply, nutrients must be obtained through diffusion from the perichondrium, which is a covering of connective tissues that surround cartilagenous structureThis lack of direct nutrients causes low levels of cell division and longer healing times
29 Specialized Connective Tissue CartilageCartilage can be divided into three types based on differences in the extracellular matrixHyaline cartilageHas very fine collagenous fibers in the extracellular matrixMost common typeFound on the ends of bones in many joints, in the soft part of the nose, and in the supporting rings of the respiratory passagesImportant in the development and growth of most bonesParts of an embryo’s skeleton actually begin as hyaline cartilage “models” that bone slowly replacesElastic cartilageHas a dense network of elastic fibers in its extracellular matrix (making it flexible)Provides the framework for the external ears and parts of the larynxFibrocartilageHas many large collagenous fibers in its extracellular matrix (making it very tough)Provides a “shock absorber” for structures that are subjected to pressure, such as vertebrae, knees, and the pelvic girdle.
33 Specialized Connective Tissue Bone (osseous tissue)Most rigid type of connective tissueDue to mineral salts (such as calcium carbonate and calcium phosphate) and abundant flexible collagenous fibers being located between cellsSupports body structures internally, protects vital structures in the thoracic and cranial cavities, serves as an attachment for muscles, forms blood cells in red marrow, and stores and releases inorganic chemicals such as calcium and phosphorous
34 Specialized Connective Tissue Bone (osseous tissue)StructureBone matrix forms thin layers called lamellae that are located in concentric patterns around capillaries that are located within tiny longitudinal tubes called central (Haversian) canals.Each central canal contains a blood vessel, so each bone cell has a close supply of nutrientsIn addition, each bone cell has many cytoplasmic processes that extend outward, pass through minute tubes in the extracellular matrix called canaliculi, and are attached by gap junctions to the membranes of nearby cells, leading to rapid movement of materials between blood vessels and bone cells and rapid healing.Bone matrix is deposited by cells called osteoblasts (which mature into osteocytes) that are located in lacunaeOsteoblasts are evenly spaced within the lamellae and also form concentric circlesTogether, the osteocytes, layers of extracellular matrix and the central canals around which they are clustered form a cylindrical shaped unit called an osteon, or Haversian systemMany of these units become cemented together to form the substance of bone
36 Specialized Connective Tissue BloodComposed of cells suspended in a fluid extracellular matrix called plasmaMost blood cells form in special tissues called hematopoietic tissues in the red marrow that is located in the hollow part of certain bonesTypes of blood cellsRed blood cellsTransport gasesFunction completely within the blood vesselsWhite blood cellsFight infectionTypically migrate from the blood through capillary walls to connective tissues where they carry out their major activities and usually remain until they diePlateletsInvolved in blood clotting