Most Abundant and Widely Distributed of Primary Tissues

Chapter 4 Connective Tissue * Most abundant and widely distributed of primary tissues * Four main classes: connective tissue proper, cartilage, bone, blood Major Functions of Connective Tissue * Binding and support * Protecting * Insulating * Storing reserve fuel * Transporting substances (blood) Characteristics of Connective Tissue * Have varying degrees of vascularity (blood vessels)-affects healing * Have extracellular matrix * Connective tissue not composed mainly of cells * Largely nonliving extracellular matrix separates cells * So can bear weight, withstand tension, endure abuse Structural Elements of Connective Tissue * Three elements * Ground substance-matrix * Fibers * Cells Ground Substance * Unstructured material that fills space between cells * Medium through which solutes diffuse between blood capillaries and cells * Trap water in varying amounts, affecting viscosity of ground substance Connective Tissue Fibers * Three types of fibers provide support * 1. Collagen * Strongest and most abundant type * Tough; provides high tensile strength * 2. Elastic fibers * Networks of long, thin, elastin fibers that allow for stretch and recoil * 3. Reticular * Short, fine, highly branched collagenous fibers (different chemistry and form than collagen fibers)

© 2013 Pearson Education, Inc. * Branch, forming networks that offer more "give" Cells * "Blast" cells * Immature form; mitotically active; secrete ground substance and fibers * Fibroblasts in connective tissue proper * Chondroblasts in cartilage * Osteoblasts in bone * "Cyte" cells * Mature form; maintain matrix * Chondrocytes in cartilage * Osteocytes in bone

Other Cell Types in Connective Tissues * Fat cells * Store nutrients * White blood cells * Neutrophils, eosinophils, lymphocytes * Tissue response to injury * Mast cells * Initiate local inflammatory response against foreign microorganisms they detect * Macrophages * Phagocytic cells that "eat" dead cells, microorganisms; function in immune system Types of Connective Tissues: Connective Tissue Proper * All connective tissues except bone, cartilage and blood * Two subclasses * 1. Loose connective tissues * Areolar * Adipose * Reticular * 2. Dense connective tissues (also called fibrous connective tissues) * Dense regular * Dense irregular * Elastic

© 2013 Pearson Education, Inc. Areolar Connective Tissue * Support and bind other tissues * Universal packing material between other tissues * Provide reservoir of water and salts * Defend against infection * Store nutrients as fat * Fibroblasts * Loose arrangement of fibers * Ground substance * When inflamed soaks up fluid  edema Adipose Tissue * White fat * Similar to areolar but greater nutrient storage * Cell is adipocyte * Stores nutrients * Scanty matrix * Richly vascularized * Shock absorption, insulation, energy storage * Brown fat * Use lipid fuels to heat bloodstream not to produce ATP Reticular Connective Tissue * Resembles areolar but fibers are reticular fibers * Fibroblasts called reticular cells * Supports free blood cells in lymph nodes, the spleen, and bone marrow Dense Regular Connective Tissue * Closely packed bundles of collagen fibers running parallel to direction of pull * White structures with great resistance to pulling

© 2013 Pearson Education, Inc. * Fibers slightly wavy so stretch a little * Fibroblasts manufacture fibers and ground substance * Few cells * Poorly vascularized Dense Irregular Connective Tissue * Same elements but bundles of collagen thicker and irregularly arranged * Resists tension from many directions * Dermis * Fibrous joint capsules * Fibrous coverings of some organs Elastic Connective Tissue * Some ligaments very elastic * Those connecting adjacent vertebrae * Many of larger arteries have in walls Cartilage * Chondroblasts and chondrocytes * Tough yet flexible * Lacks nerve fibers * Up to 80% water - can rebound after compression * Avascular * Receives nutrients from membrane surrounding it * Perichondrium * Three types of cartilage: * Hyaline cartilage * Elastic cartilage * Fibrocartilage Bone * Also called osseous tissue * Supports and protects body structures * Stores fat and synthesizes blood cells in cavities * More collagen than cartilage * Has inorganic calcium salts

Blood * Most atypical connective tissue – is a fluid * Red blood cells most common cell type * Also contains white blood cells and platelets * Fibers are soluble proteins that precipitate during blood clotting * Functions in transport Muscle Tissue * Highly vascularized * Responsible for most types of movement * Three types * Skeletal muscle tissue * Found in skeletal muscle * Voluntary * Cardiac muscle tissue * Found in walls of heart * Involuntary * Smooth muscle tissue * Mainly in walls of hollow organs other than heart * Involuntary Nervous Tissue * Main component of nervous system * Brain, spinal cord, nerves * Regulates and controls body functions * Neurons * Specialized nerve cells that generate and conduct nerve impulses * Neuroglia * Supporting cells that support, insulate, and protect neurons

© 2013 Pearson Education, Inc. Covering and Lining Membranes * Three types Cutaneous Membranes * Skin * Keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis) * Dry membrane Mucous Membranes * Mucosa indicates location not cell composition * All called mucosae * Line body cavities open to the exterior (e.g., Digestive, respiratory, urogenital tracts) * Moist membranes bathed by secretions (or urine) * May secrete mucus Serous Membranes * Serosae—found in closed ventral body cavity * Simple squamous epithelium (mesothelium) resting on thin areolar connective tissue * Parietal serosae line internal body cavity walls * Visceral serosae cover internal organs * Serous fluid between layers * Moist membranes * Pleurae, pericardium, peritoneum Tissue Repair * Necessary when barriers are penetrated * Cells must divide and migrate * Occurs in two major ways * Regeneration * Same kind of tissue replaces destroyed tissue * Original function restored * Fibrosis

Steps in Tissue Repair: Step 1 * Inflammation sets stage * Release of inflammatory chemicals * Dilation of blood vessels * Increase in vessel permeability * Clotting occurs Steps in Tissue Repair: Step 2 * Organization restores blood supply * The blood clot is replaced with granulation tissue * Epithelium begins to regenerate * Fibroblasts produce collagen fibers to bridge the gap * Debris is phagocytized Steps in Tissue Repair: Step 3 * Regeneration and fibrosis * The scab detaches * Fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue * Results in a fully regenerated epithelium with underlying scar tissue Regenerative Capacity in Different Tissues * Regenerate extremely well * Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue * Moderate regenerating capacity * Smooth muscle and dense regular connective tissue * Virtually no functional regenerative capacity * Cardiac muscle and nervous tissue of brain and spinal cord * New research shows cell division does occur * Efforts underway to coax them to regenerate better Aging Tissues * Normally function well through youth and middle age if adequate diet, circulation, and infrequent wounds and infections

© 2013 Pearson Education, Inc. * Epithelia thin with increasing age so more easily breached * Tissue repair less efficient * Bone, muscle and nervous tissues begin to atrophy * DNA mutations possible  increased cancer risk