Connective Tissue

  • Never exposed to the outside

  • Many have blood vessels and sensory receptors

  • All have three basic components

    • Specialized cells

    • Extracellular protein fibers

    • Fluid (ground substance)

  • Exctracellular fibers and fluid make up a matrix that surrounds cells

 

Types of connective tissues:

  • Connective tissue proper

    • Connective tissues with many types of cells and extracellular fibers in a syrupy ground substance

    • 2 types

      • Loose - fibers create a loose, open framework

        • Areolar tissue

          • Most common connective tissue proper

          • Packing material of the body

          • Has all connective tissue proper cell types

        • Adipose tissue

          • Found deep to skin in various areas of the body

          • Mostly cells (adipocytes)

        • Reticular tissue

          • Found in liver, kidney, spleen, lymph nodes, and bone marrow

          • Provides support and resists distortion

          • Many reticular fibers form a network (stroma)

      • Dense - fibers that are densely packed

        • Dense regular connective tissue

          • Found in tendons, ligaments, and organ cords

          • Has parallel collagen fibers

        • Dense irregular connective tissue

          • Found covering visceral organs -- in superficial layers of bones, cartilages, and peripheral nerves. Also in the dermis

        • Elastic

          • More elastic fibers than collagen

          • Is springy and resilient

          • Found between vertebrae, in walls of large blood vessels, erectile tissues of penis

    • Components

      • Extracellular protein fibers

        • Reticular fibers - strong and form branching network

        • Collagen fibers - thick, very strong

        • Elastic fibers - slender, very stretchy

      • Viscous ground substance

        • Clear, colorless, viscous due to presence of proeoglycans and glycoproteins

      • Cells - two classes

        • Fixed

          • Stationary, function in maintenance, repair, and storage

          • 5 types:

            • Melanocytes - synthesize melanin pigment

            • Mast cells - stimulate inflammation and mobilize defenses

            • Fixed macrophage - engulfs cell debris and pathogens

            • Fibroblasts - synthesize extracellular fibers

            • Adipocytes - store lipid reserces

        • Wandering

          • Move throughout tissue, function in defense and repair

          • 5 types:

            • Plasma cells - immune cell producing antibodies

            • Free macrophages - engulf debris and pathogens

            • Mesenchymal cells - stem cells that aid tissue repair

            • Neutrophils and eosinophils - phagocytic blood cells

            • Lymphocytes - immune system cells

 

  • Fluid connective tissues

    • Distinctive populations of cells suspended in a watery matrix that contains dissolved proteins - normally has no fibers

    • 2 types:

      • Blood - flows within the cardiovascular system, exchanges water and solutes between plasma and interstitial fluid

        • Watery Matrix (Plasma)

        • Cells and Cell Fragments (formed elements)

          • Red blood cells - transport oxygen

          • White blood cells - bodily defense, 4 types

            • Monocytes - large phagocytes

            • Lymphocytes - uncommon in blood

            • Eosinophils/neutrophils - small phagocytes

            • Basophils - promote inflammation

          • Platelets - clotting response

 

  • Lymph - flows within the lymphatic system, colleccted from interstitial fluid, returned to blood at large veins near the heart

    • Function: to maintian solute levels, blood volume, and alert immune system of infection

    • Parts:

      • Watery Matrix (Lymph)

      • Cells (mainly lymphocytes)

  • Supporting connective tissues

    • Less diverse cell population

    • Matrix contains much more densely packed fibers than connective tissue proper

    • Protect soft tissues and support the weight of part or all of the body

    • 2 types:

      • Cartilage - soft, rubbery matrix

        • Set apart from surrounding tissues by perichondrium, which has 2 layers:

          • Outer layer of dense regular connective tissue -- provides mechanical support, protection, and attachment

          • Inner cellular layer - where cartilage growth and maintenance occur

        • Components:

          •  firm gel containing polysaccharide derivatives

            • Forms complexes with proteins producing proteoglycans

          • Cells (chondrocytes)

            • Only cells in the cartilage matrix

            • Occupies small chambers called lacunae

        • Types:

          • Hyaline cartilage

            • Found between ribs and sternum, covering bones in mobile joints, certain areas of respiratory system

            • Stiff but flexible support and reduces friction

          • Elastic cartilage

            • Supports external ear and other smaller internal structures

            • Increased flexibility

          • Fibrous cartilage

            • Found within knee join, between pubic bones of pelvis, in intervertebral discs

            • Resists compression, prevents bone to bone contact, and limits relative movement

        • Types of cartilage growth

          • Appositional growth - cartilage enlarges by the addition of cartilage to the outer surface

          • Interstitial growth - cartilage expands from within

      • Bone - solid crystalline matrix, Osseous tissue

        • Bony matrix

          • Small volume of ground substance

          • 2/3 of matrix is calcium salts, which provide strength

            • Mostly calcium phosphate

            • Some calcium carbonate

          • Many collagen fibers, which provide flexibility

        • Long bone structure

          • Hollow with two types of bone

            • Spongy bone lines the internal cavity

            • Compact bone is the outer layer of bone

              • Matrix organized in concentric layers

                • Organized into functional units (osteons)

                • Cells (osteocytes) located between layers

                • Canaliculi (little canals) connect osteocytes

                • Superficial layer of bone prevents interstitial growth

              • Surrounded by periosteum

                • Outer fibrous layer allows attachment of ligaments

                • Inner cellular layer allows appositional growth and repair

    • Cartilage vs. Bone

      • Both support and protect

      • Cartilage is avascular, bone is highly vascular

      • Cartilage cannot grow or repair

      • Bone is capable of extensive remodeling and repair

  • Membranes and Fasciae

    • Membranes

      • Line or cover body surfaces

      • Consist of epithelium supported by connective tissue

      • Four types:

        • Mucous membranes

          • Line organs that communicate to exterior

          • Must be kept moist to facilitate movement, absorption, or secretion - lubricated by mucus or bodily fluids

          • Supported by areolar connective tissue (lamina propria)

        • Serous membranes

          • Mesothelium supported by areolar connective tissue

          • Delicate and never connected to exterior

          • Transudate (liquid layer) coats surface

          • Three line subdivisions of ventral body cavity

            • Pleura (pleural cavity and visceral organs)

            • Peritoneum (peritoneal cavity and visceral organs)

            • Pericardium (pericardial cavity and heart)

        • Cutaneous membrane

          • Covers surface of body = skin

          • Relatively thick, waterproof, and dry comparatively

        • Synovial membranes

          • Line mobile joint cavities

          • Similar to epithelia but with distinct differences

            • Develops within connective tissue

            • No basal lamina

            • Gaps between cells (up to 1mm)

            • Exchange fluid (synovial fluid) and solutes with cardiovascular capillaries

    • Fasciae

      • Connective tissue layers and wrappings

      • Support and surround organs

      • Three types:

        • Superficial fascia

          • Under the skin

          • Consists of areolar and adipose tissue

        • Deep fascia

          • Continuous with capsules, ligaments, and other connective tissue structures

          • Consists of dense irregular connective tissue

        • Subserous fascia

          • Between serous membranes and deep fascia

          • Consists entirely of areolar tissue

 

Functions of connective tissue:

  • Establishing a structural framework for the body

  • Transporting fluids and dissolved materials

  • Protecting delicate organs

  • Supporting, surrounding, and interconnecting other types of tissue

  • Storing energy reserves, especially in the form of triglycerides

  • Defending the body from invading microorganisms