EXAM 2 Connective Tissue

Connective Tissue

General Features

• Definition: Connective tissue is the most abundant tissue in the body.

• Major Functions:

  • Strength and Support: Provides structural support to various organs and systems.

  • Protection: Cushions and protects organs.

  • Insulation: Helps regulate body temperature through insulating properties.

  • Transport of Substances: Facilitates the movement of nutrients, waste products, and other substances throughout the body.

• Extracellular Matrix (ECM) / Extracellular Fluid (ECF):

  • Substantial in connective tissue, varying with each type of connective tissue.

  • Basis for classification is determined by:

    • The predominant type of matrix present in the tissue.

    • The composition of each type of matrix, which can include various protein fibers and ground substances.

Protein Fibers

• Types of Protein Fibers:

  1. Collagen Fibers:

     • Characteristics:

       • Long, strong, rope-like structure, not elastic.

       • Most common protein in the body, a fibrous protein consisting of three fibers wound together.

     • Function:

       • Provides strength and resists stretch; however, once stretched, it does not bounce back.

  2. Reticular Fibers:

     • Characteristics:

       • Thin, short fibers also made from collagen protein that form a network (nets).

       • Can merge continuously with the stronger rope-like collagen fibers.

     • Distribution:

       • Most widely distributed connective tissue; provides a supportive framework around various organs.

  3. Elastic Fibers (Elastin):

     • Characteristics:

       • Long, thin proteins that create branching networks.

       • Elastic in nature, allowing them to return to their original shape after being stretched.

General Cell Types within Connective Tissue

• Cell Arrangement:

  • Cells in connective tissues are widely scattered throughout the matrix.

• Types of Cells:

  1. Blasts:

     • Definition: Immature cells that are responsible for creating/building the matrix.

     • Example: Fibroblasts which synthesize fibers and ground substance.

  2. Cytes:

     • Definition: Mature cells that maintain the matrix without actively producing it.

Types of Connective Tissue

1. Mesenchyme:

   • Definition: Embryonic connective tissue from which all connective tissue originates.

   • Characteristics:

     • Star-shaped mesenchymal cells.

     • Fluid ground substance, serving as a proliferative source for stem cells in adults.

2. Areolar Tissue:

   • Structure:

     • Gel-like matrix with loosely arranged protein fibers and scattered fibrous proteins.

     • Contains hyaluronic acid, fibroblasts, macrophages, mast cells, and fat cells.

   • Function:

     • Serves as a "universal packing material"

     • Allows diffusion for nutrients and wastes; acts as a reservoir for water and salts.

   • Location:

     • Most widely distributed connective tissue; surrounds organs and capillaries.

     • Attaches skin to underlying tissues.

3. Adipose Tissue:

   • Structure:

     • Comprised of closely packed cells (adipocytes) filled with triglycerides.

     • Each cell contains so much lipid that the nucleus and cytoplasm are pushed to the side just beneath the plasma membrane.

   • Function:

     • Energy storage, insulation, supports, and protects organs (padding).

   • Location:

     • Subcutaneous layer, around kidneys, and mammary glands.

4. Reticular Tissue:

   • Structure:

     • Comprised of reticular cells and reticular fibers.

   • Function:

     • Supports soft tissues of organs and small blood vessels.

   • Location:

     • Found in lymph nodes, spleen, and bone marrow.

5. Dense Regular Connective Tissue:

   • Structure:

     • Matrix formed by parallel fibers; primarily consists of fibroblasts.

   • Function:

     • Provides tensile strength and stretch resistance in one direction due to collagen alignment.

   • Location:

     • Found in ligaments and tendons.

6. Dense Irregular Connective Tissue:

   • Appearance:

     • Interwoven fibers that provide strength in multiple directions.

   • Cell Type:

     • Primarily fibroblasts.

   • Function:

     • Provides tensile strength in multiple directions.

   • Location:

     • Dermis of skin and fibrous joint capsules.

7. Elastic Connective Tissue:

   • Appearance:

     • Coiled appearance from elastin fibers arranged in parallel.

   • Function:

     • Provides elasticity; allows recoil of tissue following stretching.

   • Location:

     • Walls of large arteries and walls of bronchial tubes.

8. Cartilage:

   • General Characteristics:

     • Avascular tissue, commonly found in areas subjected to compression (e.g., knees).

     • Slow healing process due to lack of blood supply.

     • Chondrocytes dispersed within lacunae in the matrix.

     • Matrix is firm and solid yet not completely rigid; abundant in proteoglycans and short collagen fibers.

   • Types of Cartilage:

     1. Hyaline Cartilage:

        • Structure:

          • Matrix appears transparent.

          • Chondrocytes are found in lacunae.

        • Function:

          • Forms the embryonic skeleton, allows growth of long bones, and covers the ends of long bones.

        • Location:

          • Found in articular cartilage, epiphyseal plates, costal cartilage of ribs, nose, and trachea.

     2. Elastic Cartilage:

        • Structure:

          • Composed of elastin fibers and lacunae.

        • Function:

          • Provides flexibility and maintains shape.

        • Location:

          • Found in the external ear and epiglottis (flap covering the larynx).

     3. Fibrocartilage:

        • Structure:

          • Composed of bundles of collagen fibers and lacunae.

        • Function:

          • Absorbs compression (shock absorption) and provides tensile strength.

        • Location:

          • Found in intervertebral disks, articular disks, and the pubic symphysis.