Comprehensive Guide to Connective Tissues: Anatomy, Structure, and Function (copy)

General Structure of Connective Tissue

  • Extracellular Matrix Components

    • Fibers:

      • Collagen: structure to the tissue.

      • Reticular fibers: These consist of crossed collagen and provide order to the tissue.

      • Elastin: Responsible for providing elasticity.

    • Ground substance: A jelly-like material composed of sugar-protein molecules known as proteoglycans.

Specialized Cell Types in Connective Tissue

  • Fibroblasts: Responsible for the synthesis of fibres.

  • Fibrocytes: Mature cells derived from fibroblasts, found in connective tissue proper.

  • Immune/Defense Cells (specifically identified in areolar tissue):

    • Macrophages: Phagocytic cells.

    • Plasma cells: Involved in the immune response.

    • Mast cells: Involved in inflammatory responses.

    • Neutrophils: A type of white blood cell.

    • Lymphocytes: A type of white blood cell.

  • Cartilage Cells:

    • Chondroblasts: Found in growing cartilage; responsible for producing the matrix.

    • Chondrocytes: Mature cartilage cells that reside in lacunae.

  • Bone Cells:

    • Osteocytes: Responsible for the bone matrix and deposition.

    • Osteoblasts: Bone-forming cells.

    • Osteocrasts: Responsible for bone resorption (Note: listed as spelled in transcript).

  • Blood Cells:

    • Erythrocytes (RBC): Red blood cells.

    • Leukocytes (WBC): White blood cells.

    • Platelets: Cell fragments involved in clotting.

  • Fat Cells: Known as adipocytes.

Classification and Comparison of Connective Tissues

Connective Tissue Proper

  • Subclass: Loose Connective Tissue

    • Areolar:

      • Components: Gel-like ground substance; all three fiber types (collagen, reticular, elastic); cells include fibroblasts, macrophages, mast cells, and some white blood cells.

      • Function: Wraps and cushions organs; macrophages phagocytize bacteria; important role in inflammation; holds and conveys tissue fluid.

      • Location: Widely distributed under epithelia (e.g., forms lamina propria of mucous membranes); packages organs; surrounds capillaries.

      • Imaging: See photomicrograph at 300×300\times.

    • Adipose:

      • Description: Matrix is similar to areolar but very sparse; closely packed adipocytes (fat cells). The nucleus is pushed to the side by a large fat droplet.

      • Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs.

      • Location: Under skin in the hypodermis; around kidneys and eyeballs; within the abdomen; in breasts.

      • Imaging: See photomicrograph of subcutaneous layer at 350×350\times.

    • Reticular:

      • Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network.

      • Function: Fibers form a soft internal skeleton (stroma) that supports other cell types, including white blood cells, mast cells, and macrophages.

      • Location: Lymphoid organs (lymph nodes, bone marrow, and spleen).

      • Imaging: See photomicrograph of spleen at 350×350\times.

  • Subclass: Dense Connective Tissue

    • Dense Regular:

      • Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast.

      • Function: Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction.

      • Location: Tendons, most ligaments, aponeuroses.

      • Imaging: See photomicrograph of a tendon at 500×500\times.

    • Dense Irregular:

      • Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast.

      • Function: Able to withstand tension exerted in many directions; provides structural strength.

      • Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of the digestive tract.

      • Imaging: See photomicrograph of the dermis at 400×400\times.

    • Elastic:

      • Description: Dense regular connective tissue containing a high proportion of elastic fibers.

      • Function: Allows recoil of tissue following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration.

      • Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes.

      • Imaging: See photomicrograph of the aorta wall at 250×250\times.

Cartilage Classes

  • Hyaline Cartilage:

    • Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce matrix and chondrocytes lie in lacunae when mature.

    • Function: Supports and reinforces; resilient cushioning properties; resists compressive stress.

    • Location: Forms most of the embryonic skeleton; covers ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx.

    • Imaging: See photomicrograph of trachea at 750×750\times.

  • Elastic Cartilage:

    • Description: Similar to hyaline cartilage, but contains more elastic fibers in the matrix.

    • Function: Maintains the shape of a structure while allowing great flexibility.

    • Location: Supports the external ear (pinna); epiglottis.

    • Imaging: See photomicrograph of human ear pinna at 800×800\times.

  • Fibrocartilage:

    • Description: Matrix similar to but less firm than hyaline cartilage; thick collagen fibers predominate.

    • Function: Tensile strength with the ability to absorb compressive shock.

    • Location: Intervertebral discs; pubic symphysis; discs of the knee joint.

    • Imaging: See photomicrograph of intervertebral disc at 125×125\times.

Other Connective Tissues

  • Bone (Osseous Tissue):

    • Subclasses: Compact bone and Spongy bone.

    • Description: Hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized.

    • Function: Supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; hematopoiesis (blood cell formation) occurs in the marrow.

    • Location: Bones of the skeletal system.

    • Imaging: Cross-sectional view at 125×125\times; visible structures include lamellae, central canal, and canaliculi.

  • Blood:

    • Description: Red and white blood cells in a fluid matrix called plasma. Contains no fibers.

    • Function: Transport of respiratory gases (O2O_2 and CO2CO_2), nutrients, wastes, and other substances (e.g., hormones).

    • Location: Contained within blood vessels (the bloodstream).

    • Imaging: Smear of human blood at 1860×1860\times.

Questions & Review

Can you name the tissue type and its location based on characteristics?

  • Question: Delicate thin layers between tissues; present in all mucous membranes.

    • Answer: Loose (areolar) connective tissue.

  • Question: Contains cell membrane, nucleus, and fat droplets.

    • Answer: Adipose tissue; found in fat.

  • Question: Found in tendons and ligaments.

    • Answer: Dense connective tissue.

  • Question: Found in the nose, ends of long bones, and ribs.

    • Answer: Hyaline cartilage.

  • Question: Found in the outer ear and epiglottis.

    • Answer: Elastic cartilage.

  • Question: Found between vertebrae, in knee joints, and the pubic joint.

    • Answer: Fibrocartilage.

  • Question: Tissue showing lamellae, central canal, osteocyte in lacuna, and canaliculi.

    • Answer: Bone; found in the skeletal system.

  • Question: Fluid tissue seen with neutrophils, red blood cells, and lymphocytes.

    • Answer: Blood; found in the bloodstream.