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Lesson 6 - Connective Tissue Types - Fibrous Connective Tissues

Student Performance Objectives
1. Describe the function of the areolar connective tissue underlying all epithelial surfaces.
2. Explain 4 functions for the areolar connective tissue underlying skin.
3. Explain the importance of investing fascia (dense, irregular connective tissue) in the structure of the arms, legs and neck of a human being.
4. Describe the functions of deep fascia and organ capsules and give an example of each.
5. Compare extrinsic and intrinsic ligaments and give an example of each.
6. Explain why elastic ligaments differ from all other ligaments and indicate where they are found.
7. Explain the functions of tendons, tendon sheaths, bursae, and aponeuoses.

Lesson Outline
A. Loose, irregular connective tissue (areolar connective tissue) - its major characteristic is
     loose wrapping rather than strength. It also packs and fills spaces. It is the most widely
     distributed connective tissue type found throughout the body.

     1. Composed of ground substance, fibers (collagen and elastin arranged in a network)
         and fibroblasts all in about equal proportions.
     2. Attaches epithelial surfaces found throughout the body to the underlying tissues. E.g.,
         superficial fascia (or tela subcutanea) that is loose, irregular connective tissue with a
         high fat (adipose) content. It forms a continuous sheet surrounding all parts of the
         body just under the skin. It functions in
         a. Loosely but firmly attaching the skin to underlying tissues, but forming a
             subdividing plane between the skin and what underlies it.
         b. Providing a passageway for blood vessels and nerves to reach the skin.
         c. Helps in body temperature regulation.
         d. Provides insulation.
B. Dense, irregular connective tissue - separates and encloses body structures in a matrix
    possessing fewer elastic and more collagen fibers which gives the tissue greater strength than
    loose, irregular connective tissue. Fatty tissue is absent. The collagen fibers are oriented in   
    many directions in the tissue thus providing strength in many directions. The periosteum,
    the tough wrapping on the surface of bone (to which tendons attach) is a good example.
    Other examples include:
1. Investing fascia - the cylindrically shaped neck, arms and legs are made up of bone,
            nerves, blood vessels and other structures that need to be held together (restrained) in
            an overall way. Investing fascia provides such restraint and is composed or coarse
            aggregated collagenous fibers located just below (deeper than) the superficial
            fascia (see above, A2) and is tougher than the deep fascia (see next item) surrounding
            the muscles.
        2. Deep fascia - encloses individual muscles, groups of muscles with related functions,
            and separates groups of muscles from each other. Stronger than loose, irregular
            connective tissue, but weaker than investing fascia (see above item).
        3. Fibrous organ capsules - surround, help hold together and protect many soft organs
            like the brain (meninges), kidney (renal capsule) and the spleen.
C. Dense Regular Connective Tissue - composed of fibroblasts secreting dense strands of
     collagen fibers oriented in one direction - the directions of stress in the tissue. Provides great
     strength with virtually no "give" or elasticity. Examples are:
        1. Ligament - generally short, flat, tough straps that attach bone to bone at the joints by
            uniting with the bone's periosteum or the bone substance itself. Several types are:
            a. Extrinsic ligaments - external to and reinforcing to the joint, sometimes
                helping to hold several bones together. E.g., the annular ligament holding the
                radius to the humerus in the elbow.
            b. Intrinsic ligaments - located within a joint helping to hold the articulating
                bones together. E.g., the cruciate ligaments within the knee joint helping to
                hold the femur and tibia together.
            c. Capsular ligaments - thickened sections of the joint capsule that reinforce the
                capsule. (As a point of clarification - the joint space is surrounded by a weak
                but lubricating, fibrous joint capsule whose inner lining is the synovial
                membrane that secretes the lubricating synovial fluid). Capsular ligaments
                strengthen the joint capsule, and the extrinsic and intrinsic ligaments complete
                the job of stabilizing and strengthening the joint as a whole.
            d. Elastic ligaments - these are exceptions to the rule that ligaments are inelastic
                and contain only collagen. These are found in the neck and along the vertebral
                column and provide the flexibility needed for the movements of the head, neck
                and spinal column. They are yellow in color as opposed to the glistening white
                color of other ligaments. E.g., the ligamentum nuchae of the neck and the
                ligamenta flava of adjacent vertebrae.
        2. Tendon - these cylindrical or flattened (strap-like) bundles of collagenous
            fibers connect muscle to bone. Often surrounded by areolar tissue that delivers blood vessels to the tendon) .
            Structures associated with tendons are
            a. Tendon sheaths - these are fibrous tubes, interiorly lined with synovial
                membrane, that permit a tendon to move without friction in response to a
                muscle's contraction. E.g., the tendon sheaths in the hands and feet contain the tendons that transmit force from the forearm muscles to the fingers and toes.
           b. Bursae (singular, bursa)- these are fragile fibrous sacs, lined on the inside with synovial
membrane, found where tendons are in contact with and cross over bones.
               They are often near joints but are not part of the joint. The bursae relieve the
               potential friction, limited motion and potential damage that might occur to the
               tendon under these circumstances. E.g., the shoulder and knee have many
               such bursae.
       3. Aponeurosis - a tendon widened into a flat sheet to accommodate the attachment of a
           large, broad muscle (e.g., the latissimus dorsi) to several bones at the same time. An
           aponeurosis can also serve as an attachment for muscles where no bone is available
           but where strength is nevertheless needed (e.g., the three muscles of the abdominal
           wall - external and internal obliques and the transverse abdominis) each attach to the
           linea alba through their aponeuroses.