Musculoskeletal Disorders. Sean Gallagher

Musculoskeletal Disorders - Sean Gallagher


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or repairing tendons and bones. Elastin is a fibrous protein typically present as discontinuous fibrils (Figure 3.2) or sheets and confers the properties of stretch and elastic recoil (Young & Heath, 2000).

      General Subtypes: Structure and Function

      Loose connective tissue

Characteristic Description
General types Loose (adipose, areolar, reticular); dense (e.g., tendon, cartilage, and bone); fascia (e.g., epimysium)
Cells Main cell types: Fibroblasts, adipocytes, resident macrophages, plasma cells
Extracellular matrix (ECM) Main composition: Polysaccharides, water, glycosaminoglycans (GAGs), proteoglycans, glycoproteinsAdditional components: Collagen I/III, elastin, depending on subtype
Function Envelops, separates tissues and cells, cushions, supports, immune function, and more
Photos depict loose and adipose connective tissues.

       Areolar tissue

      This type of loose connective tissue is the most widely distributed and is present in the dermis, around blood vessels, and nerves. It contains at one time or another, nearly all of the cell types normally found in connective tissue, including fibroblasts, macrophages, plasma cells, mast cells, adipocytes, and a few white blood cells. Its loose, randomly arranged fibers include collagen, elastic, or reticular. The ground substance is semifluid or gelatinous and contains primarily hyaluronic acid, chondroitin sulfate, dermatan sulfate, or keratan sulfate.

       Adipose tissue

      Adipose tissue is primarily composed of adipocytes. It can be found in the subcutaneous layer of skin, the marrow of long bones, between muscles, and around nerves and joints (Figure 3.1c,d). It reduces heat loss through the skin and provides energy reserves, support, and protection.

       Reticular tissue

      This type of loose connective tissue contains a fine network of collagen III fibers, often termed reticular fibers. It is present around blood vessels and muscle, within bone marrow, and in basement membranes.

      Dense collagenous connective tissues

      Dense connective tissues contain either regularly or irregularly arranged collagen fibers and fewer intercellular substance and cells than found in loose connective tissues (Figure 3.2). Examples of dense irregular connective tissues include the dermis of skin, deep fascia, the periosteum of bone, the perichondrium of cartilage, and organ capsules. Examples of dense regular connective tissues include tendons, ligaments, aponeuroses (thin flat tendon bands that connect one muscle to another or to bone), cartilage, and bone. Each is discussed in further detail separately in subsequent sections. Elastic tissue has a preponderance of elastic fibers and constitutes the ligament flava of vertebrae and arterial walls, among others.

      Fascia

      Fascia is the term applied to the sheets or broad bands of fibrous connective tissue that (a) lies beneath the skin; (b) attaches, stabilizes, encloses, and separates muscle and tendons from each other; and (c) separates internal organs from each other. It is classified by layer (superficial, deep, visceral, or peritoneal fascia), function, or anatomical location. Superficial fascia is the subcutaneous layer of connective tissue that lies immediately deep to the skin. It serves as a storehouse of water and fat (which acts as insulation) and provides a pathway for nerves, vessels, and immune cells to travel between other tissues (Figure 3.1b). Deep fascia is a denser connective tissue that holds muscles and tendons together, fills spaces between tissues, and lines the body wall and extremities (e.g., the lower leg’s crural fascia). Functionally, deep fascia allows free movement of muscles and tendons, carries blood vessels and nerves, and sometimes provides an attachment for muscle (e.g., the palmaris brevis muscle of the hand).

Photo depicts extensions of deep fascia around and into individual muscle fibers.
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