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Connective tissue is present throughout the human body and serves a variety of crucial functions beyond connecting body parts. It takes various forms as it supports, insulates, and protects the body. Dense connective tissue, also called dense fibrous tissue, forms the body’s tendons, ligaments, joint capsules, and aponeuroses, as well as the dermis of the skin.
There are three different types of dense connective tissue: dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. Fibers are the primary components of any dense connective tissue. Collagen fibers, the strongest and most prevalent fibers in dense connective tissue, provide tensile strength and support. Elastic fibers are like rubber bands — they can stretch to a certain point and will then snap back to their original position.
Cells called fibroblasts work to produce the fibers that make up dense connective tissue. In addition, these bodily tissues also contain ground substance — the material that fills in the gaps between fibroblasts and holds the fibers themselves. Ground substance contains fluids and cell adhesion proteins, which essentially act as the glue that keeps the connective tissue attached to the extracellular matrix.
The extracellular matrix is unique and imperative to connective tissue. While all other primary bodily tissues are composed mainly of living cells, connective tissue is largely made up of the non-living extra-cellular matrix. This matrix allows connective tissues to bear weight and endure the impacts, traumas, and pulling forces that no other tissue in the body can survive.
Dense regular connective tissue is a white, flexible tissue. It contains tightly packed bundles of collagen fibers. All of these fibers run in one uniform direction — arranged parallel to the direction of forces exerted on the particular body part where the tissue is located. For example, this tissue tensile strength allows it to withstand pulling forces exerted in one direction when a person flexes his or her arm.
Generally, dense regular connective tissue forms tendons, the cords that attach muscle to bone, and aponeuroses — the flat, sheet-like tendons that attach muscles to other muscles or muscles to bone. Ligaments, the stretchier structures that bind bones together at the joints, are also made of this type of tissue. Fascia, the outer wrapping that binds together groups of muscles, blood vessels, and nerves, is also composed of dense regular connective tissue.
Body parts that are simultaneously pulled in multiple directions rely on dense irregular tissue for structural strength. Dense irregular connective tissue features the same basic structures as dense regular connective tissue, but its collagen fibers are irregularly arranged bundles and are significantly thicker than those of the regular variety.
This type of body tissue makes up the dermis — the leathery second layer of the skin. The tissue provides support to the body’s first line of defense. Dense irregular connective tissue also forms joint capsules and the fibrous coverings of kidneys, cartilages, and nerves.
Elastic connective tissue is a specialized type of dense connective tissue with a much higher proportion of elastic fibers. Due to its rubbery nature, elastic tissue can recoil after stretching. This makes it the ideal tissue to line the walls of the bronchiole tubes so that the lungs can deflate after inhaling and to line the walls of large arteries so that these vessels can pulse blood through the body. Elastic tissue also forms a few ligaments that demand extreme flexibility, such as the ligamentum nuchae of the neck.