The function of connective tissue is either to join bodily structures like bones and muscles to one another or hold tissues like muscles, tendons, or even organs in their proper place in the body. It also gives reinforcement to joints, strengthening and supporting the articulations between bones. Another function of connective tissue is the transport of nutrients and metabolic byproducts between the bloodstream and the tissues to which it adheres. Creating dense networks of fibers, connective tissue is made up of proteins like collagen, elastin, and intercellular fluid, and while its form can range from a thin sheet to a rope of fibers, its constitution is fairly similar throughout the body.
There are four major categories of bodily tissue: nervous, epithelial, muscle, and connective tissue. Nervous tissue includes that forming the brain, spinal cord, and nerves. Epithelial tissue occurs in layers and ranges from skin to the linings of organs and vessels. Muscle tissue is similar to connective tissue in that it is fibrous, but it is made up of units within muscle cells known as sarcomeres that are designed to expand and contract, allowing the tissue to change in length, and it metabolizes nutrients much differently than connective tissue.
Connective tissue is distinguished from the other fiber types by both its form and its function. It is made up both of specialized cells that affix to other tissues as well as what is known as the extracellular matrix. Its most distinctive attribute, this matrix is made up of fluid; gound substance, a gel that contains nutrient molecules like hyaluronic acid that are composed of carbohydrates and protein; and protein-based fibers like collagen and elastin. The fibers give the tissue its denseness and strength and are what lend to the function of connective tissue.
Affixing to bone, muscle, or other nearby tissues, connective tissue is distributed throughout the body, forming tendons, ligaments, cartilage, fat, and even contributing to blood and lymph. One function of connective tissue is to link the structures of locomotion. Muscle is attached to the bones it moves by tendons, thick lengths of connective tissue that pull on the bones like rope. Similarly, bones are joined to one another at joints by ligaments, which may resemble narrow bands or broad sheets. Ligaments not only hold the bones together but prevent the joints from moving beyond their normal range of motion, and they also support the bones at the joint, as in keeping the arm from popping out of its socket at the shoulder joint.
Yet another function of connective tissue is to encapsulate structures like muscles and joints and thereby transport vital nutrients between these structures and the bloodstream. While connective tissue itself tends not to be very dense with capillaries, it conducts oxygen and nutrients from nearby capillary beds into the tissue to which it attaches. Likewise, when waste products are removed from tissues, the connective tissue moves it back into the bloodstream for removal from the body.
Connective tissue also contributes to energy storage, as adipose tissue or fat is a form of connective tissue, as well as immune function, as many types of immune cells, such as those that create scar tissue, are forms of connective tissue. Finally, connective tissue gives many organs their shape and holds them in place in their respective body cavities. It does so by forming sacs that contain the organs and attach to nearby structures so that they do not simply float about freely.