Connective tissue proper, a class of connective tissues, is categorized as loose or dense based on the arrangement of protein fibers in the ground substance. Loose connective tissues with loosely arranged fibers in the extracellular matrix have three sub-types. The first sub-type, the areolar tissue, is abundant across organ systems like the skin, where it connects with and supports other tissue types. Next, the adipose tissue present in organs, such as the breasts, is involved in insulation and energy production, while the reticular tissue present in organs like the spleen and the lymph nodes forms a supportive framework. In contrast to the loose connective tissues, the dense connective tissues have closely packed fibers with a few cells in their ground substance. The three subtypes impart high tensile strength to withstand tension. While dense regular connective tissue predominantly contains collagen fibers arranged in parallel and is found in tendons, dense irregular connective tissue contains interwoven collagen fibers and is present in the fibrous capsules of joints. Lastly, the elastic connective tissue found in the walls of large arteries, such as the aorta, mainly contains elastin fibers.