Structure of the rat subcutaneous connective tissue in relation to its sliding mechanism.

Mammalian skin can extensively slide over most parts of the body. To study the mechanism of this mobility of the skin, the structure of the subcutaneous connective tissue was examined by light microscopy. The subcutaneous connective tissue was observed to be composed of multiple layers of thin collagen sheets containing elastic fibers. These piled-up collagen sheets were loosely interconnected with each other, while the outer and inner sheets were respectively anchored to the dermis and epimysium by elastic fibers. Collagen fibers in each sheet were variable in diameter and oriented in different directions to form a thin, loose meshwork under conditions without mechanical stretching. When a weak shear force was loaded between the skin and the underlying abdominal muscles, each collagen sheet slid considerably, resulting in a stretching of the elastic fibers which anchor these sheets. When a further shear force was loaded, collagen fibers in each sheet seemed to align in a more parallel manner to the direction of the tension. With the reduction or removal of the force, the arrangement of collagen fibers in each sheet was reversed and the collagen sheets returned to their original shapes and positions, probably with the stabilizing effect of elastic fibers. Blood vessels and nerves in the subcutaneous connective tissue ran in tortuous routes in planes parallel to the unloaded skin, which seemed very adaptable for the movement of collagen sheets. These findings indicate that the subcutaneous connective tissue is extensively mobile due to the presence of multilayered collagen sheets which are maintained by elastic fibers.