dermis
the densenncollagenous connective tissue that makes up the dermis contains fibroblasts, fat cells, and macrophages. compared with the hypodermis, the dermis has fewer fat cells glands, and lymphatic vessels into the dermis
collagen and elastic fibers are responsible for the structural strength of the dermis. in fact, the dermis is that part of an animal hide from which leather is made. the epidermis is removed, and the dermis is preserved by tanning. the collagen fibers of the dermis are oriented in many different directions and can resist stretch. more collagen fibers are oriented in some directions than in others, however. this produces cleavage, or tension, lines in the skin, and the skin is most resistant to stretch along these lines . it is important for surgeons to be aware of cleavage lines. an incision made across the cleavage lines is likely to gap and produce considerable scar tissue, but an incision made parallel with the lines tends to gap less and produce less scar tissue. If the skin is overstretched for any reson, the dermis can be damaged leaving lines that are visible through the epidermis. these lines, called striae , or stretch marks, can develop on the abdomen and breasts of a woman during pregnancy.