Tissue: A group or layer of cells that perform specific functions. For example, muscle tissue is a group of muscle cells.issue: A group or layer of cells that perform specific functions. For example, muscle tissue is a group of muscle cells.
1 The skin is a barrier to the outside world protecting the body from infection, radiation, and extremes of temperature.  There are many types of wounds that can damage the skin including abrasions, lacerations, rupture injuries, punctures, and penetrating wounds.
Two types of skin lesions exist: primary and secondary. Primary skin lesions are abnormal skin conditions present at birth or acquired over oneâs lifetime. Birthmarks are primary skin lesions. Other types include: 1  blisters: also called vesicles; these are small lesions filled with a clear fluid. 2  Vesicles can be the result of sunburns, steam burns, insect bites, friction from shoes or clothes, and viral infections. 3  macule: freckles and flat moles.