Skin may be the largest organ in the human body, measuring approximately 1.6-1.8 square meters in the adult. While its function is often assumed, any violation quickly reveals itself in pain and suffering for the owner, and extensive damage is life-threatening. Bacteria, viruses, fungi and harmful chemicals must penetrate your skin before causing injury to deeper tissues.
By giving a barrier facing outward world, the integument protects internal organs against injuries as well as prevents insensible fluid losses. In addition, skin helps you to regulate body temperature through the activity of sweat glands and blood vessels; nerves in skin also receive stimuli that are interpreted through the brain as touch, heat, cold and vibration.
Skin is composed of three layers: epidermis, dermis and subcutaneous tissue. As the deepest layer of the skin, the subcutaneous tissue connects the dermis towards the deeper structures of the body, insulates the body from cold and stores energy in the form of fat. The integument varies in thickness depending on anatomic location, sex and the age of the individual. On the back, buttocks, palms and soles of the feet, skin is often as thick as 4 mm or more.
In marked contrast, your skin from the eyelids, postauricular and supraclavicular region may be as thin as 0.5 mm. In all anatomic locations, female skin is characteristically thinner than male skin. Both the young and the old also have thin skin; the thin integument of kids thickens with age until it reaches a peak in the fourth or fifth decade of life, when it begins to thin again. In the elderly, thin skin primarily represents a dermal change, having a lack of elastic fibers, epithelial appendages and ground substance.
The skin doesn't have blood vessels, also it can only receive nutrients by diffusion in the underlying dermis with the basement membrane. On the other hand, the dermis, that is composed of the superficial papillary dermis and also the deeper reticular dermis, contains capillaries and larger arteries as well as connective tissue, elastic fibers, collagen, fibroblasts, mast cells, nerve endings, lymphatics, ground substance and epidermal appendages.
The epidermal appendages include sebaceous (holocrine) glands, eccrine and apocrine sweat glands and hair follicles. The head of hair follicles are epithelial structures lined with epithelial cells that can divide and differentiate. Found deep inside the dermis and in the subcutaneous fat deep to the dermis, they're responsible for the power of the skin to resurface even very deep cutaneous wounds that are nearly full thickness.
At times, however, skin cannot regenerate sufficiently, aesthetically and functionally to cover a wide open wound. These include full-thickness or deep partial-thickness burns as well as large exposed surfaces from surgical or traumatic extirpations. Skin grafts and skin substitutes are commonly used to provide coverage over a broad spectrum of open soft tissue defects. Unlike surgical flaps, however, skin grafts and skin substitutes don't have their own circulation and therefore are limited by their thinness. Thus, the recipient bed should be well-vascularized in order to supply the transferred skin with nutrients to survive.
Tendon may be grafted when the paratenon is intact; likewise, bone might be grafted if there is intact periosteum. On the other hand, irradiated tissue isn't a great candidate for any skin graft, as radiation often leads to capillary depletion and inadequate nutrition towards the transferred skin. Furthermore, open wounds with exposed bone often require more soft tissue padding than the usual skin graft has the capacity to provide.
Skin harvested from another species is called a xenograft. Skin harvested from another person from the same species is called an allograft. Skin that is harvested from one part of the body and used to cover another part of the same person's is called an autograft.
While xenografts and allografts enables you to provide temporary coverage over open wound defects, their MHC class II mismatch will cause rejection with time. They are very helpful as biological dressings, however, to allow a recipient bed to enhance before it is ready for an autograft. In particular, allografts are helpful to try a questionable recipient bed. Ultimately, however, an autograft is essential for permanent coverage from the wound.
There's two primary skin types autografts: split-thickness skin grafts (STSG) and full-thickness skin grafts (FTSG). A STSG includes the entire epidermis as well as varying portions of the underlying dermis. A FTSG includes both epidermis and also the entire dermis and thus retains more of the normal characteristics of skin including color, texture and thickness.
Because the FTSG contains more dermis, it's greater primary contraction than a STSG; however, full-thickness dermis impairs secondary wound contraction to some greater degree than a split-thickness graft. Of course, thicker grafts demand greater vascularity in the recipient bed in order to maintain cellular respiration.
Whether or not to make use of a full- or a split-thickness skin graft depends upon the condition and location from the defect, its size, as well as aesthetic considerations. Regions of high cosmetic concern, for example visible areas of the face or the hands, will benefit from a FTSG. A good example is applying full-thickness postauricular skin to cover the thin skin of the eyelid. In addition, areas that tolerate little wound contraction, like the interphalangeal joints or antecubital fossa, do better with a full-thickness skin graft.
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