Biomedical Engineering Reference
In-Depth Information
Fig. 2.1
The epidermis is a regenerative tissue. Following controlled injury (stripping or blister-
ing), which leaves the dermis intact (
left
), the epidermis recovers its structure completely at the
site of the defect
(
right
). Hair follicles are ensheathed in epidermal tissue and participate in the
regenerative process. (Adapted from Asmussen and Sollner 1993)
2.1.1
The Epidermocentric Viewpoint in Studies of Skin Wound
Healing
The morphology of skin is illustrated in Fig.
2.1
. A more detailed description of the
structure and function of the tissues comprising skin appears in Chap. 4.
Briefly, the skin is an organ with an approximately two-dimensional geometry,
consisting of an epidermis attached to the
basement membrane
; the latter is attached
to the dermis. Its most critical function is protection of the organism from injury and
infection originating outside the body. The epidermis is a specialized tissue consist-
ing of several layers of epithelial cells (keratinocytes) that protects the organism
from dehydration, bacteria, ultraviolet radiation, as well as insults from chemical
substances. Protection is afforded principally by the outermost cell layer of the epi-
dermis, the stratum corneum, consisting of dead, keratinized cells. The epidermis
is supported by the dermis, a tough layer often about ten times the thickness of the
epidermis, consisting primarily of collagen and elastin fibers as well as blood ves-
sels. The dermis protects mechanically the thin, epidermal layer against shear and
other mechanical insults. Highly vascularized, the dermis supplies the epidermis
with metabolites and oxygen, both transferred through the basement membrane.
We consider the response of skin to different types of injuries. In a large major-
ity of studies the outcome has been measured in terms of processes that involve the
epidermis. The emphasis on restoration of the epidermis is frequently motivated by
the clinical urgency for wound closure: An open wound invites bacteria and, if large
enough, leads to dehydration of the organism; both are life threatening contingen-
cies in the clinical setting. This approach has been carried over in several experi-
mental studies of induced skin regeneration; it suggests that a favorable outcome of
the healing process is rapid completion of processes of epithelial cell proliferation,
migration, and finally, differentiation. This widespread viewpoint of the healing re-
sponse emphasizes, almost exclusively, the fate of the keratinocytes while neglect-
ing the dermis. We will refer to this as the epidermocentric viewpoint.
