Biomedical Engineering Reference
In-Depth Information
Epidermis (5%)
Thin
Dermis (95%)
Split-thickness
skin graft
Medium
Sebaceous
gland
100%
Thick
Subcutaneous
tissue
Hair
follicle
Full-thickness
skin graft
Sweat
gland
5.1
The anatomy of skin (from Place
et al.
, 1997).
the wound's periphery but also from skin adnexal structures, including hair
follicles, sebaceous glands, and sweat glands. Given the ability of the epidermis
to regenerate, pure epidermal wounds heal without scarring (Paletta
et al
.,
2006).
The primary cell of the epidermis, the keratinocyte, forms five layers, or
strata, representing its progressive differentiation, a process known as cornifica-
tion. The five strata from deep to superficial are the stratum basale (i.e. the
basement membrane), stratum spinosum, stratum granulosum, stratum lucidum
and stratum corneum. The stratum corneum is a layer of non-viable cells that
provides a protective layer from the environment. Tight intercellular connec-
tions within the epidermis form the basis of its physical integrity and lamellar
granules, containing sterols, polar lipids and hydrolytic enzymes, released into
the intercellular space give the epidermis its impermeable quality (Landmann,
1986; Paletta
et al
., 2006). Three other cell types populate the epidermis: the
melanocyte, the Langerhans cell and the Merkel cell. Melanocytes reside in the
basal layer of the epidermis (the melanocyte to keratinocyte ratio is 1:10)
(Cochran, 1970). Melanocytes produce pigment melanin containing vesicles
known as melanosomes, which are in turn phagocytosed by nearby
keratinocytes. The primary role of melanin is to protect the skin from the
harmful effects of sunlight (Boissy, 1988). The Langerhans cell resides in the
middle layers of the epidermis and is important in immune surveillance and
allograft rejection (Choi and Sauder, 1986). Merkel cells reside in the epidermis
of the palms and soles, nail beds, and oral and genital epithelium and serve as
mechanoreceptors in a close relationship with neurons.
