3.7: Boundary between Epidermis and Dermis
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- 83978
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The boundary between the epidermis and the dermis is important for the maintenance of the structure and functioning of the skin. For example, it is the region through which nutrients pass upward to the epidermis and wastes pass downward to the dermis. This exchange is essential for the epidermis, which has no blood vessels to service its cells. Keratinocytes in the epidermis have special projections that attach to the dermis to help in this exchange, which is also helped by many blunt projections from the dermis that extend up into the epidermis. These projections, called dermal papillae, increase the rate of exchange of materials by increasing the contact (i.e., surface area) between the two layers. The dermal papillae also contain special tufts of capillaries that further increase the ability of the dermis to service the epidermis (Figure 3.1 ).
besides improving the exchange of materials, the boundary between the epidermis and the dermis provides a strong attachment between the layers. The keratinocyte projections help by gripping the dermis, and the dermal papillae also help in this regard. As a result, the boundary can prevent separation of the epidermis from the dermis when sliding or pulling forces are applied to the surface of the skin.
The dermal papillae are usually scattered about in most areas of the skin. However, they are in very regular rows in the skin on the front of the hands and the bottom of the feet. These rows produce the ridges known as fingerprints, which make the skin less slippery and improve a person's ability to grip objects.
Age Changes in the Epidermal‑Dermal Boundary
As a person ages, the projections from the keratinocytes decrease in number and both the number and length of the dermal papillae decrease. The distribution of small vessels in the papillae becomes uneven. The result is a reduction in the functions of the boundary. First, there is less exchange of materials b dermis. Therefore, the epidermis is weakened, is injured more easily, and heals more slowly. Second, the weakening of the connection between the epidermis and dermis leads to easier blister formation in the elderly when the skin is subjected to physical forces. Such forces are encountered when one performs ordinary activities such as sweeping and gardening. They are also present when the skin is pulled, as occurs during the removal of adhesive bandages. The resulting injuries not only are painful but also increase the risk of skin infection. Finally, as the fingerprints become less prominent, keeping a firm grip on objects is more difficult.