3.9: Subcutaneous Layer - Structure and Functions
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- 83980
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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 subcutaneous layer lies under the dermis (Figure 3.1 ). While this layer is usually not considered part of the skin, it makes up the innermost layer of the integumentary system.
Loose Connective Tissue
The foundation material of the subcutaneous layer is made of loose connective tissue that contains a soft gel consisting of a large amount of water with some protein and other substances dissolved in it. Within the gel are various types of cells and widely scattered collagen and elastin fibers.
The soft gel serves as a cushion under the skin. It is slippery and therefore allows the skin to slide easily over the underlying muscles and bones. As in the dermis, some cells produce the gel and fibers, while others defend the body against microbes and harmful chemicals. The fibers hold the other components in place and attach the skin to the body. Since these fibers are relatively low in number, they allow the skin to move easily, though only a limited distance over the underlying structures.
Fat Tissue
Fat tissue is also found within the subcutaneous layer. Some areas of the body (e.g., buttocks) have a thick layer of fat, while other areas (e.g., hands) have a thinner layer. There is also a wide degree of difference among individuals in terms of fat in the subcutaneous layer.
Fat tissue is a very important component of the subcutaneous layer. First, the soft but somewhat firm consistency of fat allows it to cushion the inner body parts, protecting them from injury by pressure and forceful blows. Second, because of its firmness, fat helps maintain the contour of the skin. Thus, in moderate amounts and when distributed well, fat contributes to a pleasing appearance. Third, since fat is a thermal insulator, it helps maintain proper body temperature by reducing the rate of heat loss through the skin. Finally, fat is a nutrient storage material. If the diet does not provide enough energy or building materials for the body, the cells break down fat molecules. Body cells can obtain a great deal of energy and raw materials in this way.
Age Changes in the Subcutaneous Layer
There is little information about the effects of aging on the loose connective tissue of the subcutaneous layer. There is a general decrease in the amount of subcutaneous fat tissue with aging, but there is little decrease in the total amount of fat in the body. The explanation is that while the amount of subcutaneous fat is decreasing, the amount of fat increases in the inner regions of the body, such as around the organs inside the abdomen. One effect of the generalized thinning of subcutaneous fat is a decrease in the ability of an older person to stay warm in a cold environment. Another effect is a reduction in the support of the skin. This, with changes in the dermis, makes the skin appear loose. The skin may even seem to hang in folds on the face and other parts of the body. The thinning of the fat may also contribute to the more translucent appearance of the skin of elderly individuals.
Changes in the proportion of fat in different areas of the body also seem to be very important. This is currently a topic of considerable research, but only a few conclusions can be drawn. For example, the substantial decrease in fat on the bottom of the feet reduces their ability to cushion the body. It also seems that the distribution of body fat is related to the incidence of certain diseases (e.g., coronary artery disease, diabetes).
Though the immediate biological effects of an altered distribution of subcutaneous fat on healthy survival are uncertain, the cosmetic effects are very apparent. The subcutaneous fat of the arms and legs thins, as do the muscles in those areas. At the same time, there is a thickening e trunk of the body. The result is a dramatic change in body proportions, with the waist seeming to get much larger with age. This change occurs to a greater degree in women than in men. Weakening of the abdominal muscles and other muscles important in maintaining good posture can exaggerate the result.
These changes in subcutaneous fat are believed to occur in most people because of aging. However, there is an enormous degree of variability among individuals because many factors besides aging can affect fat tissue. For example, alterations in diet, exercise, and hormone levels can profoundly change the amount and distribution of fat. Therefore, as individuals get older, a considerable change in their appearance may alter their social interactions, psychological health, and economic status.