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Dermal papillae are relatively high and numerous in palmar and plantar skin but low and few in number

Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

196 Part Two Support and Movement in skin of the face and abdomen. What do you think is the functional significance of this difference?

There are two zones of dermis called the papillary and reticular layers (fig. 6.4). The papillary7 (PAP-ih-lerr-ee) layer is a zone of areolar tissue in and near the dermal papillae that forms about one-fifth of the thickness of the dermis. The loosely organized tissue of the papillary layer allows for mobility of white blood cells and other defenses against organisms introduced through breaks in the epidermis.

The reticular layer of the dermis, the deeper four-fifths, consists of dense irregular connective tissue. The boundary between the papillary and reticular layers is often vague. In the reticular layer, the collagen forms thicker bundles with less room for ground substance, and there are often small clusters of adipocytes. Stretching of the skin, as occurs in obesity and pregnancy, can tear the collagen fibers and produce striae (STRY-ee), or stretch marks. These occur especially in areas most stretched by weight gain: the thighs, buttocks, abdomen, and breasts.

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