2 1 Section 1: Skin and subcutaneous tissues Chapter 1 The structure and function of skin ● The skin or integument is a double-layered membrane cover- ing the exterior of the body and is continuous with the mu- cous membranes lining the body’s orifices. It shows a marked variation in thickness, measuring from less than 1 mm (on the eyelid) to more than 4 mm (on the back). The wide range of properties of the skin is summarized in Box 1–1. ● The skin can be divided into two parts, the epidermis (outer layer) and dermis (inner layer), which rests on and is at- tached to the subcutaneous fat (Fig. 1–1). ● The epidermis is comprised of four clearly defined layers, or strata (Fig. 1–2): 1. Basal layer (stratum basale, stratum germinativum): my- cotic activity of keratinocytes is confined to this layer, result- ing in an epidermal turnover time of approximately 4 weeks. Melanocytes, which produce melanin pigment, are found in this layer. 2. Prickle cell layer (stratum spinosum): contains polyhe- dral cells with intercellular attachments and Langerhans cells (specialized antigen-presenting cells involved in con- tact hypersensitivity) 3. Granular cell layer (stratum granulosum): characterized by loss of cell nuclei and acquisition of dense keratohyalin granules 4. Keratin layer (stratum corneum): acellular layer contain- ing keratin fibrils. It serves as a protective barrier. Its thickness varies with location (maximum thickness on palms and soles, minimum thickness at flexural sites). Box 1–1 Properties of the skin • Maintains integrity of the body • Protects from injurious stimuli • Absorbs and excretes liquids • Regulates temperature • Waterproofs • Absorbs ultraviolet light • Metabolizes vitamin D • Detects sensory stimuli • Provides cosmetic functions • Acts as a barrier against microorganisms From McKee PH, Calonje E, Granter SR (eds): Pathology of the Skin With Clinical Correlations, 3rd ed. St. Louis, Mosby, 2005. Hair Arrector pili muscle Apocrine gland Hair follicle Eccrine gland Fat tissue Blood vessels Sebaceous gland Basal cell layer Basement membrane Dermal papillae Stratum corneum Melanocytes SUBCUTANEOUS TISSUE DERMIS EPIDERMIS Fig 1–1 Cross section through the skin, showing the structures in the epidermis and subcutaneous tissues. (From Swartz Swartz MH: Textbook of Physical Diag- nosis, 5th ed. Philadelphia, WB Saunders, 2006.)

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21 Section 1: Skin and subcutaneous tissues

Chapter 1 The structure and function of skin

The skin or integument is a double-layered membrane cover-ing the exterior of the body and is continuous with the mu-cous membranes lining the bodys ori ces. It shows a marked variation in thickness, measuring from less than 1 mm (on the eyelid) to more than 4 mm (on the back). The wide range of properties of the skin is summarized in Box 11.

The skin can be divided into two parts, the epidermis (outer layer) and dermis (inner layer), which rests on and is at-tached to the subcutaneous fat (Fig. 11).

The epidermis is comprised of four clearly de ned layers, or strata (Fig. 12):1. Basal layer (stratum basale, stratum germinativum): my-cotic activity of keratinocytes is con ned to this layer, result-ing in an epidermal turnover time of approximately 4 weeks. Melanocytes, which produce melanin pigment, are found in this layer.2. Prickle cell layer (stratum spinosum): contains polyhe-dral cells with intercellular attachments and Langerhans cells (specialized antigen-presenting cells involved in con-tact hypersensitivity)3. Granular cell layer (stratum granulosum): characterized by loss of cell nuclei and acquisition of dense keratohyalin granules4. Keratin layer (stratum corneum): acellular layer contain-ing keratin brils. It serves as a protective barrier. Its thick-ness varies with location (maximum thickness on palms and soles, minimum thickness at exural sites).

Box 11 Properties of the skin Maintains integrity of the body Protects from injurious stimuli Absorbs and excretes liquids Regulates temperature Waterproofs Absorbs ultraviolet light Metabolizes vitamin D Detects sensory stimuli Provides cosmetic functions Acts as a barrier against microorganisms

From McKee PH, Calonje E, Granter SR (eds): Pathology of the Skin With Clinical Correlations, 3rd ed. St. Louis, Mosby, 2005.

Hair

Arrector pili muscle

Apocrine gland Hair follicle Eccrine gland Fat tissueBlood vessels

Sebaceous gland Basal cell layerBasement membraneDermal papillae

Stratum corneumMelanocytes

SUBCUTANEOUSTISSUE

DERMIS

EPIDERMIS

Fig 11Cross section through the skin, showing the structures in the epidermis and subcutaneous tissues.(From Swartz Swartz MH: Textbook of Physical Diag-nosis, 5th ed. Philadelphia, WB Saunders, 2006.)

Ch01-13_X4919_001-046.indd 2 10/9/08 2:20:57 PM
3Chapter 1: The structure and function of skin 1 The dermis is the brous part of the skin, which provides

strength. It supports the epidermis and is composed of a -brous connective tissue component (collagen and elastic bers) in intimate association with ground substance. Within the dermis are the epidermal appendages (sur-rounded by a connective tissue sheath), blood vessels and nerves, and a cellular component, including mast cells, -broblasts, myo broblasts, and macrophages. Smooth mus-cle is also represented in the erector pili muscles.

Fig 12Normal skin from the ngertip showing the clearly de ned layers of the epidermis.(From McKee PH, Calonje E, Granter SR [eds]: Pathology of the Skin With Clinical Correlations, 3rd ed. St. Louis, Mosby, 2005.)

Ch01-13_X4919_001-046.indd 3 10/9/08 2:20:58 PM