The skin surface is not smooth, but is laced with multiple net-works of fine grooves called sulci cutis. These can be deep orshallow. The slightly elevated areas that are surrounded by shal-lower areas of sulci cutis are called cristae cutis. Sweat pores fedby the sweat glands open to the cristae cutis (Fig. 1.1).

The orientation of the sulci cutis, which differs depending onbody location, is called the dermal ridge pattern. Fingerprints andpatterns on the palms and soles, which are unique to each person,are formed by the sulci cutis. Elastic fibers also run in specificdirections in deeper parts of the skin, with the direction depend-ing on the site. Some skin diseases, such as epidermal nevus, areknown to occur along specific lines distributed over the body, theBlaschko lines (Fig. 1.2). These lines are thought to be associated

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crista cutis

sulcus cutis

Fig. 1.1 Appearance of the skin surface. a: Cristae cutis (triangle) and sulci cutis (arrows).b: Nevus-cell nevus along the cristae cutis. c:Sweat pores fed by sweat glands open to thecristae cutis (arrows).

1 Structure and Function of the Skin

The skin is the human body’s its largest organ, covering 1.6 m2 of surface area and accounting for approximate-ly 16% of an adult’s body weight. In direct contact with the outside environment, the skin helps to maintain fouressential bodily functions: ① retention of moisture and prevention of permeation or loss of other molecules, ②regulation of body temperature, ③ protection of the body from microbes and harmful external influences, and ④sensation. To understand cutaneous biology and skin diseases, it is very important to learn the structure andfunctions of normal human skin.

A. Skin surface

Fig. 1.2 The Blaschko lines. Many dermatological disorders appear along these lines, such as epider-mal nevus and linear scleroderma (Bolognia JL, et al. J Am Acad Derma-tol 1994; 31:175-90).

aa b c d e f ha g i j k l m n o p q r

a bb c d e f hb g i j k l m n o p q r

a b cc d e f hc g i j k l m n o p q r

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Chapter

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with the direction in which the differentiated cell clones extendduring fetal skin development.

Skin generally consists of a three-layer structure: the epider-mis, dermis and subcutaneous tissues (Fig. 1.3). At the boundarybetween the epidermis and dermis are finger-like projectingstructures (the dermal papillae) that project into the overlying tis-sue (the epidermis) (Fig. 1.30). The portion of the epidermis thatprojects into the dermis is called the epidermal rete ridge, and theportion of the dermis that projects into the epidermis is called thedermal papilla.

2 1 Structure and Function of the Skin1

hairhair

sweat poresweat pore

eccrine sweat glandeccrine sweat gland

sebaceous glandsebaceous gland

epidermal basement membraneepidermal basement membrane

dermal papilladermal papilla

hair bulgehair bulge

arrector pili musclearrector pili muscle

apocrine sweat glandapocrine sweat gland

papillary dermispapillary dermis

fasciafascia

subcutaneous tissuesubcutaneous tissue

dermis

dermis

epidermis

epidermis

muscle

muscle

horny cell layerhorny cell layer

subpapillary dermissubpapillary dermis

reticular dermisreticular dermis

dermal hair papilladermal hair papilla

hair matrixhair matrix

hair folliclehair follicle

hair bulbhair bulb

infundibuluminfundibulum

epidermal rete ridgeepidermal rete ridge

hair

sweat pore

eccrine sweat gland

sebaceous gland

epidermal basement membrane

dermal papilla

hair bulge

arrector pili muscle

apocrine sweat gland

papillary dermis

fascia

subcutaneous tissuederm

isepiderm

ism

uscle

horny cell layer

subpapillary dermis

reticular dermis

dermal hair papilla

hair matrix

subcutaneous subcutaneous fatfatsubcutaneous fat

hair follicle

hair bulb

infundibulum

epidermal rete ridge

Fig. 1.3 Structure of the skin.(Nakagawa H, editor. Dermatological disorders. In: Symphonia Medica Nursing (Vol.19). Nakayama-Shoten; 2001. p.3).

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