Porth's Essentials of Pathophysiology, 4e

13 U N I T

Integumentary Function

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Structure and Function of the Skin Epidermis

C h a p t e r

Keratinocytes Melanocytes Langerhans Cells Merkel Cells

Dermis

Structure and Function of the Integumentum

Papillary Dermis Reticular Dermis

Immune Cells Blood Vessels Innervation Basement Membrane Zone

Appendages of the Skin

Sweat and Sebaceous Glands Hair and Hair Follicles Nails Manifestations of Skin Disorders Lesions and Rashes Pigmentary Skin Disorders Pruritus Dry Skin Variations in Dark-Skinned People

T

he integumentary system, including the skin and its appendages (sweat and sebaceous glands, hair folli- cles, and nails), constitutes a complex organ with many cell types. The diversity of these cells and their ability to work together provide many functions needed to cope with the constantly changing external environment.

Structure and Function of the Skin

The skin is one of the largest and most versatile organs in the body. It has a surface area of 1.5 to 2 square meters, weighs approximately 4 kg (9 pounds), and forms the major interface between the internal organs and the external environment. Besides providing a covering for the entire body surface, the skin performs many other functions, including protection against physical injury, sunlight, and microorganisms; prevention of loss of fluids from the internal environment; regulation of body temperature; continual reception of sensations from the environment, such as touch, temperature, and pain; and synthesis of vitamin D through the action of sunlight on the skin. The properties of the skin, such as the thickness of skin layers, their cell types, the distribution of sweat and sebaceous glands, and the number and size of hair fol- licles, vary in different parts of the body. Nevertheless, certain properties are common to the skin on all areas of the body. Structurally, the skin consists of two main

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