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  • This chapter will provide an overview of the form and function of healthy human skin.


  • There are two arterial plexuses in the dermis: the superficial plexus and the deep plexus. Venules follow the arterioles in these areas.

  • The lymphatic system follows arterioles and venules and is arranged into an upper and lower plexus. It maintains plasma volume and prevents increased tissue pressure.


  • There are seven important functions of the human skin. It functions as a barrier, a sensory organ, and a site of transport, and it is involved in immune function, thermoregulation, protection against ultraviolet (UV) radiation, and secretion of pheromones.

  • The cutaneous innate immune system controls the initial pathogenic assault, while more specific recognition and destruction of the pathogen occurs via the acquired immune system.


  • The human skin is the largest organ in the body and helps maintain our internal homeostasis and protects from external factors, including bacteria, UV rays, and other factors.

  • Human skin plays an important role in regulating the body’s fluids and temperature.


The skin is the body’s largest organ. The average adult human skin has a surface area of about 1.8 m2 and weighs about 4.7 kg; however, these values can differ greatly across individuals.1 The skin is also one of the body’s most versatile organs, completing a wide array of vital functions that will be explored throughout this chapter.

The human skin consists of two mutually dependent layers, the epidermis and the dermis, which overlie the subcutaneous fatty layer or hypodermis. The epidermis, which is derived from the ectoderm, consists mainly of keratinocytes. The dermis, which is developed from the mesoderm, is made up mostly of collagen. It houses the adnexal structures and contains blood vessels, nerves, and lymphatics.2 The hypodermis, also derived from the mesoderm, contains adipose tissue. These layers vary in both cell type and function, which will be discussed throughout this chapter. There are two major types of skin: glabrous skin and nonglabrous skin. Glabrous skin exists on the palms and soles and contains no hair follicles or sebaceous glands. Nonglabrous skin has both hair follicles and sebaceous glands but lacks the encapsulated sense organs found in glabrous skin (Figure 1-1).

Figure 1-1

Overview of normal skin. This illustration demonstrates the major layers of skin and entities that can be found within each layer, including hair follicles, vasculature, and sensory receptors. Reproduced with permission from Mescher AL: Junqueira’s Basic Histology: Text and Atlas, 16th ed. New York, NY: McGraw Hill; 2021.


The epidermis is the outermost layer of the skin. Its thickness varies across body sites, averaging about 75 to 150 microns in thickness on ...

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