Chapter 9. The Integumentary System
Jonathan Akin
Unit Outline
Learning Objectives
At the end of this unit, you should be able to:
I. Identify and describe the components of the integumentary system.
II. Identify and describe the five layers of the epidermis of the skin, including the location and function of keratinocytes and melanocytes.
III. Specify the function(s) of epidermal derivatives, including hair, sebaceous glands, sudoriferous glands, ceruminous glands, and nails.
IV. Describe five major functions of the integumentary system.
V. Explain the origin of variation in pigmentation in skin and integumentary derivatives.
VI. Explain underlying causes of common integumentary system conditions.
What do you think of when you look at your skin in the mirror? Do you think about cleaning and caring for it, checking for damage from the sun, or maybe adding a tattoo? Or do you think about the fact that the skin is an organ belonging to one of the body’s most essential and dynamic systems, the integumentary system? The skin makes up about 16% of the body weight of an adult and covers an area of 1.5 to 2 m2, making it the largest organ system in the human body.
The integumentary system refers to the skin, as well as accessory structures, such as hair, nails, and glands. The skin is responsible for much more than your outward appearance, beginning with acting as a protective covering between your internal and external environments. This chapter will introduce the structure and many other functions of the integumentary system.
Part 1: Layers of the Skin
Although you may not typically think of the skin as an organ, it is in fact composed of different types of tissues that work together to perform unique and critical functions. The skin is composed of two main layers: an outer epidermis and a deeper dermis (Figure 9.1). The deeper layer of skin is well vascularized (i.e., has numerous blood vessels). It also has numerous sensory and nerve fibers, ensuring communication to and from the brain. The skin is ultimately affixed to deeper body structures, such as muscle, by connective tissue in a subcutaneous layer known as the hypodermis.
Epidermis
The epidermis (Figures 9.2 & 9.3) is composed of keratinized, stratified squamous epithelium. Like all epithelial tissue, it is avascular. The dark-staining epithelial cells of the epidermis are arranged in multiple strata with the outermost cells appearing the most squamous in shape. The majority of skin areas is classified as thin skin, meaning that it has four visible layers (i.e., strata) of cells (Figure 9.2). From deepest to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Thick skin, however, is found exclusively on the palms of the hands and the soles of the feet. This type of epidermis has an additional fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum (Figures 9.3 & 9.4).
Regardless of whether