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# 6.1 Composition and Functions of the Integument The integument is the body's largest organ composed of all the tissue types that function together to protect internal body structures. Its surface is an epithelium that protects underlying body layers. The connective tissue deep to the epithelium...

# 6.1 Composition and Functions of the Integument The integument is the body's largest organ composed of all the tissue types that function together to protect internal body structures. Its surface is an epithelium that protects underlying body layers. The connective tissue deep to the epithelium provides strength and resilience to the skin. This connective tissue also contains smooth muscle associated with hair follicles (arrector pili) that alters hair position. Finally, nervous tissue within the integument detects and monitors sensory stimuli, thus providing information about touch, pressure, temperature, and pain. The integument accounts for 7% to 8% of the body weight and covers the entire body surface with an area that varies between about 1.5 and 2.0 square meters (m2). Its thickness ranges between 1.5 millimeters (mm) and 4 mm or more, depending on body location. For comparison, a sheet of copier paper is about 0.1 mm thick, so the thickness of the skin would range between 15 and 40 sheets of paper. The integument consists of two distinct layers: - a layer of stratified squamous epithelium called the epidermis - a deeper layer of both areolar and dense irregular connective tissue called the dermis The subcutaneous layer is not part of the integumentary system, however, it is described in this chapter because it is closely associated with both the structure and function of the skin. ## 6.1a Epidermis ### Learning Objectives 1. Describe the structure, composition, arrangement, and functions of the five layers (strata) of the epidermis. 2. Compare the variations in thickness, color, and markings of the epidermis. The epithelium of the integument is called the **epidermis** (ep-i-derm'is; epi = on, derma = skin). It is a keratinized, stratified squamous epithelium. While the entire integument thickness ranges from 1.5-4 mm, the thickness of only the epidermis ranges between 0.075 mm and 0.6 mm. Careful examination of the epidermis, from the basement membrane to its surface, reveals several specific layers, or strata. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (found in thick skin only), and stratum corneum (figure 6.2). The first three strata listed are composed of living cells, whereas the most superficial two strata contain dead cells. ## Figure 6.1 Layers of the Integument **A diagrammatic sectional view through the integument shows its relationship to the underlying subcutaneous layer**. - Integument - Epidermis - Papillary layer - Dermis - Reticular layer - Subcutaneous layer - Hair follicle - Tactile (sensory) receptors - Areolar connective tissue - Sensory nerve fiber - Hair shaft - Sweat pore - Epidermal ridge - Dermal papilla - Arrector pili muscle - Sebaceous (oil) gland - Sweat gland duct - Merocrine sweat gland - Vein - Artery - Adipose connective tissue