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Integumentary System

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

Chapter 23: Integumentary System STRUCTURES AND FUNCTIONS  The epidermis is the outermost skin layer. The dermis is the second skin layer; it contains the collagen bundles while it supports the nerve and vascular network.  The subcutaneous layer is composed of fat and loose connective tissue.  The primary function of skin is to protect underlying body tissues by serving as a surface barrier to the external environment. Skin also is a barrier against bacteria, viruses, and excessive water loss. Fat in the subcutaneous layer insulates the body and provides protection from trauma.  Two major types of epidermal cells include melanocytes (5%) and keratinocytes (90%). o Melanocytes contain melanin, a pigment giving color to skin and hair and protecting the body from damaging ultraviolet (UV) sunlight. More melanin results in darker skin color. o Keratinocytes produce fibrous protein, keratin, which is vital to protective barrier function of skin.  The dermis is the connective tissue below the epidermis. It is highly vascular and assists in the regulation of body temperature and blood pressure.  The dermis is divided into two layers: upper thin papillary layer and deeper, thicker reticular layer.  Collagen forms the largest part of the dermis and is responsible for the mechanical strength of the skin.  Skin appendages include hair, nails, and glands (sebaceous, apocrine, and eccrine). These structures develop from the epidermal layer and receive nutrients, electrolytes, and fluids from the dermis. Hair and nails form from specialized keratin that becomes hardened.  Nail color ranges from pink to yellow or brown, depending on the skin color. Pigmented longitudinal bands (melanonychea striata) may occur in the nail bed in most people with dark skin.  Sebaceous glands secrete sebum, which is emptied into hair follicles. Sebum prevents skin and hair from becoming dry.  Apocrine sweat glands are located in the axillae, breast areolae, umbilical and anogenital areas, external auditory canals, and eyelids. They secrete a thick, milky substance that becomes odoriferous when altered by skin surface bacteria.  Eccrine sweat glands are widely distributed over the body, except in a few areas such as lips. These glands cool the body by evaporation, excre
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