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## 6.2 Integumentary Structures Derived from Epidermis The nails, hair, and exocrine glands of the skin are all derived from the epithelium that forms the epidermis. These structures are also known as epidermal derivatives, or epidermal appendages, of the integument. They formed during embryologic...

## 6.2 Integumentary Structures Derived from Epidermis The nails, hair, and exocrine glands of the skin are all derived from the epithelium that forms the epidermis. These structures are also known as epidermal derivatives, or epidermal appendages, of the integument. They formed during embryologic development as portions of the epidermis invaginated into the dermis. Both nails and hairs are composed primarily of dead keratinocytes, whereas the exocrine glands are composed of living epithelial cells. ### 6.2a Nails **Learning Objective** * Describe the structure and function of nails. Nails are scalelike modifications of the stratum corneum layer of the epidermis that form on the dorsal edges of the fingers and toes. They protect the distal tips of the digits during jumping, kicking, or catching. Fingernails also assist us in grasping objects. Each nail has a distal light-colored free edge, a darker colored nail body, and a nail root, which is the proximal part embedded in the skin (figure 6.9). Together, these parts form the nail plate. The nail body covers a layer of epidermis called the nail bed, which contains only the deeper, living cell layers of the epidermis. ## Clinical View 6.3 Nail Disorders Changes in the shape, structure, or appearance of the nails are clinically significant. In fact, the state of a person's fingernails and toenails can be indicative of his or her overall health. ### Brittle Nails Brittle nails are prone to vertical splitting and separation of the nail plate layers at the free edge. Overexposure to water or to certain household chemicals can cause brittle nails. Keeping the nails moisturized and limiting exposure to water and chemicals can alleviate brittle nails. ### Ingrown Nails An ingrown nail occurs when the edge of a nail digs into the skin around it. This painful condition is first characterized by pain and inflammation at the site. If left untreated, some ingrown toenails can cause infection. Ingrown nails may result from overly tight shoes and improper trimming of the nails. ### Nail Pitting Nail pitting refers to tiny depressions or shallow holes that appear in the nail body. The name derives from the fact that the nails look like an ice pick poked the holes in them. Nail pitting usually is a symptom of another disorder, such as psoriasis, alopecia areata, dermatitis, or a connective tissue disorder. ### Nail Clubbing In nail clubbing, the tip of the finger enlarges (or clubs) and the edges of the nail grow and curve around the tip. Nail clubbing occurs over a period of years and is indicative of **hypoxia** (inadequate blood flow to the tissue). Nail clubbing is often seen in conditions that are associated with hypoxia, such as smoking, cardiovascular disease, and diabetes. ### Onychomycosis Onychomycosis (on'i-kō-mī-kō'sis; onych = nail, mykes = fungus, osis = condition) is a fungal infection that occurs in nails constantly exposed to warmth and moisture. The fungus starts to grow under the nail and eventually causes a yellowish discoloration, a thickened nail, and brittle, cracked edges. ### Yellow Nail Syndrome Yellow nail syndrome occurs when growth and thickening of the nail slows or stops completely. As the nail growth slows, the nails become yellowish or sometimes greenish. Yellow nail syndrome often, but not always, may be an outward sign of respiratory disease, such as chronic bronchitis. ### Spoon Nails Spoon nails, or **koilonychia** (koy-lō-nike-a; koilos = hollow), are a nail malformation where the outer surface of the nails are concave instead of convex. Spoon nails frequently are a sign of an iron deficiency. Treating the iron deficiency should alleviate the spoon nail condition. ### Beau's Lines Beau's lines run horizontally across the nail and indicate a temporary interference with nail growth at the time this portion of the nail was formed. Injury to the nail or severe illness can cause Beau's lines. They also may be seen in individuals suffering from chronic malnutrition. ### Vertical Ridging Vertical ridging of the nails is common and usually does not indicate any serious medical problem. The condition occurs more frequently as we get older.