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## Clinical View 6.7: Botox and Wrinkles Many individuals have explored ways to diminish the appearance of age-related wrinkles. One popular treatment for wrinkles caused by repeated facial muscle expression is botulinum toxin type A (Botox). This medicine is derived from the toxin produced by the...

## Clinical View 6.7: Botox and Wrinkles Many individuals have explored ways to diminish the appearance of age-related wrinkles. One popular treatment for wrinkles caused by repeated facial muscle expression is botulinum toxin type A (Botox). This medicine is derived from the toxin produced by the bacterium *Clostridium botulinum*. Although large doses of this toxin may be deadly, small therapeutic doses temporarily block nerve impulses to the facial expression muscles, thereby decreasing or eliminating the wrinkles they produce. The procedure is done in a doctor's office, where the doctor injects Botox in the specific facial muscles responsible for the wrinkles, such as frown lines and crows' feet. The effect is temporary, and an individual must repeat the procedure after about 4 months, as the muscles regain their function. Botox is relatively safe, but some individuals may experience adverse effects, and overuse of Botox can produce a face that appears frozen and devoid of facial expression. ## 6.4a Development of the Integument and Its Derivatives **Learning Objectives** - Describe how integument develops from ectoderm and mesoderm. - Explain the developmental origins of nails, hair, and glands. By the end of week 7 of development, the ectoderm forms a layer of squamous epithelium that flattens and then becomes both a covering layer, called the periderm, and an underlying basal layer. The basal layer will form the stratum basale and all other epidermal layers. By week 21, the stratum corneum and friction ridges form. During the fetal period (weeks 9-38), the periderm is eventually sloughed off. The sloughed-off cells mix with sebum secreted by the sebaceous glands, producing a waterproof protective coating called the *vernix caseosa* that coats the skin of the fetus. The dermis is derived from mesoderm. During weeks 3-8, this mesoderm becomes *mesenchyme* (see section 5.2c). The mesenchymal cells begin to form the components of the dermis at about 11 weeks. Fingernails and toenails start to form in the tenth week of development. The fingernails reach the tips of the fingers by 32 weeks, whereas the toenails become fully formed by about 36 weeks. Hair follicles begin to appear between 9 and 12 weeks of development as pockets of cells, called *hair buds*, invade the dermis from the overlying stratum basale of the epidermis. These hairs do not become easily recognizable in the fetus until about 20 weeks. Finally, sweat and sebaceous glands develop from the stratum basale of the epidermis and first appear at about 20 weeks on the palms and soles and later in other regions. **What Did You Learn** - What two primary germ layers form the integument? ## 6.4b Aging of the Integument **Learning Objectives** - List the changes that occur in the skin during aging, and explain the factors that contribute to those changes. - Describe the risk factors, warning signs, and characteristics of skin cancer. Although some adolescents develop acne when they enter puberty, most skin changes do not become obvious until an individual reaches middle age. Then, the skin repair processes take longer to complete because of a reduced number and activity of stem cells. Skin repair and regeneration activities that took 3 weeks in a healthy young person often take twice that time for a person in the seventh decade of life. Additionally, the reduced stem cell activity in the epidermis results in a thinner skin that is less likely to protect against abrasive, mechanical trauma. Collagen fibers in the dermis decrease in number and organization, and elastic fibers lose elasticity. Years of particular facial expressions (squinting, smiling) produce crease lines in the integument. As a result, the skin forms wrinkles and becomes less resilient. In addition,