Anatomy & Physiology

Anatomy & Physiology Study Guide The body of the nail consists of dead, tightly compressed cells packed with keratin. The cells producing the nails can be affected by conditions that alter body metabolism; thus, changes in the shape, structure, or appearance of the nails can provide useful diagnostic information. For example, the nails may turn yellow in individuals who have chronic respiratory disorders, thyroid gland disorders, or AIDS. Skin Cancers Tumors are not uncommon in the integumentary system. Most skin tumors never metastasize and, thus, are benign. However, there are three common cancers of note. Basal cell carcinoma affects the cells of the stratum basale. They invade through the basement membrane into the dermis and subcutaneous layer. It has a good prognosis and is characteristically slow growing, rarely metastasizes, and is usually curable by surgical excision. Another skin cancer called squamous cell carcinoma develops from the keratinocytes of stratum spinosum. These cells grow rapidly, but squamous cell carcinoma has a good prognosis if treated prior to metastasis. The skin cancer with the worst prognosis is melanoma. It is cancer of the melanocytes and is highly metastatic and resistant to chemotherapy. 6.3 Integumentary Injury and Repair Several steps are involved in repairing the integument following an injury. The integumentary system displays a significant degree of functional independence—it often responds directly and automatically to local influences without the involvement of the nervous or endocrine systems. For example, when the skin is continually subjected to mechanical stresses, stem cells in the stratum germinativum divide more rapidly and the depth of the epithelium increases. That is why calluses form on the palms when performing manual labor. The skin can regenerate effectively, even after considerable damage has occurred because stem cells persist in both the epithelial and connective tissue components. Germinative cell divisions replace lost epidermal cells, and mesenchymal cell divisions replace lost dermal cells. The process can be slow. When large surface areas are involved, problems of infection and fluid loss complicate the situation. The relative speed and effectiveness of skin repair vary with the type of wound involved. A slender, straight cut, or incision may heal relatively quickly compared with a deep scrape or abrasion that involves a much greater surface area to be repaired. When damage extends through the epidermis and into the dermis, bleeding generally occurs. The blood clot, or scab, that forms at the surface temporarily restores the integrity of the epidermis. The clot’s color reflects the presence of trapped red blood cells. Cells of the stratum germinativum undergo rapid divisions and begin to migrate along the edges of the wound to replace the missing epidermal cells. Meanwhile, macrophages patrol the damaged area of the dermis, and phagocytose any debris and pathogens.

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