Gartner_BRS Cell Biology & Histology, 9e

BRS Cell Biology and Histology

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Clinical PEARLS Keloids are abnormal proliferation of scar tissues that form at the site of skin injury. Instead of regressing as they should, the scar tissue grows beyond the margins of the original injury. The incidence of keloids is 15 times higher in persons with higher pigmented skin than in persons with less pigmentation, and the typical age at onset is 10 to 30 years. Keloids are benign and have no malignant potential but can cause some dis comfort, such as itching and pain. Further, if the keloid forms across a joint, then the patient’s mobility across that joint may become impaired. There is no single most effective therapeutic measure for keloids; therefore, prevention should be the number one consideration. Treatments for keloids can be as extensive as surgical removal, injection of steroids into the keloid, and cryotherapy (using liquid nitrogen) as well as laser therapy. PEARLS Burn injuries , lesions caused by contact with heat, friction, caustic agents, electricity, or exposure to radi ation, are classified into three categories depending on the number of cell layers that are damaged. 1. Superficial (first-degree) burns are lesions in which the damage is limited to the superficial layers of the epithelium (usually the epidermis of the skin or the epithelial lining of the mouth). There is pain, swelling, and redness, but no blisters form. Mitotically active cells remain viable in the deeper layers of the epidermis, which divide and replace the damaged or destroyed cells. 2. Partial-thickness (second-degree) burns are of two types: superficial partial thickness and deep partial thickness . a. Superficial partial-thickness burns affect not only the superficial layers but also deeper layers of the epithelium and the papillary layer of the dermis (superficial connective tissue layer of the skin). It is very painful, there is swelling and redness, and blisters form. b. Deep partial-thickness burns affect the entire thickness of the epithelium and partial thickness of the reticular layer (deep layer) of the dermis. Instead of pain, there is pressure, blisters may or may not form, and the lesion is white to yellowish in color. 3. Full-thickness (third-degree) burns affect the entire thickness of both the epidermis and the dermis. Because the nerves of the skin are destroyed, there is minimal pain. The lesion is white to light brown in color. Clinical During development, epidermal cells in certain regions proliferate and grow down into the dermis. The cells in the deeper regions of the downgrowth differentiate into the secretory cells, and the super ficial regions that maintain continuity with the epidermis differentiate into the ducts. A. The 3 to 4 million eccrine sweat glands (see Fig. 12.4) are simple coiled tubular glands consisting of a secretory unit and a single duct. These glands are present in the skin throughout most of the body, but not in the lips and not in certain regions of the external genitalia. Eccrine sweat glands function in controlling body temperature, conserving electrolytes, and excreting watery sweat containing a low concentration of urea and lactic acid. They are stimulated by sympathetic innervation as a result of elevated body temperature. 1. The secretory unit of eccrine sweat glands is approximately 0.4 mm in diameter and is em bedded in the dermis; it is composed of three cell types. IV. GLANDS IN THE SKIN (Fig. 12.5)

Copyright © 2024 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. a. Dark cells line the lumen of the gland and contain many mucinogen-rich secretory granules. b. Clear cells underlie the dark cells and contain abundant mitochondria and glycogen. They possess intercellular canaliculi that extend to the lumen of the gland. These cells secrete a watery, electrolyte-rich material.

c. Myoepithelial cells lie scattered in an incomplete layer beneath the clear cells. They stain well with acidophilic dyes and are easily identified in histologic sections due to the rich content of contractile proteins in their cytoplasm. Their contractions aid in expressing the gland’s secretions into the duct. 2. The ducts (see Fig. 12.4) of eccrine sweat glands are long, narrow, and lined by a stratified cuboidal epithelium , which contains many keratin filaments and has a prominent terminal web. a. The duct leads from the secretory unit through the superficial portions of the dermis to pen etrate an interpapillary peg of the epidermis, where the duct cells end. From this point, the