The Integument as an Organ (p. 102)

1. The skin is considered an organ because it consists of several kinds of tissues.

2. The appearance of the skin is clinically important because it provides clues to certain body conditions or dysfunctions.

    

Layers of the Integument (pp. 103–109)

1. The stratified squamous epithelium of the epidermis is composed of five structural and functional layers: the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
   1. Normal skin color is the result of a combination of melanin and carotene in the epidermis and hemoglobin in the blood of the dermis and hypodermis.

   2. Fingerprints on the surface of the epidermis are congenital patterns, unique to each individual; flexion creases and flexion lines are acquired.

2. The thick dermis of the skin is composed of fibrous connective tissue interlaced with elastic fibers. The two layers of the dermis are the papillary layer and the deeper reticular layer.

3. The hypodermis, composed of adipose and loose connective tissue, binds the dermis to underlying organs.

    

Functions of the Integument (pp. 109–111)

1. Structural features of the skin protect the body from disease and external injury.
   1. Keratin and acidic oily secretions on the surface of the skin protect it from water and microorganisms.

   2. Cornification of the skin protects against abrasion.

   3. Melanin is a barrier to UV light.

2. The skin regulates body fluids and temperatures.
   1. Fluid loss is minimal as a result of keratinization and cornification.

   2. Temperature regulation is maintained by radiation, convection, and the antagonistic effects of sweating and shivering.

   3. The skin permits the absorption of UV light, respiratory gases, steroids, fat-soluble vitamins, and certain toxins and pesticides.

   4. The integument synthesizes melanin and keratin, which remain in the skin, and has a role in the synthesis of vitamin D, which is used elsewhere in the body.

   5. Sensory reception in the skin is provided through cutaneous receptors throughout the dermis and hypodermis. Cutaneous receptors respond to precise sensory stimuli and are more sensitive in thin skin.

   6. Certain emotions are reflected in changes in the skin.

       

   Epidermal Derivatives (pp. 111–118)

   1. Hair is characteristic of all mammals, but its distribution, function, density, and texture varies across mammalian species.
      1. Each hair consists of a shaft, root, and bulb. The bulb is the enlarged base of the root within the hair follicle.

      2. The three layers of a hair shaft are the medulla, cortex, and cuticle.

      3. Lanugo, angora, and definitive are the three distinct kinds of human hair.

   2. Hardened, keratinized nails are found on the distal dorsum of each digit, where they protect the digits; fingernails aid in grasping and picking up small objects.
      1. Each nail consists of a body, free border, and hidden border.

      2. The hyponychium, eponychium, and nail fold support the nail on the nail bed.

   3. Integumentary glands are exocrine, since they either secrete or excrete substances through ducts.
      1. Sebaceous glands secrete sebum onto the shaft of the hair.

      2. The two types of sudoriferous (sweat) glands are eccrine and apocrine.

      3. Mammary glands are specialized sudoriferous glands that secrete milk during lactation.

      4. Ceruminous glands secrete cerumen (earwax).