Structure of the Skin

1. Structure of the Skin • Dermis • Sometimes called “true skin”—much thicker than the epidermis and lies beneath it • Gives strength to the skin • Serves as a reservoir area for storage of water and electrolytes

2. Structure of the Skin • Dermis • Contains various structures: • Arrector pili muscles and hair follicles • Sensory receptors • Sweat and sebaceous glands • Blood vessels • Rich vascular supply plays a critical role in temperature regulation

3. Structure of the Skin • Dermis • Layers of dermis: • Papillary layer—composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers; contains the dermal-epidermal junction; forms a unique pattern that gives individual fingerprints • Reticular layer—contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processed from animal skin, produces leather

4. Structure of the Skin • Dermis • Dermal growth and repair • The dermis does not continually shed and regenerate itself as does the epidermis • During wound healing, the fibroblasts begin forming an unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar • Cleavage lines (Figure 6-6)—patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines

5. Structure of the Skin • Hypodermis • Also called subcutaneous layer or superficial fascia • Deep to the dermis, forming connection between the skin and other structures • Not part of the skin

6. Skin Color • Melanin • Basic determinant of skin color is quantity, type, and distribution of melanin • Types of melanin • Eumelanin—group of dark brown (almost black) melanins • Pheomelanin—group of reddish and orange melanins

7. Skin Color • Melanin (cont.) • Melanin formed from tyrosine by melanocytes (Figure 6-7) • Melanocytes release melanin in packets called melanosomes • Melanosomes are ingested by surrounding keratinocytes and form a cap over the nucleus • Albinism—congenital absence of melanin

8. Skin Color • Other pigments • Beta carotene (group of yellowish pigments from food) can also contribute to skin color • Hemoglobin—color changes also occur as a result of changes in blood flow • Redder skin color when blood flow to skin increases • Cyanosis—bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide • Bruising can cause a rainbow of different colors to appear in the skin • Jaundice

9. Functions of the Skin (Table 6-2) • Protection • Physical barrier to microorganisms • Barrier to chemical hazards • Reduces potential for mechanical trauma • Prevents dehydration • Protects (via melanin) excess UV exposure

10. Functions of the Skin • Protection (cont.) • Surface film • Emulsified protective barrier formed by mixing of residue and secretions of sweat and sebaceous glands with sloughed epithelial cells from skin surface; shedding of epithelial elements is called desquamation

11. Functions of the Skin • Surface film • Functions • Antibacterial, antifungal activity • Lubrication • Hydration of skin surface • Buffer of caustic irritants • Blockade of toxic agents

12. Functions of the Skin • Surface film • Chemical composition • From epithelial elements—amino acids, sterols, and complex phospholipids • From sebum—fatty acids, triglycerides, and waxes • From sweat—water and ammonia, urea, and lactic acid and uric acid

13. Functions of the Skin • Sensation • Skin acts as a sophisticated sense organ • Somatic sensory receptors detect stimuli that permit us to detect pressure, touch, temperature, pain, and other general sensations