structure of the skin dermis –sometimes called “true skin”—much thicker than the epidermis...

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

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

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

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

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

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

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

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

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

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

Functions of the Skin

– Surface film• Functions

– Antibacterial, antifungal activity– Lubrication– Hydration of skin surface– Buffer of caustic irritants– Blockade of toxic agents

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

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