Transcript Structure of the Skin

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:
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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