Transcript Essentials of Human Anatomy Skin Anatomy of Skin • Skin (integument) is body’s largest organ • Approximately 1.6 to 1.9 m2 in average-sized adult •

Essentials of Human Anatomy
Skin
1
Anatomy of Skin
• Skin (integument) is body’s largest organ
• Approximately 1.6 to 1.9 m2 in average-sized
adult
• Integumentary system describes the skin
and its appendages—the hair, nails, and
skin glands
• Thin and thick skin
– “Thin skin”—covers most of body surface
(1 to 3 mm thick)
– “Thick skin”—soles and palms
(4 to 5 mm thick)
Slide 2
Functions of Skin
Function of Integumentary System
A. Regulation of Body Temperature
B. Protection from Dehydration and Infection
C. Respond to Temperature, Pressure, Pain
D. Excretion of Water, Salts, Urea (nitrogenous waste)
E. Synthesis Vitamin D (essential for Ca + P absorption)
F. First Defensive Barrier of Immune Response
Functions of the Skin
• Protection
– Physical barrier to microorganisms
– Barrier to chemical hazards
– Reduces potential for mechanical trauma
– Prevents dehydration
– Protects (via melanin) excess UV exposure
Slide 4
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
Slide 5
Functions of the Skin
• Flexibility
– Skin is supple and elastic, thus permitting
change in body contours without injury
• Excretion
– Water
– Urea/ammonia/uric acid
Slide 6
Functions of the Skin
• Hormone (Vitamin D) production
– Exposure of skin to UV light converts
7-dehydrocholesterol to cholecalciferol—
a precursor to vitamin D
– Blood transports precursor to liver and
kidneys, where vitamin D is produced
– Process and end result fulfill the necessary
steps required for vitamin D to be classified as
a hormone
Slide 7
Functions of the Skin
• Immunity
– Phagocytic cells destroy bacteria
– Langerhans cells trigger helpful immune
reaction working with “helper T cells”
Slide 8
Functions of the Skin
– Heat loss
• approximately 80% of heat loss occurs
through the skin; remaining 20% occurs
through the mucosa of the respiratory,
digestive, and urinary tracts
Slide 9
Layers of Skin
• Epidermis
• Dermis
• Subcutaneous layer
• beneath dermis
• not part of skin
Epidermis
• Lacks blood vessels
• Keratinized
• Thickest on palms and soles (0.8-1.4mm)
• Melanocytes provide melanin
• Rests on basement membrane
• Stratified squamous
Structure of the Skin
• Epidermis
– Cell types
• Keratinocytes— constitute over 90% of cells present;
principal structural element of the outer skin
• Melanocytes— pigment-producing cells (5% of the total);
contribute to skin color; filter ultraviolet light
• Langerhans cells— dendritic (branched) antigen-presenting
cells (APCs), they play a role in immune response
Slide 13
Epidermis
Layers of Epidermis
• stratum corneum
• stratum lucidum
• stratum granulosum
• stratum spinosum
• stratum basale
Structure of the Skin
• Epidermis
– Cell layers
• Stratum germinativum (growth layer)—
describes the stratum spinosum and stratum
basale together
– Stratum basale (base layer)—single layer of
columnar cells; only these cells undergo mitosis, then
migrate through the other layers until they
are shed
– Stratum spinosum (spiny layer)—cells arranged in 8
to 10 layers with desmosomes that pull cells into spiny
shapes; cells rich in RNA
Slide 15
Structure of the Skin
– Cell layers
• Stratum granulosum (granular layer)—cells
arranged in two to four layers and filled with
keratohyalin granules; contain high levels of
lysosomal enzymes
• Stratum lucidum (clear layer)—cells filled with
keratin precursor called eleidin; absent in thin skin
• Stratum corneum (horny layer)—most superficial
layer; dead cells filled with keratin (barrier area)
Slide 16
Structure of the Skin
• Dermal-epidermal junction
– A definite basement membrane,
specialized fibrous elements, and a
polysaccharide gel serve to “glue” the
epidermis to the dermis below
– The junction serves as a partial barrier to
the passage of some cells and large
molecules
Slide 17
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
Slide 18
Dermis
• On average 1.0-2.0mm thick
• Contains dermal papillae
• Binds epidermis to underlying tissues
• Irregular dense connective tissue
• Muscle cells
• Nerve cell processes
• Specialized sensory receptors
• Blood vessels
• Hair follicles
• Glands
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
Slide 20
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
Slide 21
Lines of Cleavage
• Tension lines in the skin identify the
predominant orientation of collagen fiber
bundles.
• Clinically and surgically significant because cuts
can result in slow healing and increased
scarring.
Subcutaneous Layer
• hypodermis
• loose connective tissue
• adipose tissue
• insulates
• major blood vessels
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
Slide 26
Slide 27
Skin Color
Genetic Factors
Physiological Factors
• varying amounts of
• dilation of dermal blood
melanin
vessels
• varying size of melanin
• constriction of dermal blood
granules
vessels
• albinos lack melanin
• accumulation of carotene
• jaundice
Environmental Factors
• sunlight
• UV light from sunlamps
• X rays
• darkens melanin
Skin Color
– Melanin
• Basic determinant of skin color is quantity, type, and
distribution of melanin
– 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 (Figure 6-9)
– Bruising can cause a rainbow of different colors to
appear in the skin
Slide 29
Basis of Skin Color
• The color of skin and mucous membranes
can provide clues for diagnosing certain
problems, such as
– Jaundice
• yellowish color to skin and whites of eyes
• buildup of yellow bilirubin in blood from liver disease
– Cyanosis
• bluish color to nail beds and skin
• hemoglobin depleted of oxygen looks purple-blue
– Erythema
• redness of skin due to enlargement of capillaries in
dermis
• during inflammation, infection, allergy or burns
Slide 30
Skin glands
Sebaceous glands
• Secrete sebum—oily substance that keeps hair
and skin soft and pliant; prevents excessive water
loss from the skin
• usually associated with hair follicles
• Lipid components have antifungal activity
• Simple, branched glands
• Found in dermis except in palms and soles
• Secretion increases in adolescence; may lead to
formation of pimples and blackheads
Slide 31
Sweat Glands
• Widespread in skin
• Originates in deeper dermis
Or hypodermis
• Eccrine glands
• Apocrine glands
• Ceruminous glands
• Mammary glands
Sweat glands
• Eccrine glands
–Most numerous sweat glands; quite
small
–Distributed over total body surface with
exception of a few small areas
–Simple, coiled, tubular glands
–Function throughout life
–Secrete perspiration or sweat; eliminate
wastes; and help maintain a constant
core temperature
Slide 33
Sweat glands
• Apocrine glands
–Located deep in subcutaneous layer
–Limited distribution—axilla, areola of breast,
and around anus
–Large (often more than 5 mm in diameter)
–Simple, branched, tubular glands
–Begin to function at puberty
–Secretion shows cyclic changes in female
with menstrual cycle
Slide 34
Hair
• Distribution—over entire body except
palms of hands and soles of feet and a
few other small areas
• Fine and soft hair coat present before birth called
lanugo
• Coarse pubic and axillary hair that develops at
puberty called terminal hair
Slide 35
Functions of Hair
• Protection
• Heat retention
• Prevents the loss of conducted heat from the
scalp to the surrounding air
• Facial expression
• Sensory reception
• Visual identification
• Chemical signal dispersal
Hair Follicles
• Epidermal cells
• Tube-like depression
• Extends into dermis
• Hair root
• Hair shaft
• Hair papilla
• Dead epidermal cells
• Melanin
• Arrector pili muscle
A. Shaft - projects above surface of
epidermis
1. medulla - polyhedral cells with eleidin
2. cortex - elongated cells with/out
pigment
3. cuticle - outermost layer, like shingles
on roof
B. Root - below epidermis, penetrates
into the dermis
C. Hair Follicle - at the base a single
hair
1.
external root sheath - basale and
spinosum extension
2.
internal root sheath - internal hair
cell layers
3.
bulb - base of hair cell
4.
papilla - in the bulb, provides
nourishment for hair
5.
matrix - origin of new hair cells
D. arrector pili - smooth muscle, cause
hair to rise
nerve bundle responds to touch
E. hair root plexuses
Slide 39
Slide 40
Slide 41
Appearance of hair
• Color
– result of different amounts, distribution, types of melanin in
cortex of hair
• Growth
– hair growth and rest periods alternate; hair on head averages 5
inches of growth per year
• Sebaceous glands
– attach to and secrete sebum
(skin oil) into follicle
• Male pattern baldness results from combination of genetic
tendency and male sex hormones
Slide 42
Hair Thinning and Baldness
• Alopecia – hair thinning in both sexes
• True, or frank, baldness
– Genetically determined and sex-influenced
condition
Nails
– Consist of epidermal cells converted to hard
keratin
– Nail body—visible part of each nail
– Root—part of nail in groove hidden by fold of
skin, the cuticle
– Lunula—moon-shaped white area nearest
root
Slide 44
• Nail bed—layer of epithelium under nail body
– contains abundant blood vessels
• Appears pink under translucent nails
• Growth—nails grow by mitosis of cells in stratum germinativum
beneath the lunula; average growth about 0.5 mm per week, or
slightly over 1 inch per year
Slide 45
Types of Burns
• First-degree
– only epidermis (sunburn)
Slide 46
Types of Burns
• Second-degree burn
–
–
–
–
destroys entire epidermis & part of dermis
fluid-filled blisters separate epidermis & dermis
epidermal derivatives are not damaged
heals without grafting in 3 to 4 weeks & may scar
Slide 47
Types of Burns
• Third-degree or full-thickness
– destroy epidermis, dermis & epidermal derivatives
– damaged area is numb due to loss of sensory nerves
Slide 48