The Integumentary System
Skin (Integument)
Overview of the Skin
• Largest organ of the body (15% of body weight)
• Skin thickness variable, normally 1-2 mm
• Protection
– chemical barrier (waterproof)
– physical barrier (tough)
– immune system activator
• Body temperature regulation
– blood flow through the skin
– sweat glands
– hairs
• Sensation
– sense touch, temperature and pain
• provides information outside of the body
Functions of the Integumentary
System
• Largest organ of the body
• Protection – chemical, physical, and mechanical barrier:
Stratified layers of keratinized cells create a tough barrier
impermeable to most foreign invaders.
• Body temperature regulation is accomplished by:
– Regulation of blood flow to skin: dilation (cooling) and
constriction (warming) of dermal vessels
– Increasing sweat gland secretions to cool the body
Functions of the Integumentary
System
• Metabolic functions – synthesis of vitamin D in
dermal blood vessels
• Blood reservoir – skin blood vessels store up to
5% of the body’s blood volume
• Excretion – limited amounts of nitrogenous
wastes are eliminated from the body in sweat
Skin (Integument)
• Consists of three major regions
– Epidermis – outermost superficial region
– Dermis – middle region
– Hypodermis (superficial fascia) – deepest
region
• Deep Fascia: lies under the hypodermis.
– Lines the muscles arteries and nerves
Epidermis
• Outer portion of the skin is exposed to the
external environment and functions in protection.
• Composed of keratinized stratified squamous
epithelium, consisting of four distinct cell types
and four or five layers (strata).
• Cell types include keratinocytes, melanocytes,
Merkel cells, and Langerhans cells.
Cell and Layers of the Epidermis
Layers of the Epidermis: Stratum Basale
(Basal Layer)
• Deepest epidermal layer firmly attached to the dermis.
• Consists of a single row of the youngest keratinocytes
melanocytes and merkel cells.
– Keratinocytes – produce the fibrous protein keratin which
makes the cells more resistant to punctures and
abrasions.
– Melanocytes – produce the brown pigment melanin. The
darker your skin the greater the concentration of these
cells. Protects against UV radiation (sunlight) damage.
– Merkel cells – function as touch receptors in association
with sensory nerve endings.
• Cells undergo rapid division, hence its alternate name,
stratum germinativum.
Stratum Spinosum
(Prickly Layer)
• Keratinocytes form desmosomes which hold the
cells together.
• The spiny appearance is the result of the forces that
pull these cells apart.
• Langerhans( dendritic) cells: macrophages from
bone marrow that migrate to the epidermis.
– Capture foreign material and present it to the immune
system are abundant in this layer.
Stratum Granulosum
(Granular Layer)
• 3-5 cell layers thick made of keratinocytes.
• Keratinocytes undergo apoptosis
– (programmed cell death).
– Keratinocytes produce keratin
• A tough protein that makes the skin resistant to
abrasions.
– Exocytose glycolipids accumulate in between the cells of
this layer.
• Providing the waterproofing property to skin
– This will also cut off nutrients for the more
superficial layers of the epidermis
Stratum Lucidum
• Thin translucent zone seen only in thick skin( Lips,
palms of hands and soles of feet.
• Keratinocytes have no nucleus or organelles
– dead cells since they no longer have a blood
supply.
– does not stain well which give a clear appearance.
Stratum Corneum
(Horny Layer)
• Outermost layer of keratinized cells
• Accounts for three quarters of the epidermal
thickness
– ( approximately 30 layers thick)
• Functions include:
– Waterproofing and preventing water loss.
– Protection from abrasion and penetration.
Dermis
Papillary layer
Reticular layer
Layers of the Dermis
• Papillary layer
– Its superior surface contains finger like projections called
dermal papillae which adhere to the basal layer of the
epidermis.
– Dermal papillae contain capillary loops, Meissner’s
corpuscles ( light touch), and free nerve endings ( pain )
• Reticular layer
– Accounts for approximately 80% of the thickness of the skin
– Dense irregular Collagen fibers in this layer add strength
and resiliency to the skin
– Has a rich blood supply
– Location of several types of glands and sensory receptors
– Contains hair follicles and associated nerve and arrector
pili muscle
Hair Function and Distribution
• Functions of hair include:
– Thermoregulation
• When skin senses cold piloerector muscles are
stimulated. Hair becomes erect and goose
bumps form.
– Hair protects against physical trauma, heat loss,
and sunlight.
– Provide sensory perception.
– Hair is distributed over the entire skin surface
except palms, soles, and lips, nipples and portions
of the external genitalia.
Hair
Sweat Glands
• Different types prevent overheating of the body; secrete
cerumen and milk
– Eccrine (Merocrine) sweat glands – found in palms,
soles of the feet, and forehead.
• Are found all over the body. Cool body off.
– Apocrine sweat glands – found in axillary and
anogenital areas.
• Ceruminous glands
– modified apocrine glands in external ear canal that
secrete cerumen. ( ear wax)
• Mammary glands
– specialized sweat glands that secrete milk.
Sebaceous Glands
• Sebaceous Glands
– Simple alveolar glands found all over the
body.
– Secrete an oily secretion called sebum.
– Soften skin when stimulated by hormones.
Glands
Hypodermis
• Subcutaneous layer deep to the skin.
• Composed of adipose and areolar
connective tissue.
• Functions to insulate and cushion the body
the body.
• Adipose provides a source of energy for
ATP production.
Deep Fascia
• Dense fibrous connective tissue
– surrounds the muscles, bones, nerves and blood vessels.
Skin Color
• Three pigments contribute to skin color
– Melanin – yellow to reddish-brown to black
pigment, responsible for dark skin colors
• Freckles and pigmented moles – result from local
accumulations of melanin.
– Carotene – yellow to orange pigment, most
obvious in the palms and soles of the feet.
– Hemoglobin – reddish pigment responsible for
the pinkish hue of the skin.
Assessment of Skin color
• Cyanosis is a bluish discoloration of the skin or mucous membranes
• caused by lack of oxygen in the blood.
• Yellowish color
• may indicate cirrhosis of the liver due to accumulating bile
pigments in body tissue.
• Pallor or Blanching:
• can be sign of anemia or emotional or physical stress ( Heart
Attack)
• Black and Blues:
• Bruises caused by blood escapes circulation and clots
underneath the skin.
• Red color( erythema)
• indicate fever, allergy, infection inflammation and
embarrassment.
Skin Cancer
•
•
Most skin tumors are benign and do not
metastasize however:
The three major types of skin cancer are:
a) Basal cell carcinoma
b) Squamous cell carcinoma
c) Melanoma
Basal Cell Carcinoma (a)
• Least malignant and most common skin
cancer.
• Stratum basale cells proliferate and invade
the dermis and hypodermis.
• Slow growing and do not often
metastasize.
• Can be cured by surgical excision in 99%
of the cases.
Squamous Cell Carcinoma (b)
• Arises from keratinocytes of stratum
spinosum.
• Arise most often on scalp, ears, and lower
lip.
• Grows rapidly and metastasizes if not
removed.
• Prognosis is good if treated by radiation
therapy or removed surgically.
Melanoma (c)
• Cancer of melanocytes is the most
dangerous type of skin cancer because it
is:
– Highly metastatic
– Resistant to chemotherapy
• Treated by wide surgical excision
accompanied by immunotherapy.
• Chance of survival is poor if the lesion is
over 4 mm thick.
Melanoma
• Melanomas have the following
characteristics (ABCDE rule)
– A: Asymmetry; the two sides of the
pigmented area do not match.
– B: Border is irregular and exhibits
indentations.
– C: Color (pigmented area) is black, brown,
tan, and sometimes red or blue.
– D: Diameter is larger than 6 mm. (size of a
pencil eraser)
– E: Evolution : Is the mole changing?
Burns
• Hot water, sunlight,
radiation, electric shock
or acids and bases.
– Death from fluid loss and
infection.
First-degree – only the
epidermis is damaged
– Symptoms include
localized redness,
swelling, and pain.
Second-degree –
epidermis and upper
regions of dermis are
damaged.
– Symptoms mimic first
degree burns, but
blisters also appear.
• Third-degree – entire
thickness of the skin
is damaged.
– Burned area appears
gray-white, cherry red,
or black; there is no
initial edema or pain
(since nerve endings
are destroyed.)
Rule of Nines
• Estimates the severity
of burns
• Burns considered
critical if:
– Over 25% of the body
has second-degree
burns
– Over 10% of the body
has third-degree burns
• third-degree burns on
face, hands, or feet.