Download Skin

General Facts:
A.First line of defense, skin is an organ
B.Vital to homeostasis
C.Largest body organ
4 Types of Membranes:
a. Serous Membrane:
lack
1. Lines the body cavities that
external openings.
2. Lubricates membrane surfaces
b. Mucous Membranes:
1. Line caviteis that open externally
2. Secrete mucous
c.Synovial Membranes
1.Line joints cavities
2.Lubricate ends of bones at joints
D. Cutaneous Membrane
1. External body covering
2. Protection
Functions of the skin:
1. protection
2. Regulate body temperature
3. Retard water loss
4. House sensory receptors
5. Synthesize biochemicals
6. Excrete waste
Regions
Epidermis –
outermost
superficial region
Dermis – middle
region
Subcutaneous
(superficial fascia)
– deepest region
Epidermis
• Composed of stratified squamous
epithelium, consisting of four distinct cell
types and four or five layers and lacks blood
vessels
• Cell types include keratinocytes,
melanocytes, Merkel cells, and Langerhans’
cells
• Outer portion of the skin is exposed to the
external environment and functions in
protection
Cells of the Epidermis
• Keratinocytes – produce the
fibrous protein keratin
• Melanocytes – produce the
brown pigment melanin
• Langerhans’ cells –
epidermal macrophages
that help activate the
immune system
• Merkel cells – function as
touch receptors in
association with sensory
nerve endings
Touchy,
Touchy
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
• Cells undergo rapid
division
• Well nourished by
dermal blood vessels
Cells are pushed upward as new cells are
formed and become keratinized as they
die.
Protects against water loss, injury, harmful
chemicals & bacteria.
Melanocytes lie deep in the epidermis &
the underlying dermis, produce a pigment
called melanin that protects deeper cells
from the sun’s UV rays.
Melanocytes pass melanin to nearby cells
through cytocrine secretion.
Skin Color
• Three pigments contribute to
skin color
• Melanin – yellow to reddishbrown 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
Genetic differences result from different amounts of
melanin & in the size of pigment granules.
Sunlight causes the melanin production to increase.
Circulation with dermal blood vessels affects skin color.
Dermis
• Second major skin region
containing strong, flexible
connective tissue (collagen
fibers) and blood vessels
that carry nutrients to upper
layers of skin and help
regulate body temperature
• Cell types include
fibroblasts, macrophages,
and occasionally mast cells
and white blood cells
Also consists of
nerves, hair
follicles, sweat
glands, oil glands
and muscles.
Subcutaneous (Hypodermis)
• Subcutaneous layer deep to the skin
• Composed of adipose (fat layer) and
areolar (loose) connective tissue
• It binds the skin to underlying organs and
contains the blood vessels that supply the
skin.
• There is no sharp boundary between the
dermis and the hypodermis
Accessory
Organs of
the Skin
Hair Function and Distribution
• Hair is distributed over the entire skin
surface except:
• Palms, soles, and lips
• Nipples and portions of the external
genitalia
Hair Follicle
• Individual hairs develop from cells at the base of the
hair follicle, an invagination of the lower epidermis that
dips down into the dermis
• As new cells are formed, old cells are pushed outward
and become keratinized, forming the hair shaft
• A bundle of smooth muscle cells, called the arrector
pili muscle, is attached to each hair follicle
• Hair color is determined by genetics; melanin from
melanocytes is responsible for most hair colors, but
red hair also contains the pigment trichosiderin
Hair Function and Distribution
• Functions of hair include:
• Helping to maintain warmth
• Alerting the body to presence of insects on
the skin
• Guarding the scalp against physical
trauma, heat loss, and sunlight
Sebaceous Glands (Oil Glands)
• Simple ~alveolar
glands found all over
the body
• Soften skin when
stimulated by
hormones
• Secrete an oily
secretion called
sebum
Structure of a Nail
• Scalelike modification of the epidermis on
the distal, dorsal surface of fingers and
toes
• Consist of stratified squamous epithelial
cells overlying the nail bed, with the lunula
as the most actively growing region of the
nail root
• As new cells are produced, older ones are
pushed outward and become keratinized.
Sweat Glands
• Different types prevent overheating of the body;
secrete cerumen~ and milk
• Eccrine sweat glands – found in palms, soles of the
feet, and forehead. Respond to body temperature
• Apocrine sweat glands – found in axillary and
anogenital areas. Respond to body temperature,
stress, & sexual arrousal
• ~Eruminous glands – modified apocrine glands in
external ear canal that secrete cerumen (wax)
• ~Mammary glands – specialized sweat glands that
secrete milk
Functions of the Integumentary System:
Regulation of Body Temperature
• Body temperature regulation is
accomplished by:
• Dilation (cooling) and constriction
(warming) of dermal vessels
• Increasing sweat gland secretions to cool
the body
• Excessive cooling: inactivates sweat
glands, shivering
Healing of
Wounds &
Burns
Wounds
•Inflammation, in which blood vessels dilate and
become more permeable, causing tissues to become
red and swollen, is the body’s normal response to
injury.
•Superficial cuts are filled in by reproducing
epithelial cells.
•Deeper cuts are closed off by clots, covered by
scabs, and eventually filled in by fibroblasts, making
connective tissue. Blood vessels extend into the
area, injured tissues are replaced, and the scab falls
off.
•Large wounds leave scars and healing may be
accompanied by the formation of granulations.
Burns
• 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)
Skin Cancer
• Most skin tumors are benign and do not
metastasize
• A crucial risk factor for nonmelanoma skin
cancers is the disabling of the p53 gene
• Newly developed skin lotions can fix
damaged DNA
Skin Cancer
• The three major types of skin cancer are:
– Squamous cell carcinoma
– Basal cell carcinoma
– Malignant Melanoma
Squamous Cell Carcinoma
• 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
Basal Cell Carcinoma
• 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
Malignant Melanoma
• Cancer of melanocytes is the most
dangerous type of skin cancer because it
is:
– Highly metastatic
– Resistant to chemotherapy
Melanoma (cont.)
• Melanomas have the following
characteristics (ABCD 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)
Prognosis and Treatment
• Treated by wide surgical excision
accompanied by immunotherapy
• Chance of survival is poor if the lesion is
over 4 mm thick