Skin

Integumentary system

•Composed of the skin and a number
of skin derivatives (hair, nails, and
glands).

•Largest organ in the body

•Accounts for 15 % of body’s weight


Functions:

1. Protection
a) Physical barrier
b) Waterproofs
c) Protects against sun’s
ultraviolet light – pigment in
the skin called melanin


Functions:

2. Temperature regulation
skin allows body to lose heat by
evaporation, convection,
conduction, and sweat
3. Excretion
excretes water, fatty substances
and ions


Functions:

4. Metabolism
 Vitamin D

5. Absorption
 if applied to the skin will absorb
Vitamin A, E, and K, steroid
hormones released by glands


Functions:

6. Communication
Stimuli are received by skin
receptors which will
communicate with the central
nervous system


2 Layers of the Skin

Epidermis - Top layer of stratified
squamous epithelium

Dermis - Layer underneath the
epidermis made of connective
tissue


Other parts of the skin:
Epidermal – dermal junction is
where the epidermis and dermis
meet.

Hypodermis – is the layer of tissue
under the dermis.


Two Layers of the Dermis:
1. Papillary layer
 Upper dermis
 Has ridges that protrude up into
the epidermis called the dermal
papillae
 It is composed of loose
connective tissue


Functions of Dermal papillae:
•Increased blood flow to epidermis

•Increased surface area for dermis
and epidermis to connect to each
other to hold it strongly together


Functions of Dermal papillae:

•Contains sensory touch receptors

•Keeps skin from tearing

•Aids in gripping

•Gives you finger prints

Dermal papillae = finger prints


Layers of the dermis:
1. Papillary layer

2.Reticular layer
 Lower dermis
 Further keeps from tearing
 Contains deep pressure sensors
 Contains sweat glands, lymph
vessels, smooth muscle, and hair
follicles


Layers of the dermis:
1. Papillary layer
2. Reticular layer

 Made of dense irregular
connective tissue
 Has criss-cross collagen fibers that
give it a strong elastic network
 This forms lines of cleavage or
Langer’s Lines or Line of tension

Langer’s Lines
Note: Incisions
parallel to the
Langer’s Lines
will heal faster
and with less
scarring.


Hypodermis
Made of adipose tissue to insulate
and loose connective tissue
Functions to:
1.Conserve heat
2.Connects skin to layer below
3.Contains blood, lymph, base of hair
follicles and sweat glands
4. Stores lipids and cushions the body

Hypodermis
Functions to:

Hypodermis is 8% thicker in
females than males

Hypodermis

Also known as the subcutaneous
tissue

Where medical personal will give
a subcutaneous injection because
of the rich blood supply


Blister – a separation between the
epidermis and the dermis

Burn - destruction of the different
layers of the skin and the structures
within the skin.

The severity of the burn is dependent
upon the depth of the damage.


Three Classifications of burns:
1. First degree or 1 is when there
has been some damage to the
epidermis



2. Second degree or 2 is when the
epidermis is completely destroyed
and there is some damage to the
dermis


2. Second degree

Note: New epidermis will be
regenerated from the cells
surrounding the hair follicles. The
hair follicles are lined with
epidermal cells non-keratinized.



3. Third degree or 3 is when the
epidermis and dermis are
completely destroyed and there is
damage to
the
hypodermis.

Must have a skin graft to heal.


Layers of the epidermis:

composed of 4-5 layers depending on
the region of skin being considered

Those layers in descending order are
the stratum corneum, stratum lucidum,
stratum granulosum, stratum
spinosum, and stratum basale.


1. Stratum basale
 also referred to as "basal cell layer”

 is the deepest layer

 Single layer of
cuboidal/columnar cells that
undergoes rapid mitosis

1. Stratum basale

 Cells migrate upward from here and
begin to differentiate

 Also known as the stratum
germinativum


2. Stratum spinosum
 is several cell layers thick
 Carries out mitosis as well

 Some cells produce
Keratin


3. Stratum granulosum
 flat cells (squamous)
 Layer where keratinization begins
 cells overproduce the protein
keratin and smother themselves
 cells in this layer are beginning to
die


4. Stratum lucidum
 found only in the thick skin of the
palms of the hand and soles of the
feet
 cells in this layer are
dead
 three to four strata
(layers) thick
 Helps protect against UV rays


5. Stratum corneum
outermost layer of squamous cells
cells filled with keratin
dead cells that have migrated up from
the stratum granulosum
 is true protective layer of skin
 is 25 – 30 cell layers thick

5. Stratum corneum

these dead cells slough off and are
continuously replaced by new cells

the sloughing off of
cells is known as
desquamation

5. Stratum corneum

Just for your additional information:

In the human forearm, for example,
about 1300 cells/cm2/hr are shed and
commonly accumulate as house dust

Desquamation – term in Latin for
scaling a fish


Melanin
Is a brown pigment found in the skin and
hair
primary determinant of skin color
produced by melanocytes in the stratum
basale
through phagocytosis vesicles of melanin
will enter cells of stratum basale and
spinosum

Melanin

Note: The concentration of
melanocytes in the skin of people is
about the same, but some don’t
produce as much melanin due to
genetics.

UV light will
trigger melanin production

Melanin

Some individual animals and humans
have very little or no melanin in their
bodies, a condition known as albinism.

There are a number of different types
of melanin giving different colors of
skin (ex. Eumelanin most common) and
hair plus other pigments.


Skin Cancers
There are three main types of skin
cancer:

1. Malignant melanoma
• cancer cells are found in the melanocytes

• characterized by uncontrolled mitosis of
melanocytes in the stratum basale

Skin Cancers
There are three main types of skin cancer:

 usually occurs in adults
 is the rarest, but worst form of skin
cancer
 has the highest death rate and is
responsible for 75 percent of all deaths
from skin cancer
 Usually in fair-skinned people

Skin Cancers

2. Squamous cell carcinoma
uncontrolled mitosis of cell of the
stratum spinosum
Not as dangerous as melanoma, but
more dangerous than basal cell
carcinoma

Skin Cancers

95% cure rate when properly treated
may appear as nodules, or as red,
scaly patches of skin
 second most common skin cancer
found in fair skinned individuals

Skin Cancers

3. Basal cell carcinoma
Uncontrolled mitosis of stratum
basale layer cells

usually appears as a small, fleshy
bump or nodule on the head, neck, or
hands

Skin Cancers
3. Basal cell carcinoma

easily detected and has an excellent
successful treatment, when properly
treated
is the most common skin cancer, but
most treatable
found in fair-skinned individuals

Skin Cancers

Myth: Darker skinned people can’t
get skin cancer.
The darker the skin the less likely,
but the more fatal.
Usually melanoma the worst kind.
Usually late diagnosis or diagnosed
incorrectly

Skin Cancers
Myth: Darker skinned people can’t get skin cancer.

 almost always arise on the sole of the
foot, palms, fingers, toes, under the
nails and mucosal surfaces like in the
mouth


Hair Follicle
 part of the skin that grows hair by
packing old cells together

Cover entire body except eyelids,
palms, soles, and lips

 Attached to the hair follicle is a
sebaceous gland (oil gland)


Hair Follicle
The thicker density of hair, the more
sebaceous glands are found

•Also attached to the follicle is a tiny
bundle of muscle fiber called the
arrector pili that cause hair to stand up
and a goose bump.


Hair Follicle
 has two parts based on location:
1. Shaft – protrudes from the skin
2. Root – imbedded beneath the
skin

 At the base of the root is the hair
bulb

Hair shaft

Hair root

Hair bulb


Hair
 has no nerves

Composed of hair structure and hair
follicle

Has a protective function


Hair Strand has three layers:
1. Medulla
 center layer that is 2-3 cell layers
thick
Composed of soft keratin (less
sulfur) and air


2. Cortex
 middle layer
Composed of many cell layers
Is hard keratin (contains more
sulfur)
Makes up most of hair strand
contains melanin and maybe red
hair pigments

2. Cortex

Hair color:
• melanin is produced and through
phagocytosis it is incorporated into cells
of cortex
•the more melanin the darker the hair
color
•red hair also contains a red pigment,
the more melanin the darker the red
•gray hair lacks melanin at all


3. Cuticle
 outer most layer of hard keratin
One cell layer thick, but cells
overlap like shingles on the roof


Hair Follicle layers:

1. Internal epithelial root sheath
2. External epithelial root sheath

Two layers are covered by dermal root
sheath

Hair bulb – expanded end of follicle

Dermal
Root Inner sheath
sheath
Outer sheath

Hair Follicle

Papilla – extends into the bulb and
provides nutrients

Hair Follicle

Hair matrix
 Is at the base of the hair bulb
 Where cell mitosis/reproduction
occurs
 Cells are undifferentiated (all look
the same)
 Hair electrolysis damages the cell in
the matrix cells don’t reproduce


Hair Growth

Not all hair grows at the same rate

Eyelashes/brows vs. hair on head

Hair grow and then stops

Hair Growth

Three stages of hair growth:
1. Anagen
 a growth phase when hair is growing
in length
 Eyelids – spend 30 days in this phase
 Head strand of hair spends 3 – 7 years
in this phase
 90% of head hair is in this phase

Hair Growth
1. Anagen

2. Catagen

 Hair stops growing; transition
phase
 Club hair or replacement hair is
formed
 Head hair spend 2-3 weeks in this
phase

Hair Growth
1. Anagen
2. Catagen

3. Telogen
 Resting phase – 10% of hair on
head is in this phase
 head hair spends about 100 days
in this phase, eyelids 9 months
 Hair falls out
 You lose about 100 hairs on your
head per day


Nails

Functions:
protections
reinforce the finger/toe tips

Nails

Parts of the Nail
oNail body – the part that is visible
oNail root – extends underneath the
skin
oNail matrix – part of nail root where
cells reproduce. Cells differentiate and
fill with keratin
oLunula – upper part of the nail matrix,
is thicker and appears white

Nails
Parts of the Nail

oNail bed – thick epithelial tissue that
the nail rest on

oFree edge – part that sticks out past
the digit

oCuticle – fold of skin on proximal end

Nails

Grow constantly – no growth and
resting phases

Grow at a rate of about 3 mm a month


Glands

Two types based on what they secrete:
1. Sweat – water and electrolytes,
sweat

2. Sebaceous - oil

Glands

Two types of sweat glands:
A. Merocrine
 Found all over skin, heaviest in soles
of feet and palms of hands

 Secrete a clear liquid to surface of
skin

 Are a merocrine gland

Glands
A. Merocrine

 Regulates body temperature

 Smaller and more numerous than
apocrine sweat glands

 Don’t secrete into hair follicle

Glands

B. Apocrine glands
 Found armpits, groin and nipples
 Secrete a milky substance; odorous
 Actually merocrine glands, but were
once thought apocrine
 Secrete into hair follicle
 Found deeper in skin than merocrine

Glands
Two types based on what they secrete:
1. Sweat – water and electrolytes, sweat

2. Sebaceous - oil

Sebaceous glands

Secrete an oily matter called sebum
into hair follicles
Pore = opening of hair follicle to allow
oil to lubricate the skin
Holocrine glands
Overproduction of sebum = acne

Skin

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