Chapter 4: Skin

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Transcript Chapter 4: Skin

Part 2
Outer layer of skin
 Does not contain blood
vessels (avascular).
Therefore when you slightly
scratch your arm it doesn’t
Most cells of the epidermis are
keratinocytes (keratin cells), which
produce keratin (the fibrous protein that
makes the epidermis tough).
Epidermis Structure
Composed of 5 zones
or layers called strata.
Stratum Corneum
(most superficial)
Stratum Lucidum
Stratum Granulosum
Stratum Spinosum
Stratum Basale
Epidermis Structure: Stratum Corneum
Stratum Corneum –
Outermost layer of
the epidermis
 It
accounts for almost ¾
of the epidermal thickness.
 Contains shinglelike dead cell remnants, completely
filled with keratin, called cornified or horny cells.
 Its
overabundance of keratin in this layer allows it to
provide a durable “overcoat” for the body which protects
the deeper cells.
Epidermis Structure: Stratum Corneum
Not able to get adequate nutrients and oxygen.
 This
is because it is so far away from a blood source.
Therefore, the cells of this layer are dead. Nearly
everything we see when we look at someone is dead!
This layer rubs and flakes off slowly and steadily.
 This
layer is replaced by the cells produced in the
stratum basale.
We have a
totally “new”
epidermis every
25-45 days.
Epidermis Structure: Stratum Lucidum
Stratum Lucidum – Layer is formed by the cells
that were produced in the stratum basale and
pushed up, which are now flatter, increasingly full
of keratin, and are dead.
 Clear
layer; only occurs where the skin is hairless and extra
thick such as the palms of hands and the soles of feet.
 Not able to get
adequate nutrients
and oxygen
because it is so far
away from a blood
Epidermis Structure: Stratum
Granulosum and Stratum Spinosum
Stratum Granulosum –
The living cells produced
in the stratum basale
are pushed up through
this layer.
Stratum Spinosum –
The living cells produced
in the stratum basale
are pushed up through
this layer.
Epidermis Structure: Stratum Basale
Stratum Basale - Deepest cell layer of
the epidermis
 Lies
closest to the dermis and contains the only epidermal
cells that receive adequate nourishment via diffusion of
nutrients from the dermis.
 These cells are constantly undergoing cell division. The
daughter cells are pushed upward and become part of
the more superficial layers.
Melanin – Pigment that
ranges in color from yellow
to brown to black; found
chiefly in the stratum basale.
Melanocytes – Cells that
produce melanin.
Tanning Occurs: When the skin
is exposed to sunlight, it
stimulates the melanocytes to
produce more melanin.
 Freckles and Moles: Are seen
where melanin is concentrated in
one spot.
How Melanin Protects
The stratum basale cells phagocytize (eat) the
As it accumulates within them, the melanin
forms a protective pigment “umbrella” over
the superficial, or “sunny,” side of their nuclei.
The “umbrella” shields their DNA from the
damaging effects of UV radiation.
Excessive Sun Exposure
Despite melanin’s protective effects,
excessive sun exposure damages the skin:
Leathery skin (elastic fibers clump together).
Depresses the immune system.
 People
infected with herpes simplex (cold sores) are
more likely to have an eruption after sunbathing.
Can alter the DNA of skin cells, resulting in skin
 Black
people seldom have skin cancer, attesting to
melanin’s amazing effectiveness as a natural
Inner layer of the skin
Is your “hide.”
Located between the
epidermis and the
When you purchase leather
goods, you are buying the
treated dermis of animals.
It is a strong, stretchy
envelope that helps hold
the body together.
The dermis varies in thickness.
 It
is thick on the palms of the hands.
 It is thin on the eyelids.
The dense (fibrous) CT
making up the dermis
consists of two major
Papillary Layer
Reticular Layer
Papillary Layer of the Dermis
Papillary Layer –
Upper dermal
 Uneven
and has
projections from its
superior surface,
called dermal
papillae, which
indent the
epidermis above.
Papillary Layer of the Dermis
Many contain capillary loops, which furnish
nutrients to the epidermis.
Papillary Layer of the Dermis
Others house
pain receptors
(free nerve
endings) and
touch receptors
Papillary Layer of the Dermis
On the hands and feet,
the papillae are
arranged in definite
patterns that increase
friction and gripping
 Fingertips have sweat
pores and leave unique,
identifying films of sweat
called fingerprints.
Reticular Layer of the Dermis
Reticular Layer - Deepest
skin layer.
 Contains:
 Blood
 Sweat and oil glands
 Deep pressure receptors
called Pacinian corpuscles.
 Many
phagocytes are
found here.
 To
prevent bacteria from
penetrating any deeper.
Both Layers of the Dermis
Collagen and elastic fibers
are found throughout the
 Collagen:
 Responsible
for the toughness
of the dermis.
 Attract and bind water and
thus help to keep the skin
 Elastic
 Give
the skin its elasticity.
The dermis also has a rich
nerve supply.
The dermis is abundantly supplied
with blood vessels that play a role
in maintaining body temperature homeostasis.
 If
 Blood
vessels in the dermis narrow, helping to limit heat loss.
 Blood bypasses the dermis capillaries temporarily, which
allows internal body temperature to stay high.
 If
 Blood
vessels widen, bringing heat from the body's core to
the skin and increasing heat loss.
 Skin becomes reddened and warm and allows body heat to
radiate from the skin surface.
Decubitus Ulcers (Bedsores)
Occurs in bedridden patients who are not turned or
who are dragged or pulled across the bed
 The
weight of the body puts pressure on the skin,
especially over bony projections.
 A restriction of blood supply occurs and results in cell
Which Pigments Affect Skin Color
Three pigments contribute to skin color:
The amount and kind (yellow, reddish
brown, or black) of melanin in the
The amount of carotene (orangeyellow pigment found in foods such
as carrots) deposited in the stratum
corneum and subcutaneous tissue.
The amount of oxygen bound to
hemoglobin (pigment in red blood cells) in the
dermal blood vessels.
How Do These Pigments Affect Skin
Lots of melanin = browntoned skin.
Less melanin = light-toned
 In
light skinned people, the
crimson color of oxygen-rich
hemoglobin in the dermal
blood supply flushes through
the transparent cell layers
and gives the skin a rosy
Cyanosis – When
hemoglobin is poorly
 Cyanosis
is common during
heart failure and severe
breathing disorders.
 Both
the blood and the skin of
Caucasians appear blue.
 In black people, the skin does not
appear cyanotic because of the
masking effects of melanin, but
cyanosis is apparent in their
mucous membranes and nail
Other Influences of Skin Color
Redness or Erythema –
 May
indicate embarrassment (blushing),
fever, hypertension, inflammation, or
Pallor or Blanching –
 Under
certain types of emotional
stress (anger, fear, and others)
some people become pale.
 May also signify anemia, low
blood pressure, or impaired
blood flow into the area.
Other Influences of Skin
Jaundice or a Yellow Cast –
 Usually
signifies a liver disorder in which
excess bile pigments are absorbed into
the blood, circulated throughout the body,
and deposited into body tissues.
Bruises or Black-and-Blue Marks –
 Reveal
sites where blood has escaped
from the circulation and has clotted in the
tissue space. Clotted blood masses are
called hematomas.
Appendages of the Skin
Skin appendages include:
 Cutaneous
 Hairs and hair follicles
 Nails
Each of these
appendages arises from
the epidermis and plays
a role in maintaining
body homeostasis.
Cutaneous Glands
Cutaneous glands are all
exocrine glands that
release their secretions to
the skin surface via ducts.
Reside almost entirely in
the dermis.
Two groups of cutaneous
Sebaceous (Oil) Glands
Sweat Glands
Sebaceous (Oil) Glands
Sebaceous Glands – Oil glands
 Found
all over the skin except on the palms of
the hands and the soles of the feet.
 Their ducts usually
empty into a hair
follicle, but some
open directly onto
the skin surface.
Sebaceous (Oil)
Sebum – The product of
the sebaceous gland.
 Mixture
of oily substances
and fragmented cells.
 Function:
 Lubricant
that keeps the skin soft and moist and prevents
the hair from becoming brittle.
 Also contains chemicals that kill bacteria on the surface of
the skin.
 Sebaceous
glands become very active when male sex
hormones (in both sexes) become more active during
Acne – Active infection of
the sebaceous glands
accompanied by pimples
on the skin.
 Whitehead
– Occurs when
a sebaceous gland’s duct
becomes blocked by sebum.
 Blackhead – If the
accumulated material
oxidizes and dries and
Sweat Glands
Also called Sudoriferous
They are widely distributed
in the body – more than 2.5
million per person!
There are two types of
sweat glands:
Eccrine Glands
Apocrine Glands
Eccrine Glands
Far more numerous than apocrine glands and are
found all over the body.
They produce sweat, a clear secretion.
 Sweat
primarily water plus :
 Some
salts (sodium
 Vitamin C
 Traces of metabolic
wastes (ammonia,
urea, uric acid)
 Lactic acid (the
chemical that attracts mosquitos)
Characteristics of Sweat
Sweat is acidic (pH from 4 to 6): Inhibits the growth
of bacteria, which are always present on the skin
Sweat reaches the skin surface via a duct that
opens externally as a funnel-shaped pore.
 The
“pores” that we commonly
refer to when we talk about our
complexion are not these sweat
pores, but the external outlets of
hair follicles.
Eccrine Glands
Are an important and
highly efficient part
of the body’s heatregulating equipment.
They are supplied
with nerve endings
that cause them to
secrete sweat when
the external
temperature or body
temperature is high.
When sweat evaporates off the
skin surface, it carries large
amounts of body heat with it.
 On
a hot day, it is possible to lose
up to 7 liters of body water in this
 If internal temperature changes
more than a few degrees, life
threatening changes occur.
Apocrine Sweat Glands
Location: Largely
confined to the axillary
and genital areas.
 Size: Usually larger than
eccrine glands.
 Ducts: empty into hair
Apocrine Sweat Glands
Secretions: Same secretion as
eccrine glands PLUS fatty acids
and proteins.
 Consequently,
it may have a milky
or yellowish-color.
 Are odorless, but when bacteria
that live on the skin use its proteins
and fats as a source of nutrients
for their growth, it takes on a
musky, unpleasant odor.
Function of Apocrine Glands
Precise function is not yet known.
 Play
a minimum role in
 Begin to function during puberty.
 Their secretion is produced almost
 They are activated by nerve fibers
during pain and stress and during
sexual foreplay.