THE INTEGUMENTARY
SYSTEM
The Integument (skin) - largest and heaviest organ
- highly complex organ or a structurally integrated
organ system.
~ 16 % of total body weight.
Its surface (1.5-2.2 m2) continuously abused, abraded, attacked by
microorganisms, irradiated by sunlight, and exposed to environmental
chemicals.
Waterproof, stretchable, washable, and permanent-press,
that automatically repairs small cuts, rips and burns and is
guaranteed to last a lifetime
Of all the body
systems, the integument
is the only one you see
every day
The general functions include:
Protection {the FIRST LINE OF DEFENSE}
++ against abrasion & UV light
++ entry of microorganisms
++ prevent dehydration
Excretion
++ salts, water, and organic wastes.
Temperature regulation
Synthesis of vitamin D (cholcalciferol)
++ important to normal calcium & phosphorus metabolism.
Cutaneous sensation
++ touch, pressure, pain & temperature.
Nonverbal communication
++ complex skeletal muscles insert on dermal collagen fibers & pull
on the skin to create varied facial expressions.
2 major components:—
CUTANEOUS
MEMBRANE
(Skin)
ACCESSORY STRUCTURES
(appendages)
Hair
Nails
Exocrine glands
Skin = integument, is the largest organ in the body
The skin + its appendages = INTEGUMENTARY SYSTEM
CUTANEOUS MEMBRANE (SKIN)
composed of :-
Epidermis
Skin
Dermis
Hypodermis
Epidermis
Dermis
Basement membrane
Epidermis
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Avascular (non-vascular)
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nourished by diffusion from capillaries of the dermis
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Consists of a stratified squamous epithelium
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Composed of cells arranged into layers or strata
Epidermal Cells
Cell types:Keratinocytes
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most abundant cells
produce keratin (a fibrous protein) for strength
formed in the lowest layer of the epidermis
Become dead and scale-like
Melanocytes
- produce pigment for skin color
- same number of melanocytes in all
people.
Desquamation:
Dendritic (Langerhans’) cells
part of the immune system
Tactile (Merkel’s) cells
Detect light, touch, and
superficial pressure
cells of the deeper layers undergo mitosis; as they move toward the surface,
older cells slough off
>>Millions rub off everyday<<
Keratinization: as cells move outward through the layers, they fill with keratin, die and
serve as a layer that resists abrasion and forms permeability layer
Layers of the Epidermis
Beginning at the basement membrane and traveling toward the free surface
Stratum Corneum
Outermost
layer
Stratum Lucidum
Stratum Granulosum
Stratum Spinosum
Stratum Germinativum
Innermost
layer
Thick and Thin Skin
Thick skin
- all 5 epithelial strata
- ~ 6x thicker than thin skin
- found in areas subject to pressure or friction
~ palms of hands, fingertips, soles of feet ~
Thin skin
- more flexible than thick skin (4 layers)
- covers rest of body (~ 0.08mm thick)
XXX
Epidermis and dermis of (a) thick skin and (b) thin skin
(which one makes the difference?)
Stratum Germinativum
The innermost epidermal layer
Dominated by large germinative cells, or basal cells (stem cells)
The stem cells divided to replace the more superficial keratinocytes that
are lost or shed at the epithelial surface.
Also contain specialised epithelial cells known as Merkel cells.
They are sensitive to touch; when compressed or disturbed, Merkel cells
release chemicals that stimulate sensory nerve endings.
Stratum Spinosum
- spiny layer –
consists of 8-10 layers of cells
Each time a stem cell divides, one of the daughter cells is pushed above
the germinativum into the stratum spinosum
also contains Langerhans cells, part of the immune response.
These cells are responsible for stimulating a defense against:(1) microorganisms that manage to penetrate the superficial layers of the epidermis
(2) superficial skin cancers.
Stratum Granulosum
- grainy layer consists of 3-5 layers of keratinocytes displaced from the stratum spinosum
By the time cells reach this layer, most have stopped dividing.
They begin manufacturing large quantities of the proteins keratohyalin &
keratin (keros, horn)[ = dead cells].
In humans, keratin, a fibrous protein, also is the basic structural component of
hair and nails.
Stratum Lucidum
In the thick skin of the palms and
layer) covers the stratum granulosum
soles, a glassy stratum lucidum (clear
The cells in this layer are flattened, densely packed, and filled with keratin.
Stratum Corneum
stratum corneum = ‘cornu’, horn
found at the surface of both thick and thin skin
normally 15-30 layers of keratinised cells (dead cells)
Keratinisation, or cornification, occurs on all exposed skin surfaces except
the surfaces of the eyes.
Everything you see on a human is
DEAD!!!
➢ Dandruff
➢ Average person shed ~ 20 kg of these cells
in their lifetime.
The House Dust Mite,
Dermatophagoides.
Normally, the surface of the stratum corneum is relatively dry, so it is
unsuitable for the growth of many microorganisms.
Maintenance of this barrier involves coating the surface with lipid secretions
from sebaceous and sweat glands
Stratun Corneum ~ water-resistant but not waterproof
Water from the interstitial fluids slowly penetrates the surface, to be
evaporated into the surrounding air = insensible perspiration
Human lose roughly 500 ml (about 1 pt) of water in this way each day
Damage to the epidermis can increase the rate of fluid movement.
When the skin is immersed in water, osmotic forces may move water into or
out of the epithelium.
Hypotonic solution [freshwater] - water to move into the epidermis.
The epithelial cells may swell to four times
their normal volumes
Hypertonic solution [ocean] - water leaves the body, crossing the epidermis from
the underlying tissues.
The process is slow, but long-term exposure to seawater accelerating dehydration.
Disorders of Keratin Production
Not all skin signs are the result of infectious,
traumatic, or allergic conditions.
Excessive production of keratin is called
hyperkeratosis.
e.g. in calluses and corns formation.
Calluses
thickened patches that appear on thick skinned
areas, in response to chronic abrasion and
distortion.
Corns
more localized areas of excessive keratin
production that form in areas of thin skin
on or between the toes
Psoriasis
stratum germinativum becomes unusually active, causing hyperkeratosis in
specific areas, including the scalp, elbows, palms, soles, groin, and nails.
Normally,
Stem cell divides once every 20 days
In psoriasis it may divide every day and a half
The affected areas appear to be covered
with small, silvery scales that continuously
flake off.
Develop in 20-30 % of the individuals with
an inherited tendency for the condition
Most cases are painless and treatable.
Skin Color
Skin colour is due to an interaction between:-
pigment composition and concentration
the dermal blood supply
Skin Pigmentation
The epidermis contains variable quantities of two pigments:CAROTENE
Orange-yellow pigment
Most apparent in cells of the
stratum corneum of light-skinned
individuals [Oriental skin]
@ when carotene-rich food are
eaten (in large amount!!)
MELANIN
Brown, yellow-brown, or black pigment
produced by melanocytes
Melanocytes are located in the stratum
germinativum, squeezed between or deep
to the epithelial cells
HEMOGLOBIN
RBC gives a pinkish hue to fair skin
The melanin in keratinocytes protects epidermis and dermis from the
harmful effects ultraviolet (UV) radiation of sunlight
A small amount of UV radiation is beneficial, for it stimulates synthetic
activity in the epidermis.
However
UV radiation can damage DNA, causing mutations and promoting cancer
development.
The ratio between melanocytes and germinative cells -
1: 4 and 1: 20
depending on the region of the body.
Higher concentrations (about 2000/mm 2) found in the:
cheeks and forehead
nipples
genital region (scrotum - ♂ ; labia majora -♀).
Differences in skin color among individuals/races do not
reflect different numbers of melanocytes but merely
different levels of synthetic activity.
albinism = melanocytes distributed normally but incapable of producing melanin [inherited lack of tyrosinase]
freckles or liver spots = melanocytes in a patch
vitiligo = autoimmune loss of melanocytes in areas of the skin produces white patches
Dermal Circulation
Blood contains RBCs filled with the pigment hemoglobin (Hb).
Hb + O2
HbO2 [Oxyhemoglobin]
HbO2 - bright red color
- giving blood vessels in the dermis a reddish tint that is most
apparent in lightly pigmented individuals
When those vessels are dilated (inflammation), the red tones
become much more pronounced
Circulatory supply , the skin becomes relatively pale/ "turn white"
- because of a sudden drop in blood supply to the skin
Sustained reduction in circulatory supply, the tissue oxygen levels decline,
and the hemoglobin in these tissues releases oxygen and changes color to
a much darker red tone.
The skin takes on a bluish coloration called cyanosis (kyanos, blue).
It can be a response to :
extreme cold
circulatory disorders {{heart failure}}
respiratory disorders {{severe asthma}}
THE DERMIS
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lies beneath the epidermis.
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+ Gives structural strength.
+ C.T. (collagen, elastic fibers ) fibers,
fibroblasts, macrophages.
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+ Some adipocytes and blood vessels.
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+ Contains nerves, blood vessels, hair
follicles, smooth muscles, glands, and
lymphatic vessels.
+ Sensory functions: pain, itch, tickle,
temperature, touch, pressure, two-point
discrimination.
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• Cleavage (tension) lines: elastin and
collagen fibers oriented in some
directions more than in others
• Important in surgery
– If incision parallel to lines, there is less
gapping, faster healing, less scar tissue
:::::: If skin is overstretched, striae
(stretch marks) occur :::::::
RICE
The Innervation of the Skin
Nerve fibers in the skin;
❖ control blood flow
❖ adjust gland secretion rates
❖ monitor sensory receptors in the dermis and
the deeper layers of the epidermis.
Merkel cells - deeper layers of the epidermis.
These cells are monitored by sensory terminals known as Merkel's discs.
The epidermis also contains the extensions of sensory neurons that provide
sensations of pain and temperature.
The dermis contains similar receptors + more specialized receptors:Meissner's corpuscles
[located in dermal papillae]
- receptors sensitive to light touch -
Pacinian corpuscles
[in the reticular layer]
- Sensitive to deep pressure and vibration -
ACCESSORY STRUCTURES
hair follicles
sebaceous glands
sweat glands
originate from the epidermis
also known as epidermal derivatives
nails
Although located in the dermis, they project through the
epidermis to the integumentary surface.
Hair Follicles and Hair
Hairs project above the surface of the skin almost everywhere except;-
the sides and soles of the feet; the palms of the hands;
the sides of the fingers and toes; the lips; and portions
of the external genitalia
5 million hairs on the human body
98% on the general body surface, not on the head.
Hairs originate in complex organs called hair follicles
Functions of Hair
~ 100,000 hairs on the head protect scalp from ultraviolet light, help
cushion a blow to the head, and insulate the skull.
Guarding the entrances & help prevent the entry of
foreign particles and insects
(e.g. nostril, external ear canal, eyelashes)
sensory nerves surrounds the base of
each hair follicle provides sensitivity
for an early-warning system that help
prevent injury
Insulating coat ~ contraction of the arrector pilli muscle force the hair
to stand erect.
~ contraction may be the result of emotional states (fear/rage)
or
response to cold, producing the characteristic "goose bumps.“
In a furry mammal, this action increases the coat’s thickness.
Although humans do not receive any comparable insulating benefits, the reflex persists
ATTRACTION !!!!!!!!!!!!!
Glands in the Skin
The skin contains two types of exocrine glands:
sebaceous glands
sweat glands
Sebaceous (Oil) Glands
discharge a waxy, oily secretion into hair follicles = SEBUM
Sebum provides lubrication (natural skin cream), keeps hair moist, prevents skin from
drying and inhibits the growth of bacteria
numerous on the face and scalp
Sebaceous glands - very sensitive to changes in the
concentrations of sex hormones, and their secretory activities
accelerate at puberty.
Excessive secretion plugs the gland and hair follicle, producing a
skin disorder called acne.
Sweat Glands
The skin contains two different types of sweat glands:
sudoriferous glands — apocrine sweat glands
merocrine (eccrine) sweat glands
**names refer to the mechanism of secretion**
Apocrine Sweat Glands
In the armpits (axillae), around the nipples, and in the groin
Apocrine glands communicate with hair follicles.
Produce a sticky, milky white substance, and potentially odorous secretion
{pheromones}
<<<Pheromones >>>
substances that enable olfactory communication with other
members of the species
This communication provokes certain behavioral responses such as sexual arousal.
Apocrine glands respond to stress and sexual activity by secreting sweat with a
characteristic odor.
Apocrine sweat glands begin secreting at puberty
Merocrine (Eccrine) Sweat Glands
Far more numerous, smaller and widely distributed than apocrine glands
The adult integument contains 2-5 million merocrine sweat glands
Discharge their secretions directly onto the surface of the skin
Palms and soles have the highest numbers
The sweat secretion = sensible perspiration.
Sweat is 99 % water & some electrolytes (chiefly sodium chloride), organic
nutrients, and waste products.
It has a pH of 4-6.8
The functions of merocrine sweat gland activity include:
Cooling the surface of the skin to reduce body temperature.
This is the primary function of sensible perspiration, and the degree of secretory
activity is regulated by neural and hormonal mechanisms
Excretion of water and electrolytes.
A number of ingested drugs are excreted as well.
Protection from environmental hazards.
Sweat dilutes harmful chemicals and discourages the growth of microorganisms.
::Detecting Lies::
Emotional sweating is used in lie detector tests, because sweat gland activity increase when person tells a lie
Other Integumentary Glands
MAMMARY GLANDS
Related to apocrine sweat glands.
A complex interaction between sex hormones and pituitary hormones
controls their development and secretion.
CERUMINOUS GLANDS
Modified sweat glands located in the external auditory canal.
Their secretions called cerumen, or ear wax.
Ear wax, together with tiny hairs along the ear canal, helps trap foreign
particles or small insects and keeps them from reaching the eardrum
AGING AND THE INTEGUMENTARY SYSTEM
Aging affects all the components of the integumentary system.
These changes include:
The epidermis thins as
germinative cell activity
declines, making older people
more prone to injury and skin
infections
The number of Langerhans cells  to about
50 % of levels seen at maturity (roughly, age
21). This reduce the sensitivity of the immune
system and further encourage skin damage
and infection
Vitamin D3 production  by 75 %.  calcium and phosphate absorption,
leading to muscle weakness &  in bone strength
Melanocyte activity declines, the
skin becomes very pale. With less
melanin in the skin, people become
more sensitive to sun exposure and
more likely to experience sunburn.
Glandular activity declines.
The skin becomes dry and often scaly because
sebum production is reduced. Merocrine sweat
glands are also less active; with impaired
perspiration, older people cannot lose heat as
fast as younger people can
The blood supply to the dermis is reduced at the
same time that sweat glands become less active
The dermis thins, and the elastic fiber
network decreases in size. The integument
becomes weaker and less elastic; sagging and
wrinkling occur.
Hair follicles stop
functioning or produce
thinner, finer hairs. With
decreased melanocyte
activity, these hairs are
gray or white
Causes of Burn:
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Heat
Radiation
Electricity
Chemicals
The seriousness of a burn is measured by:How many layers of skin affected
How much surface area affected
Classification
of burns
1st-degree burn:
Affect only the epidermis….eg. sunburn
Skin reddens, slight-moderate pain with no blisters & swelling
Burns heal without scarring
2nd-degree burn:
Also called a partial-thickness burn.
Affect the entire epidermis & top part of the dermis
Skin redness, pain and blisters
Usually heal within 10-14 days with minimal scars but….
If the burn goes deep into the dermis, healing ~ 1-4 months &
scarring is probable.!!
+++ infection may delay healing ++++
3rd-degree burn:
Also called a full-thickness burn.
Affect the entire epidermis & the dermis, destroy the blood vessels, glands,
hair follicles, & the pain receptors.
Color of the wound --- white – tan, brown-black or plain red.
Very slow healing process.
Infection occurs easily – immune system down!!!
Dehydration ---- the main problem.
Regulating body temperature becomes difficult.
4th-degree burn:
Burns all the down to the bone.
Little chance of survival!!!!!
Rule of Nines
is used to determine the amount of
burn-affected body surface