Download Skin and Body Membranes

Skin and Body
Membranes
Chapter 4
Skin Functions
 Protection
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Mechanical damage – physical bumps
Chemical damage – relatively impermeable
Bacterial damage – unbroken surface w/ acid
mantle
Ultraviolet radiation – Melanin
Thermal – Contains hot/cold/pain receptors
Desiccation – resists drying out.
Skin Functions
 Aids in heat loss or heat retention
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Sweat glands
Closes capillaries
 Aids in excretion of urea and uric acid
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Contained in sweat
 Synthesizes Vitamin D
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Sunlight converts cholesterol into vit. D
Skin Structure
 Two True skin layers: epidermis and
dermis
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Epidermis is stratified squamous cells.
 Can
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become keratinized – hard and tough
Dermis is dense connective tissue
 Epidermis and Dermis are firmly
connected
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Become separated due to friction or a burn
 This
allows fluid to accumulate between
layers causing a blister
Skin Structure
Skin Structure
 Unofficial third layer – subcutaneous
tissue (aka hypodermis)
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Mostly adipose (fat) tissue
Connects skin to underlying tissues and
organs
Shock absorber.
insulator
Epidermis Strata (layers)
 From the bottom up
 Stratum Basale – nourished by blood in
the connective tissue, constantly going
through mitosis. Daughter cells are
constantly pushed upward to become
new layers of superficial skin.
 Stratum spinosum and granulosum –
living cells that are being pushed up by
new cells from the Basale
Epidermis Strata
 Stratum Lucidum: found in extremely
thick, hairless, skin (palms and soles)
 Stratum Corneum: 20-30 cells thick.
Fully keratinized (extremely durable).
Slowly flakes off naturally but is
replenished from beneath by the basale
layer.
Epidermis Strata
Melanin
 Yellow/brown pigment
 Made by melanocytes directly above
basale layer
 Melanin acts like an umbrella, protecting
basale cell nuclei from harmful UV light.
 Melanocytes are activated by sunlight to
create more melanin (tanning)
Melanin
Melanin
 Melanin does have protective effects,
however excessive sun exposure will
damage the skin.
 Elastic fibers like collagen to clump and
produce “leathery skin”
 Depresses the immune system
 Alter DNA of Basale cells causing cancer
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People with naturally high melanin levels
have a low rate of skin cancer.
Dermis Strata
 Papillary layer – the top layer, directly below the
epidermis.
 Dermal papillae are the projections that loop up
and down. Filled with capillaries to supply
blood to the basale epidermis. Also contains
nerves for touch.
 Tips of the fingers and palms have a genetically
determined pattern that forms your fingerprints
(increases friction for grip).
Dermis Strata
Dermis Strata
 Reticular Layer – the deepest skin layer,
contains blood vessels, sweat and oil
glands, and deep pressure receptors
Dermis Characteristics
 Has phagocytes to kill bacteria
 Full of nerves for environmental interpretation.
 Both collagen and elastic fibers present
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With age, the number decreases and skin sags and
wrinkles
 Supplied with blood
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Capillaries can rise and fall in the dermis to
stabilize body temp. Too hot – capillaries rise to
release heat (blushing). Too cold – capillaries sink
to hold heat (blue fingertips)
Tattoos
 When a tattoo is applied, ink pigment is
directly injected into the dermis of the
skin.
 Overtime, pigments can fade or migrate
in the dermis, changing the appearance
of the tattoo.
Skin Color
 The amount and type of melanin produced
 Amount of Carotene (orange) pigment
 Amount of dermal blood vessels
 Others
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Redness due to embarrassment, hypertension,
inflammation or allergy
Pallor due to LBP or fear
Jaundice – yellowing due to liver problem
Bruises – blood released into tissue space causing
hematomas.
Skin Appendages
 Cutaneous Glands
 Sebaceous (oil) glands
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Usually empty into hair follicle (oily hair)
Produce Sebum – keeps skin soft and has
chemical that kills bacteria
Become very active in adolescence
causing oily skin
When sebaceous glands become blocked
they can become infected and cause acne.
Skin Appendages
 Sweat Glands – sweat is clear secretion that is
mostly water. Contains salts, vitamin C and
metabolic waste (ammonia, urea, uric acid)
 Sweat is acidic (4-6pH) which inhibits bacterial
growth
 Nerves near sweat glands cause them to sweat
when body temp goes up. Evaporative cooling.
Hair
 Relatively useless, used to be for
insulation
 Minor protective properties
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Help insulate head from heat loss
Shield eyes from debris
keep debris out of respiratory tract (nose
hair)
Hair
 Flexible epithelial structure that is
created in a follicle.
 Part of hair in the follicle is called to root.
Part above the skin surface is shaft.
 In the follicle, cell division occurs,
pushing cells upward as this continues.
The new cells become keratinized and
die
Hair
 Each hair has a central
core called Medulla
surrounded by cortex.
Both of these are covered
by the cuticle
 Cuticle prevents hair
sticking together, when
broken, split ends
 Melanocytes in the follicle
give hair its color.
Hair
 Shaft shape determines hair types
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Oval shaft would produce smooth, wavy
hair
Flat shaft would produce curly hair
Round shaft would produce coarse,
straight hair.
Hair
 Arrector Pili – small muscle that
connects each hair to the dermis. When
contracted, hair stands on end, and
goose bumps are produced.
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Reaction is due to fear or cold: This
reaction is evolutionary for us, it is used in
animals to fluff up the fur to create an
insulating layer.
Nails
 Scale like modifications like a hoof or
claw in other animals
 Has a free edge and a root
 Three borders of nails are covered by
skin folds, the most prominent is the
cuticle.
 Nails are almost completely clear, but
appear pink due to the blood supply
directly underneath.
Skin Ailments
 Athletes foot – caused by fungus
growing in the epidermis
 Boils – inflammation of hair follicles
 Cold sores – Small fluid blisters caused
by the herpes simplex virus. Outbreaks
caused by stress, fever, or UV
 Contact Dermatitis – Chemical exposure
(poison ivy)
Skin Ailments
 Impetigo – Water filled lesions caused by
infection
 Psoriasis – overproduction of skin cells
that leads to scaling.
Burns
 Tissue damage caused by heat, electricity, UV
light or chemicals
 Can cause severe dehydration and chemical
imbalance.
 Rule of nines deals with percent of body
burned. Head, right arm, left arm, anterior
superior trunk, anterior inferior trunk, posterior
superior trunk, posterior inferior trunk, anterior
right leg, posterior right leg, anterior left leg,
posterior left leg. 11 sections 9% each = 99%
 Final 1% would be the genital region.
Burn Degrees
 First Degree – only the epidermis is
damaged, redness and irritation. Will
resolve on its own. Sunburn
 Second Degree – the epidermis and
upper dermis are damaged. Blisters will
form between the two layers. Usually
will heal without scaring since sufficient
epithelial cells remain.
Burn Degrees
 Third Degree – The
entire epidermis and
dermis are
destroyed.
Regeneration is not
possible. Skin grafts
are needed to cover
the area.
Skin Cancers
 Most common form of cancer effecting 1
in 5 people during their life.
 Multiple causes, mostly UV Light
exposure, or chemical exposure.
 Basal Cell Carcinoma
ABCD Rule
 Four signs of potential skin cancer:
refers to moles
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Asymmetry – not symmetrical
Border Irregularity – not a clean edge
Color – pigmented spots, black and brown
Diameter – larger then 6mm