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Lindsey BilyAnatomy & Physiology
Austin High School
The largest and thinnest organ in the body.
Boundary between the internal body and the external environment.
17 to 20 square feet Thickness ranges from 1/50 of an inch to
1/8 of an inch. Integument means “skin”. The skin and
its appendages (hair, nails, and glands) is the Integumentary System.
Keratinized cells
Cutaneous membrane 2 main layers
Epidermis: (thin, outer layer) Dermis: (thicker, inner layer)
Dermal-epidermal junction: where the epidermis cells meet the dermal cells.Subcutaneous layer ( aka: hypodermis or superficial fascia): beneath the dermis. Contains adipose and loose connective tissue.
The Skin
Most of the skin is “thin” Skin that covers the palms, fingertips,
soles of the feet and other areas subject to friction are “thick”
Thinness or thickness only refers to the epidermal layer.
Fingerprints and footprints are present in thick skin.
No hair is in thick skin.
Thin vs. Thick Skin
Epidermis Keratinocytes: Make up 90% of the cells and
are full of the fibrous protein keratin. Melanocytes: Make up 5% of the cells.
Contain the pigment “melanin” which contributes to skin color and decreases the amount of UV light that can penetrate to deeper layers of the skin.
Langerhans cells and Helper T Cells help to trigger immune reactions.
The green arrow is pointing to the melanocytes.
Epidermis has 5 layers (strata)1. Stratum Corneum (most superficial): the cells are dead and
is called the barrier layer.2. Stratum lucidum (clear layer): Only present in thick skin. Keratinocytes are full of a soft gel like substance called eleidin (a precursor to keratin). Blocks water penetration or loss.3. Stratum granulosum (granular layer): The keratinocytes begin keratinization. The cells have started to degenerate so they contain a lot of lysosomal enzymes and the nuclei are missing.
4. Stratum spinosum (spiny layer): 8 to 10 layers of irregularly
shaped cells that look prickly due to the desmosomes. Cells
are full of RNA so they undergo translation to produce keratin.
5. Stratum basale (base layer): single layer of columnar cells.
Only this layer undergoes mitosis.
Stratum spinosum and stratum basale are sometimes lumped together and called the stratum germinativum (growth layer).
Stratum basale/germinativum (indicated by the red arrow) Stratum spinosum (indicated by the light blue bracket) Stratum granulosum (indicated by the green arrow) Stratum lucidum (indicated by the black arrow) Stratum corneum (indicated by the dark blue bracket)
The stratum corneum grows thicker than normal.
Thick, dry, scaly skin and can open up and cause painful fissures.
Dead cells in the stratum corneum absorb water like sponges and expand.
The skin puckers over the live cells that retain their shape.
Result from injury to cells in the epidermis or from the separation of the dermal-epidermal junction.
Formed when the desmosomes between cells are broken
Skin literally falls apart from the body.
Poison ivy, heat, friction injuries (tight shoes), chemicals that break Hydrogen or disulfide bonds.
VERY GRAPHIC PICTURES ON THE NEXT SLIDE!
Epidermal Growth and Epidermal Growth and RepairRepair
“Turnover” and “Regeneration Time”: time period required for a population of cells to mature and reproduce.
New cells must be formed at the rate that old keratinized cells flake off, so that we maintain a constant thickness of the epidermis.
A body’s work is never done. Even at rest, it is producing millions on millions of new cells to replace old ones.
Epidermal Growth and Repair
Regeneration time: Mitosis, differentiation, and movement of
keratinocytes from the stratum basale to the statum corneum is about 35 days.
May be faster if there is an abrasion. If there is constant abrasion over a prolonged
period of time, a callus or corn may form. About 10% to 12% of the cells in the stratum
basale enter mitosis each day.
Dermal-Epidermal Junction
Composed of basement membrane. Specialized fibrous elements and a
polysaccharide gel “glue” the epidermis to the dermis.
Acts as a partial barrier to the passage of cells and large molecules. This is how tattoos work. The tattoo ink is
injected into the dermis. It stays there and cannot permeate to the epidermis.
The Dermis
The dermis is called “true skin”. 2 layers
Papillary layer: thin Reticular layer: thick
The dermis is much thicker than the epidermis. Thinnest at eyelids and penis: about 0.5 mm Thickest on soles and palms : about 4 mm
Dermis: Papillary Layer
Contain dermal papillae which project into the epidermis.
These give us fingerprints and footprints.
Allow us to grip surfaces and walk well on slippery surfaces. Like treads on a tire.
Dermis: Reticular Layer Composed of
collagen fibers and some elastic fibers.
The dermis is attached to the muscles by fascia
Dermis: Reticular Layer
The dermis is the point of attachment for lots of skeletal and smooth muscles.
(skeletal muscle in face allows for expressions)
Dermis: Reticular Layer
Arrector pili are smooth muscles surrounding each hair follicle.
Contraction of the arrector pili cause hair to “stand on end” when we are cold or frightened.
Goose Bumps.
Dermal Growth and Repair
Unlike the epidermis, the dermis does not continually shed and regenerate.
It does maintain itself, but rapid regeneration only occurs if it is healing a wound.
Langer’s Cleavage Lines The collagen
fibers in the dermis arrange themselves in different patterns over the body.
Surgeons make incisions parallel to cleavage lines so that the wound won’t pull apart and scarring is less visible.
Stretch Marks
If the elastic fibers in the dermis are stretched too much, they will weaken or tear.
Originally they are pink or bluish but then fade to silvery-white scars.
Caused by rapid weight gain or growth
Skin Cancer
Arises from abnormal growth of epidermal cells.
Squamous cell carcinoma: Arises in epidermis in areas that were exposed
to a lot of sunlight. Seen on scalp, tops of ears, backs of hands,
forehead
Basal cell carcinoma: most common. Malignancy begins at the stratum basale. Seen in the nose and face most often. Rarely metastasize.
Skin Cancer
Skin Cancer
Malignant melanoma Most deadly of all skin cancers Highest incidence in older people (median age
is 53)light skin, eyes, and hair and who have poor ability to tan and have had previous severe sunburns.
Can start from a pigmented mole that spreads.
Check benign moles with the “ABCD rule”
Skin Cancer
“ABCD rule” Asymmetry:
lopsided Border: irregular
border Color: unevenly
colored and a mixture of shades
Diameter: larger than 6 mm
Moh’s Surgery
Created more than 60 years ago by Dr. Frederick Mohs at the University of Wisconsin.
Microscopic surgery that is used to remove skin cancers that have projections into the dermis.
If tumors aren’t completely removed, they can grow back. You must get all of the cancerous cells.
Moh’s Surgery
This technique is time consuming and technically difficult, but it ensures that the least amount of healthy tissue is removed.
Cure rates are about 95% to 99%. The tumor is cut from the skin in thin
layers. During surgery, the edges of the tumor and each layer of tumor removed are viewed through a microscope to check for cancer cells. Layers continue to be removed until no more cancer cells are seen.
Moh’s Surgery
Moh’s Surgery
Pre OpPost Op
4 months after surgery
Skin Color
Skin color is due to the amount of melanin in the melanocytes.
All races have almost the same number of melanocytes.
Melanocytes convert the amino acid tyrosine to the dark brown pigment (melanin).
The pigment is then transferred to other epidermal cells.
The process of producing melanin is regulated by the enzyme tyrosinase.
Skin Color
Hereditary
If tyrosinase is missing from birth due to a genetic defect, you have albinism.
Albinos lack any pigment. Their cells cannot produce any melanin.
Albinism
Skin Color Factors
Sunlight-Ultraviolet radiation ACTH secretion- Adrenocorticotropic
hormone secreted by the anterior pituitary gland in the brain. ACTH levels are higher when you are under stress and other diseases.
Age- as we age, the melanocytes are not as active and tyrosinase activity decreases causing gray hair.
Melasma- (pregnancy mask). High levels of estrogen and progesterone stimulate the melaonocytes.
Skin Color Changes
We can become red or pale depending on the volume of blood flowing through the capillaries in the skin. Capillaries constrict or blood volume
decreases: pale Capillaries dilate or blood volume increases:
skin is pinker (blushing)
Cyanotic: We can become a blue color if the blood is unoxygenated.
Skin Color
Pregnancy Mask and A cyanotic baby
Vitaligo
The melanocytes stop producing melanin.
Can be injured by a virus or immune cells.
Can be treated by UV treatment, melanocyte transplantation, or other drugs that stimulate melanin production.
The skin functions to maintain homeostasis in the body.
Take care of it!
The skin has a “surface film” that is composed of… Sweat: water, ammonia, lactic acid, urea, and uric
acid Oil: fatty acids, triglycerides and wax Epithelial cells constantly being shed: amino acids,
sterols, phospholipids
All of these chemicals in the skin allow for the protection. Skin acts as a…1. antibacterial and antifungal2. Lubricant3. Hydration of the skin surface4. Buffering of caustic irritants 5. blockade of many toxic agents
Millions of sensory receptors are found in the skin.
The receptors react to stimuli Pressure Touch Temperature Pain Vibration
WE WILL LEARN MORE ABOUT SENSES IN CH. 15
The skin is supple and elastic. It grows as we grow and can stretch and
recoil so that we don’t tear our skin when we move.
The skin regulates the volume of sweat and the chemical composition of it.
Waste products excreted in the sweat is uric acid, ammonia, and urea.
Usually the skin plays a minor role in excretion.
UV Radiation stimulates the production Vitamin D.
7-dehydrocholesterol is in the skin cells and will be converted to cholecalciferol.
Cholecalciferol then travels to the liver and kidneys where it is converted to Vitamin D.
Vitamin D aids in helping the body absorb Calcium
The skin contains white blood cells that eat and destroy harmful microorganisms.
Helper T Cells and Langerhans cells are in the skin as well and help with immune response.
Heat production Heat is produced by the metabolism of foods. The muscles, liver, and glands are the most
active tissues and carry on metabolism the most.
During exercise and shivering, metabolism increases greatly, so that produces heat.
During sleep, very little muscular work is being done, so metabolism decreases.
Exercise:Lots of heat is produced
when we exercise. The heat has the capability to raise the body’s core temperature greatly.
The body sends the heated blood to the skin for cooling, so that is why we turn red.
The body’s 3 million sweat glands produce up to 3L/hr of sweat during heavy exercise.
Heat Loss The body controls the blood vessels in the skin to
regulate heat loss. If we want to keep heat in, the blood vessels constrict. If we need to lose heat, the blood vessels dialate.
Burns that are caused by exposure to UV radiation.
Can cause tissue damage that leads to secondary infections and fluid loss.
People who have had 2 more blistering sunburns before age 20 have a greater risk of developing melanoma.
Injury or death of skin cells that can be caused by heat, UV radiation, electricity or chemicals.
First Degree Burns A typical sunburn Causes minor discomfort and
some reddening of the skin No blistering occurs and tissue
damage is minimal The surface layers of the skin
may peel in 1 or 2 days.
Second Degree Burns Injury to the deeper layers
of the epidermis and the upper layer of the dermis.
Sweat glands, sebaceous glands, and hair follicles may be damaged.
Some tissue death Blisters, severe pain,
swelling and edema occur. Scarring is common
Third Degree Burns Destruction of the
epidermis and the dermis Tissue death extends
beyond the glands and hair follicles
Underlying muscles and fascia, and the bones may be burned as well.
Pain is not felt as the receptors and nerves are killed.
Scarring is imminent.
Hair grows everywhere except… Palms Soles Lips Nipples Some areas of the
genitalia
Hair follicles develop several months before birth.
The fetus is covered by a fine and soft hair coat called lanugo. Most of it is lost prior to birth.
Any lanugo that is present at birth soon is lost and replaced by vellus hair. It is stronger, fine, and less pigmented.
Terminal hair replaces vellus hair during puberty.
Epidermal cells spread into the dermis and form a small tube: the hair follicle
Cells from the stratum germanitivum form the germinal matrix of the hair follicle and these cells will undergo mitosis over and over again and become keratinzed to become hair.
In the germinal matrix, there is a small bit of dermis that is the papilla. It contains the capillaries that nourish the germinal matrix.
Parts of the hair… Root: hidden in the
follicle Shaft: visible part of
the hair Medulla: inner core of
the hair Cortex: outer core of
the hair
Melanin in the cells of the cortex account for hair color
Melanin with iron forms red hair
Decreased levels of melanin form gray or white hair.
Melanin also makes the hair strong.
Straightness or waviness in hair is related to the shape of the hair’s shaft
Straight Hair: round, cylindrical shaft
Wavy Hair: flat shaft that is not as strong as straight hair.
Wavy Hair is more easily damaged or broken than straight hair
Sebaceous glands secrete sebum into each hair follicle to keep hair from becoming dry and brittle.
Hair goes through periods of growth and rest.
Hair on the head grows a little less than ½ inch per month (5 inches per year).
Body hairs grow more slowly. Head hairs last between 2 and 6 years
and then die and shed.
Baldness: when hair that is lost is not replaced.
Hair can be removed by various methods: Shaving: temporary Plucking, tweezing, or waxing: temporary. Hair is
pulled from the follicle Electrolysis: Electric current destroys the hair follicles
and allows you to remove the hair by tweezing. Dipilatories: ex. Nair, Veet: Hair is dissolved Vaniqua: A prescription drug that inhibits Ornithine
decarboxylase required in hair growth.
Nails
Nails are composed of heavily keratinized epidermal cells.
Nail Body: Visible part of the nail Root: part of nail that lies under the cuticle Lanula (means “little moon”): crescent
shaped white area. Nail Bed: epithelium under the nail. It is
pink because it contains blood vessels.
Nail Growth Nails grow by cells
undergoing mitosis in the stratum germanitivum under the lanula.
Fingernails grow faster than toenails.
Nails grow faster in the summer than in the winter.
Trauma to the nails can cause it to separate from the nail bed. This is called onycholysis.
Nails
Skin Glands Sweat Glands:
Can be classified as Eccrine or Apocrine
Eccrine are most common and secrete sweat (water, salts, uric acid, ammonia, urea)
Apocrine are found in the armpit, areola of the breast, pigmented skin around the anus. : They begin to enlarge at puberty and produce a thicker colored secretion different than sweat.: The odor is not the actual secretion, it’s from the bacteria decomposing the secretion on the skin.
Skin Glands
Sebaceous Glands Secrete oil (sebum) in the hair and skin. Two sebaceous glands are located around
each hair follicle Keep the hair and skin supple and the skin
soft. The chemicals in the sebum (fatty acids,
triglycerides, and wax) are an antifungal agent.
Sebum secretion increases during adolescence
Acne
Occurs most frequently during adolescence.
Overactive sebaceous glands. The ducts can become plugged with dead
skin cells and sebum that has been contaminated with bacteria.
The inflamed plug is called a comedo. When the hair follicle or sweat pore
becomes infected then you get a pus filled pimple.
Acne
Skin Glands
Ceruminous Glands Modified apocrine sweat glands Secrete brown, waxy substance called
cerumen. This is ear wax.
Skin Disorders
Impetigo: highly contagious infection caused by a Staph or Strep bacteria.
Tinea: fungus that causes, ringworm, jock itch and athlete’s foot
Warts: Growths of the skin caused by papillomaviruses. Usually are benign but can become malignant.
Boils: infection of the hair follicles caused by Staph bacteria. Large and pus filled.
Skin Disorders
Urticaria (hives): raised lesions on the skin that leak fluids from the skin’s blood vessels.
Decubitus (“lying down”) ulcers: Also called bedsores. These are pressure sores that occur because blood flow has slowed to that area.
Scleroderma: Autoimmune disease where the skin hardens.
Psoriasis: chronic inflammatory disorder. Scaly skin due to excessive rate of the epidermis.
Eczema: Inflammatory response to an allergy. Bumps, blisters, red skin
Skin Disorders Fever: hypothalamus causes the set point to be
higher than 98.6 degrees F. Malignant hyperthermia: inherited condition
where the body’s temperature is always higher than normal.
Heat exhaustion: when the body loses large amounts of fluids usually in hot weather. Weakness, dizziness, nausea, muscle cramps.
Heat stroke: the body’s temperature increases to 105 degrees F or higher.
Hypothermia: body temperature falls below 95 degrees F or lower.
Frostbite: ice crystals form in the tissues. Necrosis (tissue death) and gangrene (decay of dead tissue) can occur.
ringworm impetigo
warts boil
bedsoreschleroderma
eczemahives psoriasis
