1. Protection - cushions and insulates the deeper organs & protects body from bumps, scrapes, cuts, chemicals, & invading microorganisms
2. Temperature regulation - the skin's rich capillary network & sweat glands regulate the loss of heat from the body, helping to control body temperature
3. Excretion - acts as a miniature excretory system when urea, salts, & water are lost through sweat
4. Production of Vitamin D (metabolic function) - epidermal cells use UV radiation to synthesize vitamin D
5. Sensory Reception (cutaneous sensory organ) - by sensing touch, pressure, temperature, & pain, these receptors keep us aware of conditions at the body surface
6. blood reservoir
7. water proofing - does not dissolve in water
8. insulation - maintain certain body temperature
What is the epidermis?
- a keratinized stratified squamous epithelium
- the superficial region that is a thick epithelial tissue
- depends on the diffusion of these materials from the underlying dermis
- responds to pressure or injury to the skin
What are keratinocytes?
- produce keratin, a tough fibrous protein that gives the epidermis its protective properties
- also produce antibiotics & enzymes that detoxify the harmful chemicals to which our skin is exposed
- arise at lower part of epidermis & are pushed up as new ones are created. as they reach the top they flatten out & then filled with keratin & have died.
- we get a new epidermis every month
What are melanocytes?
- make melanin (dark pigment) which is transferred to keratinocytes
- protects DNA from UV ray damage
- production is increased as a result of UV exposure
- made in membrane-walled granules & then transferred through the cell procfesses
(spider-legs) to nearby keratinocytes
What are merkel cells?
touch receptor associated with a sensory nerve ending
What are langerhans cells?
star shape cells that form part of immune system & use receptor mediated endocytosis to engulf foreign substances
What is the difference between thick skin and thin skin?
thick skin - covers palms & soles & consist of 5 layers (or strata-bed sheets)
thin skin - covers the rest of the body with only 4 strata present
What is stratum basale?
- deepest epidermal layer
- consists of a single row of cells, mostly stem cells representing the youngest keratinocytes
- mitosis occurs (high rate)
- contains living cells
- gives rise to newly formed keratinocytes & melanocytes
What is Stratum Spinosum?
- a spiny layer with several cell layers thick
- cells of this layer contain thick bundles of intermediate filaments, which consist of a tension-resisting protein pre-keratin
- contains living cells
- also has langerhans cells
- a layer of mature keratinocytes that have formed tonofilaments (prekeratin intermediate filaments)
What is Stratum Granulosum?
-a granular layer that is thin
- consists of three to five layers of flattened keratinocytes that change to become waterproof and keratinized
- contains living cells
- has many tonofilaments, granules of keratohyalin (forms keratin), & lamellaeted granules (waterproofing glycolipids)
- plasma membrane also thickens
What is stratum lucidum?
- a clear layer occuring in thick skin only (not thin skin)
- consists of a few rows of flat, dead keratinocytes
- too far from capillaries & since the cells do not get any nutrients, they die
What is stratum corneum?
- a horny layer that is the most external part of the epidermis many cells thick (thicker in thick skin than in thin skin)
- a layer of dead cells that can still perform so many functions
- both the keratin and the thickened plasma membranes of cells in the stratum corneum protect the skin against abrasion & penetration
- glycolipid between its cells keeps this layer waterproof
- cells of this layer are shed regularly (dandruff from scalp & flakes from skin)
- protects against abrasions & entrry of foreign substances
What is the Dermis?
- a fibrous connective tissue
- has two layers: papillary & reticular layer
- collagen fibers of dermis give skin its strength & resilience
What is the papillary layer?
- makes up the top 20% of the dermis
- is areolar connective tissue containing very thin collagen & elastic fibers
- forms the dermal papillae (nipples) that are fingerlike projections that extend into the overlying epidermis
What is the reticular layer?
- makes up the second half of the dermis (80% of the thickness)
- contains dense irregular connective tissue high in collegan
- named for its networks of collagen fibers
- reticular fibers give skin its elasticity and collagen makes it strong & resilient
What is the Hypodermis?
- fatty hypodermis with two other names..superfricial fascia and subcataneous layer
- consists of both areolar & adipose connective tissue
- stores fat
- anchors skin to underlying structures
- an insulator (helps prevent heat loss from the body) due to adipose tissue
What pigments contribute to skin color?
*Melanin - ranges from yellow to reddish to brown to black and variations in skin color in humans result from differences in both the amount & type of melanin produced. areas of concentrated melanin storage are known as mole, freckles, and birth marks
*carotene - yellow-orange pigment that the body obtains from vegatable sources
*hemoglobin - when oxygenated it is red & gives skin a pinkish to red tone seen in skin low in melanin. Also in bruising hemoglobin & red blood cell break down to create blue and yellow tones
What is a nail?
- corresponds to the hoof or claw of other mammals
- enable us to pick up small objects & scratch the skin when it itches
- made up of dead, keratinized cells
- has a distal free edge, a body, and a root
What is the nail bed?
- where the nail rests on
- contains only the deeper layers of the epidermis
What is the nail matrix?
formed by the nail bed when the bed thickens at the root & the proximal end of the nail body
- the actively growing region
What is the lunule?
- lunule means "little moon"
- is white crescent
- located under the nail's proximal region
What are nail folds?
the lateral & proximal borders of the nail are overlapped by skin folds
What is the eponychium?
- another name for "cuticle"
- proximal nail fold projects onto nail body
What is hair?
- flexible strand made of dead cells filled with hard keratin
- to sense things that lightly touch the skin
- hair on the scalp protects head against direct sunlight in the summer & against heat loss on cold days
- eyelashes shield the eyes
- nose hairs filter large particles such as insects & lint from inhaled air
What is the hair root?
the part embedded in the skin
What is the hair shaft?
- the part that projects above the skin surface
- composed of three layers: cuticle, cortex, & medulla
- shape of the shaft determines the type of hair
What are hair follicles?
- the root of the hair
- extend from epidermal surface into the dermis
- deep end of follicle is expanded, forming a hair bulb, a knot of sensory nerve endings wraps around each ahir bulb to form root hair plexus
- associated with sebaceous gloands & arrector pili muscle
What is a hair bulb?
where the deep end of the follicle is expanded
What is root hair plexus?
a knot of sensory nerve endings wraps around each hair bulb
What is the arrector pili muscle?
- a bundle of smooth muscle cells
- a raiser of the hair
What are the sebaceous glands?
- skin's oil glands
- occur over entire body except palms and soles
- simple alveolar glands with several alveoli opening into a single duct
- sebum (animal fat) collects dirt, softens & lubricates hair and skin, prevents hair from becoming brittle, and keeps the epidermis from cracking
- these glands of sebaceous glands are influenced by sex hormones
- has holocrine secretion: this excretory gland releases the sebum when the glandular cells become too full of product and burst
what are sweat glands?
- another name for sudoriferous glands
- sweating prevents overheating of the body because sweat cools the skin as it evaporates
- a filtrate of blood that passes through the secretory cells of the sweat glands & is released by exocytosis
- sweat is 99% water & acidic (retards growth of bacteria on the skin)
- contains 2 types of sweat glands:P eccrine & aprocine
What are Eccrine Glands?
- produce true sweat
- opens at a pore
What are Aprocrine Glands?
- produce a special kind of sweat consisting of fatty substances & proteins
- causes body odor, respond to hormones, foreplay, & menstrual cycle changes
What are the two types of sudoriferous glands?
Aprocrine & Eccrine Glands
What is ceruminous glands?
- modified aprocrine glands in the lining of the external ear canal
What are mammary glands?
modified to secrete milk
What are Burns?
tissue damage inflicted by heat, electrcity, radiation, extreme friction, or certain harmful chemicals
What are first-degree burns and the symptoms?
- only the epidermis is damaged
- symptoms include redness, swelling, & pain
- inflamattion results
- heal in a few days without special attention
- example: sunburn is usually a 1st degree burn
What are second-degree burns?
- involve injury to the epidermis & upper part of the dermis
- inflammation occurs, blisters appear
- symptoms: blisters appearing as fluid accumulates, redness, swelling, pain
- skin regenerates with little or no scarring in 3-4 weeks if care is taken to prevent infection
What are third-degree burns?
- consume the entire thickness of the skin
- appears white, red, or blackened
- because of fluid loss and infection, should not wait for the skin to regenerate on its own. A skin graft is used on the burn area to treat it.
What is basal cell carcinoma?
least malignant and most common of skin cancer of the stratum basale, slow growing, & rarely undergoes metastasis.
- appears as nodule with a central ulcer & a pearly edge
What is squamous cell carcinoma?
arises from the keratinocytes of the stratum spinosum, grows rapidly, metastasizes
- a chance of complete cure is 99% good
- appears as reddened papule
What is melanoma cell carcinoma?
a deadly cancer of melanocytes and most dangerous kind of skin cancer
- often arises from existing moles, metastasizes quickly, and is resistant to chemotherapy
How does aging affect the skin?
*infants: born coated with a layer of vernix caseosa (an oily waterproofing substance)
*adolscence: onset of puberty activates sebacceous glands & increases acne. skin is at its best form in 20's and 30's, the skin damage becomes evident
*middle age: skin becomes dry & itchy because lubricating glands are not as productive, oily skin ages better