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What are the 5 functions of the integumentary system?
- 1) Protection against abrasion, UV light, microbes, and water loss
- 2) Sensation
- 3) Temperature Regulation (control of blood flow through skin and sweating)
- 4) Vitamin D Production
- 5) Excretion
What is the epidermis?
Most superficial skin, epithelial tissue, resists abrasion and water loss
What is the dermis?
Connective tissue under epidermis, depending on location can be 10-20x thicker than epidermis.
What type of tissue is underneath the skin (epidermis and dermis)?
Subcutaneous tissue= loose connective tissue. Not part of integumentary system but connects skin to underlying muscle/bone.
What are the 5 strata of the epidermis from superficial to deep?
- 1) Stratum corneum
- 2) Stratum lucidum
- 3) Stratum granulosum
- 4) Stratum spinosum
- 5) Stratum basale
What is the stratum corneum?
Most superficial stratum of epidermis, 25+ layers of dead squamous cells. Resists abrasion and water loss because lipids surround dead cells. Structural strength from keratin and protein envelope.
What is stratum lucidum?
3-5 layers of dead cells, almost transparent, usually only in thick skin with a dispersion of keratohyalin around keratin fibers.
What is stratum granulosum?
2-5 layers of flattened, diamond shaped cells. Keratohyalin granules accumulate in cytoplasm. Lamellar bodies inside cell release lipids out of cell and protein envelope forms inside cell membrane, cell dies and becomes part of corneum. Moisture barrier properties from released lipids in this layer.
What is stratum spinosum?
8-10 layers of many sided cells. As cells are pushed toward surface, they flatten. Keratin fibers and lamellar bodies (lipid filled, membrane bound organelles) form inside keratinocytes.
What is stratum basale?
Deepest layer of epidermis. Single layer of cuboidal or columnar cells. Structural strength from hemidesmosomes that anchor epidermis to basement membrane and desmosomes that hold keratinocytes together.
How often do keratinocytes divide in the stratum basale?
Every 19 days they undergo mitotic division. One daughter cell becomes new stratum basale is able to divide again, the other is pushed towards the surface, which takes 40-56 days.
What are cornified cells?
Dead, hard protein envelope, filled w/keratin (keratin fibers and keratohyalin).
Soft keratin vs. hard keratin
Soft keratin is found in skin. Hard keratin found in nails, external part of hair.
What is a callus?
A mass of tissue formed with increasing layers of stratum corneum.
What is psoriasis?
Increased cell division in stratum basale and abnormal keratin production. Causes thicker stratum corneum which sloughs off and reveals large-silvery scales that bleed if scraped off. Bleeding from dermis, because epidermis is avascular.
What is the cause and treatment for psoriasis?
Caused by genetic factors and immune system increasing cell division in stratum basale.
Treated with drugs and UV phototherapy
What is thick skin?
All 5 strate, stratum corneum is very thick. Found in areas with lots of pressure or friction (palms, soles, fingertips)
What is thin skin?
The rest of the body is covered with thin skin. More flexible than thick skin with fewer layers per strata. Stratum granulosum usually only 1-2 layers. Stratum lucidum usually absent. Hair grows here.
What is melanin?
Pigment in hair, skin, eyes. Usually brown/black, some yellow or red. Protects from UV light. Large amounts in freckels, moles, nipples, areolas, axillae, and genitalia. Less melanin in lips, palms, and soles
What are melanocytes?
Irregular shaped cells with long processes that extend between keratinocytes of stratum basale and stratum spinosum.
What part of the melanocyte packages melanin?
Golgi apparatus packages into vesicles called melanosomes and moves into cell processes (long extensions from cell body)
How do keratinocytes aquire melanin?
They phagocytize the tips of the melanocyte cell processes and aquire melanosomes.
Melanin in freckles
Increase melanin in stratum basale keratinocytes but NO INCREASE IN MELANOCYTES
Melanin in moles
Aggregation of melanocytes in epidermis or dermis
What are warts?
Uncontrolled growth of epidermis cuased by human papillomavirus. They are transmitted by contact with a contaminated object or infected person.
Effect of UV exposure on melanin
UV exposure darkens present melanin and increases melanin production thus increasing UV protection.
What is the structure of the dermis?
Connective tissue (mostly collagen, some elastin, reticular fibers, fibroblasts, some fat, and macrophages).
What is the function of the dermis?
Provides blood supply, nerves, hair follicles, smooth muscles, glands, and lymphatic vessels for epidermis.
What are the two layers of the dermis?
- 1) Papillary layer
- 2) Reticular layer
What is the papillary layer of the dermis?
More superficial layer, made of loose connective tissue. It brings blood vessels closer to the epidermis for nutrient/gas exchange. It also contains dermal papillae that form fingerprints/footprints and increase grip.
What is the reticular layer of the dermis?
Mat of collagen and elastin fibers made of dense irregular connective tissue. Main FIBROUS layer of dermis that is strong in many directions. Forms cleavage (tension) lines
What is the importance of cleavage lines in the dermis?
Incision along cleavage lines is less likely to gap vs across line incision. Decrease risk of infection and scar tissue.
What happens if skin is stretched too much?
Dermis ruptures and leave lines of scar tissue called STRIAE (stretch marks)
What is subcutaneous tissue?
Attaches skin to bone/muscles and supplies nerves and blood vessels. Made of loose connective tissue with collagen and elastin fibers. Main cells: fibroblasts, adipose cells, and macrophages. ~ 1/2 of total body fat store here.
What are the 3 types of injections?
- 1) Intradermal (TB skin test)
- 2) Subcutaneous (Insulin)
- 3) Intramuscular
What are the 3 types of hairs?
- 1) Lanugo (fetal hair ~5-6 months into development), near birth replaced by terminal hairs
- 2) Terminal hairs= long, coarse, pigmented (scalp, eyelids, and eyebrows)
- 3) Vellus hairs= short, fine, unpigmented (rest of body)
Males: 90% terminal hair, Females: ~35%
- Shaft: above surface, Root: below surface, Base of root: hair bulb
- Made of dead, keratinized epithelial cells in 3 concentric layers (cortex, medulla, and cuticle)
- Medulla: central axis of hair, 2-3 layers soft keratin
- Cortex: bulk of hair, hard keratin
- Cuticle: single layer of hard keratin, on hair surface, raised edges like roof shingles to hold hair in place.
Hair follicle structure
Invagination of epidermis into dermis. At opening, all strata are present for thin skin. At base, only stratum basale.
What is the hair bulb made of?
- Knob at end of hair root. Made of undifferentiated epithelial cells that form matrix and produce hair.
- Hair papilla: projection of dermis into hair bulb that provide blood vessels and nourishment to matrix.
- Growth stage: hair formed by matrix cells, differentiate, keratinize and die. Hair gets longer as cells aded at base of hair root, new stage starts and old hair falls out.
- Resting stage: no growth
What are arrector pili?
Smooth muscles that respond to stress such as cold or fear. Innervated by sympathetic nervous system to make hairs stand on end and cause goose bumps. Good for mammals with lots of hair to increase insulation, but useless in humans.
What are sebaceous glands?
Simple, alveolar glands in dermis, duct to surface that produce sebum. An oily, white substance that prevents drying of skin and some antimicrobial properties.
What are the two types of sweat glands?
What are merocrine sweat glands?
Simple, coiled tubular glands all over the skin, but concentrated in the palms and soles. Secretes mostly SALT AND WATER
What are apocrine sweat glands?
Simple, coiled tubular glands, open to hair follicles in axillae and genitalia. Produces THICK secretion rich in ORGANIC substances. Active at PUBERTY because of influence of sex hormones.
What causes body odor if apocrine sweat gland secretions are odorless?
Bacterial breakdown of organic substances in secretions cause odor.
What are ceruminous and mammary glands?
- Ceruminous: modified merocrine glands, make cerumen
- Mammary glands: modified apocrine glands that produce milk
What is the rule of nines?
Used for assessing % of body surface area (BSA) burned on an adult patient. Head, each UE and LE= 9% BSA. Anterior and posterior trunk= 18% BSA each. Genitalia= 1% BSA
What are partial thickness burns?
1st and 2nd degree burns.
What is a 1st degree burn?
Burns that only involve the epidermis. Symptoms include pain, erythema, slight edema. Caused by sunburn, brief hot or cold exposure. Heal in ~1 wk without scarring.
What is a second degree burn?
Burn that damages epidermis and part of dermis. Minimal dermal damage causes erythema, pain, edema and blisters. Heals in ~2 wks without scarring.
Deep dermal damage is red, tan or white appearing. Several months to heal with possible scarring.
How do 2nd degree burns heal?
All 2nd degree burns heal with the epidermis regenerating from epithelial tissue in hair follicles, sweat glands and wound edges.
What are full thickness burns?
3rd degree burns. Epidermis and dermis are completely destroyed and possible damage to deeper tissue. White, tan, brown, black, or deep cherry in color. Often times painless b/c nocireceptors are destroyed.
How do full thickness (3rd degree burns) heal?
Only from wound edges because hair follicles and sweat glands in dermis and subcutaneous tissue are destroyed. Often require skin grafts to heal.
What are nails?
Layers of dead stratum corneum with hard keratin.
- Nail body- visible part
- Nail root- part covered by skin
- Nail fold- holds lateral and proximal edges in place
What is the eponychium?
Cuticle of nail. Stratum corneum from nail fold that extend onto nail body.
What is the nail matrix?
Epithelial tissue with stratum basale that give rise to cells that form nail. Turns into nail bad. Matrix is thicker than bed and makes most of the nail.
What is the lunula?
Whitish, crescent shaped thing at base of nail, part of nail matrix
How do nails grow?
Unlike hair, nails grow continuously (.5 mm to 1.2 mm per day)
What is acne?
Inflammation of hair follicles and sebaceous glands
What 4 factors influence acne formation?
- 1) Hormones (especially testosterone)
- 2) Sebum (from sebaceous glands)
- 3) Abnormal keratinization
- 4) Propionibacterium acnes
How does acne form?
Overproduction of epidermal cells in hair follicle. Cells are shed from the wall of the follicle and stick together to form mass mixed with sebum. The mass blocks the follicle.
What is the main factor that affects sebum production?
Testosterone increases sebum production. Accumulation of sebum behind blockage causes "whiteheads". If the mass pushes out of follicle they form "blackheads".
How do pimples form?
Blockage of hair follicle causes rupture of follicle walls introducing Propionibacterium acnes and other bacteria to cause inflammatory response leading to red pimple filled with pus.
How does the skin produce Vitamin D?
7-dehydrocholesterol in skin turns into cholecalciferol when exposed to UV light. This goes to liver and kidneys which turn it into calcitriol (active vit D)
What does Vitamin D affect in the body?
Calcium and phosphate uptake and absorption in intestines.
What are the 3 main types of skin cancer?
- 1) Basal cell carcinoma
- 2) Squamous cell carcinoma
- 3) Melanoma
Basal cell carcinoma
Most common. Affect cells in stratum basale. Varied appearance: open sores, red patches, shiny, pearly or translucent bumbs, scar like tissue of shiny, taut skin. Removal or destruction of tumor cures most cases.
Squamous cell carcinoma
2nd most common. Affect cells in stratum spinosum. Wart like growth; persistent, scaly red patch, open sore, or elevated growth with central depression. Removal or destruction cures most.
Least common. 77% of skin cancer deaths. Affect melanocytes. Usually brown or black. Occasionally stop producing melanin, skin colored, purple, pink, red. Treated while only in epidermis usually successful. If invades dermis and metastasizes, can be deadly.