lecture: the integumentary system

• LARGEST organ (most visible and accessible organ)
• surface area: 1.5 - 2 m²
• 15-20% of total body weight
• first line of defense against environment
• dead skin = billions of tons of dust in environment because shed 50,000 cells every minute (holy batman, im bathing in dead cells ... i dunno how to feel about that)

• 1. protection - Protects underlying tissues and organs, Serves as barrier against infection and injury, Provides protection against UV coming from the sun
• 2. temperature regulation - helps regulate body temperature. Provides insulation to keep heat in and evaporative cooling to allow heat out.
• 3. excretion - removes waste products from the body e.g. salts, water, and organic wastes by glands
• 4. Vitamin D production
• 5. sensations -detection of touch, pressure, pain, and temperature i.e. the skin contains several types of sensory receptors

• 1. skin (cutaneous layer) = epidermis + dermis
• 2. accessory structures

• 1. epidermis - superficial layer of epithelial tissue
• 2. dermis - deep layer of connective tissue. provides nourishment of epidermis and provides structural strength (2 TYPES: papillary layer and reticular layer)
• 3. hypodermis (subcutaneous layer) - technically not part of skin [OMG then WHYYYYY is it listed], it is loose connective tissue that connects skin to underlying structures and provide insulation
• 

• Originate in the dermis extend through the epidermis to skin surface:
• 1. Hair
• 2. Nails
• 3. Glands

• -avascular so nourished by diffusion from capillaries of the papillary layer of the dermis
• composed of cells arranged into layers (strata) and is separated from dermis by basement membrane

• 1. thick = 5 layers (strata) = 0.5mm-1mm thick
• deep epidermal ridge patterns (increase surface area and provide friction; produce fingerprints)
• location: covers palm of hands and soles of feet
• 2. thin = 4 layers (strata) = < ~ 0.1 mm thick
• most of body surface area

• 1. stratum germinativum
• 2. stratum spinosum
• 3. stratum granulosum
• 4. stratum lucidum
• 5. stratum corneum
• 15-30 days to reach corneum and stay for 2 weeks before shedding

• basal cells: stem cell source of keratinocytes (15 day journey to top layer)
• Merkel cells: touch receptor cells (trigger nervous system) found in hairless skin
• Melanocytes: secrete melanin (pigment) scattered through this layer
• forms epidermal ridges: fingerprints here!!!
• attached by hemidesmosomes to basal lamina

• immunity
• "spiny layer"
• Langerhans cells: anti-microbial (from bone marrow to work as macrophages in immune system)
• 8-10 layers of keratinocytes
• new daughter keratinocytes

• strength
• "grainy"
• 3-5 layers/high keratin fiber and keratohyalin (dense granules/aggregation and cross-linking of keratin)

• waterproof
• "clear"
• thin keratinocyte layer (extra layer in THICK skin)

• disposable
• 15-30 layers of dead keratinocytes
• thicker layer in THICK skin
• strong, water resistant barrier

• 1.Gives structural strength. C.T. with many fibers, fibroblasts, macrophages. Some adipocytes and blood vessels.
• 2.Contains nerves, blood vessels, hair follicles, smooth muscles, glands, and lymphatic vessels.
• 3.Sensory functions: pain, itch, tickle, temperature, touch, pressure

• 1. papillary layer - Superficial (outer) 1/5. Areolar with lots of elastic fibers. Dermal papillae, capillary beds. Fingerprints. Whorls of ridges. Touch receptors (Meissner’s), free nerve endings sensing pain
• 2. reticular layer - Deep (inner) 4/5. Dense irregular C.T. Collagen and elastic fibers. Also see some
• adipose, hair follicles, nerves, oil glands, ducts of sweat glands, heat sensors.

• Elastin and collagen fibers oriented in some directions more than in others
• parallel cuts = faster healing
• overstretching = stretch marks (striae)

• collagen: resistance to stretching
• elastic: stretch and recoil (exceed and will damage dermis NOT epidermis due to pregnancy or weight gain)
• sagging and wrinkles occur from permanent reduction in amount of elastin in dermis due to hormones, aging, and UV light. USE RETIN-A (TRETONIN) - vitamin A derivative to increase blood flow in dermis and repairs (look young!!!)

• 1. Meissner's corpuscle - egg shape, detect light touch near the dermal papillae.
• location: fingertips, palms, soles, eyelids, tip of tongue & genitalia
• 2. Pacinian corpuscle - onion shape, detect pressure near deeper reticular and subcutaneous layer
• location: joints, tendons, muscles, mammary glands, & external genitalia

• INDISTINCT border to dermis
• attaches skin to underlying structures
• Consists of loose connective tissue with collagen and elastic fibers
• Site of lipid storage and contains about one-half of body’s
• fat. – this is where lipsuction occurs.
• Functions as: Energy source, Insulation, Padding, Blood reservoir (can hold 5-8% volume) superficial part has large veins & arteries.) e.g. can shunt blood for temperature regulation
• for needles and liposuction

• 1. carotene -orange yellow pigment found in orange vegetables accumulating in epidermal cells and fatty tissues of dermis. converts to Vitamin A
• 2. melanin -yellow brown or black pigment produced by melanocytes in stratum germinativum from amino acid TYROSINE ... package in melanosomes to send to keratinocytes by phagocytosis

• protect skin from UV damage
• same number in all races
• Vitiligo = loss of melanocytes due to possible autoimmune disease DOES NOT describe albino individuals

• production from UV exposure to get cholecalciferol --> liver --> kidneys turn it to calcitriol (active vitamin D)
• Vitamin D increases BLOOD CALCIUM for bone homeostasis, bone formation, growth and repair, nerve and muscle function
• RICKETS: insufficient vitamin D for children = abnormal bone development
• eat supplements or diet of Vitamin D

• shaft, root, hair bulb
• Hair growth: the hair bulb produces the hair in cycles with a growth stage and a resting stage
• growth: cells added at BASE as hair elongates
• rest: follicle shortens and holds hair in place when hair falls out, new hair begin (good cause i've been losing tons of hair ... boo! stress!)

• Accessory structures of hair:
• 1. arrector pili - involuntary smooth muscle, goosebumps
• 2. sebaceous gland - lubricate hair and controls bacteria

• 1. sebaceous - oil - in dermis. holocrine (lysis and secrete contents and die). secrete sebum: oily white substance rich in lipids (+ electrolytes + proteins). lubricate and protect epidermis. (lips, eyelids, and genitalia - areas of no hair!)
• 2. sudoriferous - sweat - merocrine (eccrine) in palms and soles, etc. more and superficial compared to apocrine. sensible perspiration for 3 functions:
• a) Cools skin surface (lowers body temp)
• b) Excretes water and electrolytes
• c) Flushes Microorganisms & (has a peptide w/antibiotic properties dermicidin) dilutes harmful chemicals from skin
• apocrine (secrete with no loss of cytoplasm like merocrine)- ducts terminate into follicles in armpits and groin. bacteria comes = STANK, stinky odor
• Ceruminous gland: MODIFIED merocrine sweat gland in the ear canal (+ sebum = earwax)
• Mammary gland: MODIFIED apocrine sweat gland to produce milk (lactation and pregnancy)

integument damage, infection, cancer and overheating, drying out (less function of glands), less vitamin D3 making.

• inflammation of skin
• mostly papillary layer
• allergen, irritant, or unknown immune problem
• TREATMENT: antibiotics or hydrocortisone (anti-histimines)
• ** Eczema/Atopic dermatitis (up to 40% of all kids) - crusting in stratum corneum as "messy rash"
• if dandruff (seborrheic dermatitis) - use head and shoulders (zinc pyrithione), Selsun blue (Selenium
• sulphide), Nizoral (Ketoconazole)
• if contact dermatitis (irritant) - use Tacrolimus (inhibit T cells), corticosteroids (inhibit prostaglandins from inflammation), antihistimines (to stop itching)

• silvery scales with stem cells in stratum germinativum active and dividing abnormally frequently (1.5 days vs normal 20 days).
• ~5% in U.S. and ~2% worldwide affected
• 20-30% genetic disposition

• Dermatits Psoriasis : inflammation due to high proliferation (due to T cells go to epidermis and release cytokines)
• TREATMENT: METHOTREXATE : inhibits proliferation of keratinocytes
• immune suppressing medications: antibodies --> 1) Efalizumab (Raptiva) to T Cells or to 2) Adalimumab (Humira): antibodies to TNF
• use coal tar to increase light sensitvity like for phototherapy - to decrease keratinocytes proliferation

• MOST COMMON cancer in U.S.
• 3 types:
• 1. basal-cell - MOST COMMON, BUT least malignant. basal/germinativum
• 2. squamous-cell - spinosum
• 3. melanoma - the BAD body because metastasize! cancer of melanocytes in germinativum layer

• ABCD
• 1. Asymmetry - irregular, raised, oozy
• 2. Border - indistinct, irregular
• 3. Color - mottled. combination of red, brown, tan, pink, white, blue, black tones
• 4. Diameter - greater than 1/4th inch (55 mm).

• UVA - 320 nm - 400 nm
• UVB - 290 nm - 320 nm
• (both bad and can cause skin cancer)
• Sunscreens: protect against SCC but not BCC. chemicals (Ex. PABA, zinc oxide, titanium dioxide) cause harmful free radicals.