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-largest organ in the body-is considered an organ because it consists of serveral kinds of tissues that are structurally arranged to function together
-represents ~7% of body weight (>3000 square inches)
-variable thickness(1.5-4mmm) |
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| skin, plus hair, glands and nails |
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-protection
-homeostsis
-others (absorption)
-sensory receptors
-nonverbal communication |
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Protects against water (keratin), microorganisms (oil glands), UV
light damage (melanin) |
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– “Same state”
– Ex: body fluids, temperature |
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| other functions (absorption)of skin |
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– Cutaneous absorption
– Ex: lipids can cross easily (so many toxins and pesticides can
cross)
– Synthesis of vitamin D, which causes maintenance of calcium |
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– Rash, biting fingernails
– Show emotion w/red face, etc. |
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-protective outer covering-thin
-all layers are dead cells except bottom few
-it take 6-8 weeks for bottom layer to reach top, then get sloughed off (millions of them) |
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| stratified epithelium (thickness varies) |
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| what happens when cells are alive at teh bottom layer? |
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| they secrete keratin (toughness and waterproofs the skin) |
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| what happens when keratin is increased? |
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| cornification of skin (calluses and/or corns) |
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| Relatively avascular, fairly thin relative to the dermis |
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layer of epidermis
general |
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| • 5 layers (strata) in thick skin; 4 layers in thin skin |
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-stratum basale
-stratum spinosum
-stratum granulosum
-stratum lucidum("transition zone"
-stratum corneum |
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– Deepest layer
– Single row of cells, mostly stem cells
– Rapid division
– Merkel cell: associated with touch (sensory nerve ending)
– Melanocytes: make melanin (dark pigment), shield from
UV rays |
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– Several cell layers thick
– Has spines, which don’t exist in living cells
– Langerhans or Dendritic cells: star-shaped cell, part of
immune system; use endocytosis to engulf foreign proteins and travel to lymph node |
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– 1-5 layers of flattened keratinocytes
– Keratohyaline granules: help form keratin in higher strata
– Lamellated granules: waterproofing |
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| Stratum lucidum (“transition zone”) |
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Definition
– In thick skin ONLY
– Thin, translucent band
– A few rows of dead keratinocytes |
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– Most external
– Many cells thick (even thicker in thick skin)
– Dandruff and skin flakes |
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Thickest of all 3 layers, all living cells; “hide”
• Contains connective tissue
• Contains nerves, hair follicles
• Contains elastin fibers (stretchiness decreases
w/age), collagen and reticular fibers as well
-2 layers
-temperature regulation
-Integumentary glands (exocrine) |
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| papillary layer of dermis |
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Definition
superficial 20%, areolar CT, fingerlike
projections |
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| reticular layer of dermis |
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Definition
| 80%, dense irregular CT, network of collagen |
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| integumentary glands (exocrine) |
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Definition
| arise from glandular epithelial tissue BUT drop down into dermis |
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Definition
• Binds skin to underlying layers, insulates and cushions SO it’s not really part of the skin (just does binding)
• Subcutaneous adipose tissue (females have a thicker hypodermis than males ~8%)- function of adipose is to insulate, protect, store energy- SKINFOLDS here |
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| loose (areolar) CT, some collagen and elastin |
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| vascularity of hypodermis |
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Definition
| Is vascular(larger blood vessels, which feed to capillaries in dermis) |
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-melanin
-carotene
-hemoglobin |
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| melancholy- dark- black bile |
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– Made from a single amino acid (tyrosine)
– Albinos are missing the enzyme tyrosinase
– Range of color: yellow to reddish brown to black |
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| protects against UV radiation (if cells damaged, results in melanoma- cancer) |
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– Yellow-orange pigment
– Lipid substance made from cholesterol,found in stratum
corneum and fatty tissue of hypodermis |
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– In RBCs in vessels
– Gives skin pink and blue tones
– PROTEIN with iron, which picks up O2 |
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-Derive from epidermis and extend into dermis
• Hair |
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– Flexible strand made of dead, keratinized cells
• Keratin is hard
• 3 layers
– Made up of shaft and root |
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| medulla, cortex, and cuticle |
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– Hair pigment is made by melanocytes in hair follicle
and transferred into root, produces colors – black,
brown, red, blond
– White/gray hair = decreased melanin production |
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- Extend from epidermis into dermis
- Deep end forms hair bulb
- Nerve endings sense touch
- hair papilla
- hair matrix
-Each follicle has a bundle of smooth muscle cells (arrector pili) – cause hair to stand on end |
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portion of dermis with knot of
capillaries that nourish, stimulate growth |
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| epithelial cells in hair bulb |
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• Vellus or terminal
• Hair grows ~2 mm per week, but can vary
• Each follicle undergoes growth cycles
• With age, hair thins when not replaced as quickly – different from pattern baldness, which is genetic |
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| body hair of children, women (fine,short) |
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| hair on scalp (longer, coarser) |
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Originate in epidermis BUT are actually located in
dermis
• Exocrine (have ducts, secretions used locally)
• Two main kinds
• Special kinds
• Sebaceous
• Sex hormonesregulate these glands- cause the teenage acne problem when the glands secrete a lot and become infected |
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| ceruminous (ear wax), mammary |
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(Latin sebum = grease)
– Occur all over body except palms, soles
– Simple alveolar, secrete oil onto hair shaft (makes skin
and hair oily)
– Oil (sebum) is waterproof (made of lipids); keeps hair
from becoming brittle and epidermis from cracking |
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Definition
-in latin sudor means sweat(blood filtrate; 99% H2O;salt)
- Excrete sweat onto skin surface |
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excrete sweat onto skin surface
general |
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Definition
– Most numerous on palms, soles, axillary and pubic regions, and forehead
-2 types:
*eccrine(more numerous)
*apocrine (larger) |
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eccrine (more numerous)
function |
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Definition
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eccrine (more numerous)
location |
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Definition
| all over body (palms, soles, forehead) |
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eccrine(more numerous)
general |
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Definition
| simple tubular gland, coiled-releases sweat through pores |
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apocrine (larger)
location |
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apocrine (larger)
general |
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-special sweat that also contains fat and proteins
-inactive until puberty |
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aporcine (larger)
function |
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| sexual attraction (smell- body oder) |
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• Scale-like modification of epidermis made of hard keratin
• Free edge, body, root, nail bed
• Pink appearance due to capillary network of dermis underneath |
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skin disorders
1st degree burn |
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Definition
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skin disorders
2nd degree burn |
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Definition
epidermis and upper part of dermis
damaged |
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skin disorders
3rd degree burn |
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Definition
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skin disorders
basal cell carcinoma |
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Definition
| least malignant and most common, arises in stratum basale |
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skin disorders
Squamous cell carcinoma |
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Definition
| arises from stratum spinosum |
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| most dangerous, melanocytes |
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