unit 3 - integumentary system

adult skin surface area

1.5-2m² (15%) of body mass

2 layers of the skin

• epidermis = stratified squamous epithelium

• dermis = connective tissue

  • underneath = hypodermis (mostly adipose)

skin thickness

• varies around the body (average = 1-2 mm)

  • thinnest = eyelid (0.5 mm)

  • thickest = btwn shoulder-blades (6 mm)

• **when ppl reference thick skin, they think of areas w/ mostly dead skin (soles of the feet, palms)

epidermis

• keratinized stratified squamous epithelium

  • lots of dead cells @ surface filled w/ keratin (tough protein)

  • 5 layers (upper→lower: CLGSB)

stratum basale

• single layer of cuboidal/low columnar cells on basement mem

(cells from more→less):

• keratinocytes: make keratin & frequently replace cells lost @ surface

• melanocytes: make melanin = accumulates on surface side of cell to protect (mainly DNA) from UV radiation

  • more spread out = darker skin color

• tactile (Merkel) cells: touch reception

stratum spinosum

• several layers of keratinocytes (deeper ones = constant mitosis to replace cells @ surface; cells closer to surface are thinner/flatter

• dendritic cells: capture foreign cells/invaders and present to immune system to see if a response is needed

stratum granulosum

• 2-5 layers of flat keratinocytes (last layer of living cells)

• lipid-filled vesicles release into layer to block O₂/nutrients from layers above

stratum lucidum

• thin translucent layer of dead cells

  • **mostly found in areas of thicker skin

stratum corneum

• up to 30 layers of dead, scaly, keratinized cells

• constantly flaking off as dander

fingerprints

• stratum buckles on itself & forms epidermal rings

• scars would appear as a slash thru normal pattern, and can permanently alter prints

time for cells to regenerate in epidermis

30-40 days for cell to work up from stratum basale to corneum

• slows w/ age

• speeds up w injured/stressed skin

calluses

result from mechanical stress, which speeds up keratinocyte multiplication→thicker layer of dead cells (more protection)

dermis

• 0.2-4 mm thick

• connective tissue

  • collagen fibers (majority, tough/flexible)

  • reticular fibers (thinner, similar to collagen fibers)

  • elastic fibers (stretches/recoils)

  • fibroblasts (cells which secrete collagen)

• also includes:

  • blood vessels, sweat glands, sebaceous (oil) glands, hair follicles, nail roots, sensory nerve endings, smooth muscle connected to each hair

dermal papillae

• extension of dermis into epidermis

• extends further in sensitive skin (and allows nerve endings & blood vessels to be closer to the skin)

2 zones of the dermis

• papillary layer = 1/5 thickness (near surface)

  • loose areolar tissue near papillae = more room for immune cells & to move around/capture threats

• reticular layer

  • 4/5 of dermis (deeper)

  • dense connective tissue

  • collagen forms thicker bundles (less room for ground subst)

cause of stretch marks

due to torn collagen fibers in reticular layers

• as a result of growth that’s too rapid→resultingly, fibers tear bc collagen has no stretch

hypodermis/subculaneous tissue

• areolar/adipose tissue between skin/muscle

• 8% thicker in women than men (+is distributed differently)

• **boundary btwn dermis/hypodermis isn’t always clear, but more fat/adipose = better indication of hypodermis

role:

• binding skin to underlying tissue

• cushioning/insulation

• energy reseverves

skin color

results as a combination of pigments

1. melanin: variety of hues (brown/tan/red/black)

   • varies throughout body→more spread out = darker pigment

2. hemoglobin: red in blood vessels, white of collagen fibers, pink/red of dermis

   • blood vessels closer to the surface = more influence on overall skin color

3. carotene: yellow/orange pigment that builds up as a result of diet (ex: carrots, sweet potatoes, egg yolks)

4. bilirubin: yellow/orange pigment

   • produced when breaking down red blood cells & the wastes can’t be eliminated as usual

addison’s disease

• change: patchy dark spots

• pigment: increased melanin production

• cause: damage to adrenal glands

albinism

• change: pale/white skin

• pigment: little/no melanin produced

• genetic mutation

carotenemia

• change: often on palms/soles, skin turns yellow/orange

• pigment: high levels of carotene

• cause: excessive intake of carotene-rich foods

cyanosis

• change: skin/nails/lips look blue/grey/purple

• pigment: low levels of hemoglobin

• cause: not enough oxygen flowing throughout blood

erythema

• change: red-ish/hot skin, inflammation

• pigment: increased hemoglobin

• cause: heat, increased blood flow (hyperemia), medicines, infections. pregnancy, cancer

jaundice

• change: skin/whites of eyes look yellow

• pigment: built up bilirubin

• cause: liver issues, or babies being unable to process bilirubin well enough