The skin accounts for ____% of body weight
7%
What are the 3 layers of the skin from superficial to deep? What type of tissue are they?
epidermis: keratinized stratified squamous epithelium
dermis: connective tissue
hypodermis: areolar and adipose connective tissue
Functions of the skin?
- protection: cushions organs and protects from chemicals, H2O loss, UV radiation, and bumps
- regulation of body temp.
- excretion: urea, salts, and H2O lost through sweat
- absorption: vitamins, lead, mercury, poison ivy/oak
- production of vitamin D
- sensory reception: keeps us aware of conditions at body’s surface
The epidermis is composed of_________ and _______
90% keratinocytes
10% melanocytes
Where are keratinocytes located? What are their functions?
- located at stratum spinosum and dead at skin surface
- produce keratin for protection
Where are melanocytes located? What are their functions?
- located at stratum basale
- manufacture and secrete melanin
What are the layers of the epidermis (top to bottom)?
- Stratum corneum (cornified layer)
- Stratum lucidum (clear layer)
- Stratum granulosum (granular layer)
- Stratum spinosum (spiny layer)
- Stratum basale (basal layer)
Stratum corneum
- 25-30 cell layer thick of dead keratinocytes (keratin)
- continuously shed/ dandruff
- protects skin from abrasions and penetration
Stratum lucidum
- occurs in thick skin on palms of hands and soles of feet
- composed of a few rows of flat, dead keratinocytes
Stratum granulosum
- 1-5 layers of flat dying keratinocytes
- contains granules that release waterproofing glycolipid
Stratum spinosum
- 8-10 cell layers thick
- some mitosis
- contains thick bundle of intermediate filaments
- contains star shaped Langerhans cells; macrophage
Stratum basale
-attached to underlying dermis
-cells actively divide; single row of youngest keratinocytes
-contains melanocytes
~secrete melanin
Callus vs. blister
- thickening of epidermis due to repeated friction
- separation of epidermis from dermis by fluid filled pocket
What is psoriasis?
- autoimmune skin disorder
- keratinocytes divide and move more quickly through epidermis
- cells pile up on surface and resemble flaky silvery scales
Process of epidermal growth
- stem cells divide and produce keratinocytes
- they are then pushed to the surface and fill with keratin
- 4 week process
- 30-40k shed/ minute
What is the purpose of the dermis? What are its layers?
- strong and flexible connective tissue that is richly supplied with nerves and blood vessels
- holds body together like a body stocking
-papillary and reticular layer
What type of tissue is the papillary layers composed of?
areolar connective tissue
Functions of the papillary layer?
- anchors epidermis to dermis
- contains capillaries that feed epidermis
- increase SA for exchange of gases, nutrients, and waste
How are finger/palm/footprints formed?
the papillae lie on dermal ridges which elevate epidermis to epidermal ridges
What type of tissue is the reticular layer composed of?
DICT with thick interlacing collagen and elastic fibres
Functions of the reticular layer?
- provides strength, extensibility, and elasticity to skin
- gives stretch and recoil properties to skin
What happens with extreme stretching of skin?
-collagen fibres in the dermis tear causing pink/ white scars (stretch marks)
What type of tissue is the hypodermis layer composed of?
areolar and adipose connective tissue
Functions of the hypodermis layer?
- anchors skin to underlying structures
- helps insulate the body and protect against skin infections
