epidermis

epidermis

(avascular) stratified squamous epithelium. nutrients and oxygen diffuse from capillaries in the dermis

keratinocyte

body’s most abundant epithelial cell. contains large amounts of keratin

thin skin

4 layers of keratinocytes; covers most of body

basale, spinosum, granulosum, corneum

britney spears grows corn (not my best work tbh)

thick skin

5 layers of keratinocytes; covers palms and soles

basale, spinosum, granulosum, lucidum, corneum

britney spears gave lebron candy (??? idk)

stratum basale

attached to basement membrane by hemidesmosomes.

• form strong bond between epidermis and dermis

• contains epidermal ridges

• lie next to dermal papillae in dermis

• has many basal/germinative cells

• tactile discs

• melanocytes

germinative cells

stem cells that replace superficial keratinocytes

tactile discs

tactile (merkel) cells with sensory nerve endings that respond to touch. found in hairless skin

stratum spinosum (spiny layer)

8-10 layers of keratinocytes bound by desmosomes. produced by cells dividing in stratum basale, some of which continue dividing. contains dendritic (langerhans) cells

langerhans cells

bone derived dendritic cells that are active in immune response

stratum granulosum (granular layer)

3-5 layers of keratinocytes produced from cells of stratum spinosum. most cells stop dividing and start to produce keratin and keratohyalin. after protein production, cells die

keratin

tough, fibrous protein

keratohyalin

forms dense granules. promotes cellular dehydration and cellular fiber cross linking.

stratum lucidum (clear layer)

found only in thick skin and covers stratum granulosum. cells are flat, lack organelles, and are filled with keratin.

stratum corneum (horny layer)

exposed surface of skin that is water resistant.15-30 layers of keratinized cells. new cells move from SB to SC in 7-10 days, and exposed cells are shed after 2 weeks

keratinization

formation of protective layers of cells filled with keratin

insensible perspiration

water diffuses across stratum corneum and evaporates from skin; ~500 mL/day lost.

rate increases if stratum corneum is damaged

sensible perspiration

water excreted by sweat glands

epidermal growth factor (EGF)

peptide growth factor produced by salivary glands and duodenum, used in labs to grow skin grafts

function of EGF

• promotes division of basal cells

• accelerates keratin production

• stimulates epidermal repair and glandular secretion