Ch. 5.2 Strata of the Epidermis

Question 1

Epidermis

Answer 1

AVASCULAR STRATIFIED SQUAMEOUS EPITHELIA

Nutrients diffuse from capillaries in dermis

Question 2

Keratinocytes

Answer 2

• Dominant cell of epidermis
• Body’s most abundant epithelial cell

Question 3

Thin Skin

Answer 3

• Covers most of the body surface
• Contains four layers of keratinocytes
• ~thick as a sandwhich bag (0.08mm)

Question 4

Thick Skin

Answer 4

• Palms of the hands
• Soles of the feet
• Additional 5th layer: stratum lucidum
• Thicker stratum corneum layer
• 0.5mm

Question 5

What are the layers of thick skin?

Answer 5

1. Stratum corneum
2. Stratum lucideum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale

Question 6

Stratum basale

Answer 6

• Innermost epidermal layer
• Hemidesmosomes attach to basement membrane

Question 7

stratum germinativum

Answer 7

stratum basale

Question 8

epidermal ridges

Answer 8

• Ridges formed by the stratum basale that project into the epidermis
• Adjacent to dermal papillae

Question 9

dermal papillae

Answer 9

dermal projections that project into the epidermis. The strength of attachment is proportions to SA of basement membrane.

These ridges form fingerprints.

Question 10

Basal cells (germinative cells)

Answer 10

dominate the stratum basale. Stem cells whose divisions replace the superficial keratinocytes.

Question 11

Tactile cells (Merkel cells)

Answer 11

• Found on skin surfaces that lack hair, in stratum basale.
• Sensitive to touch

Question 12

Melanocytes

Answer 12

Found in stratum basale. Produce brown skin tones (melanin). Cell processes extend into superficial layers.

Question 13

stratum spinosum

Answer 13

• “Spiny layer” - chemicals shrunk the cytoplasm of keratinocyte, leaving cytoskeletal elements
• Superficial to stratum basale.
• 8-10 layers of keratinocytes bound together by desmosomes.
• Generated from one of the daugher cells of dividing stem cells in stratum basale
• Cells continue divide, increasing thickness

Question 14

Cells of the stratum basale

Answer 14

1. Merkel cells (hairless skin)
2. Melanocytes

Question 15

Cells of stratum spinosum

Answer 15

dendritic (langerhans) cells

1. Defense against microorganisms that penetrate superficial layers
2. Defend against superficial skin cancers

Question 16

stratum granulosum

Answer 16

• “grainy layer”
• 3-5 layers of keratinocytes derived from stratum spinosum
• Most stop dividing at this layer
• Begin making large amounts of kertain and keratohyalin
• Makes cells thinner and flatter, less permeable

Question 17

keratin

Answer 17

• a fibrous protein in stratum granulosum
• basic component of skin and nails

Question 18

keratohyalin

Answer 18

Found in stratum granulosum. Forms dense cytoplasmic granules that promotes:

• dehydration of cells
• aggregation/cross-linking of keratin fibers to lock cells together
• organelles disintegrate, cells die

Question 19

stratum lucidum

Answer 19

• “clear layer”
• Covers stratum granulosum
• Cells are flattened, densely packed, devoid of organells, filled with keratin

Question 20

stratum corneum

Answer 20

• 15-30 layers of keratinized cells
• 7-10 days for cells to move from stratum basale to stratum corneum

Question 21

kertainization (cornification)

Answer 21

• the formation of protective superficial layers of cells filled with keratin
• Occurs on all exposed skin surfaces except anterior to eyes
• Dead cells tightly linked by desmosomes

Question 22

Insensible perspiration

Answer 22

• Water from interstitial fluid slowly penetrates to surface, evaporates into surrounding air
• Unable to see or feel this water loss
• ~500 mL (1 pint)/ day

Question 23

Sensible perspiration

Answer 23

• Produced by active sweat glands
• If stratum corneum is damaged, insensible perspiration skyrockets. Complication of bruns and xerosis

Question 24

blisters

Answer 24

Fluid accumulation. Damage breaks connection between superficial and deeper layers of epidermis, or between epidermis and derms if the basement membrane is damged.

Question 25

xerosis

Answer 25

excessively dry skin. A condition that leads to excessive insensible perspiration and fluid loss.