Epidermis

Question 1

Describe the epidermis

Answer 1

-most superficial layer and composed of several cell types

-keratinocytes makes up 95% of epidermis

-creates keratin

-linked by desmosomes

Question 2

Epidermal strata (layers):

Describe stratum basale (stratum germinativum)

Answer 2

-closest to dermal blood supply; metabolically and mitotically active strata

-single layer of stem cells on basement membrane

-creates Vitamin D and replaces dead keratinocytes (lost from superficial layers)

Question 3

Describe stratum spinosum

Answer 3

-thickest layer and on top of stratum basale; close to blood supply; metabolically and mitotically active

Question 4

Describe stratum granulosum

Answer 4

-3 to 5 layers of cells; cytoplasmic granules with keratin bundles; secreted by exocytosis

-hydrophobic lipids give water proofing; maintains internal fluid and electrolyte homeostasis; leads to isolation and death of cells in layer and more superficial layers

Question 5

Describe stratum lucidum

Answer 5

-narrow layer of clear, dead keratinocytes; only in thick skin

Question 6

Describe stratum corneum

Answer 6

Outermost layer; several layers of dead, flattened keratinocytes with thickened plasma membrane

-filled with keratin bundles

-sloughed off or exfoliated mechanically as desmosomes holding cells together are lost

Question 7

Describe keratinocyte life cycle

Answer 7

Location and functions of epidermis subjects it to physical and environmental stress; stratum corneum sheds dead cells; must be replaced to maintain integrity of epidermis

-dead keratinocytes are replaced by mitosis in stratum basale and where spinosum has blood supply available

-keratinocytes in deeper strata divide and push cells above them into more superficial layers

Question 8

Where does keratinocyte life cycle begin

Answer 8

-begins life in stratum basale or spinosum; passes through each epidermal layer; shed from stratum corneum

-migration from deepest strata to stratum corneum takes 40-50 days to complete

Question 9

What are the other cells in the epidermis

Answer 9

Dendritic (langerhans) cells, merkel cells, and melanocytes

Question 10

Describe dendritic (langerhans) cells

Answer 10

-in stratum spinosum; phagocytes of immune system; protects skin and deeper tissues from pathogens

Question 11

Describe merkel cells

Answer 11

-oval cells scattered thru stratum basale; sensory receptors associated with small neurons in dermis

-detects light touch and discriminate shapes and textures

-large number of regions specialized for touch: fingers, lips, and base of hairs

Question 12

Describe melanocytes

Answer 12

-in stratum basale; produces melanin (protein pigment ranging from orange-red to brown-black