Lipids in Skin

Question 1

structure of the lipid barrier

Answer 1

• intercellular lipids surround corneocytes in the SC
• multilamellar, anchored covalently to corneocyte envelope
• ceramides, cholesterol and fatty acids in roughly 1:1:1 molar ratio
• broad narrow broad pattern (6 and 13 nm periodicities)

Question 2

T/F: Sebum secreted from the sebaceous gland is considered part of the lipid barrier

Answer 2

FALSE: Sebum secreted from the sebaceous gland is NOT considered part of the lipid barrier

Question 3

2 types of epidermal lipids

Answer 3

covalently bound

intercellular

Question 4

covalently bound lipids charactertistics

Answer 4

• attached to involucrin protein in envelope of corneocyte
• omega hydroxy ceramides and fatty acids
• serve as anchor for lamellar structure

Question 5

intercellular lipids charactertistics

Answer 5

• superficial SC contains ceramides, cholesterol, and fatty acids in a 1:1:1 molar ratio
• multilamellar - dark and light bands show up on EM

Question 6

What happens to intercellular lipids during maturation?

Answer 6

Phospholipids are eliminated, free fatty acids produced, glucoceramides are formed and converted to ceramides, cholesterol esters are formed and converted to cholesterol

Question 7

As the SC lipids are formed, the pH _____ (increases/decreases) and the SC becomes more _____ (hydrated/dehydrated)

Answer 7

decreases

dehydrated

Question 8

How are free fatty acids and linking ceramides attached to cornified cell envelope?

Answer 8

covalently attached with omega-hydroxy ceramide

Question 9

proposed Michaels model

Answer 9

Brick and mortar 2 compartment system with heterogeneous protein and homogeneous lipid

Question 10

proposed Wertz/Downing model

Answer 10

stacked monlayer model

Question 11

proposed Friberg model

Answer 11

layered structure, lamellar liquid crystalline or hexagonal gel at normal relative humidity and skin temperature

Question 12

proposed Norlen model

Answer 12

Single gel phase

single coherent lamellar gel phase with mixtures of hairpin and splayed arrangements of ceramide 1 depending on water %

Question 13

proposed Forslind model

Answer 13

domain mosaic

coexistence of a gel domain surrounded by liquid crystalline grain borders

Question 14

proposed Bouwstras model

Answer 14

Sandwich model

a liquid sublattice is located in the center of the lipid layers surrounded by a crystalline layer on each side

Question 15

proposed Kiselev model

Answer 15

multilamellar structure with mixtures of hair pin and splayed arrangements of the ceramide 1 depending on water %

Question 16

Lipids in vivo appear to exist as a balance between what 2 states?

Answer 16

a solid crystalline (orthorhombic packing) state and a gel/liquid crystalline (hexagonal packing) state

Question 17

What is issue with too much orthorhombic solid crystal or liquid crystalline?

Answer 17

• too much liquid crystal with a disordered and fluid lattice leads to excessive penetration of hydrophobic substances and lacks rigidity
• a crystalline orthorhombic lattice is too rigid and lacks flexibility that may become leaky