Skin Lipid Structure Lec 2 Flashcards
What is in the lipid barrier?
intercellular lipids surrounding corneocytes, it is multilamellar and anchored covalently to corneocyte, has ceramides, cholesterol, fatty acids in a 1:1:1 ratio, and has a broad narrow broad pattern.
Epidermal Lipids
covalently-bound lipids, attached to π-sheet on Cell Envelope that surrounds dead corneocytes. They are attached to involucrin protein in envelope, and π-Hydroxy ceramides and fatty acids.
What is the process of lipid processing in the epidermis?
The intercellular lipids are primarily generated from exocytosis of lipid-containing granules called lamellar bodies during the terminal differentiation of the epidermal keratinocytes. The lipid granules originate from the golgi. This primarily occurs at the granular layer/stratum corneum interface.
Where are phospholipids found?
In basal and granular cells. not tolerated in stratum corneum.
What happens when covalently bound ceramides are reduced with UV exposure?
TEWL (trans epidermal water loss) is increased.
Metabolic Activity in the stratum corneum
Conversion of phospholipids to fatty acids and glucosyl ceramides to ceramides, hydrolysis of desmosomes to slough off SC, conversion of cholesterol sulfate to cholesterol, and filaggrin to NMF.
Pro-barrier lipids for barrier function
Glycolipids, free sterols, and phospholipids
Catabolic enzymes for desquamation
acid phosphatase, proteases, lipases, and glycosides.
pH of skin
~5.0 in upper layers as it is dehydrated, ~7.3 in more hydrated lower layers.
What happens when the conversion of glucosyl ceramides to cerimides is inhibited?
The barrier is disrupted.
Friberg Model
combined all epidermal and surface lipids in proportions found in skin plus 32% water. This made a milky emulsion. Then they adjusted to skin pH of 5.
Key findings in friberg model
The structure is liquid crystalline, could be lamellar or haxagonal structure but multese crosses were sen. These results suggest that a fatty acid/soap is the basis of the layered structure.
How do lipids in SC exist?
in phases, and the individual lipids can move around depending on hydration/dehydration
Requirements of actual lipid structure
Flexibility to mechanical stress, barrier to water transport, barrier to penetration of foreign substances, resistance to environmental insults, resistance to phase separation, and resiliency when challenged.
Lamellar phases of Stratum Corneum
Can be LC, gel, or Orthorhombic Crystal, but double bonds are not conducive to Orth, so there is a mixture. At room temp, more OC, but less at 32 degrees, as well as more OC at bottom of SC
What is required for formation of the LLP (long lamellar phase)?
Ceramide 1 with linoleic acid extension
What is required for formation of SLP (short lamellar phase)?
Fatty acid
What stabilizes the LLP and SLP from phase separation?
Cholesterol
Wertz/Downing Stacked Monolayer Model
ceramides open up depending on amount of dehydration to form the different βlayersβ
Forsling Domain mosaic Models
Coexistence of a gel domain surrounded by liquid crystalline grain borders
Norlen Single Gel Phase Model
In the presence of water, ceramide does not exhibit splayed chains, and the phase is swelled.
Lipids in Atopic skin
Contain reduced amounts of reduced FAs and ceramide-1. The barrier is amorphous and too liquid because the barrier lipid is too fluid.
Ichthyosis
Reduction in free FA and ceramide-1, consistant with tendency to be enriched in hexagonal packing, with too fluid lipids.
