stratum corneum

Vikhyati Patel15MCT111

SEM IICE-1 of PDCF

STRATUM CORNEUM

2

CONTENT

3

PERMEATION BARRIER• Stratum corneum is the horny layer of

the epidermis.• Acts as the primary permeability

barrier of the skin.

"Delivery system Handbook for personal care and cosmetic products", Meyer R. Rosen, William Andrew Publishing, NY. USA, 2005 edition, Skin physiology and penetration pathway- Stratum corneum.

4

ULTRA-STRUCTURE• Corneocytes: cell of this layer.• Corneocytes are hexagonal or pentagonal in shape; aligned and stacked like plates.• Intercellular spaces of the stratum corneum contain many stacked membranous structures.• Membrane lipids are organized into trilaminar units


5

• The abundant lamellar arrangement include ones with three, six and nine lucent band pattern.

• The three band pattern is mainly seen between the ends of the adjacent Corneocytes.

• Six-band pattern is found between the broad, flat surfaces of adjacent Corneocytes.

• Nine-band pattern contain 3 broad-narrow-broad lucent band units.

• The first lucent band adjacent to the electron-dense protein band of the cornified envelope is covalently attached lipids.

• The paired bilayer are attached by edge-to-edge fusion of flattened lipid vesicles extruded from the lamellar granules.

• The narrow lucent band bands in the centre of the nine-band pattern is formed by the eversion of the linoleate chains from acyl ceramide molecules in the adjacent lamellae to form a zipper-like central narrow lamella.

• "Delivery system Handbook for personal care and cosmetic products", Meyer R. Rosen, William Andrew Publishing, NY. USA, 2005 edition, Skin physiology and penetration pathway- Stratum corneum.

• https://books.google.co.in/books?id=As1eHSlUIggC&pg=PA83&lpg=PA83&dq=linoleate+chains+in+stratum+corneum+ultrastructure&source=bl&ots=b-Sj5wPMSh&sig=UQjFPpF5UxlDreFAsJwpuuSIoA&hl=en&sa=X&ved=0ahUKEwi9v6GQgqLKAhWBbY4KHfWmA9QQ6AEIHjAA#v=onepage&q=linoleate%20chains%20in%20stratum%20corneum%20ultrastructure&f=false

6

STRUCTURAL PROTEINS OF SC• Keratin is the major structural protein of SC.• They are a type of intermediate filament.• There are approximately 30 different keratin genes.• 50% code for Type I Acidic keratin• 50% code for Type II Neutral-Basic keratin polypeptide. acidic-basic genes heteroduplexes building blocks for keratin fibres


7

• At the end of the differentiation, proteins are deposited at the cell periphery-

Involucrin Envoplakin Periplakin• 80% of the protein I the epidermal cornified envelope

is loricrin.• There are two linkages- 1. Isopeptide linkages 2. Disulphide linkages between envelope proteins• The cross-linked proteins of the envelope is 10-12nm.• Covalently bound lipids are 4-5nm thick.• Epidermis keratin filaments are anchored to the

cytoplasmic sides of the desmosomes through specialized adapter proteins.

• This network provides physical strength to the epidermis and important in the dissipation of shearing forces.

• Desmosomes are made up of three protein families: cadherins, plakins, armadillo.


8

MODELS1. TWO COMPARTMENT MODELS:o Bricks-and-mortar modelo Impermeable, keratin-filled cells.o Cells embedded in continuous lipid phaseo Corneocytes= brickso Lipids= mortaro Provides tortuous pathway.o Hence helps in skin barrier function.

• "Delivery system Handbook for personal care and cosmetic products", Meyer R. Rosen, William Andrew Publishing, NY. USA, 2005 edition, Skin physiology and penetration pathway- Stratum corneum.

• http://www.medscape.org/viewarticle/473453_1

9

2. Domain Mosaic model• Ceramides or free fatty acids are rod-like

or cylindrical in shape.• Therefore, they form relatively

impermeable, membrane domain.• Cholesterol fluidize the stratum corneum

membrane.• This model was proposed by Forslind.• Gel phase domain are embedded in in a

continuous liquid crystalline phase.• Penetrants diffuse primarily through the

liquid crystalline phase.


10

2. Single- gel phase model• Lamella have low water content

and low lipid mobility due to close packing of the lipid chains.

3. Sandwich model• Based on molecular geometry.• Outer two lamellae of tri-

lamellar membrane unit are in the gel phase while central lamella in liquid crystalline state.


11

STRATUM CORNEUM LIPIDS• In epidermal SC, lipids

compromise 10-15% of the dry weight of the tissue.

• Ceramides (50%), cholesterol (25%) and saturated fatty acids (10%) are the principle lipids of SC.

• Cholesterol esters, cholesterol sulphate, glycosylceramides are present in minor amounts.

• Pig skin is excellent model for human skin.


12

CERAMIDES• Structurally heterogeneous.• Nomenclature was proposed by Motta,

et. Al• Base is designated as S: Sphingosine,

P: phytosphingosine or H:6- hydroxysphingosine.

• Amide- linked fatty acid are designated as N: normal fatty acid, A: α-hydroxyacid or O: ω-hydroxyacid.

• Ester-linked fatty acid is designated with prefixed E.

• Least polar is CES EOS.


13

• CER-EOS: 34- carbon ω- hydroxyacid amide-linked to sphingosine bases with linoleic acid ester- linked to the ω- hydroxyl group.

• CER-NS: linked to sphingosine and dihydroxysphingosine bases.

• CER-NP: similar to CER-NS but linked to phytosphingosine bases.

• CER-EOP: minor component and is a phytosphingosine containing variant acyl- ceramide.

• CER-AS: short C16 and long C24-28 α-hydroxyacid amide. They are linked to sphingosines and dihydroxysphingosine.


14

CHOLESTEROL• Sterol found in porcine and

Human stratum corneum.• Widely distributed

membrane component.• It either increases or

decreases membrane fluidity, depending on proportion of cholesterol.

• Variation in fluidity has major impact on molecular diffusion across the membranes.


15

FATTY ACIDS• Contains aliphatic chains longer than 18C• They are entirely saturated chains.• Fatty acids that are abundant are generally 22-24C entities.• Fatty acids and cholesterol sulphate are ionizable lipids in Stratum

corneum. Therefore, they are important for formation of lamellae.• These impart negative charge to the skin surface, which results in

trapping of any cationic substances.


16

THANK YOU!

stratum corneum

Science