Epidermis Flashcards
What are the four layers of the epidermis?
Stratum basale - closest to the basement membrane Stratum spinosum Stratum granulosum Stratum lucidium (in thick skin only!) Stratum corneum
Where do dividing keratinocytes reside?
They reside in the stratum basale. As they travel up the epidermis, they stop proliferating and take on barrier functions, becoming more cornified/keratinized and losing their nucleus.
What types of junctions exist between keratinocytes and the basement membrane?
Hemidesmosomes
What types of junctions exist between different types of keratinocytes?
Desmosomes.
These link keratin fibers in different keratinocytes to each other using cadherins.
What is terminal differentiation?
The process in which cells withdraw from the cell cycle and begin the processes by which they take on the unique features of a particular tissue.
What is terminal differentiation called in keratinocytes?
Keratinization or cornification
What happens during keratinization?
Outward migration/Loss of ability to proliferate
- Lipid synthesis and the formation of the permeability barrier
- Loss of the nucleus and cytoplasmic organelles
- Keratin filament aggregation
- Cornified envelope formation
- Desquamation of cornified cells
Why do keratinocytes make lipids?
To form the intercellular permeability barrier. As they move up the epidermal layers, they synthesize neutral rather than polar lipids, which help to form a hydrophobic barrier.
What are Odland (AKA lamellar) bodies?
- Lipid transport vesicles that contain “stacks” of lipids, hydrolytic enzymes, and antimicrobial peptides.
- vesicles fuse with the outer membrane, dumping their contents into the space between the stratum granulosom and stratum corneum
- most prominent in the stratum graulosum
When do keratinocytes lose their nucleus and organelles?
In the stratum granulosum before entering the stratum corneum.
How are keratin filaments formed?
In the stratum granulosum keratin intermediate filaments and fillagrin aggregate together forming bundles that are then crosslinked with disulfide bonds.
- keratohyalin bundles can be seen in the stratum granulosum
What is the cornified envelope?
A structure of crosslinked proteins that located on the inside of the plasma membrane of the cornified cell. This eventually replaces the plasma membrane and is much more resistant to external forces.
