Biochemistry and Metabolism- Cornea Flashcards
How is corneal avascularity maintained
soluble vascular endothelial growth factor receptor 1
Where do corneal stem cells exist
Corneal stem cells repopulate the desquamating epithelium. Recent research suggests that corneal stem cells exist in the central cornea as well as at the limbus.
How does cornea get its oxygen supply
Because of the lack of blood vessels in the cornea, oxygen is provided to the cornea via the precorneal tear film, or tear film (which obtains oxygen from the air and eyelid vasculature), and aqueous humor. The stroma receives glucose primarily from the aqueous humor by carrier-mediated transport through the endothelium; the epithelium receives glucose by passive diffusion through the stroma and from the tear film.
How is glucose metabolised in the cornea
- hexose monophosphate (HMP) shunt
- tricarboxylic acid (TCA) cycle
- glycolysis
Components contributing to optical properties of cornea
Similar to enzyme crystallins of the lens, both aldehyde dehydrogenase and transketolase are thought to contribute to the optical properties of the cornea
What percentage of the corneal thickness does the epithelium contribute?
5-10%
What are palisades of Vogt
The limbus is characterized by stromal invaginations known in humans as the palisades of Vogt
Function of Palisades of Vogt
- protects stem cells from traumatic and environmental insults
- allows epithelial–mesenchymal interactions
- provides access to chemical signals that diffuse from the rich underlying vascular
network
Which type of molecule poorly penetrates cornea
Hydrophilic molecules penetrate the epithelium poorly, but they may pass through tight junctions if the polar molecule has a mass lower than 500 Da
What collagen fibres are in Bowman layer
randomly packed type I and type V collagen fibers that are 30 nm in diameter
Can bowman layer regenerate
It is acellular and does not regenerate when damaged
What percentage of the corneal thickness does the stroma contribute?
approximately 90% of the total corneal thickness
What collagen fibres are in stroma
Type I is the major collagen component of the corneal stroma. normal adult corneal stroma also contains collagen types V, VI, VII, XII, and XIV
Which collagen type is associated uniquely with stromal wound healing
type III collagen
After collage, what are the second most abundant biological constituents of the cornea
proteoglycans constitute approximately 10% of the dry weight of the cornea and confer hydrophilic properties to the stroma.They are glycosylated proteins with at least 1 glycosaminoglycan (GAG) chain covalently bound to the protein core. GAGs are composed of repeating disaccharides.
