9- Corneal Metabolism And UV Absorption Flashcards
What are some considerations with glucose metabolism in the cornea
Source of glucose
O2 availability
What are the active pathways in the glucose metabolism in the cornea
Glycolysis Krebs HMP shunt ETC Glycogen storage
What causes metabolic distress in the cornea
Low O2
What does most of the glucose come from?
Aqueous humor
What is the minor source of glucose?
Tears
Limbaugh capillaries
Where can glucose be derived from?
Glycogen in the EPITHELIUM
How many ATP are made in the Krebs and ETC
36 ATP from 1 glucose
Where does the epithelium get its oxygen from
Limbus
Pre-corneal tear film (atmosphere)
Where does the endothelium gets its O2 from?
Aqueous humor
What is aerobic condition
Normal O2 levels
What is anaerobic condition
Reduced O2, restricts metabolism
What pathway is very important in the cornea
HMP shunt
What is the HMP shunt needed for
Regeneration of new corneal epithelial cells that are constantly being produced
What does the HMP shunt produce
Intermediates for nucleotide production
And amino acid formation
What affect does hypoxia cause?
Pyruvate is converted to lactic acid
What affect does lactic acid have?
Diffuses to stroma, causes stress, stromal swelling
What affect does stromal swelling have
Halos and rainbows
Increased glare sensitivity
Decreased CS
What can cause corneal hypoxia
Contact lenses
Sleeping
What is photokeratitis?
Eye damage from UV radiation exposure
What affect does low level UV exposure have in the cornea
Inhibit mitosis
What effect does medium level UV exposure have in the cornea
Swollen nuclei and cell death
What affect does extreme level UV exposure have on the cornea
Sloughing of epithelium
At the higher levels of UV damage this molecule contributes to the damage
O2
UV damage causes these to form
Thymine dimers
How are thymine dimers repaired?
- Exinuclease cuts on wither side of damage
- Removal of damaged area
- Gap filled in by Pol1
- DNA lipase seals the nick
What are DNA repair molecules in eukaryotes
Pol beta and epsilon
What is xeroderma pigmentosum?
What are the symptoms?
A rare genetic disorder caused by DNA exinuclease deficiency.
Symptoms: skin damage (increased risk of cancer), eye lid scarring, corneal ulcerations
