Corneal Metabolism And UV Absoprtion Flashcards
Considerations of glucose metabolism in the cornea
Glucose source
O2 availability
Active pathways of glucose metabolism in the cornea
- glycolysis
- TCA/Krebs cycles
- HMP shunt
- ETC
- glycogen storage
Metabolic distress in corneal metabolism
Low O2
Where does most glucose come from
Aqueous humor
Where is the glucose from the aqueous humor supplied to
Epithelium and endothelium
Where is a minor supply of glucose to the cornea from
Tears and limb always capillaries
In what corneal layer can glucose be derived from glycogen
Epithelium
During glycolysis, 1 glucose molecule will produce
- a net gain of 2 ATP
- 2 Peruvic acid
During the krebs cycles and ETC complete oxidation _______ ATP are produced
36
How many ATP produced from lipids
136
Where are all the possible places the cornea can get glucose
Aqueous humor
Tears
Glycogen in epithelium
Where does corneal epithelium get O2
Mostly from the atmospheric O2 found in the tear film
Some from the limbus
Where does the corneal endothelium obtain O2
From the aqueous humor
Aerobic condition
ETC
Normal environment with adequate O2
Anaerobic condition
Only glycolysis
Reduced O2, requires restricting metabolism
What is needed for corneal regeneration
Need DNA, AA, fatty acids. The primary reason of moderate activity in the cornea is because it is constantly regenerating
When is lactate produced
Anaerobic metabolism
Important for the production of a variety of components required for the rapid regeneration of new corneal epithelial cells that are constantly being produced. Acquiring these components from the vasculature is very limited
HMP shunt
What does the HMP shunt do
- Produce intermediates for nucleotide production, used n DNA replication
- produce some amino acids
HMP shunt and ATP
Less ATP produced in contrast to that from the ETC, but important biomolcules are generated
Reduced O2 levels int he cornea
Can restrict metabolism to anaerobic glycolysis
Lactate in the cornea
- diffuses into the stroma
- causes osmotic stress
- induces epithelial and stromal edema
Clinical complaints of lactate in the cornea (low O2)
- halo and rainbow type visual anomoles
- increased glare
- decrease CS
Chronic effects of reduced O2 in cornea
- corneal edema
- Limbal redness
- vascular response
- epithelial microcysts
- endothelial plymegethism
What might be some different causes of lack of O2 in the cornea
CL wear abuse
Sleep
A painful eye condition caused by exposure of insufficiently protected eyes to the UV rays from either natural or artificial sources
Photokeratitis or UV keratitis
What wavelengths can cause photokeratitis
Less than 400nm
What wavelengths damage the epithelium
Shorter wavelengths
What wavelengths damage the endothelium and the more posterior ocular structures
Longer wavelengths
Low level exposure to UV in the cornea
Inhibited cell mitosis
Medium to high level exposure of UV to the cornea
Swollen nuclei and cell death
Extreme level exposure of UV to the core an
Complete sloughing of epithelial cells
At higher levels of damage, O2 contributes to the damage
UV light damage causes what to DNA
Pryrimidine dimers
-usually thymine dimers
DNA repair
- UV specific endonuclease (exinuclease)
- cuts DNA on both sides of damage
- removes damaged region
- gap filled in by repair DNA polymerase
- DNA ligament seals backbone
Zero dream pigmentosum
Deficiency in the excision endonuclease and a reduced ability to repair damage from UV light and other effectors
What is xeroderma pigmentosum a defect in
Excision endonuclease
Symptoms of xeroderma pigmentosum
- increased risk of cancer
- eye lid scarring
- corneal ulceration
