Corneal Metabolism And UV Absoprtion

Question 1

Considerations of glucose metabolism in the cornea

Answer 1

Glucose source

O2 availability

Question 2

Active pathways of glucose metabolism in the cornea

Answer 2

• glycolysis
• TCA/Krebs cycles
• HMP shunt
• ETC
• glycogen storage

Question 3

Metabolic distress in corneal metabolism

Answer 3

Low O2

Question 4

Where does most glucose come from

Answer 4

Aqueous humor

Question 5

Where is the glucose from the aqueous humor supplied to

Answer 5

Epithelium and endothelium

Question 6

Where is a minor supply of glucose to the cornea from

Answer 6

Tears and limb always capillaries

Question 7

In what corneal layer can glucose be derived from glycogen

Answer 7

Epithelium

Question 8

During glycolysis, 1 glucose molecule will produce

Answer 8

• a net gain of 2 ATP

- 2 Peruvic acid

Question 9

During the krebs cycles and ETC complete oxidation _______ ATP are produced

Answer 9

36

Question 10

How many ATP produced from lipids

Answer 10

136

Question 11

Where are all the possible places the cornea can get glucose

Answer 11

Aqueous humor
Tears
Glycogen in epithelium

Question 12

Where does corneal epithelium get O2

Answer 12

Mostly from the atmospheric O2 found in the tear film

Some from the limbus

Question 13

Where does the corneal endothelium obtain O2

Answer 13

From the aqueous humor

Question 14

Aerobic condition

Answer 14

ETC

Normal environment with adequate O2

Question 15

Anaerobic condition

Answer 15

Only glycolysis

Reduced O2, requires restricting metabolism

Question 16

What is needed for corneal regeneration

Answer 16

Need DNA, AA, fatty acids. The primary reason of moderate activity in the cornea is because it is constantly regenerating

Question 17

When is lactate produced

Answer 17

Anaerobic metabolism

Question 18

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

Answer 18

HMP shunt

Question 19

What does the HMP shunt do

Answer 19

• Produce intermediates for nucleotide production, used n DNA replication
• produce some amino acids

Question 20

HMP shunt and ATP

Answer 20

Less ATP produced in contrast to that from the ETC, but important biomolcules are generated

Question 21

Reduced O2 levels int he cornea

Answer 21

Can restrict metabolism to anaerobic glycolysis

Question 22

Lactate in the cornea

Answer 22

• diffuses into the stroma
• causes osmotic stress
• induces epithelial and stromal edema

Question 23

Clinical complaints of lactate in the cornea (low O2)

Answer 23

• halo and rainbow type visual anomoles
• increased glare
• decrease CS

Question 24

Chronic effects of reduced O2 in cornea

Answer 24

• corneal edema
• Limbal redness
• vascular response
• epithelial microcysts
• endothelial plymegethism

Question 25

What might be some different causes of lack of O2 in the cornea

Answer 25

CL wear abuse | Sleep

Question 26

A painful eye condition caused by exposure of insufficiently protected eyes to the UV rays from either natural or artificial sources

Answer 26

Photokeratitis or UV keratitis

Question 27

What wavelengths can cause photokeratitis

Answer 27

Less than 400nm

Question 28

What wavelengths damage the epithelium

Answer 28

Shorter wavelengths

Question 29

What wavelengths damage the endothelium and the more posterior ocular structures

Answer 29

Longer wavelengths

Question 30

Low level exposure to UV in the cornea

Answer 30

Inhibited cell mitosis

Question 31

Medium to high level exposure of UV to the cornea

Answer 31

Swollen nuclei and cell death

Question 32

Extreme level exposure of UV to the core an

Answer 32

Complete sloughing of epithelial cells At higher levels of damage, O2 contributes to the damage

Question 33

UV light damage causes what to DNA

Answer 33

Pryrimidine dimers | -usually thymine dimers

Question 34

DNA repair

Answer 34

- 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

Question 35

Zero dream pigmentosum

Answer 35

Deficiency in the excision endonuclease and a reduced ability to repair damage from UV light and other effectors

Question 36

What is xeroderma pigmentosum a defect in

Answer 36

Excision endonuclease

Question 37

Symptoms of xeroderma pigmentosum

Answer 37

- increased risk of cancer - eye lid scarring - corneal ulceration