Corneal Metabolism (M1)

Question 1

What does the endothelium use its energy on? 1. The stroma? 2. The epithelium? 3

Answer 1

1. maintain pump function
2. Maintenance/production GAGs and collagen fibrils
3. Mitosis and migration of epithelial cells.

Question 2

What provides the main source of glucose for the entire cornea (90%)?

Answer 2

aqueous humor?

Question 3

What is the major transporter of glucose into corneal cells?.

Answer 3

GLUT1

Question 4

What are the three ways glucose is utilized in the cornea?

Answer 4

1. Anaerobic glycolysis (85% of corneal glucose utilization)
2. Aerobic glycolysis (Krebs/Citric acid cycle/TCA + Oxidative phosphorylation [Ox. Phos.])
3. Hexose-Monophosphate Shunt (HMS)

Question 5

What is glucose metabolism dependent on?

Answer 5

partial pressure of oxygen

Question 6

Where does TCA/Ox. Phos. occur? 1. What is required? 2

Answer 6

1. mitochondria

2. oxygen

Question 7

What does the citric acid cycle (TCA) produce?

Answer 7

2 net ATP (8 NADH,2 FADH2 6 CO2)

Question 8

What does glycolysis produce?

Answer 8

2 ATP, 2 NADH, 2 3-Carbon pyruvic acid

Question 9

How much ATP does each FADH2 produce? 1. Each NADH? 2

Answer 9

1. two

2. two

Question 10

How much ATP does aerobic metabolism produce? 1. Anaerobic? 2

Answer 10

1. 36

2. 2

Question 11

What are the two functions of the Hexose Monophosphate Shunt (HMS)
?

Answer 11

1. Produces NADPH used in synthesis of lipids and to limit reactive oxygen species generated by aerobic glycolysis
2. Produces ribose-phosphate, needed for nucleic acid (RNA and DNA) synthesis.

Question 12

What are the two functions of the Hexose Monophosphate Shunt (HMS)
?

Answer 12

1. Produces NADPH used in synthesis of lipids and to limit reactive oxygen species generated by aerobic glycolysis
2. Produces ribose-phosphate, needed for nucleic acid (RNA and DNA) synthesis.

Question 13

What facilitates lactate movement into the aqueous?

Answer 13

monocarboxylate cotransporters (MCTs)

Question 14

What determines type of GAG production?

Answer 14

NAD:NADH ratio

Question 15

When low O2 (NADH:NAD toward NAD) what GAG is produced?

Answer 15

Keratan

Question 16

When high O2 (NADH:NAD toward NADH) what GAG is produced?

Answer 16

Dermatan

Question 17

When the eye is closed what happens to the [HCO3-] is tears?

Answer 17

goes down in tears

Question 18

What happens in people when climbing to high elevations? and why?

Answer 18

corneal edema Due to a decrease in atmospheric pO2 which increases anaerobic metabolism and therefore [lactate]

Question 19

What is considered the minimum level of O2 exposure at corneal surface to prevent physiological changes?

Answer 19

74 mmHg

Question 20

What are the minimum Dk/t values to prevent anoxia throughout the entire corneal thickness when the eye is closed? 1. open? 2

Answer 20

1. 35

2. 125

Question 21

What is an early sign of epithelial hypoxia?

Answer 21

Epithelial microcysts

Question 22

What occurs due to the differential swelling of the posterior versus anterior stroma? 1. When does this happen? 2

Answer 22

1. Stromal Striae

2. stromal edema >~6%

Question 23

What occurs due to the differential swelling of the posterior versus anterior stroma? 1. When does this happen? 2

Answer 23

1. Stromal Striae

2. stromal edema >~6%

Question 24

What occur within minutes of contact lens wear, but of no known pathological consequence?

Answer 24

Endothelial blebs

Question 25

What is typically seen over long periods of contact use?

Answer 25

Endothelial polymegethism