outer coat

Question 1

How do we get our o2 to our cornea when we’re sleeping?

Answer 1

• Essentially when we close our eyelid, we cut off the o2 supply. As there’s very little o2 that can diffuse through the full thickness of the eyelid. So o2 levels are reduced considerably
• The modification of the conjunctiva at that particular region is a very vascular
• The blood vessels are sitting just under the epithelium, so a very short diffusion distance

Question 2

How much o2 does the cornea need?

Answer 2

anything below 10%, the corner starts to: suffer, swollen, lose it’s transparency

Question 3

why much thinner is the cornea during waking hours vs during sleep?

Answer 3

5% thinner during waking hours than during sleep

Question 4

what is the term used to define the ‘thicker nature’ of the cornea on waking

Answer 4

overnight swelling

Question 5

what is the reason for overnight swelling?

Answer 5

• overnight oedema may be a result of reduced o2 availability or the result of changes in tear tonicity due to reduced tear evaporation
• once our eyes are closed the osmolarity of the tears is slightly higher than it is during the day. as our eyes open , a proportion of tears start to evaporate. we’re losing water & retaining salt rises & losing h20
• essentially the conc. of te
• osmolarity is the concentration of salt in a particular fluid
• during the open eye tears evaporate, creating a slight tear hypertonicity & subsequent corneal dehydration

Question 6

what are the 3 ways that glucose can be metabolised ?

Answer 6

1. Anaerobic metabolism (partially broken down)
2. Aerobic respiration (completely broken down
3. Hexose monophosphate shunt (Pentose phosphate pathway)

Question 7

explain how anaerobic respiration breaks down glucose, (is it partially or fully broken down?)

Answer 7

• partially broken down
• glucose is broken down through glycolysis into pyruvate & then lactic acid

Question 8

explain how aerobic respiration breaks down glucose, (is it partially or fully broken down?)

Answer 8

• it’s completely broken
• glucose is broken down in pyruvate going into mitochondria
  then aerobic metabolism, full oxidative phosphorylation
• glucose is completely broken down into co2 + h20

Question 9

products of anaerobic respiration

Answer 9

pyruvate + lactic acid

Question 10

products of aerobic respiration

Answer 10

co2 + h20

Question 11

does anaerobic respiration release ATP and if so how much?

Answer 11

anaerobic respiration only releases part of the ATP that is trapped within the glucose molecule

Question 12

does aerobic respiration release ATP and if so how much?

Answer 12

aerobic respiration generates significant amounts of ATP

Question 13

What is the cornea’s main energy source

Answer 13

glucose

Question 14

Why is the cornea transparent, despite being composed of collagen fibrils?

Answer 14

• Collagen fibrils are small in diameter and regularly arranged within the cornea
• as collagen fibrils have the potential to scatter light, the smaller the fibres = less light scatter
• the scattered light is eliminated through the process of destructive interference
• in order for destructive interference to happen, the cornea needs to have regularity in the spacing between the fibrils. to allow light to pass through & maximise the amount light getting through to the cornea. therefore, light scatter is eliminated through destructive inference

Question 15

what are the 3 main proteoglycans that make up the cornea ?

Answer 15

1) lumican
2) keratocan
3) mimican

Question 16

How to maintain the cornea in a relatively dehydrated state, to maintain it’s transparency?

Answer 16

1) stop the water from getting in
- by having barrier in the from+back, so the cells are linked by tight junctions, limiting the flow of water into the tissue

2) endothelial pump mechanism
- pumps ions out of stroma, to bring water from stroll side to the aqueous humour

Question 17

How the cornea responds to damage?

Answer 17

• the epithelium has a great capacity to regenerate & repair quickly
• limbal conjunctival cells are stem cells - that ultimately lead to epithelial cell regeneration
• this means that damage to the limbal stem cells or trauma on the limbus - means that the cornea loses there ability to repair itself

Question 18

how many days does it take for the corneal epithelium to replenish ?

Answer 18

7 days to completely replenish