topic 7 crystalline lens pt 1

Question 1

what is the lens thickness and diameter?

Answer 1

4mm

10mm

Question 2

what is the anterior and posterior lens curvature?

Answer 2

10mm

6mm (steeper)

Question 3

what is the refractive power of the lens?

Answer 3

10-20D

Question 4

what are 4 features of the lens?

Answer 4

1. avascular
2. transparent
3. highly refractive
4. able to change shape

Question 5

what are the 3 layers of the lens? briefly describe them

Answer 5

1. capsule (envelops lens, acts as barrier to maintain structural integrity, moulds shape of lens)
2. epithelium (only present in ant region, single layer, cuboidal, helps to transport nutrients)
3. lens fibres (newer fibres seen in cortex, older fibres pushed yo center and form lens nucleus)

Question 6

what is the formation of lens fibres? how is the lens bow and crystallin protein formed?

Answer 6

1.cuboidal cells transformed into columnar cells at equator
columnar cells elongate to form lens fibres

2. cells lose nuclei during transformation and forms lens bow
3. displaced lens organelles from cells transform into crystallin protein

Question 7

what are the 3 characteristics of crystallin proteins?

Answer 7

1. makes up 90% of lens proteins
2. present in lens cortex
3. water soluble

Question 8

what are the 3 characteristics of albuminoids?

Answer 8

1. makes up 10% of lens proteins
2. present in lens nucleus
3. water insoluble

Question 9

what are the 3 Aas that make up glutathione? where is glutathione synthesized?

Answer 9

glycine, cysteine, glutamic acid

synthesized in lens (process req energy)

Question 10

what is the function of glutathione? what happens to the amt of glutathione when someone ages?

Answer 10

it prevents/protects the lens from oxidation damage

oxidation dmg results in decreased transparency of lens

amt of glutathione decreases w age.
increases risk of oxidation dmg and cataract

Question 11

what is the source of nutrition for the lens?

Answer 11

1. aq humour
2. vit humour

**lens is avascular hence no bld v

Question 12

what are the 4 metabolic pathways for the lens?

Answer 12

1. kerb’s cycle (aerobic)
2. anaerobic glycolytic pathway
3. hexose monophosphate shunt (anaerobic)
4. sorbitol pathway

Question 13

what are 4 changes that happen to the lens with age?

Answer 13

1. increase in lens size, diameter and thickness
2. hardening of older lens fibres in nucleus and hence loss of accommodation
3. yellowing of crystallin proteins
4. loss of lens transparency