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opb353-qut > Lens > Flashcards

Lens Flashcards

1
Q

What are the dimension of lens? *

A

10mm equator
4mm axial

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2
Q

What is the curvature of anterior and posterior lens?

A

Anterior = 10mm
Posterior =6mm

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3
Q

What is the thickness of equator and posterior capsule*

A

Equator=20micron
Posterior=3micron

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4
Q

What are the major components of lens

A

-lens capsule
-anterior epithelial layer
-lens fiber (cortex and nucleus)

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5
Q

What are the layers of nucleus

A

Embryonic = primary lens fiber
Foetal = secondary lens fiber
Adult=after birth

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6
Q

How often is lens added*

A

5 fibers /day

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7
Q

What are suture?

A

When lens meet anteriorly and posteriorly

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8
Q

How new lens are formed*

A

Receive fibroblast growth factor stimulation

central zone
Germinative zone=lens division
Transitional zone=lens elongation

Then move anteriorly to cortex (lens bow)

Continue to loose organelle during maturation

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9
Q

Explain the process of denucleation

A

Differentiated fiber -> loss nucleus and other organelles -> mature -> filled with crystalline protein

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10
Q

Explain abnormal nucleation

A

Cells still have organelles
Vacuoles formation
Abnormal cluster of crystallin protein
Form cataracts

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11
Q

What is lens shell

A

Elongated epithelial cell that is produced at the same time

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12
Q

How many shells are added*

A

5 shells/year

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13
Q

How many lens shells are in an aged lens

A

2500 shells

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14
Q

What is suture

A

Anterior and posterior meeting point of lens fiber

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15
Q

How many points do foetal and adult lens have

A

Foetal = 3 points
Adults = 9 points

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16
Q

Why is the lens transparent*

A

-lack of nerve, vessel, and connective tissue
-optical homogeneity (smooth surface?)
-dense lens fiber packing
-no organelle
-lens is dehydrated -> no fluctuating n

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17
Q

What are amino acids that form glutathione

A

Glycine, cysteine, glutamate

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18
Q

What is the role of glutathione

A

Protect lens from antioxidant

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19
Q

How does lens protein change with age

A

-cystallin degrade -> protein accumulation -> turn soluble protein into insoluble protein

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20
Q

Why does the lens require energy?

A

-maintain dehydration and transparency
-transport ions and amino acid
-synthesize protein and lipid
-ATP give phosphate during protein snthesis

21
Q

What are metabolic pathways in “lens” *

A

-aerobic
-anaerobic
-sorbitol
-hexose monophosphate shunt

22
Q

How ATP-efficient of each metabolic pathways*

A

Anaerobic = 80% glucose, 66ATP generated
Aerobic = 3% glucose, 20% ATP
Sorbitol = 5% glucose, no ATP -> prevent development of diabetic cataract
Hexose monophosphate shunt = 15%, no ATP -> nucleic acid synthesis

23
Q

What are the axial thickness of young adults and 65 years old *

A

Young adult = 3.5 mm
65 YO = 5 mm

24
Q

What is accommodative amplitude
How accommodative amplitude change with age

A

Maximum optical power that eye can achieve when look far -> near

Decrease with age

25
Q

How age-related cataracts are formed*

A

There is an internal barrier preventing diffusion of small molecule

26
Q

Give an example of age-related cataract

A

Cuneiform Spoke Opacities

27
Q

explain how lens maintain transparency (prevent oxidation)

A

-lens epithelium synthesise Glutathione (GSH)
-GSH is the source of H+ ready for oxidation
-GSSG is reduced to be GSH with the aid of NADPH+glutathione reductase
-NADPH turns into NADP+

28
Q

according to glutathione, why aged nucleus is vulnerable to oxidative stress?

A

-low level of glutathione reductase -> GSSG don’t turn to GSH anymore
-low ratio of GSH/protein is low
-can lead to protein-protein disulphide -> water insoluble

29
Q

explain the overview of lens morphogenesis

A
  1. surface ectoderm thicken above optic vesicle
  2. form a pit -> lens pit
  3. lens pit closes -> lens vesicle
  4. cells at the back of the vesicle elongate -> primary lens fiber
30
Q

why does presbyopia occur?

A

It is harder to change the lens shape
-hardening of lens substance
-higher diameter, thickness, weight

-shift in zonular insertion points
-decrease elasticity of lens capsule

31
Q

what is the depression of lens on the vitresous surface

A

patella fossa

32
Q

what is zone of discontinuity

A

junction between lens layers

33
Q

what is the role of lens capsule

A

-maintain structural integrity
-give lens shape
-restrict molecule to go inside the lens

34
Q

properties of central zone of epi

A

-polygonal
-transport substance from aqueous into the lens
-secrete capsule material

35
Q

properties of germinative zone

A

-more cuboidal
-have interdigitation
-mitosis

36
Q

properties of transitional zone

A

-no mitosis
-more columner
-differentiate into lens fiber

37
Q

lens substance in percentage

A

35% protein, 65% water, <1% carbs and ions

38
Q

percentage of soluble and insoluble protein

A

90% soluble and <15% insoluble

39
Q

what are the types of soluble and insoluble protein*

A

soluble = alpha, beta, gamma
insoluble = cell membrane, cytoskelelton, enzyme

40
Q

soluble and non-soluble protein is predominant where

A

soluble = cortex
insoluble = nucleus

41
Q

what is the difference in alpha, beta and gamma protein

A

alpha=largest, 2nd most common
beta=most common
gamma=monomer

42
Q

what are insoluble protein responsible for

A

cytoskeleton protein = cell structure, cell mobility, cell differentiation

membrane protein = intrinsic (gap junction) and extrinsic

enzyme = ATPase, dehydrogenase

43
Q

where is the sight that mitochondria locate

A

lens epithelium

44
Q

how sorbitol is related to glucose level and diabetes

A

-sorbitol involve aldose reductase -> protect the lens from hyperglycaemia
-diabetes = too much sorbitol

45
Q

what is lens circulation of ions (current flow)

A

There is the differnce between charge of the equator and the pole -> lead to circulation of ions (out from the equator, into the pole) -> circulation of solutes

circulatio of solutes = solute can go deeper in the lens, waste can be removed easier

46
Q

why there is the current flow

A

unequal distribution of K+ channel

47
Q

what are the cations and anions in the lens*

A

cation: high K+, low Na+ (higher in cortex), Ca2+

anion: Cl-, HCO3-, PO3-, SO42-

48
Q

how epithelium ion homogenity

A

-Na+/K+ ATPase pump (Na+ out, K+ in)
-work against passive diffusion of both ions

opb353-qut (5 decks)

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