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opb353-qut > Lens > Flashcards

Lens Flashcards

(48 cards)

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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?

Study These Flashcards
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” *

Study These Flashcards
A

-aerobic
-anaerobic
-sorbitol
-hexose monophosphate shunt

22
Q

How ATP-efficient of each metabolic pathways*

Study These Flashcards
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 *

Study These Flashcards
A

Young adult = 3.5 mm
65 YO = 5 mm

24
Q

What is accommodative amplitude
How accommodative amplitude change with age

Study These Flashcards
A

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

Decrease with age

25
How age-related cataracts are formed*
There is an internal barrier preventing diffusion of small molecule
26
Give an example of age-related cataract
Cuneiform Spoke Opacities
27
explain how lens maintain transparency (prevent oxidation)
-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
according to glutathione, why aged nucleus is vulnerable to oxidative stress?
-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
explain the overview of lens morphogenesis
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
why does presbyopia occur?
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
what is the depression of lens on the vitresous surface
patella fossa
32
what is zone of discontinuity
junction between lens layers
33
what is the role of lens capsule
-maintain structural integrity -give lens shape -restrict molecule to go inside the lens
34
properties of central zone of epi
-polygonal -transport substance from aqueous into the lens -secrete capsule material
35
properties of germinative zone
-more cuboidal -have interdigitation -mitosis
36
properties of transitional zone
-no mitosis -more columner -differentiate into lens fiber
37
lens substance in percentage
35% protein, 65% water, <1% carbs and ions
38
percentage of soluble and insoluble protein
90% soluble and <15% insoluble
39
what are the types of soluble and insoluble protein*
soluble = alpha, beta, gamma insoluble = cell membrane, cytoskelelton, enzyme
40
soluble and non-soluble protein is predominant where
soluble = cortex insoluble = nucleus
41
what is the difference in alpha, beta and gamma protein
alpha=largest, 2nd most common beta=most common gamma=monomer
42
what are insoluble protein responsible for
cytoskeleton protein = cell structure, cell mobility, cell differentiation membrane protein = intrinsic (gap junction) and extrinsic enzyme = ATPase, dehydrogenase
43
where is the sight that mitochondria locate
lens epithelium
44
how sorbitol is related to glucose level and diabetes
-sorbitol involve aldose reductase -> protect the lens from hyperglycaemia -diabetes = too much sorbitol
45
what is lens circulation of ions (current flow)
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
why there is the current flow
unequal distribution of K+ channel
47
what are the cations and anions in the lens*
cation: high K+, low Na+ (higher in cortex), Ca2+ anion: Cl-, HCO3-, PO3-, SO42-
48
how epithelium ion homogenity
-Na+/K+ ATPase pump (Na+ out, K+ in) -work against passive diffusion of both ions

opb353-qut (5 decks)

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