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Ocular Physiology #2 > Lens > Flashcards

Flashcards in Lens Deck (142)
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2

what type of tissue is the lens

two types of specialized epithelial tissue: cuboidal and elongated fiber cells

3

what 3 things must the lens have in order to project an image onto the retina

transparent, higher refractive index than the medium its suspended in, and have flexible refractive surfaces with the proper curvature

4

what happens to the lens if there is disruption of precise organization or damage to the proteins

destroys the transparency of the lens and cataract formation

5

what type of tissue is the lens epithelium

a sheet of cubodial cells

6

what type of tissue is the bulk of the lens

elongated fiber cells

7

what secretes the lens capsule

the epithelial and superficial fiber cells

8

where is the germanitive zone

near the equatorial margin of the lens epithelium

9

when do the fibers stop elongating

when they reach the Y sutures

10

what are the lens sutures

junctions between the apical and basal ends of the cells from opposite ends of the lens

11

where do the mature lens fibers go

they get buried deeper as fibers elongate and differentiate

12

when does synthesis stop

just before the organelle degradation

13

how do the mature fiber cells compare to those in the rest of the body

the components of mature fiber cells are more stable

14

what are the zonules

the inelastic microfibrils that suspend the lens

15

where do the zonules originate and insert

in the NPE of the ciliary epithelium and insert into the lens capsule near the equator

16

what is responsible for changing the lens curvature during accommodation

the zonules

17

what contributes to the refractive nature of the lens

the high concentration of crystallins in the cells and the curvature of the surfaces

18

what is the concentration of crystallins in the lens compared to typical cells

3 times higher concentration

19

what causes refractive error is younger individuals

corneal curvature or the length of the globe (rarely by the lens)

20

what does the transparency of the lens depend on

minimizing light scattering and absorption

21

why does light pass smoothly through the lens

regular structure of lens fibers, absence of membrane-bound organelles and small /uniform extracellular space between fiber cells

22

what happens to the nearly colorless lens as we age

becomes more yellow- lens absorbs short wavelength light (blues)

23

what is aphakia

the absence of the natural crystalline lens from natural causes or removal

24

what is congenital aphakia

caused by Rubella infection in first 4 weeks of pregnancy (mutation in PAX-6 gene)

25

what is pseudophakia

substitution of the natural crystalline lens with a synthetic lens

26

what does lens fiber differentiation depend on

synthesis and accumulation of large amounts of crystallin proteins

27

what percentage of the wet weight of the lens fiber is crystillins

40% (3 times the amount in a typical cell)

28

what are the classic crystallins that all vertebrae lenses accumulate

alpha-crystallin family and beta/gamma-crystallin superfamily

29

do adults have taxon-specific crystallins

no- high levels in the embryonic nucleus

30

why are taxon-specific crystallins important

for certain events to take place- development of the human lens

31

what taxon-specific crystallin is present at high levels in embryonic nucleus

betaine-homocysteine methyltransferase