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Ocular Physiology - Emelline > Lens > Flashcards

Lens Flashcards

1
Q

What type of tissue is the Lens?

A

Specialized epithelial tissues

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2
Q

What is the process where the precise organization of the lens fiber cells is disrupted or there is damage to the proteins that ends up destroying the transparency of the lens.

A

Cataract formation.

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3
Q

What kind of cells make up the bulk of the lens?

A

elongated fiber cells

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4
Q

Which cells are on the anterior surface of the lens closest to the cornea?

A

Sheet of cubodial cells, the lens epithelium.

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5
Q

What secretes the lens capsule? What is it?

A

An elastic ECM that surrounds the entire lens and is secreted by cuboidial and elongated fiber cells.

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6
Q

Cell proliferate slowly in THIS layer that is near the equatorial margin in the lens epithelium.

A

Geminative Zone

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7
Q

Sutures are junctions between the ____ and _____ ends of the cells from the opposite side of the lens.

A

Apical and basal

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8
Q

Once fiber cells reach the sutures, they _____ elongating and their _____ ends detach from the capsule.

A

Elongating

Basal

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9
Q

True/False:

As lens differentiate, the lens continues to increase in size and synthesis continues just before organelle degradation.

A

False:

Synthesis CEASES just before organelle degradation.

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10
Q

Components of mature fiber cells must be more _____ than those in cells found in other parts of the body.

A

Stable

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11
Q

What are the inelastic microfibrils that suspend the lens?

A

Zonules

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12
Q

Zonules originate in the ______________ layer of the ciliary epithelium and insert into the ________ ________ near the equator.

A

Non-Pigmented

Lens capsule

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13
Q

Changes in the tension applied to the zonules are responsible for the alterations in lens curvature during what process?

A

Accommodation

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14
Q

What gives lens its refractive nature?

A

Crystallins in cells (3x higher than in normal cells)

Curvature of the surfaces

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15
Q

In younger individuals, refractive error is often caused by:

A

Corneal curvature
Length of the globe
Rarely by Lens

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16
Q

Light passes smoothly through lens due to (3)

A
  1. regular structure of lens fibers
  2. Absence of membrane-bound organelles
  3. Small/uniform extracellular space between fiber cells
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17
Q

True/False:
Although the lens absorbs increasing amounts of the longer wavelengths of visible light as it ages, the young human lens is nearly colorless.

A

FALSE:

Lens absorbs SHORTER wavelengths of visible light.

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18
Q

The absence of the natural crystalline lens, from natural causes or removal.

A

Aphakia

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19
Q

Rubella infection in first 4 weeks of pregnancy can cause this type of aphakia.

A

Congenital Aphakia; causes mutation in the PAX 6 gene

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20
Q

The substitution of the natural crystalline lens with a synthetic lens.

A

Pseudophakia

21
Q

Crystallins make up (%) of the wet weight of the lens fiber

A

40%

22
Q

The taxon-specific crystallin that is present at high levels in the embryonic nucleus.

A

Betaine-homocysteine methyltransferase

23
Q

Functional enzymes or proteins that are structurally similar to enzymes but that lack enzymatic activity.

A

Taxon-specific crystallins

24
Q

What are the classical crystallins that all vertebrae lenses accumulate?

A

Alpha crystallin family and beta/gamma crystallin superfamily

25
Q

What are alphaA and alphaB’s roles?

A

Prevent protein aggregation and precipitation. If you knock one of these out, you get cataracts.

26
Q

Composition of lens

A

65% water

35% organic matter (33% structural proteins)

27
Q

The absence of the natural crystalline lens, from natural causes or removal.

A

Aphakia

28
Q

Rubella infection in first 4 weeks of pregnancy can cause this type of aphakia.

A

Congenital Aphakia; causes mutation in the PAX 6 gene

29
Q

The substitution of the natural crystalline lens with a synthetic lens.

A

Pseudophakia

30
Q

Crystallins make up (%) of the wet weight of the lens fiber

A

40%

31
Q

The taxon-specific crystallin that is present at high levels in the embryonic nucleus.

A

Betaine-homocysteine methyltransferase

32
Q

Functional enzymes or proteins that are structurally similar to enzymes but that lack enzymatic activity.

A

Taxon-specific crystallins

33
Q

What are the classical crystallins that all vertebrae lenses accumulate?

A

Alpha crystallin family and beta/gamma crystallin superfamily

34
Q

What are alphaA and alphaB’s roles?

A

Prevent protein aggregation and precipitation. If you knock one of these out, you get cataracts.

35
Q

Composition of lens

A

65% water

35% organic matter (33% structural proteins)

36
Q

Microtubules are important in (3):

A
  1. Stabilizing fiber cell membrane
  2. Transporting vesicles to the apical and basal ends of elongating fiber cells.
  3. Give lens its birefringent property
37
Q

Cell membranes of len fibers have high/low proportion of cholesterol and sphingomyelin compared to other plasma membranes.

This causes the membrane to the rigid/soft.

A

High cholesterol and sphingomyelin

Causes it to be rigid.

Cholesterol increases as cell matures.

38
Q

The cholesterol/phospholipid ration is nearly _____-fold greater in nuclear than in cortical fiber cells.

A

Three times grreater in nuclear than in cortical fold.

39
Q

True/False

As you get older, growth of lens increases. And continues at a linear rate after 10 years old.

A

False, it decreases

40
Q

hyaloid artery, Iris stroma, anterior papillary membrane, tunica vasculosa lentis:

Capillaries
Anterior: from_____________
Posterior: from ___________ and form _____________

A

Anterior from iris stroma and form the anterior papillary membrane.

Posterior from hyaloid artery, and form tunica vasculosa lentis.

41
Q

True/False

Capillaries of the tunica vasculosa lentis and the anterior papillary membrane regress during the 3rd trimester.

A

False:

SECOND Trimester

42
Q

What happens if you have an absence of the lens in early embryogenesis

A

Absence of corneal endothelium, iris, ciliary body, and anterior chamber.
Abnormal differentiation of the corneal stroma.

43
Q

Where does the lens get most of its energy?

A

glycolysis; which causes lactic acid buildup, decrease in pH

44
Q

Molecular oxygen causes the most oxidative damage, which is why you need a __________ oxygen tension around/within the lens to protect it from oxygen damage.

A

Low oxygen tension (15 mm Hg)

45
Q

Oxygen comes from ______ because the lens needs ATP through this process.

A

Oxidative phosphorylation

46
Q

True/False

If light is not absorbed, it produces no damage.

A

True

47
Q

Absorption of UV by: (5)

A

DNA, protein, nucleoside-containing metabolites, flavonoids, and pigments.

48
Q

Flavonoids and pigments absorb visible light, especially ______ wavelengths.

A

Shorter wavelength.

Ocular Physiology - Emelline (3 decks)

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