Lens Flashcards
What type of tissue is the Lens?
Specialized epithelial tissues
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.
Cataract formation.
What kind of cells make up the bulk of the lens?
elongated fiber cells
Which cells are on the anterior surface of the lens closest to the cornea?
Sheet of cubodial cells, the lens epithelium.
What secretes the lens capsule? What is it?
An elastic ECM that surrounds the entire lens and is secreted by cuboidial and elongated fiber cells.
Cell proliferate slowly in THIS layer that is near the equatorial margin in the lens epithelium.
Geminative Zone
Sutures are junctions between the ____ and _____ ends of the cells from the opposite side of the lens.
Apical and basal
Once fiber cells reach the sutures, they _____ elongating and their _____ ends detach from the capsule.
Elongating
Basal
True/False:
As lens differentiate, the lens continues to increase in size and synthesis continues just before organelle degradation.
False:
Synthesis CEASES just before organelle degradation.
Components of mature fiber cells must be more _____ than those in cells found in other parts of the body.
Stable
What are the inelastic microfibrils that suspend the lens?
Zonules
Zonules originate in the ______________ layer of the ciliary epithelium and insert into the ________ ________ near the equator.
Non-Pigmented
Lens capsule
Changes in the tension applied to the zonules are responsible for the alterations in lens curvature during what process?
Accommodation
What gives lens its refractive nature?
Crystallins in cells (3x higher than in normal cells)
Curvature of the surfaces
In younger individuals, refractive error is often caused by:
Corneal curvature
Length of the globe
Rarely by Lens
Light passes smoothly through lens due to (3)
- regular structure of lens fibers
- Absence of membrane-bound organelles
- Small/uniform extracellular space between fiber cells
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.
FALSE:
Lens absorbs SHORTER wavelengths of visible light.
The absence of the natural crystalline lens, from natural causes or removal.
Aphakia
Rubella infection in first 4 weeks of pregnancy can cause this type of aphakia.
Congenital Aphakia; causes mutation in the PAX 6 gene
The substitution of the natural crystalline lens with a synthetic lens.
Pseudophakia
Crystallins make up (%) of the wet weight of the lens fiber
40%
The taxon-specific crystallin that is present at high levels in the embryonic nucleus.
Betaine-homocysteine methyltransferase
Functional enzymes or proteins that are structurally similar to enzymes but that lack enzymatic activity.
Taxon-specific crystallins
What are the classical crystallins that all vertebrae lenses accumulate?
Alpha crystallin family and beta/gamma crystallin superfamily
What are alphaA and alphaB’s roles?
Prevent protein aggregation and precipitation. If you knock one of these out, you get cataracts.
Composition of lens
65% water
35% organic matter (33% structural proteins)
The absence of the natural crystalline lens, from natural causes or removal.
Aphakia
Rubella infection in first 4 weeks of pregnancy can cause this type of aphakia.
Congenital Aphakia; causes mutation in the PAX 6 gene
The substitution of the natural crystalline lens with a synthetic lens.
Pseudophakia
Crystallins make up (%) of the wet weight of the lens fiber
40%
The taxon-specific crystallin that is present at high levels in the embryonic nucleus.
Betaine-homocysteine methyltransferase
Functional enzymes or proteins that are structurally similar to enzymes but that lack enzymatic activity.
Taxon-specific crystallins
What are the classical crystallins that all vertebrae lenses accumulate?
Alpha crystallin family and beta/gamma crystallin superfamily
What are alphaA and alphaB’s roles?
Prevent protein aggregation and precipitation. If you knock one of these out, you get cataracts.
Composition of lens
65% water
35% organic matter (33% structural proteins)
Microtubules are important in (3):
- Stabilizing fiber cell membrane
- Transporting vesicles to the apical and basal ends of elongating fiber cells.
- Give lens its birefringent property
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.
High cholesterol and sphingomyelin
Causes it to be rigid.
Cholesterol increases as cell matures.
The cholesterol/phospholipid ration is nearly _____-fold greater in nuclear than in cortical fiber cells.
Three times grreater in nuclear than in cortical fold.
True/False
As you get older, growth of lens increases. And continues at a linear rate after 10 years old.
False, it decreases
hyaloid artery, Iris stroma, anterior papillary membrane, tunica vasculosa lentis:
Capillaries
Anterior: from_____________
Posterior: from ___________ and form _____________
Anterior from iris stroma and form the anterior papillary membrane.
Posterior from hyaloid artery, and form tunica vasculosa lentis.
True/False
Capillaries of the tunica vasculosa lentis and the anterior papillary membrane regress during the 3rd trimester.
False:
SECOND Trimester
What happens if you have an absence of the lens in early embryogenesis
Absence of corneal endothelium, iris, ciliary body, and anterior chamber.
Abnormal differentiation of the corneal stroma.
Where does the lens get most of its energy?
glycolysis; which causes lactic acid buildup, decrease in pH
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.
Low oxygen tension (15 mm Hg)
Oxygen comes from ______ because the lens needs ATP through this process.
Oxidative phosphorylation
True/False
If light is not absorbed, it produces no damage.
True
Absorption of UV by: (5)
DNA, protein, nucleoside-containing metabolites, flavonoids, and pigments.
Flavonoids and pigments absorb visible light, especially ______ wavelengths.
Shorter wavelength.
