Anatomy of the Lens

Question 1

Where is the lens located

Answer 1

It is suspended by zones in the posterior chamber

Question 2

What are the 5 divisions of the lens

Answer 2

Embryonic nucleus, fetal nucleus, adult nucleus, cortex, and capsule.

Question 3

Lens vesicle

Answer 3

Stage 1 of lens production. During gestation, a hollow sphere (3D) of epithelial cells forms. Posterior cells elongate to become primary lens fibers. They fill the lens vesicle to form the embryonic nucleus.

Question 4

Primary lens fibers

Answer 4

Elongated posterior cells of the lens vesicle. These elongated cells from the posterior lens vesicle will form the embryonic nucleus.

Question 5

What forms the fetal nucleus

Answer 5

The elongation of anterior cells near the equator (secondary lens fibers)

Question 6

Cell elongation of the secondary fibers continues until

Answer 6

Nasal and temporal cells meet at a suture. They form interlocking junctions (ball and socket and tongue and groove). Allows cells to remain tightly connected during accommodation.

Question 7

As anterior cells elongate and meet, they form sutures. What do the sutures look like?

Answer 7

The anterior suture is a “Y” shape and the posterior suture is an upside down “Y”

Question 8

As anterior elongated cells/secondary fibers reach ___, their nuclei and organelles are degraded

Answer 8

The sutures. At this point, cells consist only of a cell membrane, cytoskeleton, and crystallines (lens proteins).

Question 9

Secondary fibers that reach the sutures have what remaining?

Answer 9

All nuclei and organelles are degraded. All that is left is a cell membrane, cytoskeleton, and crystallines (lens proteins)

Question 10

After birth, which lens fibers form the adult nucleus?

Answer 10

The secondary fibers (anterior elongated cells). This surrounds the fetal nucleus.

Question 11

Are new or old secondary lens fibers produced after birth located in the cortex or middle?

Answer 11

Cortex. New fibers continue to surround older, more central fibers. This growth results in concentric layers of secondary lens fibers.

Question 12

Are cells ever removed from the lens?

Answer 12

No. Cells in the center of the lens are the oldest cells in the body.

Question 13

The basement membrane of the outer epithelial cells is called the lens capsule, or the

Answer 13

Bag. Anterior/posterior capsules.

Question 14

The lens capsule/bag is composed of primary what type of collagen

Answer 14

Mainly collagen type 4 (like most basement membranes are). Also contains GAGs.

Arrangement of collagen fibers makes the lens capsule highly elastic.

Question 15

Which side of the lens capsule thickens throughout life?

Answer 15

The anterior lens capsule. Since this is the only side of the lens that has activate epithelial cells, therefore, the cells will secrete and produce more of the BM. Eventually, the anterior side of the lens will become the thickest BM in the body

Question 16

Which side of the lens capsule remains the same throughout life?

Answer 16

The posterior lens capsule. Since there are no living epithelial cells to secrete the BM/capsule components.

Question 17

Where do zonules insert into the lens at? and where do zonules originate from?

Answer 17

They insert into the capsule at the equatorial regions of the lens. They originate from the BM of the non-pigmented epithelium of the ciliary body.