Lens Flashcards
1
Q
function of the lens is to
- ____ light onto the retina while maintaining ______ and at the same time undergoing various degrees of deformation as it ______
- _____ the retina from UV light by absorbing the higher energy shorter wavelength light
A
refract, transparency, accomodates
-protects
2
Q
the lens is a thick tissue and has the _________ protein concentration of any tissue in the body :O!
A
highest
3
Q
the lens can only get sick one way and that is through a ……
A
cataract
4
Q
the lens is avascular. what provides its nourishment
the ____ of the lens can affect the angle
A
aqueous
location
5
Q
what are the 6 regions of the lens
A
- capsule
- anterior epithelium
- equatorial region
- cortex
- nucleus
- sutures
6
Q
the basement membrane of the capsule is homologous to that of the …
A
corneal epithelium
7
Q
the capsule is composed of …
A
collagenous fiber and fibrillin
8
Q
____ confers elasticity to the lens
______ limits the ability to stretch
A
fibrillin
collagen
9
Q
the capsule is not much of a barrier to protection. T or F
A
T. most molec except proteins move through the capsule
10
Q
the zonules attach to the capsule. T or F
A
T.
11
Q
when looking at near, the ciliary muscle ring ______, moving __________
- zonules are _______
- lens ______
A
contracts, forward and inward
-loosened
bulges
12
Q
a fibrillin disease where the lens is dislocates due to weak zonules
A
marfan’s syndrome
13
Q
what is the only actively metabolizing area of the lens
A
anterior epithelium
14
Q
the anterior epithelium comprises ____% of all metabolism that occurs w/in the lens.
-this is good bc the highest oxygen concentration is at the _____
A
90%
-anterior portion of the lens
15
Q
the anterior epithelium contains ___% of all the pumps of the lens. the other ___% are in the posterior-intermediate area
A
90%
10%
16
Q
what is the region of greatest energy use because of pumps, area of mitosis
=>which makes it the maximum synthetic area
A
pre-equatorial region
17
Q
where si the region of active mitosis in the lens
A
pre-equatorial region
18
Q
where is the pre-equatorial region located
A
under the iris from which it gains its protection
19
Q
what area contains all the mitotic elements of the lens including DNA
-in danger of mitotic cell damage by UV
A
pre-equatorial region
boss ass region
20
Q
cortex have hexagonal fibers because…….
A
it can be packed to its maxiumum.
more cells per unit area
more proteins per cell
=> more proteins total
21
Q
the older lens cells are located in the ….
the younger ones are in the …….region
these are zones of inconsistencies
A
center
peripheral
22
Q
in the cortex,
______ in protein concentration towards nucleus
_____ in refractive power towards the nucleus
A
increase
increase
23
Q
fibers lose all of their ______ as they are pushed into the interior of the lens
A
organelles
24
Q
the protein concentration ramps upward in the center of the lens, which increases….
A
refractive power
25
the nucleus has ____ fibers, packed in a ____ array with ______ extracellular space located btwn them
hexagonal, regular, very little
26
why will the scattered light be reflected and scattered in a regular manner
the fibers are regularly spaced
27
the explanation of transparency of the lens is because of the....... of light
destructive interference of light
28
the upright Y suture is ______
| the upside-down Y suture is ____
anterior
| posterior
29
the increased branching of the sutures produces better....
optical qualities
30
which suture are where the lens fibers meet inside the lens?
what do they do to water in the lens?
how do they radiate?
the y-sutures
keep the water out so the lens is dry
outward
31
what is a reason that water does not flow through the center of the lens
there are less interdigitations in the periphery of the lens than in its center
32
as fibers reach the sutures, the membranes become progressively more interlocked, forming interlocking__________ junctions
ball and socket
33
these junctions may stabilize the lateral membranes of the fiber cells and ensure the cells remain tightly connected during accommodation
ball and socket junction
34
extensive intercellular communication exists via_____
the lens gap junction ...
35
where is the smallest extracelllular substance located in any tissue of the body
the lens - no room for lakes
36
what are lens fibers linked by
N-cadherin connections
37
the embryonic optic vesicles form as an ____ of the neural tube connected to it by stalks
neural tube
38
as the optic vesicle approaches the surface ectoderm, it induces the formation of the...
lens placode
39
the sides of the vesicle grow down reducing the gap to a narrow cleft called the...
the structure is now the optic cup
embryonic fissure
aka choroidal fissure, ocular fissure, optic fissure. thanks for all the fucking names T__T
40
what start to form the vascular capsule of the lens
hyaloid vessels
41
early lens vesicle develops.....which cells elongate to reach the anterior epithelium
posterior cells
42
lens development
1. _______ form as an extension of the neural tube
2. as these approach the surface ectoderm the ______ and _____ form
3. narrow cleft called the _______ forms in the walls of the optic cup
4. _____ vessels start to form the vascular capsule of the lens
5. early lens vesicle devleops w/ post cells elongating to reach the _____
1. embryonic optic vesicles
2. lens placode, lens vesicle
3. embryonic fissure
4. hyaloid
5. anterior epithelium
43
what is the area of nuclei of elongating fiber cells called
germinative zone
44
(transcript) mitosis in the pre-equatorial layer produces...
(mitosis occurs in the sub-epithelial layer in slides).....................wtf
new fibers
45
once the fibers reach the sutures, they stop elongating and their _______ detach from the capsule
basal ends
46
lens fiber growth
1. mitosis occurs in the ____
2. new fibers migrate along the _____, elongating to reach to _____
3. _____ detach from capsule at sutures
4. _____ are buried deeper in the lens w/ successive generations
1. sub-epithelial layers
2. capsule, sutures
3. basal ends
4. mature fiber cells
47
pattern of movement
1. _____of fibers move along capsule surfcae
2. _____ ends slide beneath epithelium until they meet elongating cell from other side near midline
3. stop elongating = _________
4. _____ ends detach from capsule
5. organelles then degrade by ______
6. _____ scatter declines
1. basal ends
2. apical
3. suture
4. basal ends
5. apoptosis
6. light
48
organelle free zone:
- diffrentiating fibers = outer ____% some organelles
- mature fibers = inner ____%
- 20%
| - 80%
49
order of lens development from center to out is....
1. ____ nucleus
2. _____nucleus
3. _____ nucleus
4. cortex
5. _____ capsule
1. embryonal
2. fetal
3. adult
4. cortex
5. anterior capsule
50
what fibers from the posterior epithelium form the embryonic nucleus
primary lens fibers
51
where are secondary lens fibers formed? and by what
pre-equatorial region by mitosis
52
what fibers form the fetal nucleus
the fibers laid down before birth
53
between birth and sexual maturation form the ......
adult nucleus
54
what is formed by the fibers laid down after sexual maturation
cortex
55
the lens in a child is _____
the adults is ____
why does the lens change with age?
clear
cloudy
reflect both migration inward and changes in protein synthesis rates
56
variables affecting transparency
1. ____ level
2. ____ level
3. water
4. ____ remains
1. cellular
2. molecular
3. water
4. embryonic
57
what is dependent on the regularity of the lens fibers as well as their contructive/destructive interferenece properties
transparency of the lens
58
how is scatter related to the wavelength of light
independent or slightly dependent
59
the scatter produced by disruption of the regular array takes place when scattering particles are very _____ compared to the wavelength of light
large
60
water in the cornea can be a sign of....( 2 things)
closed angle glaucoma (high IOP)
| contact lens over wear (lack of oxygen and buildup of osmotic pressure by lactate)
61
what are factors that promote transparency
1. ____ lens fibers
2. _____ of lens fibers
3. _____ of packing
4. ______ of organelles
5. _____
1. small
2. uniformity
3. regularity
4. paucity (lack of organelles)
5. avascular
62
molecular level or transparency
1. fibers accumulate large amounts of _____ as they elongate x2 other cells
2. lens proteins are ____ and _____
3. _____ arrangement
4. ________ density
1. proteins
2. small and uniform (90% crystallins)
3. ordered
4. high packing
63
scatter at the MOLECULAR level is dependent on the ................. of their proteins
size and shape and their concentration
64
why is water the destroyer?
disrupts fibers and destroys the regular array, creating refractive lakes bc of the difference in refractive index
65
effects of water
1. water produces ______
2. ______in extracellular space
3. disrupts ______
4. pump/leak system:_____ pump maintains constant lens volume
1. refractive lakes
2. increase
3. fibers
4. anterior
66
the pump/leak system in transparency osmoregulates by pumping out ____ ions and passive efflux of _____ is accompanied by water
sodium
| chloride
67
what do the interdigitations and zonula occludens do to permeability
decrease it. they impose a barrier to water flow btwn cells especially in the center of the lens
68
what is the disease from congenital origin that arose from the posterior lens attachment of the hyaloid artery
mittendorf's dot
69
tunica vasculosa lentis-arises from the hyaloid artery
| -regress during 2nd trimester
posterior lens
70
anterior pupillary membrane-arises from the developing iris stroma
-regress during 2nd trimester
anterior lens
71
the lens proteins leak and the body reacts to the foreign proteins w/ an antigen-antibody response
hypermature cataract
72
the antigetn-antibody response occurs and the preceipatates can clog the angle leading to
secondary open angle glaucoma
73
where is the mittendorf's dot located
inferior nasal to posterior pole of lens
74
what is the remnant of hyaloid artery at the center of the optic disk that has a small tuft of fibrous tissue
bergmeister's papilla
75
what is the lens power at rest
| lens w/ accomodation?
15D
| 15D MORE
76
factors that affect refractoin are...
1. _____ concentration is proportional to RI
2. ________ polymerization ________ RI cuasing myopic shift in refraction
1. protein
| 2. protein, increaes
77
accommodation decreases by........
1/4 age
78
lens protects the retina from ________ by:
1. _____ light < 400nm including blue, UVB and UVC light
2. _____ o2 levels
3. ____ lipids
4. sloughing _______
1. absorbs
2. low
3. saturated
4. inwards
79
99% of the lens energy is for...
pumping
80
the lens fibers need lubrication to slide which is provided for by the...
mucopolysaccharids (GAGs)
81
the tight junctions or barrier is located in the.....
______ replace tight junctions in the rest of the lens
anterior epithelium
| interdigitations
82
what are the 2 functions of actinomyosin and microtubulin
1. control the lens fiber growth and migration
| 2. somehow involved in accomodation
83
the sphingomyelin need to be ____ inorder to allow the lens to smoothly accommodate in different stages
-the lipids are _____ and ____chained
HARD. (like eveyrthing else to work)
-saturated and short chained
84
the scatter of light creates the _____ of the lens and there is NO _____yellowing
yellowing
| posterior
85
what light is more scattered as pts dvelop catarcs
blue light
86
where are anterior pole and post pole cataracs located at in the lens
center
87
light is _______by the lens and this means that the posteriror subcapsular catarct is more _____ to light than the anterior
converged
| obstructive
88
in the posterior catarct:
more light will pass through if pupil is ______
less light will pass through if pupil is _____
dilated
| constricted
89
a pt w/ a post cataract will have a worse VA at ______ bc the pupil will constrict during accommodation.
-pt will have more problems in ____light
near than at distance
-bright
90
a nucleosclerotic cataract (NSC) is located in the ______
- the main problem with it is....
- it is worse when the pupil is....
lens nucleus
- scatters light
- dilated
91
the major lens proteins are...
water soluble ___%
urea soluble ____%
insoluble _____%
90%
5%
5%
92
what makes the lens very osmotically active
high protein content
93
the urea soluble and insoluble proteins make up the...
cell membranes and nucleus of the lens
94
what kind of proteins are urea soluble in lens
cytoskeletal and crystallin
95
what kind of proteins are insoluble in lens
crystallin and membrane protein albuminoid
96
what are the 3 different types of crystallins in humans?
| -crystallins make up ___% of water soluble proteins of the lens
alpha, beta, gamma
| -90%
97
which crystallins act as chaperones?
alpha A and alpha B
98
which crstyallin is importnat for the normal function of lens epithelial cells and fiber cells?
alpha A
99
which crystallin has cataracs and myopathy when a mutation in it occurs
alpha B
100
what is a protein that stabilizes other proteins, preventing them from aggregating
chaperones
101
the location of the lens proteins
- these decrease towards nucleus. 1. 2.
- these increases towards nucleas. 1. 2.
1. alpha
2. beta
1. gamma
2. albuminoid
102
albuminoid is thought to arise via ______ and ____ bond formation.
-how do alpha, beta, and gamma convert to albuminoid?
oxidation, s-s bond formatoin
| -oxidation
103
the lens is more permeable anteriorly or posteriorly?
posteriorly so that the ions enter and water follows in the back
104
how does water move from cell to cell ?
| which surface does it move towards
through gap junctions and aqueous pore
| -anterior surface
105
the nucleus of the lens is relatvively ______ so that motion of ions and water is mainly cortical
impermeable
106
where are most of the leaks located?
| where are most of the pumps located?
posterior surface
| anterior surface
107
anterior epithelium has ____ pumps than the intermediate layers of the lens, which has _____ than the nucleus and then ____ than the capsule
more
more
more
capsule has none
108
anything detrimental to the pumps will lead to.....
| anything that decreases ATP causes pump protein activity to.....
cataracts
| decrease
109
the cells in the posterior portion of the lens have _____ membrane and lack ______
weaker
| tight junctions
110
the _____ barrier exists across the anterior epithelium. the next strongest barrier is the .....
anterior epithelium
| nucleus of the lens bc firmly packed and very impermeable to water
111
where does most of the osmolarity occur
in the front of the lens. stronger osmotic gradients across the front
112
in the osmotic gradient: anything that will increase the osmolarity inside the lens will increase....
water movement into the lens
113
cataracts caused by leaky membranes will be in the .....portion of the lens while those caused by osmotic gradients will be located in the .........
posterior portion
| anterior portion
114
the electrolyte and water content resemble that of an....
| the electrolyte and water content of aqueous and vitreous resumels that of...
intact cell
cerebrospinal fluid, plasma, or extracellular fluid
115
the inside of the lens is high in....and low in....
the outside of the lens is low in....and high in...
K+ , Na+
K+, Na+
116
most of the pumps are in the...
anterior epithelium
117
facilitated diffusion is passive. but it is carrier mediated and can become...
saturated
118
permeable to small molecular weight proteins including low molecular weight crystallins but prevents diffusion of large molecules
capsule
119
water tends to move into the lens bc the protein content inside the cell is ___ and the water content is-____
high , low
120
in the na/k atpase pump it exchanges sodium pumped out for k pumped in:
-Na passive diffuses down a concentration gradient in the _____, across the ____ into the lens, and diffuses to the ______ epithelium where it is pumped out into the _____
vitreous, capsule, ant lens ep, aqueous
121
potassium diffuses the the other direction of na towards the....
-tend to diffuse down its _____ out of the lens but is pumped back _____ the lens
vitreous
| -concentration gradient, into
122
Cl: ____ down its concentration gradient into the cell
Ca: moves _____ its conc. gradidnet
glucose: supplied by the _____so there is higher concentration ______ the cell
-passes through the cell membrane through ....
-lactate: higher concentration ____ the cell so it
leaks
-ascorbic acid: ___ element
-inositol: high concentration in ____ and ____ the cell
diffuses
down
aqueous humor, outside
-facilitated diffusion and passive diffusion
- inside
- redox
- aqueous humor, inside
123
protein is very _____ inside the lens
high. cell membrane is not permeable to proteins proteins synthesized inside the cell from aa
124
glutathion is made up of ____ aa
3
125
the source of energy used to run the pumps is...
glucose
126
glucose winds up in the lens cell as
glucose - 6-P
127
an important reducing agent in the protection against superoxide
NADPH
128
the lens has no turnover of cells and needs the pathway....
pentose shunts to take care of superoxide
129
what percent of glucose-6-p enters the pentose shunt to produce ribose-5-p and NADPH?
what percent ends up at pyruvate?
15%
85%
130
majority of glucose is used to make lactate, even though only produces a small amount of ATP. what percent.
minor used for aerobic pathway
80%
131
movements of ions and water from aqueous and vitreous: (3 things)
passive diffusion
active transport
facilittated diffusion
132
anaerobic atp generation, how many?
| aerobic?
160
| 180
133
nucleus requires _____ for pumps
nucleus uses ______ phosphate
conc. of _____ highest in nucleus
protein content ____ in nucleus
energy
creatinine phosphate
CP
highest
134
sorbitol pathway
1. conversion of glucose to ______
2. conversion of sorbitol to _____
1. sorbitol
| 2. fructose
135
the highest productivity of any pathway lies in the...
pre-equatorial epithelium bc it is the area of active mitosis
136
change in osmolarity causes changes in:
| 3 things
1. thickness
2. radius of curvature
3. rx
137
unusual changes in rx may indidcate...
diabetes
138
superoxide production
1. superoxide _______
2. ___ wavelenths
superoxide reduction
1. superoxide ____
2. _____
1. synthetase
2. short
1. dimutase
2. glutathione
139
how free radicals cause damage
1. cross-linking of DNA =>
2. corss-linking of lipids=>
3. cross-linking of proteins=>
1. gene mutations
2. leaky membranes
3. non-functional enzymes
140
some pathways to cataracts (3)
1. sunlight
2. posterior inflammations (uveitis)
3. diabetes
