Block 11 Flashcards
(174 cards)
1
Q
What is RPE
A
A monolayer of pigmented cells
2
Q
Where is RPE located
A
Between choriocapillaris and outer segment of photoreceptors
3
Q
Whe apical side of the RPE faces
A
Photoreceptors
4
Q
The basal side of RPE faces
A
Bruchs membrane
5
Q
General Light absorption in the RPE is due to
A
Melanin
6
Q
Blue light is absorbed in the RPE due to
A
Lutein and zeaxanthin
7
Q
What damage does RPE protect from
A
Oxidative damage
8
Q
T/F the outer retina is exposed to an oxygen -rich environment
A
True
9
Q
What does the RPE transport nutrients and wastes between
A
Photoreceptors and choriocapillaris
10
Q
What are the 2 divisions of transepithelial transport in RPE
A
Transport from photoreceptors to blood
Transport from blood to photoreceptors
11
Q
How is water removed from the RPE
A
It is active transport driven by an active transport of Cl from the retina to blood side
12
Q
What is Best’s Vitelliform Macular Degeneration
A
Degeneration of RPE
Bulls eye lesion
Lesion composed of extracellular fluid
There is a reduction in epithelial Cl- transport
13
Q
What is required to removal of lactic acid from apical side
A
Tight regulation of intracellular pH
14
Q
What are some other substances that are transported to blood to photoreceptor
A
Glucose
All-trans-retinol
DHA
15
Q
Where does the reduction of all-trans-retinAl into all-trans-retinOl occur
A
Photoreceptors
16
Q
Where does the reisomerization of all-trans-retinOl into 11-cis-retinAl occur
A
RPE
17
Q
What causes retinitis pigmentosa
A
Mutations in the Genes of the visual cycle
There is an inability of the RPE to phagocytose photoreceptor outer segment
18
Q
What causes Stargardt disease
A
Mutations in the genes of the visual cycle
19
Q
What is phagocytosis controlled by
A
Circadian control
It is triggered by the onset of light in the morning
20
Q
RPE cell faces an average of ___ photoreceptors in the fovea
A
23
21
Q
Every ___ days a whole length of photoreceptor outer segment is renewed
A
11
22
Q
What is Usher syndrome
A
A defect of RPE photoreceptor phagocytosis
Causes retinal degeneration in Usher type 1B patients
23
Q
PEDF does
A
Antiangiogenic factor
Inhibits endothelial cell proliferation
Stabilizes the endothelium of the choriocapillaris
24
Q
VEGF does
A
Low concentrations in healthy eye
Prevents endothelial cell apoptosis
Stabilizes the endothelium in the choriocapillaris
25
What are some other factors that the RPE secrete
- Growth factors
- factors that maintain structure of retina
- cytokines or immune modulators
26
What happens in choroidal neovascualrizations
RPE cells secreted VEGF at a higher rate
Most severe complication in age-related MD
27
What is the retinal-blood barrier
Tight junctions between retinal pigment epithelium
28
What is photoreception
Light detection that leads to vision
29
What does photoreception depend on
Photoreceptors
30
What is photon absorption done by
Visual pigment that is lying on one of the discs in the outer segment of the photoreceptors
31
What is scotopic (peripheral vision)
Dim light
| Motion
32
What is photopic (central) vision
Color
| Detail
33
Scotopic vision utilizes
Rods
34
Photopic vision utilizes
Cones
35
Describe rods
```
Not good for detail
No color
Very sensitive
Good for dim
Lower sensitivity to rapidly changing stimuli
```
36
Describe cones
Specialized for detail
Color vision
Less sensitive
Higher sensitivity for rapidly changing stimuli
37
T/F there are rods in the fovea
False
38
Where is the peak for cones
Fovea
39
Rods comprise of ____ of photoreceptors
97%
40
What is the rod peak wavelength sensitivity
500-510 nm
41
Rod convergence increases ______
Sensitivity
42
Cones are ____ of photoreceptors
3%
43
Where are their more cones
In the periphery
44
What are the 3 different cones
Red
Blue
Green
45
Red cone
L cone
| Long wavelength
46
Green cone
M
| Medium wavelength
47
Blue cone
S
| Short wavelength
48
T/F there is convergence in the fovea
False
49
What are photopigments
Unstable pigments that undergo a chemical change when they absorb light
50
What makes up photopigments
Protein(opsin) + chromophore
51
What is rhodopsin
Opsin + 11-CIA-retinAl
52
What is rhodopsin used for
Dim light vision
53
Describe rhodopsin
Insoluble in water
More stable than cone pigments
More abundant
54
What are the 3 different iodopsins
Erythrolabe
Chlorolabe
Cyanolabe
55
What is the max absorption of erythrolabe
Yellow/red (L cones)
56
What is the max absorption for chlorolabe
Green
| M cones
57
What is the max absorption for cyanolabe
Bluefish/violet
| S cones
58
What makes up erythrolabe
Photopsin I + 11-cis-retinal
59
What makes up chlorolabe
Photopsin II + 11-is-retinal
60
What makes up cyanolabe
Photopsin III + 11-CIA-retinal
61
What is phototransduction
Series of biochemical events that lead from photon capture by a photoreceptor cell to its hyperpolarization and slowing of neurotransmitter release at the synapse.
It is essentially the transformation of light into electrical and chemical signals that produce the perception of light
62
What are the steps of phototransduction
Photoreception> biochemical cascade> electronic spread> slowing of neurotransmitter release
63
What channel closes in phototransduction
CNG channel
64
What is the CNG channel
Cyclic GMP gated cation channel
65
What does CNG channel do
Allow NA and K and Ca to enter the cell
Cell will be partially depolarized
66
What is the dark current
Flow of cations into and out of the cell while in the dark
67
Know diagram on lecture 2 slide 18
Biochemical cascade
68
Where does the reduction of all-trans-retinal into all-trans-retinol occur
Photoreceptors
69
Where does the reisomerization of all-trans-retinol into 11-cis-retinal occur
RPE
70
Look over the G protein activation on slide 21
Confusion
71
Step 3 is PDE6 activation
Activated G protein binds with a molecule named cGMP phosphodiesterase PDE6
PDE6 converts cGMP into GMP
72
Step 4 is channel closing
Reduction of cGMP concentration causes CNG channel closure
73
What does closing of the Channels do
Reduces the flow of NA and Ca ions in the cell
Reduces the dark current and makes membrane potential more -
74
What is the photocurrent in the dark
Cations move into the cell
75
What is the photocurrent in light
A single photo isomerization closes ion channels and causes a 2% reduction in the photocurrent
76
How do Rhodes communicate with downstream bipolar cells
Glutamate
77
What does a high level of glutamate release signal
Darkness
78
What causes a reduction in the level of glutamate due to
Absorption of light
79
What is adaptation
Alters sensitive to light
Decreases sensitive to bright
Increases sensitivity to dim light
Controlled by Ca influx
80
What are the major energy producing metabolic pathways
Glycolysis
TCA
ETC
81
What are the sources of metabolites for the retina
Glycogen stores (retina)
Glucose (aqueous)
Amino acids (aqueous)
Saturated and unsaturated fatty acids (aqueous)
82
How is glucose delivered
Derived from the serum
| Simple diffusion into the aqueous
83
What is the glucose level in the aqueous due to
There is a constant flux of glucose from the plasma in t het aqueous
84
What is the aqueous glucose level compared to serum glucose
80%
85
What contributes to the production of lactic acid (even in aerobic conditions)
Glucose metabolism of RETINA, ciliary epithelium, lens, cornea
86
Why doesn’t lactic acid accumulate in the aqueous
There is quick trafficking away from the aqueous
87
When is the most lactic acid made
During sleep of conditions that block atmospheric O2 from being absorbed by the eye
(Topical epinephrine in the eye)
88
Where does the eye get O2 from
Atmosphere
| Vitreous
89
How is the O2 concentration in the vitreous from posterior to anterior
Higher posterior
| Anterior is lower
90
What does the vitreous serve as for the retina
An metabolic reservoir
| Provides short-term nutrients during emergencies
91
What is ascorbic acid
High levels in the vitreous
Vitreous to serum 9:1
Concentrated by active transport in ciliary epithelium
Supplied by the diet
92
What are the reasons for high ascorbic acid
- Absorb UV light
- Free radical scavenger
- Protect against oxidative damage from inflammation
- protect the retina and lens from metabolic and light induced production fo singlet oxygen
93
What is the evidence for the benefits of ascrobic acid
Supplements in dark-reared rats reduce irreversible type 1 light damage
And shift the light damage to reversible the 2 light damage
94
What is the implication of ascorbic acid in inflammation
Ascorbic acid synthesis is unregulated in repsonse to inflammatory mediators such as histamine
95
What transporter is responsible for the transport of glucose to the retina
GLUT3
96
What transporter is insulin dependent and thus is NOT found in the retina
GLUT 4
97
When the eye s subject to endotoxins that produce an inflammatory response what will protect the eye
Ascorbic acid
98
What is a synapse
A junction between 2 nerve cells
| Consists of a minute gap across which impulses pass by diffusion of a NT
99
What type of NT is glutamate
excitatory
100
What type of NT are GABA and Glycine
Inhibitory
101
What is hyperpolarization
Makes cell membrane potential MORE NEGATIVE
| Inhibits AP
102
What is depolarization
Makes cell membrane potential more negative
103
What are light-evoked signals transferred onto
Bipolar and horizontal cells
104
What do horizontal cells provide interactions to
Lateral interactions in the OPL
105
Where do bipolar cells transmit there signals to
IPL onto amacrine and ganglion cells
106
What role do ganglion cells play in light transmission
They collect signals from bipolar and amacrine cells and transmit these signals to the visual centers in the brain
107
What is the NT at the cone pedicle
Glutamate
108
When is glutamate high
In darkness
It is reduced by light
109
OFF cone bipolar cells and horizontal cells are _______ by light
Hyperpolarized
110
ON cone bipolar cells are _______ by light
Depolarized
111
OFF cone bipolar cells transfer signals into....
OFF ganglion cells
112
ON cone bipolar cells transfer signal onto.....
ON ganglion cells
113
Describe the density of cones, bipolar cells, and ganglion cells in the retina
They increase in number towards the center of the retina
114
How do the retina cells at the center of the retina compare to those in the periphery
In the center they are smaller
In the periphery they gradually increase in size
115
What causes the high VA in the central retina
High cone density
| Low cone to RGC ratio
116
What is the midget system
On e cone connected to a midget bipolar cell connected to a midget ganglion cell (1:1)
117
What is the NT of the rod spherule
Glutamate
118
When is glutamate high
In darkness
119
What is the only type on rod bipolar cell
ON rod bipolar cells
120
ON rod bipolar cells are _____ by light
Depolarized
121
What is the rod pathway
Rod> ON rod bipolar cell (depol) > amacrine (depol) >
1) On cone bipolar the ON ganglia (glutamte)
2) Off cone bipolar > OFF ganglion cell (glycine)
122
How do horizontal cells produce feedback in rods
They modulate the glutamate release by shifting the activation curves of the rod spherule Ca2+ channels
Release GBA providing inhibition of bipolar cell dendrites
123
How do horizontal cells provide feedback for cones
Modulate the release of glutamte by shifting hot activation curves of the cone pedicab Ca2+ channels
124
What are glutamatergic neruons
Rods
Cones
Bipolar cells
Most ganglion cells
125
What are GABAergic and Glycinergic neurons
Horizontal cells
| Most amacrine cells
126
How does the optic nerve change with age
Nerve fibers decrease
| Optic cup diameter increases
127
How does the ILM change with age?
What affect does this have?
Thickens
Dimmer foveal reflex
128
How does RPE change with age
Total number of RPE decreases
Lipofuscin in RPE increases
Drusen increases
129
What change occurs in aging across the entire retina
Atrophy increases
130
What is a Tigris fundus
Age related retinal atrophy
Pigmentation in RPE/choroid decreases
131
What is reticular degeneration
Age related retinal atrophy
| Peripheral RPE degeneration
132
Is there blood flow in the lens
No
133
Is there innervation in the lens
No
134
How does the lens grow
It grows in size throughout life and does not shed cells
135
What can disrupt lens clarity
Accumulated post synthesis modified components
| Several types of accumulated materials give rise to cataract types
136
What is the lens composed of
Water
Protein
Lipids/cholesterol
137
Most simple sugars can be metabolized, but which one is most predominant
Glucose
138
Does the lens metabolize lipids and amino acids
Yes, they are incorporated in to structural components
139
Describe anaerobic glycolysis of the lens
The most active energy metabolism in the lens
| Provides 70%
140
What does the HMP shunt do in the lens
Secondary producing NADPH and -10% of lens energy
141
Where does the rest of the 20% come from
It is derived from the metabolism of lactic acid and the glucose in lens epithelium cells that utilize the TCA and ET
142
Since the lens has no blood supply where does it get its glucose from
The posterior or anterior lens surfaces that contacts other mediums such as the aqueous humor
143
How is glucose taken up by the aqueous
Facilitated diffusion
144
How is the transport of glucose among lens cells accomplished
A network of low resistance gap junctions between cells
This allows for efficient distribution of glucose, even to lens buried deep toward the center of the lens
145
Is the ens affected by anaerobic conditions?
It is unaffected because of its reliance on anaerobic glycolysis for energy
146
How are wastes removed from the lens
What are some examples of wastes removed
Ex. Lactic acid
It is removed at a steady rate via diffusion to aqueous humor and then to blood stream
147
How does the anterior Y suture appear
Y
148
How does the posterior Y suture appear
An upside down Y
149
What are the functions of the lens
- Refracts light to be focused on the retina
- 1/3 D power of eye (15D)
- allows accommodation of near objects
- absorbs UV lights and thus protects the retina from UV damage
150
What is the composition of the lens
Water (65%)
Proteins (35%)
Other stuff (1%)
151
What protein groups are contained in the lens
```
Water soluble (crystallins)
Urea soluble (crystallins and cytoskeleton)
Insoluble (membrane proteins)
```
152
What are the groups of crystallins
Alpha
Beta
Gamma
153
What do alpha crystallins do
Produce a phenomenon that contributes to lens transparency and gives the lens a significantly higher index of refraction than surrounding fluids
154
What does alpha crystallins provide resistance to
Degradation of the other crystallins beta and gamma
| It is a molecular chaperone
155
What is important of the concentration of crystallin
It varies throughout the lens
| Provides a refractive index gradient that is higher in the nucleus than the cortical surface
156
What is reduced in the lens due to gradient index system and peripheral flattening
Spherical aberration
157
What allows for transparency in the cellular level
```
Small lens fibers
Uniformity of lens fibers
Regular packing
Paucity of organelles
Avascular
```
158
What allows transparency at the molecular level
Proteins are uniform and small
The concentration increases towards the nucleus and creates an RI gradient that is higher in the nucleus than in teh cortical space
159
Hw does water contribute to the transparency of the lens
Water is pumped out of the lens from the anterior surface by Na/K pump
Water enters the lens from the back because the osmotic pressure
160
What is the mitotic activity of the lens
Mitosis of secondary fiber cells occurs in the germanitive zone of anterior lens epithelium
After mitosis, lens fiber cells gradually migrate through the transition zone and into the equator where elongation occurs
161
What is glutathione
Primary protector against oxidative damage in the lens
It is transported into the lens from the aqueous and can be synthesized from lens epithelial cells and superficial fiber cells
Glutathione detoxifies hydrogen peroxide
162
Where is ascobric acid higher
Has higher concentration in the lens than aqueous
163
How does accommodation decrease in old age
Ability of accommodation decreases by 1/4 of the age (Hofstetters formula)
164
What is age related nuclear cataract
Decline of glutathione, making the fibers susceptible to oxidative damage
Older nuclear fibers lose organelles and their nucleus and gain yellow-brown pigment
165
What is age related cortical cataract
Decrease in glutathione
Increase in Ca, Na, and water
Water forms a lake that separates cells and creates vacuoles. These create light scatter and the cells burst, proteins are exposed and oxidized. Forming a cataract
166
What is posterior subcapsular cataract
Epithelial like cells migrate from the equatorial region and accumulate in the posterior pole forming an opacity
167
What happens to crystallins with age
Decrease (especially alpha)
168
What happens to lens thickness with age
Thickens (0.22mm per year)
169
What happens to the anterior capsule with age
Posterior capsule?
Increases
Posterior: stable
170
What appends to the radius of curvature for anterior and posterior lens with age
Decreases
171
What happens to the center of the lens with age
Anterior chamber depth?
Center moves anterior with age
Anterior chamber depth decreases with age
172
What happens to the amino acids in the eye with age
Decreases
173
What is a diabetic cataract?
How does it form?
What accumulates?
Inclusion insensitive buildup of BG
There is an increase in sorbitol, osmotic pressure, and water. This causes swelling and a cataract will form
Depletion of NADPH during sorbitol production causes glutathione not being able to reduce free radicals so there will be an increase in oxidative stress.
Polymerization of proteins
174
How can there be changes in refractive error in the aging eye
Thickness Change, radius of curvature change, ex changes
Unusual changes in Rx May indicate uncontrolled diabetes
