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Ocular Phys > B11 > Flashcards

B11 Flashcards

1
Q

The RPE is a monolayer of pigmented cells, located between _________ and ________

A

Choriocapillaris and outer segments of photoreceptors

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2
Q

The apical membrane of the RPE faces the photoreceptor _______

A

Outer segments

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3
Q

What surrounds the light sensitive outer segments of the RPE?

A

Long apical microvilli

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4
Q

The _____ membrane faces Bruchs membrane

A

Basolateral

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5
Q

Light energy is concentrated on the?

A

Retina

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6
Q

General light absorption occurs via ____ in RPE

A

Melanin

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7
Q

Blue light absorption is supplemented by ___ and ___ in photoreceptors

A

Lutein and zeaxanthin

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8
Q

What is the most dangerous light to the RPE?

A

Blue light

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9
Q

The outer retina is exposed to what kind of environment?

A

Oxygen rich

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10
Q

T/F: The blood perfusion of the choriocapillaris is very high in the outer retina

A

True

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11
Q

Venous blood from the choriocapillaris shows a ___% O2 saturation

A

90%

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12
Q

RPE contains high amounts of superoxide dismutase and catalase

A

Enzymatic antioxidants

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13
Q

RPE accumulates lutein and zeaxanthin, ascorbate, alpha-tocopherol and beta-carotene

A

Non-enzymatic antioxidants

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14
Q

The RPE transports nutrients and metabolic end products

between ______and the _______

A

Photoreceptors and choriocapillaris

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15
Q

Is blood on the apical or basolateral side?

A

Basolateral

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16
Q

Are the photoreceptors on the apical or basolateral side?

A

Apical

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17
Q

The space between RPE and photoreceptors

A

Subretinal space

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18
Q

What are the two ways of transport in the RPE?

A

Photoreceptors—>blood

Blood—>photoreceptors

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19
Q

The transport of water is driven by _______ of Cl- from the retina to blood side

A

Active transport

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20
Q

Describe Bests Vitelliform Macular Degeneration

A
  • Degeneration of RPE
  • Bull’s eye shaped lesion
  • The lesion primarily contains extracellular fluid
  • Reduction in epithelial Cl- transport
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21
Q

The transport of lactic acid requires a tight regulation of the ______PH

A

Intercellular

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22
Q

The RPE contains an abundance of what 2 glucose transporters?

A

GLUT1 and GLUT3

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23
Q

An important substance of building membranes of neurons, photoreceptors as well as photoreceptor disk membrane

A

Docosahexaenoic acid (DHA)

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24
Q

What two things are removed from the apical side?

A

Water and lactic acid

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25
Q

The reduction of all-tran retinal into all trans-retinol occurs where?

A

In photoreceptors

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26
Q

Reisomerization of all-trans-retinol into 11-cis-retinal occurs in?

A

The RPE

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27
Q

Describe retinitis pigmentosa

A
  • inherited retinal degeneration
  • mutations in genes of the visual cycle
  • inability of the RPE to phagocytose photoreceptor outer segments
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28
Q

Describe stargardt disease

A
  • retinal degeneration

- mutations in the genes of the visual cycle

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29
Q

The process of phagocytosis is under what kind of control?

A

Circadian control

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30
Q

What triggers phagocytic activity?

A

The onset of light in the morning

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31
Q

Every RPE cell is facing an average of _____ photoreceptors in the fovea

A

23

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32
Q

When does the whole length of a photoreceptor outer segment get renewed?

A

Every 11 days

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33
Q

What must occur in order to keep excitability of photoreceptors ?

A

The tips of photoreceptor outer segments that contain the highest concentration of photo-damaged substances are shed from photoreceptors

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34
Q

Shed photoreceptor outer segments are phagocytosized by?

A

RPE

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35
Q

A defect of RPE photoreceptor phagocytosis may also cause retinal degeneration in usher type 1B patients

A

Usher syndrome

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36
Q

What are the 3 actions of PEDF?

A
  • Antiangiogenic factor
  • Inhibits endothelial cell proliferation
  • Stabilizes the endothelium of the choriocapillaris
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37
Q

What is secreted in low concentrations in the healthy eye?

A

VEGF

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38
Q

Name 2 actions of VEGF

A
  • Prevents endothelial cell apoptosis

- Stabilizes the endothelium of the choriocapillaris

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39
Q

What are some other factors that are essential for maintenance of the structural integrity of the retina?

A
  • TIMP1

- TIMP3

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40
Q

The most severe complication in age-related macular degeneration

A

Choroidal neovascularization

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41
Q

In choroidal neovascularization, do RPE cells secrete VEGF at higher or lower rates compared to RPE cells from eyes without neovascularization?

A

Higher

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42
Q

What are the 2 parts of the retinal-blood barrier

A
  • retinal vascular endothelium

- tight junctions between RPE

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43
Q

Photoreceptors are on the ____ side and choriocapillaris are on the _____ side of the RPE

A
  • P= apical

- C=basolateral

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44
Q

What absorbs blue light?

A

Lutein and zeaxanthin

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45
Q

The driving force to remove water form the apical side

A

Active transport of Cl- from retina to blood

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46
Q

Where does reisomerization of all-trans-retinol into 11-cis-retinal occur?

A

RPE

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47
Q

Which growth factor gets involved in choroidal neovasculization?

A

VEGF

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48
Q

Which disease is due to reduction of epithelia Cl- transport?
A. Retinitis pigmentosa
B. Best’s Vitelliform Macular Degeneration

A

B

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49
Q

What are 2 characteristics of photoreception

A
  • light detection

- photo absorption

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50
Q

Light detection that lead to vision and depends on photoreceptors (specialized light- sensitive neurons)

A

Photoreception

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51
Q

Photon absorption by visual pigment that is lying on one of the discs in the outer segment of photoreceptors

A

Photoreception

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52
Q

Dim light and motion

A

Peripheral/scotopic

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53
Q

Color and detail

A

Central/photopic

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54
Q

Scotopic visual system

A

Rods

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55
Q

Photopic visual system

A

Cones

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56
Q

Name 4 characteristics of rods

A
  • Not good for detailed vision
  • No color vision
  • Very sensitive, good for dim vision
  • Lower sensitivity to rapidly changing stimuli
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57
Q

Name 4 characteristics of cones

A
  • Specialized for detailed vision
  • Specialized for color vision
  • Less sensitive
  • Higher sensitivity to rapidly changing stimuli
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58
Q

Are there rods in the fovea?

A

No

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59
Q

Rods comprise ___ of photoreceptors

A

97%

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60
Q

Rod peak absorption

A

500-510nm

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61
Q

Does rod convergence increase of decrease sensitivity?

A

Increases

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62
Q

Where do many rods gather light information on?

A

Onto one retinal bipolar cell

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63
Q

Are there more rods or cones?

A

Rods

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64
Q

Are cones more prominent in the fovea or the periphery?

A

Fovea

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65
Q

What are the 3 different types of cones?

A
  • red (L cones)
  • green (M cones)
  • blue (S cones)
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66
Q

What is the wavelength of red cones?

A

560nm

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67
Q

What is the wavelength of green cones?

A

530nm

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68
Q

What is the wavelength of blue cones?

A

420nm

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69
Q

What type of cones are not in the fovea?

A

Blue cones (S)

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70
Q

Doe cones have convergence?

A

Nope

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71
Q

Are unstable pigments that undergo a chemical change when they absorb light

A

Photopigments

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72
Q

What makes up photopigments?

A

Protein (opsin) + chromophore

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73
Q

What makes up rhodopsin?

A

Opsin + 11-cis-retinal (chromophore)

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74
Q

What pigment is used for vision in dim light?

A

Rhodopsin

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75
Q

Is rhodopsin soluble or insoluble in water?

A

Insoluble

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76
Q

T/F: Rhodopsin is more stable and more abundant than cone pigments

A

True

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77
Q

What are the 3 types of iodopsins?

A
  • erythrolabe
  • chlorolabe
  • cyanolabe
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78
Q

Photopsin I + 11-cis-retinal absorption max for yellow/red (L-cones)

A

Erythrolabe

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79
Q

Photopsin II + 11-cis-retinal absorption max for green (M-cones)

A

Chlorolabe

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80
Q

Photopsin III + 11-cis-retinal absorption max for bluish/violet (S-cones)

A

Cyanolabe

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81
Q

Is the series of biochemical events that lead from photon capture by a photoreceptor cell to its hyperpolarization and slowing of neurotransmitter release at the synapse

A

Phototransduction

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82
Q

Is the transformation of light into electrical and chemical signals that produces the perception of light

A

Phototransduction

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83
Q

What are the steps of phototransduction?

A

Photoreception–>biochemical cascade–>electronic spread–>slowing of NT release

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84
Q

What is the important channel in the biochemical cascade?

A

Cyclic-GMP-Gated Cation Channel (CNG channel)

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85
Q

CNG channel allows what 3 things to enter the cell?

A
  • NA+
  • K+
  • Ca2+
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86
Q

T/F: CNG channel causes the cells to be partially depolarized

A

True

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87
Q

In the dark, rods have a resting membrane potential of about ___

A

-50mV

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88
Q

For other neurons, the resting membrane potential of about ____

A

-70mV

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89
Q

There is net flux of cation outer of inner segment plasma membrane and a net flux of cations into the outer segment plasma membrane, as well as electrical conductance between the inner and outer segment, a complete circuit is made

A

Dark current

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90
Q

What is the beginning step of biochemical cascade of phtototransduction?

A

Photoisomerization of rhodopsin

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91
Q

What converts 11-CIS-retinal to all-trans-retinal?

A

Light

92
Q

Reduction of all-trans-retinal into all-trans-retinol

occurs in?

A

Photoreceptors

93
Q

Reisomerization of all-trans-retinol into 11-cis-retinal

occurs in?

A

RPE

94
Q

What is the second step of the biochemical cascade of Phototransduction?

A

G-protein activation

95
Q

Metarhodopsin II encounters an _____ G protein

A

Inactive

96
Q

What comes to lie over the metarhodopsin II?

A

The Ga subunit of the G protein

97
Q

GDP is replaced by___ in the biochemical cascade

A

GTP

98
Q

Is it on or off when G protein binds to GTP?

A

On

99
Q

Is it on or off when G protein binds to GDP?

A

Off

100
Q

When is the G protein active in the biochemical cascade?

A

When GTP behinds to the Ga subunit

101
Q

The unit that separates from both Metarhodopsin

and the βγ portion of the G protein

A

Ga-GTP

102
Q

What is the 3rd step of biochemical cascade of Phototransduction?

A

PDE6 activation

103
Q

What does the activated G protein bind with in the biochemical cascade?

A

PDE6

104
Q

The activated PDE6 coverts the ____ into ___

A

cGMP into GMP

105
Q

PDE can degrade cGMP by hydrolyzing cGMP into ____

A

5’-GMP

106
Q

What is the final step of the biochemical cascade of phototransduction?

A

Channel closing

107
Q

What does the reduction of cGMP concentration cause?

A

CNG channel closure

108
Q

T/F: Opening of CNG channel put photoreceptors at resting dark-adapted state

A

True

109
Q

What are 3 characteristics of electronic spread

A
  • closing of channels
  • photocurrent in dark
  • photocurrent in light
110
Q

Closing of channels in the electronic spread reduces the flow of __ and ___ ions into the cell, reducing the dark current and make the membrane potential more ____

A

Na+ and Ca2+

Make it more negative (hyperpolarized)

111
Q

Cations moving into the cell (electronic spread)

A

Photo current in dark

112
Q

A single photo isomerization closes ion channels and cause a 2% reduction in the photocurrent

A

Photocurrent in light

113
Q

Communication of rods with downstream bipolar

cells by the release of ____

A

Glutamate

114
Q

Name the 3 characteristics of slowing of NT release

A

-Communication of rods with downstream bipolar
cells by the release of glutamate
-High level of glutamate release by rods signal total darkness to bipolar cells
-Reduction in the level of glutamate release due to absorption of light

115
Q

____ level of glutamate release by rods signal

total darkness to bipolar cells

A

High

116
Q

What are the 2 factors of phototransduction?

A
  • amplification

- adaptation

117
Q

Amplification
1 Rhodopsin: _____G proteins
1 Rhodopsin: _____PDE
1 PDE: ___cGMP hydrolysis

A

100 G proteins

800 PDE

100cGMP

118
Q

Phototransdution adaptation _____ sensitivity to light, ___ sensitivity in response to bright light, ___ sensitivity in response to dim light, controlled by ___ influx

A
  • Alters sensitivity to light
  • Decreases sensitivity in response to bright light
  • Increases sensitivity in response to dim light
  • Controlled by Ca2+ influx
119
Q

What photoreceptor sensitivity increases due to convergence?

A

Rods

120
Q

What is the key molecule of biochemical cascade to keep CNG channel open?

A

CGMP

121
Q

What is the NT between rods and bipolar cells?

A

Glutamate

122
Q

List the steps of phototransduction

A

Photoreception–>biochemical cascade (channel closure)–> electronic spread (cells hyperpolarized)–> slowing glutamate release

123
Q

a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.

A

Synapse

124
Q

An excitatory NT

A

Glutamate

125
Q

2 inhibitory NT

A

GABA and glycine

126
Q

A change in a cells membrane potential that makes it more negative

A

Hyperpolarization

127
Q

Hyperpolarization inhibits APs by ____the stimulus required to move the membrane potential to the AP threshold

A

Increasing

128
Q

A change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell.

A

Depolarization

129
Q

What 2 cells are light evoked signals transferred onto?

A

Bipolar and horizontal cells

130
Q

What cells provide lateral interactions in the outer plexiform layer (OPL)

A

Horizontal cells

131
Q

What cells transfer the light signals into the inner plexiform layer (IPL), onto the amacrine and ganglion cells

A

Bipolar cells

132
Q

collect the signals ofbipolar and amacrine cells and

transmit these signals to the visual centers of the brain.

A

Ganglion cells

133
Q

What type of NT do cone pedicles have?

A

Glutamate

134
Q

Is glutamate high or low in darkness?

A

High

135
Q

Is glutamate increased or reduced by light?

A

Reduced by light

136
Q

What are the 2 different sets of glutamate receptors in cones?

A
  • off cone bipolar cells

- on cone bipolar cells

137
Q

Are ON cone bipolar cells hyperpolarized or depolarized by light?

A

Depolarized

138
Q

Off cone and bipolar cells and horizontal cells are

____ by light

A

Hyperpolarized

139
Q

Where do OFF cone bipolar cells transfer signals onto?

A

Onto OFF ganglion cells

140
Q

Where do ON cone bipolar cells transfer signals onto?

A

ON ganglion cells

141
Q

Where do density of cones, bipolar cells, and ganglion cells increase steeply?

A

Towards e center of the retina

142
Q

The optimized visual acuity in central retina requires a ___ cone density and a ____ cone-to-RGC ratio

A

high cone density and a low cone-to-RGC ratio

143
Q

One cone connected to a midget bipolar cells connected to a midget ganglion cells

A

Midget system

144
Q

Concomitant with the increase in density, the bipolar cells and ganglion cells’ dendritic fields become smaller or larger?

A

Smaller

145
Q

What type of NT are in rod spherule?

A

Glutamate

146
Q

How many types of rod bipolar cells are there?

A

One

147
Q

What is the only rod bipolar cell?

A

ON bipolar cells

148
Q

Are ON rod bipolar cells depolarized or hyperpolarized by light?

A

Depolarized

149
Q

What is the result of ON center ganglion cells with light on the center of the receptive field only?

A

Ganglion cell fires rapidly

150
Q

What is the result of OFF center ganglion cells with light on the center of the receptive field only?

A

Ganglion cells do not fire

151
Q

What is the result of ON center ganglion cells with light on the surround only?

A

Cells do not fire

152
Q

What is the result of OFF center ganglion cells with light on the surround only?

A

Cell fires rapidly

153
Q

What is the result of ON center ganglion cells with no light on the center or surround?

A

Cells do not fire

154
Q

What is the result of OFF center ganglion cells with no light on the center or surround?

A

Cells do not fire

155
Q

What is the result of ON center ganglion cells with light on the center and surround?

A

Weak response

156
Q

What is the result of ON center ganglion cells with light on the center and surround?

A

Weak response

157
Q

Modulate the glutamate release by shifts the

activation curves of the cone pedicle Ca2+ channels

A

Cone horizontal cells

158
Q

Modulate the glutamate release by shifts the activation curves of the rod spherule Ca2+ channels

A

Rod horizontal cells

159
Q

Rod horizontal cells releases ____ providing inhibition of bipolar cell dendrites

A

GABA

160
Q

Name the 4 glutamatergic neurons

A
  • rods
  • cones
  • bipolar cells
  • most ganglion cells
161
Q

Name the 2 GABAergic and glycinergic neurons

A
  • horizontal cells

- most amacrine cells

162
Q

Name 4 aging changes in the retina

A

-Nerve fibers within the optic nerve decreases, optic
cup diameter increases
-ILM thickens with age (foveal reflex becomes
dimmer)
-Total # of RPE cells decrease significantly with
age; lipofuscin within RPE cells increases and drusen
increases
-Atrophy increases throughout the retina

163
Q

An age related retinal atrophy where there is pigmentation in RPE and choroid decreases

A

Tigroid fundus

164
Q

An age related atrophy with peripheral RPE degeneration

A

Reticular degeneration

165
Q

Which type of cells plays a role in transmitting cones signal to RGC?

A

Cone bipolar cells

166
Q

Whay types of cells plays a role in transmitting rod signals to RGC?

A

Rod bipolar cells and amacrine cells

167
Q

What change does ON bipolar cells have with light?

A

Depolarization

168
Q

What kind of NT do bipolar cells contain?

A

Glutamate

169
Q

When the center of RGCs receptive field is exposed to light, which type of RGC is stimulated?

A

ON-center RGC

170
Q

Will you have a dimmer foveal reflex when you get older?

A

Yes

171
Q

What type of GLUT transporter is insulin dependent and are not found in the retina?

A

GLUT 4

172
Q

Hat are the 3 major energy producing metabolic pathways in retinal metabolism?

A

-Glycolysis
_TCA
-ETC

173
Q

When is lactic acid produced in the largest quantities?

A

During sleep or condition that block atmospheric O2 from being absorbed by the eye

174
Q

What 3 things does ascorbic acid do in terms of protecting the retina and the lens?

A
  • scavengers free radicals
  • protects against UV damage
  • protects against inflammatory responses
175
Q

Wen the eye subjected to endotoxins which of the following compounds would protect the eye?

A

Ascorbic acid

176
Q

Consider the effect of topical epinephrine to the eye. What effect of metabolism would you expect?

A

There would be a reduction in oxygen flow due to constriction of vessels

177
Q

Considering the fact that you dont have vascularization of the lens tissue, what is the primary mechanism for the transport of metabolism for energy in the lens?

A

Low resistance gap junctions

178
Q

Name the 2 predominate energy sources for the lens

A
  • HMP shunt

- Anaerobic glycolysis

179
Q

What does the HMP shunt pathway do in the lens?

A
  • helps sends intermediates in different directions

- produces NADPH

180
Q

The process involved in maintaining the lens is limited to ____ in order to maintain transparency

A

Anaerobic respiration of glycolysis

181
Q

Since the lens is 1/3 proteins, have an energy source that is consistent throughout life is important to have clarity. So what type of energy source do you not want?

A

One that doesn’t promote oxidation effects (you want to maintain proteins)

182
Q

What are the 4 functions of the lens?

A
  • refracts light to be focused on the retina
  • provides 1/3 of the total dioptric power of the eye (15D)
  • allows for accommodation of near objects
  • absorbs UV lights and protects the retina from UV damage
183
Q

The lens is composed mainly of what 2 things?

A

Water and proteins

184
Q

The proteins make up ___% of the lens

A

30-35

185
Q

What are the percentage of water soluble proteins in the lens?

A

90%

186
Q

What type of water soluble/crystalline type is the most prominent?

A

Alpha (40%)

187
Q

Produces a phenomenon that contributes to lens

transparency, and gives the lens a significantly higher index of refraction than surrounding fluids

A

Alpha crystalline

188
Q

Offers resistance to the degradation of the other

crystalline, beta and gamma, and is called a molecular chaperone

A

Alpha crystalline

189
Q

Crystalline concentration varies among the lens, providing a refractive index gradient that is ____in the nucleus, than the outer cortical surface

A

Higher

190
Q

Spherical aberration in the lens is _____due to the gradient index system and peripheral flattening

A

Reduced

191
Q

Do we want extra water in the lens?

A

No it will be destructive

192
Q

Water is pumped out of the lens from the anterior surface by _______

A

Na+/K+ pump

193
Q

Water enters the lens from the ____ because of osmotic pressure

A

Back

194
Q

Are proteins uniform or un-uniform in the lens?

A

Uniform

195
Q

Are proteins small or large in the lens?

A

Small

196
Q

Proteins concentration ___ towards the nucleus, and creates a RI gradient that is ____ in the nucleus, than the outer cortical space

A

Increase and creates a RI gradient that is higher in the nucleus

197
Q

Where do mitosis of secondary fiber cells occur?

A

In the germinative zone of anterior lens epithelium

198
Q

After mitosis, lens fiber cells gradually migrate through the ____ and into the _____ where elongation occurs

A

Through the transition zone and into the equator

199
Q

What is the primary protector against oxidative damage in the lens?

A

Glutathione

200
Q

Glutathione detoxifies _____

A

Hydrogen peroxide

201
Q

Ascorbic acid has a ____ concentration in the lens than the aqueous

A

Much Higher

202
Q

Glutathione is transported into the lens from the aqeuous and can be synthesized from ____ cells and ____ cells

A

Lens epithelial cells and superficial fiber cells

203
Q

What are 3 forms of cataracts?

A
  • age related nuclear cataract
  • age related cortical cataract
  • posterior subcapsular cataract
204
Q

The ability of accommodation____ by one quarter of the age

A

Decreases

205
Q

Change in osmolarity causes changes in what 3 things?

A
  • thickness
  • radius of curvature
  • rx
206
Q

Unusual changes in rx may indicate _____

A

Uncontrolled diabetes

207
Q

What type of proteins does the lens contain the most of?

A

Crystalline

208
Q

T/F: the lens absorbs blue light the most to protect the retina

A

False

209
Q

Where does Na+/K+ pump located to helping pumping out of water?

A

Anterior epithelium

210
Q

What option is the best driving force of water entering the lens from the back?

A

Osmotic pressure

211
Q

Which part is responsible for formation of the secondary lens fibers?

A

Anterior epithelium

212
Q

What type of changes in the lens are caused by accumulation of sorbitol?

A

Cataract and rx changes

213
Q

What are the 5 transparency characteristics of the lens at the cellular level?

A
  • small lens fibers
  • uniformity of lens fibers
  • regularity of packing
  • paucity of organelles
  • avascular
214
Q

In an age related nuclear cataract a decline of ___ makes the fibers susceptible to oxidative damage

A

Glutathione

215
Q

When older nuclear fibers lose organelles and their nucleus and gains yellow-brown pigment

A

Age-related nuclear cataract

216
Q

In an age related cortical cataract, a decrease in glutathione activity will increase what 3 things?

A

Ca, Na, and water

217
Q

A cataract when water forms lake, lakes separate cells, water vacuoles created, cause light scatter, cells burst, proteins exposed, proteins oxidized,
cataracts are formed

A

Age related cortical cataract

218
Q

When epithelial-like cells migrate from the equatorial region and accumulate at the posterior pole forming an opacity.

A

Posterior subcapsular cataract

219
Q

Do crystalline decrease with age?

A

Yes!

220
Q

The lens thickness increases ___ per year

A

0.22mm

221
Q

The anterior lens capsule ___ with age, and the posterior lens capsule is ____ with age

A

ALC increases with age, and the PLC is relatively stable with age

222
Q

Does the radius of curvature for the anterior and posterior lens increase or decrease with age?

A

Decreases

223
Q

The center of the lens moves ___ with age, and the anterior chamber depth ___ with age.

A

The centers of the lens moves anterior, and the anterior chamber depth decreases with age

224
Q

Do amino acids decrease with age?

A

Yes

225
Q

Is sorbitol hydrophobic or hydrophilic?

A

Hydrophilic

226
Q

Glutathione required ___ to reduce free radicals

A

NADPH

227
Q

When you have insulin insensitive build-up of blood glucose with an increase in sorbitol production

A

Diabetic cataract

Ocular Phys (6 decks)

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