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Flashcards in B11 Deck (227):
1

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

Choriocapillaris and outer segments of photoreceptors

2

The apical membrane of the RPE faces the photoreceptor _______

Outer segments

3

What surrounds the light sensitive outer segments of the RPE?

Long apical microvilli

4

The _____ membrane faces Bruchs membrane

Basolateral

5

Light energy is concentrated on the?

Retina

6

General light absorption occurs via ____ in RPE

Melanin

7

Blue light absorption is supplemented by ___ and ___ in photoreceptors

Lutein and zeaxanthin

8

What is the most dangerous light to the RPE?

Blue light

9

The outer retina is exposed to what kind of environment?

Oxygen rich

10

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

True

11

Venous blood from the choriocapillaris shows a ___% O2 saturation

90%

12

RPE contains high amounts of superoxide dismutase and catalase

Enzymatic antioxidants

13

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

Non-enzymatic antioxidants

14

The RPE transports nutrients and metabolic end products
between ______and the _______

Photoreceptors and choriocapillaris

15

Is blood on the apical or basolateral side?

Basolateral

16

Are the photoreceptors on the apical or basolateral side?

Apical

17

The space between RPE and photoreceptors

Subretinal space

18

What are the two ways of transport in the RPE?

Photoreceptors--->blood
Blood--->photoreceptors

19

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

Active transport

20

Describe Bests Vitelliform Macular Degeneration

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

21

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

Intercellular

22

The RPE contains an abundance of what 2 glucose transporters?

GLUT1 and GLUT3

23

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

Docosahexaenoic acid (DHA)

24

What two things are removed from the apical side?

Water and lactic acid

25

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

In photoreceptors

26

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

The RPE

27

Describe retinitis pigmentosa

-inherited retinal degeneration
-mutations in genes of the visual cycle
-inability of the RPE to phagocytose photoreceptor outer segments

28

Describe stargardt disease

-retinal degeneration
-mutations in the genes of the visual cycle

29

The process of phagocytosis is under what kind of control?

Circadian control

30

What triggers phagocytic activity?

The onset of light in the morning

31

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

23

32

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

Every 11 days

33

What must occur in order to keep excitability of photoreceptors ?

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

34

Shed photoreceptor outer segments are phagocytosized by?

RPE

35

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

Usher syndrome

36

What are the 3 actions of PEDF?

-Antiangiogenic factor
-Inhibits endothelial cell proliferation
-Stabilizes the endothelium of the choriocapillaris

37

What is secreted in low concentrations in the healthy eye?

VEGF

38

Name 2 actions of VEGF

-Prevents endothelial cell apoptosis
-Stabilizes the endothelium of the choriocapillaris

39

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

-TIMP1
-TIMP3

40

The most severe complication in age-related macular degeneration

Choroidal neovascularization

41

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

Higher

42

What are the 2 parts of the retinal-blood barrier

-retinal vascular endothelium
-tight junctions between RPE

43

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

-P= apical
-C=basolateral

44

What absorbs blue light?

Lutein and zeaxanthin

45

The driving force to remove water form the apical side

Active transport of Cl- from retina to blood

46

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

RPE

47

Which growth factor gets involved in choroidal neovasculization?

VEGF

48

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

B

49

What are 2 characteristics of photoreception

-light detection
-photo absorption

50

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

Photoreception

51

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

Photoreception

52

Dim light and motion

Peripheral/scotopic

53

Color and detail

Central/photopic

54

Scotopic visual system

Rods

55

Photopic visual system

Cones

56

Name 4 characteristics of rods

-Not good for detailed vision
-No color vision
-Very sensitive, good for dim vision
-Lower sensitivity to rapidly changing stimuli

57

Name 4 characteristics of cones

-Specialized for detailed vision
-Specialized for color vision
-Less sensitive
-Higher sensitivity to rapidly changing stimuli

58

Are there rods in the fovea?

No

59

Rods comprise ___ of photoreceptors

97%

60

Rod peak absorption

500-510nm

61

Does rod convergence increase of decrease sensitivity?

Increases

62

Where do many rods gather light information on?

Onto one retinal bipolar cell

63

Are there more rods or cones?

Rods

64

Are cones more prominent in the fovea or the periphery?

Fovea

65

What are the 3 different types of cones?

-red (L cones)
-green (M cones)
-blue (S cones)

66

What is the wavelength of red cones?

560nm

67

What is the wavelength of green cones?

530nm

68

What is the wavelength of blue cones?

420nm

69

What type of cones are not in the fovea?

Blue cones (S)

70

Doe cones have convergence?

Nope

71

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

Photopigments

72

What makes up photopigments?

Protein (opsin) + chromophore

73

What makes up rhodopsin?

Opsin + 11-cis-retinal (chromophore)

74

What pigment is used for vision in dim light?

Rhodopsin

75

Is rhodopsin soluble or insoluble in water?

Insoluble

76

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

True

77

What are the 3 types of iodopsins?

-erythrolabe
-chlorolabe
-cyanolabe

78

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

Erythrolabe

79

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

Chlorolabe

80

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

Cyanolabe

81

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

Phototransduction

82

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

Phototransduction

83

What are the steps of phototransduction?

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

84

What is the important channel in the biochemical cascade?

Cyclic-GMP-Gated Cation Channel (CNG channel)

85

CNG channel allows what 3 things to enter the cell?

-NA+
-K+
-Ca2+

86

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

True

87

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

-50mV

88

For other neurons, the resting membrane potential of about ____

-70mV

89

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

Dark current

90

What is the beginning step of biochemical cascade of phtototransduction?

Photoisomerization of rhodopsin

91

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

Light

92

Reduction of all-trans-retinal into all-trans-retinol
occurs in?

Photoreceptors

93

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

RPE

94

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

G-protein activation

95

Metarhodopsin II encounters an _____ G protein

Inactive

96

What comes to lie over the metarhodopsin II?

The Ga subunit of the G protein

97

GDP is replaced by___ in the biochemical cascade

GTP

98

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

On

99

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

Off

100

When is the G protein active in the biochemical cascade?

When GTP behinds to the Ga subunit

101

The unit that separates from both Metarhodopsin
and the βγ portion of the G protein

Ga-GTP

102

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

PDE6 activation

103

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

PDE6

104

The activated PDE6 coverts the ____ into ___

cGMP into GMP

105

PDE can degrade cGMP by hydrolyzing cGMP into ____

5'-GMP

106

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

Channel closing

107

What does the reduction of cGMP concentration cause?

CNG channel closure

108

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

True

109

What are 3 characteristics of electronic spread

-closing of channels
-photocurrent in dark
-photocurrent in light

110

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 ____

Na+ and Ca2+
Make it more negative (hyperpolarized)

111

Cations moving into the cell (electronic spread)

Photo current in dark

112

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

Photocurrent in light

113

Communication of rods with downstream bipolar
cells by the release of ____

Glutamate

114

Name the 3 characteristics of slowing of NT release

-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

____ level of glutamate release by rods signal
total darkness to bipolar cells

High

116

What are the 2 factors of phototransduction?

-amplification
-adaptation

117

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

100 G proteins

800 PDE

100cGMP

118

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

-Alters sensitivity to light
-Decreases sensitivity in response to bright light
-Increases sensitivity in response to dim light
-Controlled by Ca2+ influx

119

What photoreceptor sensitivity increases due to convergence?

Rods

120

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

CGMP

121

What is the NT between rods and bipolar cells?

Glutamate

122

List the steps of phototransduction

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

123

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

Synapse

124

An excitatory NT

Glutamate

125

2 inhibitory NT

GABA and glycine

126

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

Hyperpolarization

127

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

Increasing

128

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

Depolarization

129

What 2 cells are light evoked signals transferred onto?

Bipolar and horizontal cells

130

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

Horizontal cells

131

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

Bipolar cells

132

collect the signals ofbipolar and amacrine cells and
transmit these signals to the visual centers of the brain.

Ganglion cells

133

What type of NT do cone pedicles have?

Glutamate

134

Is glutamate high or low in darkness?

High

135

Is glutamate increased or reduced by light?

Reduced by light

136

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

-off cone bipolar cells
-on cone bipolar cells

137

Are ON cone bipolar cells hyperpolarized or depolarized by light?

Depolarized

138

Off cone and bipolar cells and horizontal cells are
____ by light

Hyperpolarized

139

Where do OFF cone bipolar cells transfer signals onto?

Onto OFF ganglion cells

140

Where do ON cone bipolar cells transfer signals onto?

ON ganglion cells

141

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

Towards e center of the retina

142

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

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

143

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

Midget system

144

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

Smaller

145

What type of NT are in rod spherule?

Glutamate

146

How many types of rod bipolar cells are there?

One

147

What is the only rod bipolar cell?

ON bipolar cells

148

Are ON rod bipolar cells depolarized or hyperpolarized by light?

Depolarized

149

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

Ganglion cell fires rapidly

150

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

Ganglion cells do not fire

151

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

Cells do not fire

152

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

Cell fires rapidly

153

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

Cells do not fire

154

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

Cells do not fire

155

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

Weak response

156

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

Weak response

157

Modulate the glutamate release by shifts the
activation curves of the cone pedicle Ca2+ channels

Cone horizontal cells

158

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

Rod horizontal cells

159

Rod horizontal cells releases ____ providing inhibition of bipolar cell dendrites

GABA

160

Name the 4 glutamatergic neurons

-rods
-cones
-bipolar cells
-most ganglion cells

161

Name the 2 GABAergic and glycinergic neurons

-horizontal cells
-most amacrine cells

162

Name 4 aging changes in the retina

-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

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

Tigroid fundus

164

An age related atrophy with peripheral RPE degeneration

Reticular degeneration

165

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

Cone bipolar cells

166

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

Rod bipolar cells and amacrine cells

167

What change does ON bipolar cells have with light?

Depolarization

168

What kind of NT do bipolar cells contain?

Glutamate

169

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

ON-center RGC

170

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

Yes

171

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

GLUT 4

172

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

-Glycolysis
_TCA
-ETC

173

When is lactic acid produced in the largest quantities?

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

174

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

-scavengers free radicals
-protects against UV damage
-protects against inflammatory responses

175

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

Ascorbic acid

176

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

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

177

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?

Low resistance gap junctions

178

Name the 2 predominate energy sources for the lens

-HMP shunt
-Anaerobic glycolysis

179

What does the HMP shunt pathway do in the lens?

-helps sends intermediates in different directions
-produces NADPH

180

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

Anaerobic respiration of glycolysis

181

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?

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

182

What are the 4 functions of the lens?

-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

The lens is composed mainly of what 2 things?

Water and proteins

184

The proteins make up ___% of the lens

30-35

185

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

90%

186

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

Alpha (40%)

187

Produces a phenomenon that contributes to lens
transparency, and gives the lens a significantly higher index of refraction than surrounding fluids

Alpha crystalline

188

Offers resistance to the degradation of the other
crystalline, beta and gamma, and is called a molecular chaperone

Alpha crystalline

189

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

Higher

190

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

Reduced

191

Do we want extra water in the lens?

No it will be destructive

192

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

Na+/K+ pump

193

Water enters the lens from the ____ because of osmotic pressure

Back

194

Are proteins uniform or un-uniform in the lens?

Uniform

195

Are proteins small or large in the lens?

Small

196

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

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

197

Where do mitosis of secondary fiber cells occur?

In the germinative zone of anterior lens epithelium

198

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

Through the transition zone and into the equator

199

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

Glutathione

200

Glutathione detoxifies _____

Hydrogen peroxide

201

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

Much Higher

202

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

Lens epithelial cells and superficial fiber cells

203

What are 3 forms of cataracts?

-age related nuclear cataract
-age related cortical cataract
-posterior subcapsular cataract

204

The ability of accommodation____ by one quarter of the age

Decreases

205

Change in osmolarity causes changes in what 3 things?

-thickness
-radius of curvature
-rx

206

Unusual changes in rx may indicate _____

Uncontrolled diabetes

207

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

Crystalline

208

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

False

209

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

Anterior epithelium

210

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

Osmotic pressure

211

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

Anterior epithelium

212

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

Cataract and rx changes

213

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

-small lens fibers
-uniformity of lens fibers
-regularity of packing
-paucity of organelles
-avascular

214

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

Glutathione

215

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

Age-related nuclear cataract

216

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

Ca, Na, and water

217

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

Age related cortical cataract

218

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

Posterior subcapsular cataract

219

Do crystalline decrease with age?

Yes!

220

The lens thickness increases ___ per year

0.22mm

221

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

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

222

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

Decreases

223

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

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

224

Do amino acids decrease with age?

Yes

225

Is sorbitol hydrophobic or hydrophilic?

Hydrophilic

226

Glutathione required ___ to reduce free radicals

NADPH

227

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

Diabetic cataract