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Ocular Physiology > Block 11 > Flashcards

Block 11 Flashcards

1
Q

What is RPE

A

A monolayer of pigmented cells

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2
Q

Where is RPE located

A

Between choriocapillaris and outer segment of photoreceptors

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3
Q

Whe apical side of the RPE faces

A

Photoreceptors

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4
Q

The basal side of RPE faces

A

Bruchs membrane

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5
Q

General Light absorption in the RPE is due to

A

Melanin

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6
Q

Blue light is absorbed in the RPE due to

A

Lutein and zeaxanthin

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7
Q

What damage does RPE protect from

A

Oxidative damage

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8
Q

T/F the outer retina is exposed to an oxygen -rich environment

A

True

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9
Q

What does the RPE transport nutrients and wastes between

A

Photoreceptors and choriocapillaris

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10
Q

What are the 2 divisions of transepithelial transport in RPE

A

Transport from photoreceptors to blood

Transport from blood to photoreceptors

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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

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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

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13
Q

What is required to removal of lactic acid from apical side

A

Tight regulation of intracellular pH

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14
Q

What are some other substances that are transported to blood to photoreceptor

A

Glucose
All-trans-retinol
DHA

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15
Q

Where does the reduction of all-trans-retinAl into all-trans-retinOl occur

A

Photoreceptors

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16
Q

Where does the reisomerization of all-trans-retinOl into 11-cis-retinAl occur

A

RPE

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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

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18
Q

What causes Stargardt disease

A

Mutations in the genes of the visual cycle

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19
Q

What is phagocytosis controlled by

A

Circadian control

It is triggered by the onset of light in the morning

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20
Q

RPE cell faces an average of ___ photoreceptors in the fovea

A

23

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21
Q

Every ___ days a whole length of photoreceptor outer segment is renewed

A

11

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22
Q

What is Usher syndrome

A

A defect of RPE photoreceptor phagocytosis

Causes retinal degeneration in Usher type 1B patients

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23
Q

PEDF does

A

Antiangiogenic factor
Inhibits endothelial cell proliferation

Stabilizes the endothelium of the choriocapillaris

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24
Q

VEGF does

A

Low concentrations in healthy eye

Prevents endothelial cell apoptosis

Stabilizes the endothelium in the choriocapillaris

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25
Q

What are some other factors that the RPE secrete

A
  • Growth factors
  • factors that maintain structure of retina
  • cytokines or immune modulators
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26
Q

What happens in choroidal neovascualrizations

A

RPE cells secreted VEGF at a higher rate

Most severe complication in age-related MD

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27
Q

What is the retinal-blood barrier

A

Tight junctions between retinal pigment epithelium

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28
Q

What is photoreception

A

Light detection that leads to vision

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29
Q

What does photoreception depend on

A

Photoreceptors

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30
Q

What is photon absorption done by

A

Visual pigment that is lying on one of the discs in the outer segment of the photoreceptors

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31
Q

What is scotopic (peripheral vision)

A

Dim light

Motion

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32
Q

What is photopic (central) vision

A

Color

Detail

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33
Q

Scotopic vision utilizes

A

Rods

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34
Q

Photopic vision utilizes

A

Cones

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35
Q

Describe rods

A 
Not good for detail
No color
Very sensitive 
Good for dim 
Lower sensitivity to rapidly changing stimuli
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36
Q

Describe cones

A

Specialized for detail
Color vision
Less sensitive
Higher sensitivity for rapidly changing stimuli

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37
Q

T/F there are rods in the fovea

A

False

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38
Q

Where is the peak for cones

A

Fovea

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39
Q

Rods comprise of ____ of photoreceptors

A

97%

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40
Q

What is the rod peak wavelength sensitivity

A

500-510 nm

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41
Q

Rod convergence increases ______

A

Sensitivity

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42
Q

Cones are ____ of photoreceptors

A

3%

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43
Q

Where are their more cones

A

In the periphery

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44
Q

What are the 3 different cones

A

Red
Blue
Green

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45
Q

Red cone

A

L cone

Long wavelength

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46
Q

Green cone

A

M

Medium wavelength

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47
Q

Blue cone

A

S

Short wavelength

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48
Q

T/F there is convergence in the fovea

A

False

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49
Q

What are photopigments

A

Unstable pigments that undergo a chemical change when they absorb light

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50
Q

What makes up photopigments

A

Protein(opsin) + chromophore

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51
Q

What is rhodopsin

A

Opsin + 11-CIA-retinAl

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52
Q

What is rhodopsin used for

A

Dim light vision

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53
Q

Describe rhodopsin

A

Insoluble in water
More stable than cone pigments

More abundant

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54
Q

What are the 3 different iodopsins

A

Erythrolabe
Chlorolabe
Cyanolabe

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55
Q

What is the max absorption of erythrolabe

A

Yellow/red (L cones)

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56
Q

What is the max absorption for chlorolabe

A

Green

M cones

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57
Q

What is the max absorption for cyanolabe

A

Bluefish/violet

S cones

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58
Q

What makes up erythrolabe

A

Photopsin I + 11-cis-retinal

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59
Q

What makes up chlorolabe

A

Photopsin II + 11-is-retinal

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60
Q

What makes up cyanolabe

A

Photopsin III + 11-CIA-retinal

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61
Q

What is phototransduction

A

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

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62
Q

What are the steps of phototransduction

A

Photoreception> biochemical cascade> electronic spread> slowing of neurotransmitter release

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63
Q

What channel closes in phototransduction

A

CNG channel

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64
Q

What is the CNG channel

A

Cyclic GMP gated cation channel

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65
Q

What does CNG channel do

A

Allow NA and K and Ca to enter the cell

Cell will be partially depolarized

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66
Q

What is the dark current

A

Flow of cations into and out of the cell while in the dark

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67
Q

Know diagram on lecture 2 slide 18

A

Biochemical cascade

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68
Q

Where does the reduction of all-trans-retinal into all-trans-retinol occur

A

Photoreceptors

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69
Q

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

A

RPE

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70
Q

Look over the G protein activation on slide 21

A

Confusion

71
Q

Step 3 is PDE6 activation

A

Activated G protein binds with a molecule named cGMP phosphodiesterase PDE6

PDE6 converts cGMP into GMP

72
Q

Step 4 is channel closing

A

Reduction of cGMP concentration causes CNG channel closure

73
Q

What does closing of the Channels do

A

Reduces the flow of NA and Ca ions in the cell

Reduces the dark current and makes membrane potential more -

74
Q

What is the photocurrent in the dark

A

Cations move into the cell

75
Q

What is the photocurrent in light

A

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

76
Q

How do Rhodes communicate with downstream bipolar cells

A

Glutamate

77
Q

What does a high level of glutamate release signal

A

Darkness

78
Q

What causes a reduction in the level of glutamate due to

A

Absorption of light

79
Q

What is adaptation

A

Alters sensitive to light
Decreases sensitive to bright
Increases sensitivity to dim light

Controlled by Ca influx

80
Q

What are the major energy producing metabolic pathways

A

Glycolysis
TCA
ETC

81
Q

What are the sources of metabolites for the retina

A

Glycogen stores (retina)
Glucose (aqueous)
Amino acids (aqueous)
Saturated and unsaturated fatty acids (aqueous)

82
Q

How is glucose delivered

A

Derived from the serum

Simple diffusion into the aqueous

83
Q

What is the glucose level in the aqueous due to

A

There is a constant flux of glucose from the plasma in t het aqueous

84
Q

What is the aqueous glucose level compared to serum glucose

A

80%

85
Q

What contributes to the production of lactic acid (even in aerobic conditions)

A

Glucose metabolism of RETINA, ciliary epithelium, lens, cornea

86
Q

Why doesn’t lactic acid accumulate in the aqueous

A

There is quick trafficking away from the aqueous

87
Q

When is the most lactic acid made

A

During sleep of conditions that block atmospheric O2 from being absorbed by the eye
(Topical epinephrine in the eye)

88
Q

Where does the eye get O2 from

A

Atmosphere

Vitreous

89
Q

How is the O2 concentration in the vitreous from posterior to anterior

A

Higher posterior

Anterior is lower

90
Q

What does the vitreous serve as for the retina

A

An metabolic reservoir

Provides short-term nutrients during emergencies

91
Q

What is ascorbic acid

A

High levels in the vitreous
Vitreous to serum 9:1
Concentrated by active transport in ciliary epithelium
Supplied by the diet

92
Q

What are the reasons for high ascorbic acid

A
  • 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
Q

What is the evidence for the benefits of ascrobic acid

A

Supplements in dark-reared rats reduce irreversible type 1 light damage

And shift the light damage to reversible the 2 light damage

94
Q

What is the implication of ascorbic acid in inflammation

A

Ascorbic acid synthesis is unregulated in repsonse to inflammatory mediators such as histamine

95
Q

What transporter is responsible for the transport of glucose to the retina

A

GLUT3

96
Q

What transporter is insulin dependent and thus is NOT found in the retina

A

GLUT 4

97
Q

When the eye s subject to endotoxins that produce an inflammatory response what will protect the eye

A

Ascorbic acid

98
Q

What is a synapse

A

A junction between 2 nerve cells

Consists of a minute gap across which impulses pass by diffusion of a NT

99
Q

What type of NT is glutamate

A

excitatory

100
Q

What type of NT are GABA and Glycine

A

Inhibitory

101
Q

What is hyperpolarization

A

Makes cell membrane potential MORE NEGATIVE

Inhibits AP

102
Q

What is depolarization

A

Makes cell membrane potential more negative

103
Q

What are light-evoked signals transferred onto

A

Bipolar and horizontal cells

104
Q

What do horizontal cells provide interactions to

A

Lateral interactions in the OPL

105
Q

Where do bipolar cells transmit there signals to

A

IPL onto amacrine and ganglion cells

106
Q

What role do ganglion cells play in light transmission

A

They collect signals from bipolar and amacrine cells and transmit these signals to the visual centers in the brain

107
Q

What is the NT at the cone pedicle

A

Glutamate

108
Q

When is glutamate high

A

In darkness

It is reduced by light

109
Q

OFF cone bipolar cells and horizontal cells are _______ by light

A

Hyperpolarized

110
Q

ON cone bipolar cells are _______ by light

A

Depolarized

111
Q

OFF cone bipolar cells transfer signals into….

A

OFF ganglion cells

112
Q

ON cone bipolar cells transfer signal onto…..

A

ON ganglion cells

113
Q

Describe the density of cones, bipolar cells, and ganglion cells in the retina

A

They increase in number towards the center of the retina

114
Q

How do the retina cells at the center of the retina compare to those in the periphery

A

In the center they are smaller

In the periphery they gradually increase in size

115
Q

What causes the high VA in the central retina

A

High cone density

Low cone to RGC ratio

116
Q

What is the midget system

A

On e cone connected to a midget bipolar cell connected to a midget ganglion cell (1:1)

117
Q

What is the NT of the rod spherule

A

Glutamate

118
Q

When is glutamate high

A

In darkness

119
Q

What is the only type on rod bipolar cell

A

ON rod bipolar cells

120
Q

ON rod bipolar cells are _____ by light

A

Depolarized

121
Q

What is the rod pathway

A

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
Q

How do horizontal cells produce feedback in rods

A

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
Q

How do horizontal cells provide feedback for cones

A

Modulate the release of glutamte by shifting hot activation curves of the cone pedicab Ca2+ channels

124
Q

What are glutamatergic neruons

A

Rods
Cones
Bipolar cells
Most ganglion cells

125
Q

What are GABAergic and Glycinergic neurons

A

Horizontal cells

Most amacrine cells

126
Q

How does the optic nerve change with age

A

Nerve fibers decrease

Optic cup diameter increases

127
Q

How does the ILM change with age?

What affect does this have?

A

Thickens

Dimmer foveal reflex

128
Q

How does RPE change with age

A

Total number of RPE decreases

Lipofuscin in RPE increases
Drusen increases

129
Q

What change occurs in aging across the entire retina

A

Atrophy increases

130
Q

What is a Tigris fundus

A

Age related retinal atrophy

Pigmentation in RPE/choroid decreases

131
Q

What is reticular degeneration

A

Age related retinal atrophy

Peripheral RPE degeneration

132
Q

Is there blood flow in the lens

A

No

133
Q

Is there innervation in the lens

A

No

134
Q

How does the lens grow

A

It grows in size throughout life and does not shed cells

135
Q

What can disrupt lens clarity

A

Accumulated post synthesis modified components

Several types of accumulated materials give rise to cataract types

136
Q

What is the lens composed of

A

Water
Protein
Lipids/cholesterol

137
Q

Most simple sugars can be metabolized, but which one is most predominant

A

Glucose

138
Q

Does the lens metabolize lipids and amino acids

A

Yes, they are incorporated in to structural components

139
Q

Describe anaerobic glycolysis of the lens

A

The most active energy metabolism in the lens

Provides 70%

140
Q

What does the HMP shunt do in the lens

A

Secondary producing NADPH and -10% of lens energy

141
Q

Where does the rest of the 20% come from

A

It is derived from the metabolism of lactic acid and the glucose in lens epithelium cells that utilize the TCA and ET

142
Q

Since the lens has no blood supply where does it get its glucose from

A

The posterior or anterior lens surfaces that contacts other mediums such as the aqueous humor

143
Q

How is glucose taken up by the aqueous

A

Facilitated diffusion

144
Q

How is the transport of glucose among lens cells accomplished

A

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
Q

Is the ens affected by anaerobic conditions?

A

It is unaffected because of its reliance on anaerobic glycolysis for energy

146
Q

How are wastes removed from the lens

What are some examples of wastes removed

A

Ex. Lactic acid

It is removed at a steady rate via diffusion to aqueous humor and then to blood stream

147
Q

How does the anterior Y suture appear

A

Y

148
Q

How does the posterior Y suture appear

A

An upside down Y

149
Q

What are the functions of the lens

A
  • 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
Q

What is the composition of the lens

A

Water (65%)
Proteins (35%)
Other stuff (1%)

151
Q

What protein groups are contained in the lens

A 
Water soluble (crystallins) 
Urea soluble (crystallins and cytoskeleton)
Insoluble (membrane proteins)
152
Q

What are the groups of crystallins

A

Alpha
Beta
Gamma

153
Q

What do alpha crystallins do

A

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

154
Q

What does alpha crystallins provide resistance to

A

Degradation of the other crystallins beta and gamma

It is a molecular chaperone

155
Q

What is important of the concentration of crystallin

A

It varies throughout the lens

Provides a refractive index gradient that is higher in the nucleus than the cortical surface

156
Q

What is reduced in the lens due to gradient index system and peripheral flattening

A

Spherical aberration

157
Q

What allows for transparency in the cellular level

A 
Small lens fibers
Uniformity of lens fibers
Regular packing
Paucity of organelles
Avascular
158
Q

What allows transparency at the molecular level

A

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
Q

Hw does water contribute to the transparency of the lens

A

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
Q

What is the mitotic activity of the lens

A

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
Q

What is glutathione

A

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
Q

Where is ascobric acid higher

A

Has higher concentration in the lens than aqueous

163
Q

How does accommodation decrease in old age

A

Ability of accommodation decreases by 1/4 of the age (Hofstetters formula)

164
Q

What is age related nuclear cataract

A

Decline of glutathione, making the fibers susceptible to oxidative damage

Older nuclear fibers lose organelles and their nucleus and gain yellow-brown pigment

165
Q

What is age related cortical cataract

A

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
Q

What is posterior subcapsular cataract

A

Epithelial like cells migrate from the equatorial region and accumulate in the posterior pole forming an opacity

167
Q

What happens to crystallins with age

A

Decrease (especially alpha)

168
Q

What happens to lens thickness with age

A

Thickens (0.22mm per year)

169
Q

What happens to the anterior capsule with age

Posterior capsule?

A

Increases

Posterior: stable

170
Q

What appends to the radius of curvature for anterior and posterior lens with age

A

Decreases

171
Q

What happens to the center of the lens with age

Anterior chamber depth?

A

Center moves anterior with age

Anterior chamber depth decreases with age

172
Q

What happens to the amino acids in the eye with age

A

Decreases

173
Q

What is a diabetic cataract?
How does it form?
What accumulates?

A

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
Q

How can there be changes in refractive error in the aging eye

A

Thickness Change, radius of curvature change, ex changes

Unusual changes in Rx May indicate uncontrolled diabetes

Ocular Physiology (8 decks)

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