Flashcards in B11 Deck (227):
The RPE is a monolayer of pigmented cells, located between _________ and ________
Choriocapillaris and outer segments of photoreceptors
The apical membrane of the RPE faces the photoreceptor _______
What surrounds the light sensitive outer segments of the RPE?
Long apical microvilli
The _____ membrane faces Bruchs membrane
Light energy is concentrated on the?
General light absorption occurs via ____ in RPE
Blue light absorption is supplemented by ___ and ___ in photoreceptors
Lutein and zeaxanthin
What is the most dangerous light to the RPE?
The outer retina is exposed to what kind of environment?
T/F: The blood perfusion of the choriocapillaris is very high in the outer retina
Venous blood from the choriocapillaris shows a ___% O2 saturation
RPE contains high amounts of superoxide dismutase and catalase
RPE accumulates lutein and zeaxanthin, ascorbate, alpha-tocopherol and beta-carotene
The RPE transports nutrients and metabolic end products
between ______and the _______
Photoreceptors and choriocapillaris
Is blood on the apical or basolateral side?
Are the photoreceptors on the apical or basolateral side?
The space between RPE and photoreceptors
What are the two ways of transport in the RPE?
The transport of water is driven by _______ of Cl- from the retina to blood side
Describe Bests Vitelliform Macular Degeneration
-Degeneration of RPE
-Bull’s eye shaped lesion
-The lesion primarily contains extracellular fluid
-Reduction in epithelial Cl- transport
The transport of lactic acid requires a tight regulation of the ______PH
The RPE contains an abundance of what 2 glucose transporters?
GLUT1 and GLUT3
An important substance of building membranes of neurons, photoreceptors as well as photoreceptor disk membrane
Docosahexaenoic acid (DHA)
What two things are removed from the apical side?
Water and lactic acid
The reduction of all-tran retinal into all trans-retinol occurs where?
Reisomerization of all-trans-retinol into 11-cis-retinal occurs in?
Describe retinitis pigmentosa
-inherited retinal degeneration
-mutations in genes of the visual cycle
-inability of the RPE to phagocytose photoreceptor outer segments
Describe stargardt disease
-mutations in the genes of the visual cycle
The process of phagocytosis is under what kind of control?
What triggers phagocytic activity?
The onset of light in the morning
Every RPE cell is facing an average of _____ photoreceptors in the fovea
When does the whole length of a photoreceptor outer segment get renewed?
Every 11 days
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
Shed photoreceptor outer segments are phagocytosized by?
A defect of RPE photoreceptor phagocytosis may also cause retinal degeneration in usher type 1B patients
What are the 3 actions of PEDF?
-Inhibits endothelial cell proliferation
-Stabilizes the endothelium of the choriocapillaris
What is secreted in low concentrations in the healthy eye?
Name 2 actions of VEGF
-Prevents endothelial cell apoptosis
-Stabilizes the endothelium of the choriocapillaris
What are some other factors that are essential for maintenance of the structural integrity of the retina?
The most severe complication in age-related macular degeneration
In choroidal neovascularization, do RPE cells secrete VEGF at higher or lower rates compared to RPE cells from eyes without neovascularization?
What are the 2 parts of the retinal-blood barrier
-retinal vascular endothelium
-tight junctions between RPE
Photoreceptors are on the ____ side and choriocapillaris are on the _____ side of the RPE
What absorbs blue light?
Lutein and zeaxanthin
The driving force to remove water form the apical side
Active transport of Cl- from retina to blood
Where does reisomerization of all-trans-retinol into 11-cis-retinal occur?
Which growth factor gets involved in choroidal neovasculization?
Which disease is due to reduction of epithelia Cl- transport?
A. Retinitis pigmentosa
B. Best’s Vitelliform Macular Degeneration
What are 2 characteristics of photoreception
Light detection that lead to vision and depends on photoreceptors (specialized light- sensitive neurons)
Photon absorption by visual pigment that is lying on one of the discs in the outer segment of photoreceptors
Dim light and motion
Color and detail
Scotopic visual system
Photopic visual system
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
Name 4 characteristics of cones
-Specialized for detailed vision
-Specialized for color vision
-Higher sensitivity to rapidly changing stimuli
Are there rods in the fovea?
Rods comprise ___ of photoreceptors
Rod peak absorption
Does rod convergence increase of decrease sensitivity?
Where do many rods gather light information on?
Onto one retinal bipolar cell
Are there more rods or cones?
Are cones more prominent in the fovea or the periphery?
What are the 3 different types of cones?
-red (L cones)
-green (M cones)
-blue (S cones)
What is the wavelength of red cones?
What is the wavelength of green cones?
What is the wavelength of blue cones?
What type of cones are not in the fovea?
Blue cones (S)
Doe cones have convergence?
Are unstable pigments that undergo a chemical change when they absorb light
What makes up photopigments?
Protein (opsin) + chromophore
What makes up rhodopsin?
Opsin + 11-cis-retinal (chromophore)
What pigment is used for vision in dim light?
Is rhodopsin soluble or insoluble in water?
T/F: Rhodopsin is more stable and more abundant than cone pigments
What are the 3 types of iodopsins?
Photopsin I + 11-cis-retinal absorption max for yellow/red (L-cones)
Photopsin II + 11-cis-retinal absorption max for green (M-cones)
Photopsin III + 11-cis-retinal absorption max for bluish/violet (S-cones)
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
Is the transformation of light into electrical and chemical signals that produces the perception of light
What are the steps of phototransduction?
Photoreception-->biochemical cascade-->electronic spread-->slowing of NT release
What is the important channel in the biochemical cascade?
Cyclic-GMP-Gated Cation Channel (CNG channel)
CNG channel allows what 3 things to enter the cell?
T/F: CNG channel causes the cells to be partially depolarized
In the dark, rods have a resting membrane potential of about ___
For other neurons, the resting membrane potential of about ____
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
What is the beginning step of biochemical cascade of phtototransduction?
Photoisomerization of rhodopsin
What converts 11-CIS-retinal to all-trans-retinal?
Reduction of all-trans-retinal into all-trans-retinol
Reisomerization of all-trans-retinol into 11-cis-retinal
What is the second step of the biochemical cascade of Phototransduction?
Metarhodopsin II encounters an _____ G protein
What comes to lie over the metarhodopsin II?
The Ga subunit of the G protein
GDP is replaced by___ in the biochemical cascade
Is it on or off when G protein binds to GTP?
Is it on or off when G protein binds to GDP?
When is the G protein active in the biochemical cascade?
When GTP behinds to the Ga subunit
The unit that separates from both Metarhodopsin
and the βγ portion of the G protein
What is the 3rd step of biochemical cascade of Phototransduction?
What does the activated G protein bind with in the biochemical cascade?
The activated PDE6 coverts the ____ into ___
cGMP into GMP
PDE can degrade cGMP by hydrolyzing cGMP into ____
What is the final step of the biochemical cascade of phototransduction?
What does the reduction of cGMP concentration cause?
CNG channel closure
T/F: Opening of CNG channel put photoreceptors at resting dark-adapted state
What are 3 characteristics of electronic spread
-closing of channels
-photocurrent in dark
-photocurrent in light
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)
Cations moving into the cell (electronic spread)
Photo current in dark
A single photo isomerization closes ion channels and cause a 2% reduction in the photocurrent
Photocurrent in light
Communication of rods with downstream bipolar
cells by the release of ____
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
____ level of glutamate release by rods signal
total darkness to bipolar cells
What are the 2 factors of phototransduction?
1 Rhodopsin: _____G proteins
1 Rhodopsin: _____PDE
1 PDE: ___cGMP hydrolysis
100 G proteins
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
What photoreceptor sensitivity increases due to convergence?
What is the key molecule of biochemical cascade to keep CNG channel open?
What is the NT between rods and bipolar cells?
List the steps of phototransduction
Photoreception-->biochemical cascade (channel closure)--> electronic spread (cells hyperpolarized)--> slowing glutamate release
a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.
An excitatory NT
2 inhibitory NT
GABA and glycine
A change in a cells membrane potential that makes it more negative
Hyperpolarization inhibits APs by ____the stimulus required to move the membrane potential to the AP threshold
A change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell.
What 2 cells are light evoked signals transferred onto?
Bipolar and horizontal cells
What cells provide lateral interactions in the outer plexiform layer (OPL)
What cells transfer the light signals into the inner plexiform layer (IPL), onto the amacrine and ganglion cells
collect the signals ofbipolar and amacrine cells and
transmit these signals to the visual centers of the brain.
What type of NT do cone pedicles have?
Is glutamate high or low in darkness?
Is glutamate increased or reduced by light?
Reduced by light
What are the 2 different sets of glutamate receptors in cones?
-off cone bipolar cells
-on cone bipolar cells
Are ON cone bipolar cells hyperpolarized or depolarized by light?
Off cone and bipolar cells and horizontal cells are
____ by light
Where do OFF cone bipolar cells transfer signals onto?
Onto OFF ganglion cells
Where do ON cone bipolar cells transfer signals onto?
ON ganglion cells
Where do density of cones, bipolar cells, and ganglion cells increase steeply?
Towards e center of the retina
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
One cone connected to a midget bipolar cells connected to a midget ganglion cells
Concomitant with the increase in density, the bipolar cells and ganglion cells’ dendritic fields become smaller or larger?
What type of NT are in rod spherule?
How many types of rod bipolar cells are there?
What is the only rod bipolar cell?
ON bipolar cells
Are ON rod bipolar cells depolarized or hyperpolarized by light?
What is the result of ON center ganglion cells with light on the center of the receptive field only?
Ganglion cell fires rapidly
What is the result of OFF center ganglion cells with light on the center of the receptive field only?
Ganglion cells do not fire
What is the result of ON center ganglion cells with light on the surround only?
Cells do not fire
What is the result of OFF center ganglion cells with light on the surround only?
Cell fires rapidly
What is the result of ON center ganglion cells with no light on the center or surround?
Cells do not fire
What is the result of OFF center ganglion cells with no light on the center or surround?
Cells do not fire
What is the result of ON center ganglion cells with light on the center and surround?
What is the result of ON center ganglion cells with light on the center and surround?
Modulate the glutamate release by shifts the
activation curves of the cone pedicle Ca2+ channels
Cone horizontal cells
Modulate the glutamate release by shifts the activation curves of the rod spherule Ca2+ channels
Rod horizontal cells
Rod horizontal cells releases ____ providing inhibition of bipolar cell dendrites
Name the 4 glutamatergic neurons
-most ganglion cells
Name the 2 GABAergic and glycinergic neurons
-most amacrine cells
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
-Total # of RPE cells decrease significantly with
age; lipofuscin within RPE cells increases and drusen
-Atrophy increases throughout the retina
An age related retinal atrophy where there is pigmentation in RPE and choroid decreases
An age related atrophy with peripheral RPE degeneration
Which type of cells plays a role in transmitting cones signal to RGC?
Cone bipolar cells
Whay types of cells plays a role in transmitting rod signals to RGC?
Rod bipolar cells and amacrine cells
What change does ON bipolar cells have with light?
What kind of NT do bipolar cells contain?
When the center of RGCs receptive field is exposed to light, which type of RGC is stimulated?
Will you have a dimmer foveal reflex when you get older?
What type of GLUT transporter is insulin dependent and are not found in the retina?
Hat are the 3 major energy producing metabolic pathways in retinal metabolism?
When is lactic acid produced in the largest quantities?
During sleep or condition that block atmospheric O2 from being absorbed by the eye
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
Wen the eye subjected to endotoxins which of the following compounds would protect the eye?
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
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
Name the 2 predominate energy sources for the lens
What does the HMP shunt pathway do in the lens?
-helps sends intermediates in different directions
The process involved in maintaining the lens is limited to ____ in order to maintain transparency
Anaerobic respiration of glycolysis
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)
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
The lens is composed mainly of what 2 things?
Water and proteins
The proteins make up ___% of the lens
What are the percentage of water soluble proteins in the lens?
What type of water soluble/crystalline type is the most prominent?
Produces a phenomenon that contributes to lens
transparency, and gives the lens a significantly higher index of refraction than surrounding fluids
Offers resistance to the degradation of the other
crystalline, beta and gamma, and is called a molecular chaperone
Crystalline concentration varies among the lens, providing a refractive index gradient that is ____in the nucleus, than the outer cortical surface
Spherical aberration in the lens is _____due to the gradient index system and peripheral flattening
Do we want extra water in the lens?
No it will be destructive
Water is pumped out of the lens from the anterior surface by _______
Water enters the lens from the ____ because of osmotic pressure
Are proteins uniform or un-uniform in the lens?
Are proteins small or large in the lens?
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
Where do mitosis of secondary fiber cells occur?
In the germinative zone of anterior lens epithelium
After mitosis, lens fiber cells gradually migrate through the ____ and into the _____ where elongation occurs
Through the transition zone and into the equator
What is the primary protector against oxidative damage in the lens?
Glutathione detoxifies _____
Ascorbic acid has a ____ concentration in the lens than the aqueous
Glutathione is transported into the lens from the aqeuous and can be synthesized from ____ cells and ____ cells
Lens epithelial cells and superficial fiber cells
What are 3 forms of cataracts?
-age related nuclear cataract
-age related cortical cataract
-posterior subcapsular cataract
The ability of accommodation____ by one quarter of the age
Change in osmolarity causes changes in what 3 things?
-radius of curvature
Unusual changes in rx may indicate _____
What type of proteins does the lens contain the most of?
T/F: the lens absorbs blue light the most to protect the retina
Where does Na+/K+ pump located to helping pumping out of water?
What option is the best driving force of water entering the lens from the back?
Which part is responsible for formation of the secondary lens fibers?
What type of changes in the lens are caused by accumulation of sorbitol?
Cataract and rx changes
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
In an age related nuclear cataract a decline of ___ makes the fibers susceptible to oxidative damage
When older nuclear fibers lose organelles and their nucleus and gains yellow-brown pigment
Age-related nuclear cataract
In an age related cortical cataract, a decrease in glutathione activity will increase what 3 things?
Ca, Na, and water
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
When epithelial-like cells migrate from the equatorial region and accumulate at the posterior pole forming an opacity.
Posterior subcapsular cataract
Do crystalline decrease with age?
The lens thickness increases ___ per year
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
Does the radius of curvature for the anterior and posterior lens increase or decrease with age?
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
Do amino acids decrease with age?
Is sorbitol hydrophobic or hydrophilic?
Glutathione required ___ to reduce free radicals