OcPhysioT3 Flashcards
Is the outer retinal layers vascular or avascular?
How is it supplied?
Avascular
Choriocapillaris
Who does the inner 2/3rds of the retina receive nutrition from?
Retinal circulation
Describe the choroidal circulation?
High flow
Variable rate circulation.
Free transfer of metabolites of all sizes b/w it and the surrounding tissues.
Describe the retinal circulation?
Low flow
Constant rate circulation
Higher rate of oxygen extraction
Is there overlap between the retinal and choroidal circulation?
No overlap.
Can damage retinal circulation without damaging the choroidal circulation
Where is there an oversupply of oxygen in circulation?
In the choroidal circulation.
Only 3-5% of this oxygen will get extracted.
Are the retinal vessels permeable to flurescein?
No
Are the retinal vessels permeable to indocyanin?
No
Are the choroidal vessels permeable to flurescein?
Yes, they are highly permeable!
Are the choroidal vessels permeabe to indocyanin?
They are minimally permeable.
Is the ciliary body fenestrated?
Yes.
Pars Plicata
Pars Plana
Are the capillaries present in the ciliary muscle fenestrated or non-fenestrated?
Non-fenestrated!!!
Do the ciliary muscle deal with aqueous humor generation?
No they do not.
That is why they are non-fenestrated.
Is the iris fenestrated?
Nope,
it is non-fenestrated!
What happens when you have a high concentration of oxygen in the blood and low concentration of carbon dioxide?
Vasoconstriction.
Is blood flow increased or decreased in the retina in hypoxic conditions?
Blood flow is increased because low levels of oxygen results in vasodilation
What are two main mechanisms of autoregulation?
myogenic
metabolic
Is the oxygen tension in the inner parts of the retina maintained at a constant level despite fluctuating IOP?
Yes
Is there a lack of autoregulation in the choroidal circulation?
Yes.
This does not reduce the supply of nutrients to the retina.
T/F?
U get more extraction of nutrients with a decrease in blood flow?
True
What are the components of the visual pigment?
Opsin protein + chromophore
What does the absorption spectrum of a visual pigment depend on?
Nature of the chromophore
Bond b/w the chromophore and opsin
Shape of the protein and quality of the fit
Orientation of the chromophore in the plasma membrane
Does sodium flow into the outer segment?
Yes.
Does potassium flow out of the inner segment?
Yes
In the absence of light, are the photoreceptors depolarized or hyperpolarized?
Relatively depolarized.
Membrane resting pot is -40 to -50mV.
Regular resting potential is -70mV.
What is the initialization step?
Conversion of 11-cis-retinal to all-trans retinal. Causes a conformational change in rhodopsin into the activated form called metarhodopsin II
What does activated transducin do?
Increase the level of cGMP phosphodiesterase.
This hyrdolyzes GMP to 5’GMP
What is Gain 1?
Over a hundred transducin molecule is activated by a single metarhodopsin II molecule.
What is Gain 2?
cGMP phosphodiesterase hydrolyze cGMP at a rate close to the limit set by diffusion.
Is the combined amplification set by rhodopsin and phosphodiesterase very low?
NO, it is very high.
This allows rods to be mad sensitive.
Thus detecting single photons.
What produces light adaptation?
Decline of Calcium resulting in negative feedback.
THe maintenance of ionic balance in rods is critical.
What does a decrease in calcium levels do to cGMP?
It allows GCAP to activate GC, thus quickly restoring the basal cGMP concentration.
What are the four layers involved in retinal synthesis
- Choriocapillaris
- RPE
- IPM (Interphotoreceptor Matrix).
- Rod Outersegment
Which layer has the ability to stor excess all-trans retinol from the diet?
RPE.
Stores it as retinyl palmitate
Why does the same intensity of flash cause different response amplitude?
Level of background illuminance changes.
What is another term used for light adaptation?
Automatic Gain control
What is the biochemical aspect of light adaptation?
Dropping intracellular calcium triggers the synthesis of cGMP, thereby opening up some of the ion channels.
What is the neural aspect of light adaptation?
Hyperpolarization of the horizontal cells feeds back onto the photoreceptors, signaling them to re-depolarize.
What are the functions of RPE?
Light absorption Secretion Visual cycle Epithelial transport Glia Phagocytosis GEL PVS
Which part is glycolysis compartmentalized to?
Muller Glial cells
Which part is oxidative phosphorylation compartmentalized to?
Photoreceptor neurons.
What does the glial cells do with the glucose?
It transforms it rather than transfer it.
Supply activated neurons with lactate or alanine.
What is the relationship between glia and glutatmate?
Glut tells glia there’s stuff to be cleaned up or regulated.
