OcPhysioT3

Question 1

Is the outer retinal layers vascular or avascular?

How is it supplied?

Answer 1

Avascular

Choriocapillaris

Question 2

Who does the inner 2/3rds of the retina receive nutrition from?

Answer 2

Retinal circulation

Question 3

Describe the choroidal circulation?

Answer 3

High flow
Variable rate circulation.
Free transfer of metabolites of all sizes b/w it and the surrounding tissues.

Question 4

Describe the retinal circulation?

Answer 4

Low flow
Constant rate circulation
Higher rate of oxygen extraction

Question 5

Is there overlap between the retinal and choroidal circulation?

Answer 5

No overlap.

Can damage retinal circulation without damaging the choroidal circulation

Question 6

Where is there an oversupply of oxygen in circulation?

Answer 6

In the choroidal circulation.

Only 3-5% of this oxygen will get extracted.

Question 7

Are the retinal vessels permeable to flurescein?

Answer 7

No

Question 8

Are the retinal vessels permeable to indocyanin?

Answer 8

No

Question 9

Are the choroidal vessels permeable to flurescein?

Answer 9

Yes, they are highly permeable!

Question 10

Are the choroidal vessels permeabe to indocyanin?

Answer 10

They are minimally permeable.

Question 11

Is the ciliary body fenestrated?

Answer 11

Yes.
Pars Plicata
Pars Plana

Question 12

Are the capillaries present in the ciliary muscle fenestrated or non-fenestrated?

Answer 12

Non-fenestrated!!!

Question 13

Do the ciliary muscle deal with aqueous humor generation?

Answer 13

No they do not.

That is why they are non-fenestrated.

Question 14

Is the iris fenestrated?

Answer 14

Nope,

it is non-fenestrated!

Question 15

What happens when you have a high concentration of oxygen in the blood and low concentration of carbon dioxide?

Answer 15

Vasoconstriction.

Question 16

Is blood flow increased or decreased in the retina in hypoxic conditions?

Answer 16

Blood flow is increased because low levels of oxygen results in vasodilation

Question 17

What are two main mechanisms of autoregulation?

Answer 17

myogenic

metabolic

Question 18

Is the oxygen tension in the inner parts of the retina maintained at a constant level despite fluctuating IOP?

Answer 18

Yes

Question 19

Is there a lack of autoregulation in the choroidal circulation?

Answer 19

Yes.

This does not reduce the supply of nutrients to the retina.

Question 20

T/F?

U get more extraction of nutrients with a decrease in blood flow?

Answer 20

True

Question 21

What are the components of the visual pigment?

Answer 21

Opsin protein + chromophore

Question 22

What does the absorption spectrum of a visual pigment depend on?

Answer 22

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

Question 23

Does sodium flow into the outer segment?

Answer 23

Yes.

Question 24

Does potassium flow out of the inner segment?

Answer 24

Yes

Question 25

In the absence of light, are the photoreceptors depolarized or hyperpolarized?

Answer 25

Relatively depolarized. Membrane resting pot is -40 to -50mV. Regular resting potential is -70mV.

Question 26

What is the initialization step?

Answer 26

Conversion of 11-cis-retinal to all-trans retinal. Causes a conformational change in rhodopsin into the activated form called metarhodopsin II

Question 27

What does activated transducin do?

Answer 27

Increase the level of cGMP phosphodiesterase. | This hyrdolyzes GMP to 5'GMP

Question 28

What is Gain 1?

Answer 28

Over a hundred transducin molecule is activated by a single metarhodopsin II molecule.

Question 29

What is Gain 2?

Answer 29

cGMP phosphodiesterase hydrolyze cGMP at a rate close to the limit set by diffusion.

Question 30

Is the combined amplification set by rhodopsin and phosphodiesterase very low?

Answer 30

NO, it is very high. This allows rods to be mad sensitive. Thus detecting single photons.

Question 31

What produces light adaptation?

Answer 31

Decline of Calcium resulting in negative feedback. | THe maintenance of ionic balance in rods is critical.

Question 32

What does a decrease in calcium levels do to cGMP?

Answer 32

It allows GCAP to activate GC, thus quickly restoring the basal cGMP concentration.

Question 33

What are the four layers involved in retinal synthesis

Answer 33

1. Choriocapillaris 2. RPE 3. IPM (Interphotoreceptor Matrix). 4. Rod Outersegment

Question 34

Which layer has the ability to stor excess all-trans retinol from the diet?

Answer 34

RPE. | Stores it as retinyl palmitate

Question 35

Why does the same intensity of flash cause different response amplitude?

Answer 35

Level of background illuminance changes.

Question 36

What is another term used for light adaptation?

Answer 36

Automatic Gain control

Question 37

What is the biochemical aspect of light adaptation?

Answer 37

Dropping intracellular calcium triggers the synthesis of cGMP, thereby opening up some of the ion channels.

Question 38

What is the neural aspect of light adaptation?

Answer 38

Hyperpolarization of the horizontal cells feeds back onto the photoreceptors, signaling them to re-depolarize.

Question 39

What are the functions of RPE?

Answer 39

``` Light absorption Secretion Visual cycle Epithelial transport Glia Phagocytosis GEL PVS ```

Question 40

Which part is glycolysis compartmentalized to?

Answer 40

Muller Glial cells

Question 41

Which part is oxidative phosphorylation compartmentalized to?

Answer 41

Photoreceptor neurons.

Question 42

What does the glial cells do with the glucose?

Answer 42

It transforms it rather than transfer it. | Supply activated neurons with lactate or alanine.

Question 43

What is the relationship between glia and glutatmate?

Answer 43

Glut tells glia there's stuff to be cleaned up or regulated.