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Oc Physio > OcPhysioT3 > Flashcards

OcPhysioT3 Flashcards

1
Q

Is the outer retinal layers vascular or avascular?

How is it supplied?

A

Avascular

Choriocapillaris

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2
Q

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

A

Retinal circulation

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3
Q

Describe the choroidal circulation?

A

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

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4
Q

Describe the retinal circulation?

A

Low flow
Constant rate circulation
Higher rate of oxygen extraction

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5
Q

Is there overlap between the retinal and choroidal circulation?

A

No overlap.

Can damage retinal circulation without damaging the choroidal circulation

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6
Q

Where is there an oversupply of oxygen in circulation?

A

In the choroidal circulation.

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

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7
Q

Are the retinal vessels permeable to flurescein?

A

No

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8
Q

Are the retinal vessels permeable to indocyanin?

A

No

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9
Q

Are the choroidal vessels permeable to flurescein?

A

Yes, they are highly permeable!

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10
Q

Are the choroidal vessels permeabe to indocyanin?

A

They are minimally permeable.

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11
Q

Is the ciliary body fenestrated?

A

Yes.
Pars Plicata
Pars Plana

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12
Q

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

A

Non-fenestrated!!!

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13
Q

Do the ciliary muscle deal with aqueous humor generation?

A

No they do not.

That is why they are non-fenestrated.

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14
Q

Is the iris fenestrated?

A

Nope,

it is non-fenestrated!

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15
Q

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

A

Vasoconstriction.

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16
Q

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

A

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

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17
Q

What are two main mechanisms of autoregulation?

A

myogenic

metabolic

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18
Q

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

A

Yes

19
Q

Is there a lack of autoregulation in the choroidal circulation?

A

Yes.

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

20
Q

T/F?

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

A

True

21
Q

What are the components of the visual pigment?

A

Opsin protein + chromophore

22
Q

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

A

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

23
Q

Does sodium flow into the outer segment?

A

Yes.

24
Q

Does potassium flow out of the inner segment?

A

Yes

25
Q

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

A

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

26
Q

What is the initialization step?

A

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

27
Q

What does activated transducin do?

A

Increase the level of cGMP phosphodiesterase.

This hyrdolyzes GMP to 5’GMP

28
Q

What is Gain 1?

A

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

29
Q

What is Gain 2?

A

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

30
Q

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

A

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

31
Q

What produces light adaptation?

A

Decline of Calcium resulting in negative feedback.

THe maintenance of ionic balance in rods is critical.

32
Q

What does a decrease in calcium levels do to cGMP?

A

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

33
Q

What are the four layers involved in retinal synthesis

A
  1. Choriocapillaris
  2. RPE
  3. IPM (Interphotoreceptor Matrix).
  4. Rod Outersegment
34
Q

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

A

RPE.

Stores it as retinyl palmitate

35
Q

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

A

Level of background illuminance changes.

36
Q

What is another term used for light adaptation?

A

Automatic Gain control

37
Q

What is the biochemical aspect of light adaptation?

A

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

38
Q

What is the neural aspect of light adaptation?

A

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

39
Q

What are the functions of RPE?

A 
Light absorption
Secretion
Visual cycle
Epithelial transport
Glia
Phagocytosis
GEL PVS
40
Q

Which part is glycolysis compartmentalized to?

A

Muller Glial cells

41
Q

Which part is oxidative phosphorylation compartmentalized to?

A

Photoreceptor neurons.

42
Q

What does the glial cells do with the glucose?

A

It transforms it rather than transfer it.

Supply activated neurons with lactate or alanine.

43
Q

What is the relationship between glia and glutatmate?

A

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

Oc Physio (7 decks)

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