Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry > Retinal Metabolism - Week 5 > Flashcards

Retinal Metabolism - Week 5 Flashcards

1
Q

For what processes in the body is ATP usage the highest?

A
  • Dark current
  • Neurotransmission
  • Ionic Transport
  • cGMP, GTP production
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the metabolic role of NADPH (a reductin)?

A

is used in:

  • chromophore recycling
  • membrane synthesis
  • as an antioxidant
  • membrane integrity + photopigment function
  • RNA synthesis/DNA repair
  • Vasomotor regulation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the metabolic role of Ribose-5-Phosphate?

A

is used in RNA synthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where in the rod photoreceptor does Rhodopsin de-activation occur?

A

Outer segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where in the rod photoreceptor is rhodopsin found?

A

Outer segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Where in the photoreceptor does cGMP synthesis occur?

A

Outer segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the main role of the photoreceptor inner segment?

A

Provide ATP for the sodium potassium pump

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the main role of the photoreceptor outer segment?

A

Absorption of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where in the photoreceptor does phototransduction occur?

A

Outer segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Briefly describe the outer segment of a photoreceptor

A

are actually modified cilia that contain discs filled with opsin (the molecule that absorbs photons), and has voltage gated sodium channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where in the photoreceptor does RNA synthesis take place?

A

Inner segment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What results from impaired transport or defective proteins in the inner segment of the photoreceptor?

A

Some form of retinal degeneration e.g. RP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What pathway is the primary source of NADPH?

A

Pentose Phosphate Pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where does glucose get stored?

A

In the muscle

Note: it does NOT get stored in the brain or retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the main product of Glycolysis?

A

Precursors that feed kreb cycle (and a little bit of ATP as well)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Briefly describe the Kreb/TCA cycle

A

a series of enzymatic reactions that loop back on themselves where you are breaking carbon off molecules resulting in the carbons getting shorter as you go around the cycle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What happens when you break a carbon off a molecule in the Kreb/TCA cycle?

A

you generate a reductin (either NADH or FADH)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do reductins help generate ATP?

A

When added to the ETC, reductins can drive an electron gradient to create ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What happens to the amino acids produced by the Kreb/TCA cycle?

A

They become our Neurotransmitters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What 2 things provide vascular supply to the two halves of the iris?

A

Minor arterial circle - bottom half

Aqueous - top half

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Where does the ophthalmic artery originate from?

A

Internal carotid artery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Where do the the short posterior ciliary arteries enter the eye?

A

They pierce the sclera posteriorly to enter the choroid layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Where do the long posterior ciliary arteries enter the eye?

A

travel medially and laterally along the sides of the optic nerve and past the anterior aspect of the eyeball, piercing the choroid layer

24
Q

Which part of the retina does the central retinal artery supply?

A

internal surface of the retina (it pierces close to the optic nerve)

25
Q

What supplies the outer layer of the retina?

A

Choroidal vessels (choriocapilaris)

26
Q

What supplies the inner layer of the retina?

A

Retinal vessels and their capillaries

27
Q

Where in the posterior segment of the eye is oxygen tension maximal?

A

Choriocapillaris

28
Q

Compare the autoregulation of the blood supply to the outer and inner retina. Where does it occur?

A

Inner layers of retina = locally autoregulated (via myogenic + metabolic mechanisms)

Outer layers of retina = NO local autoregulation

29
Q

Compare the flow rate for the outer and inner retina. Where is it highest?

A

Outer retina = Very high flow rate

Inner retina = Low flow rate

30
Q

Compare the venous oxygen saturation for the outer and inner retina? Where is it highest?

A

Outer retina = High venous oxygen saturation

Inner retina = Low venous oxygen saturation

31
Q

Define autoregulation

A

Intrinsic ability to maintain a constant blood flow despite changes in perfusion pressure

32
Q

How does autoregulation compensate for low blood pressure?

A

low b.p – reduced sheer – increased NO (vasodilator) – relaxes muscle fibres – increased vessel diameter

*Note: increasing vessel diameter allows us to get more blood to the area (increased blood flow)

33
Q

How does autoregulation compensate for high blood pressure?

A

high b.p – increased sheer – increased Endothelin-1 release from vessel wall – reduced vessel diameter

Endothelin-1 is a vasoconstrictor

*Note: since we have high b.p, we constrict the vessel supplying the area so less blood flows to it.

34
Q

Define sheer stress

A

The dragging force of the blood on the vessel wall

35
Q

When is oxygen tension lower, in the dark or light?

A

Oxygen tension is lower in the dark. O2 is being consumed in dark current

36
Q

How much O2 is generally utilised by the retina per hour?

A

1.5umol/mg dry weight/hour

37
Q

Which uses more oxygen: retina or brain?

A

Retina (2x more than brain)

38
Q

Where is oxygen used in the retina?

A

70% of O2: TCA cycle, glycolysis, oxidative phosphorylation

Remainder of O2: oxidation of pyruvate, lactate, amino acids

39
Q

What mechanism actively transports glucose across membranes?

A

Na+/Glucose symports

40
Q

What mechanisms passively transport glucose across membranes?

A

Glucose transporter (GLUT) family. 5 types: GLUT1-5. GLUT-1 most important.

are ‘uniports’

41
Q

What are the normal glucose levels in serum?

A

4-8mM

42
Q

is ATP excitatory or inhibitory for GLUT-1

A

inhibitory

43
Q

at what serum glucose level does GLUT-1 operate at 50% efficiency?

A

1mM

44
Q

Where is GLUT-1 found

A

Basically everywhere in the retina. Anything that’s brown

45
Q

Where is GLUT3 found?

A

Inner retina

46
Q

Where is GLUT-2 found?

A

Only found in ELM and ILM (External and Internal limiting membrane)

*it’s a muller cell glucose transporter

47
Q

What what serum glucose levels does GLUT-2 operate at 50% efficiency?

A

15mM

48
Q

Where is GLUT-4 and GLUT-5 found?

A

Nowhere in the retina

49
Q

What can you use as an indicator of the level of oxygen usage in an area of the retina?

A

The level of certain aerobic vs anaerobic enzymes
Aerobic: Malate dehydrogenase (MDH) and Glutamate dehydrogenase (GDH)

Anaerobic: Lactate dehydrogenase (LDH)

50
Q

Where can you find high levels of malate dehydrogenase (MDH)?

A

Photoreceptors and inner plexiform layer

*photoreceptors are oxygen demanding

51
Q

Where can you find high levels of lactate dehydrogenase?

A

Mid-retina

52
Q

Where can you find low levels of lactate dehydrogenase?

A

photoreceptors

53
Q

How does the distribution (amount) of Aminotransferases in the retina compare to MDH?

A

similar to MDH

54
Q

Describe the level of TCA activity from MDH?

A

Very high TCA activity

55
Q

Where would you find areas of high oxidative enzymes?

A

Areas of low oxygen tension (i.e. high O2 usage)

e.g. photoreceptor inner segments and inner plexiform layer

56
Q

In the context of light difference, how does O2 usage compare in central vs peripheral retina?

A

Peripheral retina: less O2 in dark in outer retina, and pO2 spike in INL/GCL
Central retina: Little to no difference in outer segment (light vs dark), some in inner segment

57
Q

Describe the action of the pentose phosphate pathway in the cornea vs in the lens?

A

A larger percentage of glucose metabolism occurs through the PPP for the cornea (35%) compared to the lens (10-20%).
- this is because the lens is exposed to air more, and needs the resulting NADPH as an antioxidant

OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry (49 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions