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Anatomy and Biochemisty > Exam 2 Koh- Retina Biochem 4 > Flashcards

Exam 2 Koh- Retina Biochem 4 Flashcards

1
Q

What is important to RPE function?

A

Proteins, lipids, and nucleic acids

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2
Q

____% of wet weight of the retina is water

A

> 80

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3
Q

What is the primary carbon source used for energy?

A

Glucose

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4
Q

Glucose is not converted to _______ in the RPE

A

Glycogen

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5
Q

Nearly ______ proteins have been identified in RPE

A

850

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6
Q

What gene is RPE specific

A

RPE 65

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7
Q

______ compose of ~3% of the wet weight of the RPE

A

Lipids

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8
Q

______% of wet weight are phospholipids with PC and PE

A

5

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9
Q

Higher saturated FAs in the RPE include what?

A

Palmitic/stearic acid

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10
Q

About 1% of the wet weight of the RPE is contributed by _____

A

RNA

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11
Q

Retinal pigment epithelium is a single layer of cells with what type of junction?

A

Tight

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12
Q

The RPE is a single layer of _____ epithelial cells

A

Columnar

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13
Q

Where is the outermost layer of the retina located?

A

Between the choroid and outer segments

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14
Q

How many RPE cells per eye?

A

4-6 million

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15
Q

What is the ratio of photoreceptor cells to RPE cells?

A

45:1

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16
Q

Epithelial cells are polarized with long ____ microvillous processes interdigitating the outer segment, and____ aspects adjacent to Bruch’s membrane

A

Apical, basal

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17
Q

What serves as a blood-retinal barrier?

A

Polarized cells in the RPE

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18
Q

What are the retinal pigment epithelium functions?

A

Light absorption, epithelial transport, glia, visual cycle, phagocytosis, secretion

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19
Q

How does the RPE increase optical quality?

A

Forming a dark pigmented wall, aids in absorption of scattered light

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20
Q

Blood perfusion of the choriocapillaris is ____ than the kidney

A

Higher

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21
Q

Venous blood from the choriocapillaris shows ___% O2 saturation

A

90

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22
Q

By comparison, venous blood from retinal vessels shows a O2 saturation of ____%

A

45

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23
Q

What is OCA?

A

Oculocutaneous albinism

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24
Q

OCA1 and OCA2 are due to defects in what?

A

The tyrosinase gene and the pink-eyed dilution gene

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25
Q

What happens when melanin levels are below a critical level?

A

Lack of foveal development, low vision, nystagmus and stabismus

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26
Q

What is the RPEs 3 lines of defense against toxins?

A

Light absorption, antioxidants and repairment

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27
Q

There is absorption and filtering of light via melanin in ________

A

Melanosomes

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28
Q

There is additional light absorption in the RPE by what 3 things?

A

Carotenoids, lutein, and zeaxanthin

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29
Q

What does blue light do in the RPE?

A

Permits the photoxidation of lipofuscin components to cell toxic substances

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30
Q

Lipofuscin ______ in the RPE during life

A

Accumulates

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31
Q

Lipofuscin might first be ____ for visual function

A

Beneficial

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32
Q

The RPE contains high amounts of what?

A

Superoxide dismutase and catalase

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33
Q

The RPE accumulates what?

A

Carotenoids (lutein and zeaxanthin), ascorbate, alpha-tocopherol, and beta-carotene; this is supplemented by glutathione and melanin, which itself can function as an antioxidant

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34
Q

What leads to retinal degeneration?

A

Increasing imbalance of protective and toxic factors

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35
Q

What is the most common cause for blindness in industrialized countries?

A

AMD

36
Q

What is AMD?

A

An accumulation of lipofuscin in the RPE, a reduction in the cell density of RPE cells, a reduction in an important antioxidants, alpha-tocopherol

37
Q

What happens to the organelles in AMD?

A

Age-related changes in pigmentation, age-dependent reduction of melanosomes, melanolysosomes (a sign of melanin degradation and melanolipofuscin granules)

38
Q

What happens due to oxidative stress in Bruch’s membrane?

A

Accumulation of AGEs

39
Q

AGEs play an important role in what?

A

Induction of choroidal neovascularization

40
Q

What is VEGF?

A

The major angiogenic factor in CNV in response to AGE exposure

41
Q

What is produced when RPE can’t convert all all-trans-retinol into 11-cis-retinal?

A

A2E

42
Q

What does A2E do?

A

Increases the sensitivity of the RPE to blue light and has several toxic effects

43
Q

Coupled with oxygen, A2Eis converted by ____ light into A2E-epoxides

A

Blue

44
Q

What do A2E epoxides do?

A

Destabilize mitochondrial membrane and lysosomal membranes

45
Q

A2E epoxides can inhibit ___ ___ in the respiratory chain

A

Cytochrome oxidase

46
Q

What does A2E produce?

A

More reactive oxygen species

47
Q

What is A2E?

A

N-retinylidene-N-retinylethanolamine

48
Q

Loss of RPE cells denotes the beginning of the formation of what?

A

Drusen

49
Q

What is the most important sign of AMD?

A

Drusen

50
Q

What does drusen consist of?

A

Basal laminar deposits that are located between RPE and Bruch’s membrane and basal linear deposits that are located inside Bruch’s membrane

51
Q

Metabolic waste products in the RPE include what?

A

Metbolic end prodcuts: lipoproteins and other hydrophobic material from both photoreceptors and RPE

52
Q

What happens in the end stages of AMD?

A

The end stages of the disease are either geographic atrophy (GA), a loss of RPE and photoreceptors over large areas, or CNV with subsequent intraocular bleeding and formation of a disciform scar

53
Q

What were the conclusions of the AREDS study?

A

Antioxidant vitamins and zinc therapy reduced the risk of developing advanced AMD in participants with intermediate and greater risk of developing AMD (categories 3 and 4) by 25%, antioxidants and zinc are now recommended for participants who have an intermediate risk of developing advanced AMD

54
Q

The RPE transports nutrients and ions between what two layers?

A

Photoreceptors and choriocapillaris

55
Q

____ leads to a movement of water from the vitreous body into the retina

A

IOP

56
Q

Water in the inner retina is transported by ____ cells and water in the _____ ____ is eliminated by the RPE

A

Muller, subretinal space

57
Q

What is required for an adhesive force between RPE and the retina?

A

Water transport

58
Q

Where does the RPE transport ions and water?

A

From the subretinal space or apical side to the blood or basolateral side

59
Q

The RPE has the structural properties of an ___ ____ ____

A

Ion transporting epithelium

60
Q

Tight junctions establish a barrier between what 2 layers?

A

Subretinal space and choriocapillaris

61
Q

Where are the majority of mitochondria located in the RPE?

A

Basolateral side

62
Q

Where is the Na-K-ATPase located in the RPE? Function?

A

Located in the apical membrane, provides the energy for transepithelial transport

63
Q

What do the Cl and K transports do in the RPE?

A

At the apical membrane this gradient facilitates uptake of HCO4 via the Na-HCO3 cotransporter and uptake of K and Cl via the Na-K-2Cl cotransporter

64
Q

How does the RPE transport glucose?

A

RPE contains high amounts of glucose transporters in both the apical and the basolateral membranes

65
Q

How is vitamin A (all-trans-retinol) taken up from the bloodstream?

A

Via a receptor-mediated process with recognition by a serum retinol-binding protein/transthyretin (RBP/TTR) complex

66
Q

What are the factors of retinal adhesion?

A

Passive hydrostatic forces, interdigitation of outer segments and RPE microvilli, active transport of subretinal fluid, and the complex structure and binding properties of the interphotoreceptor matrix

67
Q

What is the net rate of fluid transport across the RPE?

A

4-6 microliters per cm^2 per hour

68
Q

Clinical RPE detachments may result from what?

A

Breakdown of the transport mechanisms for fluid across the RPE as a result of focal damage

69
Q

What is the space between the RPE and photoreceptors?

A

IPM

70
Q

What does the IPM do?

A

Mediates adhesion between the RPE and photoreceptor layer, phagocytosis by the RPE and nutrient exchange between RPE and the photoreceptors

71
Q

What is the composition of the matrix?

A

Interphotoreceptor retinal binding protein, basic fibroblast growth factor (bFGF), hyaluronan and hyaluronan binding proteoglycans, sulfated glycosaminoglycans and matrix metalloproteases

72
Q

Delivery of ______ ____ to photoreceptors is a third kind of transport of importance for visual function

A

Docosahexaenoic acid

73
Q

Membranes of neurons and photoreceptors are selectively built from ________

A

Phospholipids

74
Q

How does the RPE take up docosahexaenoic acid?

A

Concentration-dependent manner

75
Q

Photoreceptor outer segments are newly built from the _____ of outer segments, at the ____

A

Base, cilium

76
Q

What is at the tip of POS?

A

Highest concentration of radicals, photo-damaged proteins, and lipids are phagocytosed by the RPE

77
Q

What is recycled to photoreceptors?

A

Retinal or docosahexaenoic acid

78
Q

In the processof phagocytosis, every RPE cell is facing an average ranging between what?

A

20-45 photoreceptors

79
Q

The turnover rate for one entire photoreceptor outer segment is what?

A

10-14 days

80
Q

What growth factors does the RPE secrete?

A

Fibroblast growth factors (FGF-1, FGF-2, and FGF-5), transforming growth factor- (TGF-beta), insulin-like growth factor-I (IGF-I), ciliary neurotrophic factor (CNTF), platelet-derived growth factor (PDGF), VEGF, lens epithelium-derived growth factor (LEDGF), members of the interleukin family and pigment epithelium-derived factor (PEDF)

81
Q

What is PEDF?

A

To protect neurons against glutamate-induced or hypoxia induced apoptosis, antiangiogenic factor that inhibits endothelial cell proliferation, abnormal growth factor regulation contributes CNV

82
Q

What is VEGF?

A

Secreted in low concentrations by the RPE in the healthy eye, prevents endothelial cell apoptosis and is essential for an intact endothelium of the choriocapillaris, also acts as a permeability factor stabilizing the fenestrations of the endothelium

83
Q

VEGF is ____ side, PEDF is ____ side

A

Basolateral, apical

84
Q

RPE sits on what prominent basement membrane?

A

Bruch’s membrane

85
Q

How many layers is Bruch’s membrane?

A

5

86
Q

What does Bruch’s membrane consist of?

A

Proteoglycans, matrix proteins, hyaluronic acid, chondroitin sulphate plus types I, III, VI, and VII collagen, and elastin

Anatomy and Biochemisty (15 decks)

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