Exam 2 Koh- Retina Biochem 4 Flashcards Preview

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

Flashcards in Exam 2 Koh- Retina Biochem 4 Deck (86):
1

What is important to RPE function?

Proteins, lipids, and nucleic acids

2

____% of wet weight of the retina is water

>80

3

What is the primary carbon source used for energy?

Glucose

4

Glucose is not converted to _______ in the RPE

Glycogen

5

Nearly ______ proteins have been identified in RPE

850

6

What gene is RPE specific

RPE 65

7

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

Lipids

8

______% of wet weight are phospholipids with PC and PE

5

9

Higher saturated FAs in the RPE include what?

Palmitic/stearic acid

10

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

RNA

11

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

Tight

12

The RPE is a single layer of _____ epithelial cells

Columnar

13

Where is the outermost layer of the retina located?

Between the choroid and outer segments

14

How many RPE cells per eye?

4-6 million

15

What is the ratio of photoreceptor cells to RPE cells?

45:1

16

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

Apical, basal

17

What serves as a blood-retinal barrier?

Polarized cells in the RPE

18

What are the retinal pigment epithelium functions?

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

19

How does the RPE increase optical quality?

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

20

Blood perfusion of the choriocapillaris is ____ than the kidney

Higher

21

Venous blood from the choriocapillaris shows ___% O2 saturation

90

22

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

45

23

What is OCA?

Oculocutaneous albinism

24

OCA1 and OCA2 are due to defects in what?

The tyrosinase gene and the pink-eyed dilution gene

25

What happens when melanin levels are below a critical level?

Lack of foveal development, low vision, nystagmus and stabismus

26

What is the RPEs 3 lines of defense against toxins?

Light absorption, antioxidants and repairment

27

There is absorption and filtering of light via melanin in ________

Melanosomes

28

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

Carotenoids, lutein, and zeaxanthin

29

What does blue light do in the RPE?

Permits the photoxidation of lipofuscin components to cell toxic substances

30

Lipofuscin ______ in the RPE during life

Accumulates

31

Lipofuscin might first be ____ for visual function

Beneficial

32

The RPE contains high amounts of what?

Superoxide dismutase and catalase

33

The RPE accumulates what?

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

34

What leads to retinal degeneration?

Increasing imbalance of protective and toxic factors

35

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

AMD

36

What is AMD?

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

What happens to the organelles in AMD?

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

38

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

Accumulation of AGEs

39

AGEs play an important role in what?

Induction of choroidal neovascularization

40

What is VEGF?

The major angiogenic factor in CNV in response to AGE exposure

41

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

A2E

42

What does A2E do?

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

43

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

Blue

44

What do A2E epoxides do?

Destabilize mitochondrial membrane and lysosomal membranes

45

A2E epoxides can inhibit ___ ___ in the respiratory chain

Cytochrome oxidase

46

What does A2E produce?

More reactive oxygen species

47

What is A2E?

N-retinylidene-N-retinylethanolamine

48

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

Drusen

49

What is the most important sign of AMD?

Drusen

50

What does drusen consist of?

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

51

Metabolic waste products in the RPE include what?

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

52

What happens in the end stages of AMD?

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

What were the conclusions of the AREDS study?

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

The RPE transports nutrients and ions between what two layers?

Photoreceptors and choriocapillaris

55

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

IOP

56

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

Muller, subretinal space

57

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

Water transport

58

Where does the RPE transport ions and water?

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

59

The RPE has the structural properties of an ___ ____ ____

Ion transporting epithelium

60

Tight junctions establish a barrier between what 2 layers?

Subretinal space and choriocapillaris

61

Where are the majority of mitochondria located in the RPE?

Basolateral side

62

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

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

63

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

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

How does the RPE transport glucose?

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

65

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

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

66

What are the factors of retinal adhesion?

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

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

4-6 microliters per cm^2 per hour

68

Clinical RPE detachments may result from what?

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

69

What is the space between the RPE and photoreceptors?

IPM

70

What does the IPM do?

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

71

What is the composition of the matrix?

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

72

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

Docosahexaenoic acid

73

Membranes of neurons and photoreceptors are selectively built from ________

Phospholipids

74

How does the RPE take up docosahexaenoic acid?

Concentration-dependent manner

75

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

Base, cilium

76

What is at the tip of POS?

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

77

What is recycled to photoreceptors?

Retinal or docosahexaenoic acid

78

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

20-45 photoreceptors

79

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

10-14 days

80

What growth factors does the RPE secrete?

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

What is PEDF?

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

82

What is VEGF?

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

VEGF is ____ side, PEDF is ____ side

Basolateral, apical

84

RPE sits on what prominent basement membrane?

Bruch's membrane

85

How many layers is Bruch's membrane?

5

86

What does Bruch's membrane consist of?

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