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Anatomy > Lecture 18/19 > Flashcards

Lecture 18/19 Flashcards

1
Q

What are the three circulatory systems serving the retina?

A
  1. central retinal circulation
  2. choroidal circulation
  3. optic nerve head circulation
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2
Q

the central retinal artery enters the optic nerve how far behind the globe? what does it supply?

A

12 mm

optic nerve and pia mater

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3
Q

what surrounds the central retinal artery? once in the eye the CRA branches into what?

A

sympathetic nerve plexus (or nerve of tiedemann)

superior, inferior, nasal and temporal branches

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4
Q

central retinal circulation supplies what and is made up of?

A 
inner retina (ganglion and bipolar cells)
made up of central retinal artery and veins (in nerve fibre layer), capillary system (double layered system in most of outer retina) and radial peripapillary circulation.
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5
Q

CRC has what major concepts?

A

sparse and thin to allow light to reach PR layer, high resistance. slow supply of blood with virtually all the oxygen extracted.

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6
Q

the radial peripapillary circulation follows which arteries? stops wherE?

A

superior and inferior temporal arteries, stops short of macula

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7
Q

what is the only blood supply to the macula?

A

choroid.

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8
Q

choroidal circulation supplies what? what type of capillaries?

A

outermost layers, photoreceptors and RPE (lies posterior to RPE, HUGE blood supply)
fenestrated

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9
Q

what are the three arteries involved in CC?

A
  1. short posterior ciliary arteries (further branches into paraoptic (near optic nerve head, supplies ONH and choroid)) and distal (further from optic nerve head, branches further once in choroid))
  2. LPCA: one lateral, one medial (sometimes one superior)
  3. Cilioretinal artery (small supply to retina, 25% of population)
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10
Q

how many SPCA?

A

8-10

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11
Q

distal SPCA branch into how many more? each branch supplies what? what do terminal arterioles supply (the ones at the end of the smaller branches from distal SPCA)?

A

10-12 (within each branch, smaller branches supply smaller segments)
a sector of the choroid
a lobule

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12
Q

two anterior ciliary arteries arise from each of what? what is the exception?

A

rectus muscles

lateral rectus only gives rise to one

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13
Q

what is the amount of oxygen located in the CC compared to CRC?

A

much more in CC (excess reserve)

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14
Q

cilioretinal arteries originate from what?

A

SPCA

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15
Q

how many LPCA?

A

usually two, can be up to five.

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16
Q

do medial and lateral LPCA supply the same thing?

A

both supply small sector of ciliary body and iris. lateral will supply the peripheral choroid that is not reached by the medial LPCA.

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17
Q

what is a watershed zone?

A

border between the territories of distribution of any two end arteries, poor vasculairty and most vulnerable to ischaemia (inadequate blood supply)

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18
Q

the choriopcapillaris is divided into? if one lobule is destroyed are all the others? does the central lobule have its own blood supply? does the macula receive any blood supply from the CRC?

A

lobules
NO
NO (gets from others around it)
NO ONLY CC

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19
Q

where are watershed zones located?

A

medial and lateral LPCA
segments supplied by SPCA
SPCA and LPCA

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20
Q

Are all watershed zones the same?

A

NO, major individual variation

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21
Q

what is a choroidal occlusion? what is a pro about this?

A

loss of a lobule (happens very fast and can be irreversible within hours/days)
only affects a very small area therefore not a HUGE issue

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22
Q

cilioretinal arteries act as a alternative blood supply for? is it sufficient? are these arteries a good thing?

A

central retinal artery (for retina), NOT sufficient to supply retina on its own.
not always, they tend to bleed more often.

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23
Q

optic nerve head circulation is comprised of? this circulation is implicated in which two disease groups?

A

paraoptic short posterior ciliary arteries and CRA.

glaucoma and ischemic optic neuropathy (loss of blood flow to ONH)

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24
Q

circle of zinn haller is made up of anastomoses between which three circulatory systems?

A
  1. CRC
  2. choroidal circulation
  3. optic nerve head circulation
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25
Q

what are the four parts of the ONH circulation?

A
  1. superficial nerve fibre layer (most superficial)
  2. pre lamina
  3. lamina
  4. retrolamina (most deep)
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26
Q

what are the six possible hemorrhages and where are they usually found?

A
  1. dot and blot (bipolar cell layer)
  2. flame shaped (superficial layer)
  3. pre retinal (before the retina, into vitreous)
  4. Boat (between retina and vitreous)
  5. sub-retinal (beneath retina)
  6. choroidal (choroid layer)
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27
Q

what is coats disease?

A

abnormal development in blood vessels behind the retina. seen mostly in males (69% of cases are males). almost always unilateral. pupil can appear yellow due to RPE leaking fluid (serum) into retina.

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28
Q

CRA occlusion can cause what symptoms? is the macula affected?

A
  1. ganglion cell death
  2. cotton wool spots (liquid accumulation)
  3. no oxygen or glucose reserves
  4. immediate VA drop, fast, painless, acute
    NO because not supplied by CRA therefore it is bright red and rest of retina is pale.
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29
Q

CRV occlusion causes what?

A

blockage of outflow
increase in transmural pressure (therefore blood pushed into retina)
blood and thunder retina
BP very high therefore vessels increasing in size
VA may not be affected

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30
Q

what is poiseuilles law? what pressure drives blood through a capillary bed? a decrease in perfusion pressure leads to an increase in?

A

blood flow in a vessel occurs if there is a pressure gradient between two points.
perfusion pressure
transmural pressure therefore decreasing blood flow and initiating autoregulation.

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31
Q

blood flow is autoregulated when?

A

there is an increase in blood pressure

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32
Q

what do we mean by autoregulation?

A

the ability to regulate blood flow and maintain available O2 at a constant level.

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33
Q

increase in transmural pressure leads to?

A

decrease in perfusion pressure, produces vasodilation, reduces resistance to flow, increases perfusion pressure.

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34
Q

changes in vessel diameter are due to? defective autoregulation leads to? what is the transmural pressure in veins?

A

changes in blood pressure or IOP.
isechemic damage
zero (due to IOP and venous pressure being relatively the same)

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35
Q

what systems use autoregulation?

A

central retinal circulation
capillaries in superficial nerve fibre layer in ONH
blood vessels in pre laminar layer in ONH

NOT CC

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36
Q

what receptors play a role in blood pressure detection?

A

baroreceptors in carotid sinus play a major role.

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37
Q

blood flow begins to fall at?

A

60cm water/40mmHg

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38
Q

arteries have what kind of transmural pressure? veins?

A

HIGH (TMP=Ta-IOP)

LOW (TMP=Tv-IOP, usually around 0)

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39
Q

the venous pulse was thought to disappear when?

A

IOP is too high or venous pressure is too low.

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40
Q

SVPs are present in how many of normal subjects? not present in how many normal subjects? it occurs only in people with a CSF pressure below what? when IOP=CSF pressure what happens?

A

90%
10%
190mmHg
there is no pulse

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41
Q

does normal IOP mean that CSF pressure is normal?

A

not necessarily

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42
Q

what are the three type of open angle glaucoma?

A
  1. low tension
  2. primary open angle
  3. ocular hypertension
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43
Q

is IOP increase the cause of glaucoma?

A

NO!

44
Q

What is a TIA?

A

Transient Ischemic attack: loss of blood flow, PP decreases, transient loss of vision (no vision indicates carotids are more than 50% occluded), occlusion of carotid artery, more than 50% occlusion increases chances of stroke.

45
Q

why does the carotid artery occlude in TIA?

A

due to plaque build up, little pieces of plague or clots can travel to opthalamic artery and into the eye and cause issues.

46
Q

what is perfusion pressure equal to?

A

Pa-Pv

47
Q

What are three main causes of decreased PP?

A
  1. decreased Pa
  2. increased Pv
  3. Increased Resistance
48
Q

how are frequency and wavelength related? ultraviolet light has what type of wavelength? infrared? visible range of frequency?

A

inversely related
UV= short wavelength
IR= long wavelength
435-750 THz

49
Q

which photoreceptors are more sensitive cones or rods? are both cones and rods saturable?

A

RODS

JUST RODS, at low light levels.

50
Q

what is the appearence of an S cone, foveal cone and peripheral cone?

A

S cones are rod shaped (more so than peripheral)
peripheral cones are also rod shaped
foveal cone: smaller and more cone like

51
Q

in the rod outer segment, it is filled with? has how many discs? the discs contain?

A

cytoplasm (discs float in cytoplasm), 15000 discs, discs contain rhodopsin.

52
Q

in the cone outer segment, the infolding of membranes contain what?

A

photopsin

53
Q

the inner segment of both rods and cones contain what two parts? cell body (nucleus) is found in which layer? what is a spherule?

A
  1. ellipsoid (outer part): contains miotchondria
  2. myoid (inner): contains organelles and tubules
    outer nuclear layer
    synaptic end of photoreceptor (round in rods and pyramidal in cones).
54
Q

is the macula nasal or temporal to optic disk?

A

MTO (temporal)

55
Q

rods make up what percent of photoreceptors? are they able to detect a single photon? rod peak sensitivity is at what wavelength? do rods saturate?

A

97%
YES
500-510nm
yes at low light levels, any brighter lights cones are in charge.

56
Q

cones make up what percent of photoreceptors? does convergence occur with cones? rods? diameter of cones in fovea are what compared to periphery?

A

3%
no convergence at fovea (some in periphery convergence of signals increases our sensitivity). rods have convergence.
smaller. bigger in periphery.

57
Q

in humans, how many rods for every one cone? is this the case in all species?

A

20 rods for one cone

in squirrels cones are more dominant.

58
Q

where are new discs created in rods?

A

inner part of outer segment

59
Q

what are the three different cones in humans and what is their peak sensitivity wavelength?

A 
L cones (red): 560nm
M cones (green): 530nm
S cones (blue): 420nm
60
Q

all photopigments in humans are forms of? and they all contain?

A

rhodopsin

retinal.

61
Q

rod pigment is called? L cone pigment? M cone? S cone?

A

rhodopsin
erythrolab
chlorolab
cyanolab

62
Q

what is the pigment in intrinsic photosensitive retinal ganglion cells in retina? (3rd type of photoreceptor)

A

melanopsin

63
Q

all photopigments are generally made up of?

A

photopigment= protein (opsin) +chromophore (11-cis-retinal, in humans)

64
Q

opsins belong to what family of proteins?

A

G proteins

65
Q

the chromophore is covalently bound to the protein by what type of linkage?

A

schiff base linkage with a specific lysine residue in opsin molecule.

66
Q

rhodopsin has how many AA? S cone opsin? L/M opsin? what differs and what stays the same among these?

A

348 AA
346-350AA
364 AA
AA sequences can change (which alters photosensitivity) but the length is roughly the same, N terminus also differs for each.

67
Q

which two cone types are 96% homologous? Rhodopsin is 41% homologous with which types? S cones are 43% homologous with?

A

L/M cones.
L/M/S opsin
L/M opsin

68
Q

which six genes are related to color deficiency?

A
  1. OPN1LW
  2. OPN1MW
  3. OPN1SW
  4. CNGA3
  5. CNGB3
  6. GNAT2
    (last three are disfunctional cones)
69
Q

which opsins are autosomal? which are sex linked?

A

rhodopsin and S cone.

L/M cones (only on X chromosome)

70
Q

L/M cones differ from each other at how many spectral tuning sites?

A

FIVE (five sties where diff AA’s have been subsituted).

71
Q

what are some ways in which S cones are more related to rods than other cones?

A

shape is more similar to rods, mainly in parafoveal region, AA sequence is more similar to rhodopsin than cone opsins.

72
Q

rods are mostly concentrated how far from the fovea?

A

18 degrees in the periphery.

73
Q

Vertebrates can have which two types of visual pigments? they are each made up of which opsin/chromophore? In non vertebrates what visual pigment is used?

A
  1. rhodopsins: opsin + 11-cis retinal (R1)
  2. porhyropsins: opsin + 3,4-dehydroxyretinal (R2)
  3. insects use opsin + 3-hydroxyretinal
74
Q

rhodpsins have short or long wavelength? found in which animals? porphyropsins have long or short? found in which animals? which animals have both pigments?

A

short wavelength: marine fish and terrestrial animals
long wavelength: fresh water fish
both: lampreys, teleosts and amphibians

75
Q

longer wavelengths have what kind of energy?

A

less energy (compared to shorter wavelengths)

76
Q

chicken cones are made up of?

A

photopsin+R1= iodopsin (562nm)

77
Q

fish rods are made up of?

A

opsin +R2= porphyropsin (522nm)

78
Q

artificial is made up of?

A

photopsin +R2= cyanopsin (620nm)

79
Q

when light hits rhodopsin what happens to the chromophore?

A

it causes a bend and stresses the protein (11-cis retinal), very little energy is required to straighten the bond (to all-trans retinal).

80
Q

what states make up the photoreaction?

A

opsin+11-cis retinal, light hits here and transforms this into bathorhodopsin.

81
Q

Dark reactions involve which states?

A

bathrhodopsin to lumirhodopsin to metarhodopsin-1 to metarhodopsin-2 (THIS IS WHERE TRANSDUCTION OCCURS, TRANSDUCIN CAN BIND HERE) then to pararhodopsin then to opsin +all-trans retinal.

82
Q

after all-trans retinal is made what happens?

A

it can be reduced to retinol and then made back into rhodopsin (unactive form) and can undergo cycle again once activated.

83
Q

rhodopsin is unactive when? active?

A

unactive when it is in 11-cis retinal form, becomes active once bond is straightened out to all-trans retinal.

84
Q

are the dark reactions reversible? what is the speed like of these reactions?

A

everything is reversible with blue light that occurs before metarhodopsin-2 (after this point no reversing)
reactions occuring before metarhodopsin 2 are very fast, after this it becomes longer (minutes)

85
Q

how long for chromophore release? how long for regeneration of rhodopsin?

A

10 mins

20 mins

86
Q

changes in conformation of chromophore and protein can cause changes in what?

A

spectral sensitivity of the pigments.

87
Q

what are the three different peaks for rhodopsin?

A

alpha peak: visible region
beta peak: bond between opsin and chromophore, in UV region
gamma peak: bond between tyrosine and tryptophan (also in UV region)
different bonds require different amounts of energy to break.

88
Q

what is the main thing that affects spectral sensitivity (peak sensitivity) of photopigments?

A

AA sequence.

small changes in conformation, fit, chromophores and bonds will have small affects.

89
Q

where is photopigment located in rods?

A

in the discs (in outer segment)

90
Q

what five components are needed to convert photons?

A
  1. photons
  2. rhodopsin
  3. G protein (transducin)
  4. PDE
  5. cGMP
91
Q

what is the G protein in the biochemical cascade? what is attached to this protein?

A

transducin

Galpha subunit, Gby subunit and GDP.

92
Q

what is translation?

A

the moving of transducin long its disc surface, looks for an activated rhodopsin.

93
Q

what balances the inward movement of positive ions (Ca2+, Na+ and Mg2+ mostly Na+)? when is this occuring?

A

outward movement of K+ ions.

inward movement of positive ions occurs in the dark (channels open because cGMP is bound)

94
Q

in light conditions what happens to the channel?

A

it closes because light activates rhodopsin which eventually activates PDE through cascade which hydrolyzes cGMP to GMP (cGMP needed to keep channel open therefore without it channel closes in light). HOWEVER K+ channel still open so K+ moves out no positive coming in therefore build up of positive charge outside.

95
Q

Na+ moving into the cell causes what in the dark?

A

negative current, causes depolarization

96
Q

in light what occur to membrane potential?

A

hyperpolarization.

97
Q

a single photon of light can activate rhodopsin. a single photon can cause what to photocurrent?

A

2% reduction and make membrane potential more positive.

98
Q

what two things happen to rod photocurrent when light goes on?

A
  1. 34pA change in current

2. 600+ ms duration (rods take a relatively long time to respond)

99
Q

in cones, responses are smaller but are? what is the biphasic response of cones?

A

FASTER
regeneration of guanylate cyclase which icnreases cGMP concentrations when they fall, must be faster in cones and begins to reopen channels.

100
Q

what are three factors in transduction?

A
  1. amplification
  2. adaptation (light and dark)
  3. synaptic deactivation
101
Q

what are the three types of amplification that play a role in transduction?

A
  1. photopigment amplification:one photon of light causes a change in one molecule of rhodopsin BUT hundreds of transducin molecules are activated by a single activated rhodopsin.
  2. disc amplification: single activated rhodopsin causes hydrolysis of 1400 cGMP molecules
  3. channel amplification: one PDE molecule can convert up to 100 cGMP to GMP.
102
Q

adaptation to light and dark is controlled by which molecule? what is its main function?

A

Ca2+

alters sensitivity. increases sensitivity in dim light, decreases in bright light.

103
Q

Ca2+ binds to what? which causes a reduction in synthesis of? ultimately this does what to Ca2+ concentration?

A

GCAP (makes cGMP, it is bound to guanylate cyclase)
cGMP (therefore channels close)
decreases (therefore Ca2+ released from GCAP and synthesis of cGMP is resumed)

104
Q

when channels close with light we get a reduction in which molecule that is involved with synaptic deactivation?

A

calcium (therefore decrease in glutamate NT)

therefore when calcium decreases so does release of glutamate.

105
Q

light adaptation is controlled by? when channels close what two main affects does it have on adaptation?

A

Ca2+
decrease in inflow of Na+ causing hyperpolarization of rod, decrease in Ca2+ levels inside rod causing decreased sensitivity of light.

Anatomy (18 decks)

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