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Anatomy > Lecture 15 > Flashcards

Lecture 15 Flashcards

1
Q

What is the main function of the lens?

A

to refract light onto the retina, also protects the retina from harmful UV effects by absorbing higher energy shorter wavelengths (usually in blue region). protects retina from free radicals.

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2
Q

which tissue has the highest protein concentration in the body? what is a cataract?

A

lens (yet is it transparent)

anything that decreases the transparency of the lens

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3
Q

is the lens vascular or avascular? what provides the lens with nourishment?

A

avascular (just like the cornea) BV would cause shadows.

aqueous humor

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4
Q

where is the epithelium layer located in the lens? what forms the lens sutures? what is located in the cortex? what structure surrounds the lens?

A

anterior
the fibres growing from the equatorial regions come together to form a front suture and a back suture.
fibres
capsule (this is where zonules attach)

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5
Q

the capsule in the lens acts as what? what is the capsule composed of? what is unique about the capsule in terms of permeability?

A

basement membrane
collagenous fibre (limits stretch) and fibrillin (elasticity)
permeable to most molecules EXCEPT proteins

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6
Q

marfans syndrome is what type of disease? what can happen to the lens specifically?

A

fibrillin disease

the zonule fibres weaken and therefore cant hold up the lens, the lens falls down and can dislocate.

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7
Q

90% of all pumps are located on which surface of lens? this is the only layer that is what? cells at the anterior surface of lens contain what? highest O2 concentration is located where in lens? where does the anterior surface get all of its O2 and energy from?

A 
anterior epithelium. 
actively metabolizing 
organelles (mito, nuclei, ribos etc) as we move further to center they loose these for transparency. 
anterior surface
aqueous humor
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8
Q

pre equatorial region has high energy consumption to drive what? what protects this area? what is unique about the cells here?

A

mitosis and pump
iris protects this region from damage by UV.
cells loose organelles.

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9
Q

what type of cells are located in the cortex? older cells are located where compared to newer? what happens as we move closer to center of lens in terms of protein?

A

hexagonal fibres (for maximal packing ability)
older cells are toward center of lens while newer ones are toward periphery.
as we move closer, increase in protein concentration, therefore increase in density and increases in refractive power.

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10
Q

nucleus of lens has what kind of fibres?

A

hexagonal, regular array, small cells, small spaces between cells (very little extracellular space) which are all ideal for transparency.

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11
Q

what shaped sutures are present when we are born? as we age what happens to the sutures? purpose of sutures?

A

upright= Y anteriorly
upside down= Y posteriorly
they increase in branching which improves optical quality.
keeps water out, keeping lens dry

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12
Q

interdigidations (interlocking) are more concentrated where?

A

in center of lens (less in periphery) because water does not move through center of lens only periphery.

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13
Q

as the cells of the lens reach the sutures, what happens in terms of interlocking?

A

it becomes more interlocked forming interlocking ball and socket junctions which ensure the cells remain tightly connected during accommodation.

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14
Q

can the fibres of the lens communicate?

lens fibres are connected by what type of connections?

A

yes through gap junctions

N-cadherin (Ca2+ based)

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15
Q

which tissue has the smallest amount of extracellular matrix between their cells?

A

Lens.

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16
Q

what is unique about the posterior epithelium cells during lens development?

A

they extend forward to fill in the space so that epithelium is now only located on the anterior surface.

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17
Q

once lens fibres reach the sutures what happens?

A

they stop elongating and their basal ends detach from the capsule. then there is loss of organelles by apoptosis and light scatter declines.

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18
Q

which vessels form the vascular capsule of the lens during development?

A

hyaloid vessels

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19
Q

in the organelle free zone what two types of fibres are found?

A
  1. differentiating: outer 20%, some organelles

2. mature fibres: inner 80% no organelles

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20
Q

What are the six layers of the lens starting with posterior capsule?

A

posterior capsule, embryonal nucleus (made by fibres from posterior epithelium during development), fetal nucleus (fibres laid down before birth), adult nucleus (fibres laid down before sexual maturation), cortex (laid down after sexual maturation), anterior epithelium, anterior capsule.

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21
Q

which layer contains primary lens fibres, which contain secondary?

A

ONLY embryonal nucleus contains primary fibres, rest are secondary.

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22
Q

difference between a lens in a child vs adult?

A

in child lens is very clear, as we age it becomes cloudy (due to mirgation inward and changes in protein synthesis rates)

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23
Q

what are four variables that affect transparency?

A
  1. cellular level
  2. molecular level
  3. water
  4. embryonic remains
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24
Q

at cellular level, which factors promote transparency?

A
  1. small fibres
  2. uniformity of fibres
  3. regularity of packing
  4. loss of organelles
  5. avascularity
25
Q

at molecular level which factors promote transparency?

A
  1. fibres accumulate large amounts of protein as they elongate yet they stay clear
  2. lens proteins are small and uniform (90% crystallins, so small they dont interfere with light)
  3. ordered arrangement
  4. high packing density
26
Q

how does water affect transparency?

A
  1. can produce refractive lakes
  2. increases extracellular space
  3. disrupts fibres
  4. anterior pump/leak system maintains lens volume (remember water likes to leave with ions being pumped out)
27
Q

embryonic remains can affect transparency what are examples?

A

posterior lens: tunica vasculosa lentis arises from hyaloid artery (remains of this can cause decrease in transparency)
anterior lens: anterior pupillary membrane arises from developing iris stroma (remains of this can affect transparency)
(both of these are suppose to disappear in second trimester).

28
Q

what is mittendorfs dot?

A

congenital origin, arose from posterior lens attachment of hyaloid artery. remains of attachment of hyaloid artery.

29
Q

what is bergmeisters papilla?

A

found at center of optic disc, remnant of hyaloid artery. small tuft of fibrous tissue (little outgrowth)

30
Q

the lens power at rest is what? what factors could affect refraction?

A

15D

  1. protein concentration (water concentration) is proportional to refractive index (as we get closer to nucleus RI increases)
  2. protein polymerization: increases RI causing myopic shift in refraction.
31
Q

what provides lubrication in order for lens fibres to slide in accommodation? lipids in the lens are in what form?

A 
GAGs
saturated ( we want no double bonds causing kinks which causes light scattering)
32
Q

tight junctions are present where in lens? what is present in other areas that do the same thing?

A

anterior epithelium, interdigitations do the same thing in rest of layers.

33
Q

in young eyes what can they usually accommodate?

A

15D

34
Q

does the lens grow throughout life?

A

yes (lens cells slough inward)

35
Q

whcih type of light is scattered most by the lens?

A

blue light which is good for retina but the lens will look yellow (as we get older)

36
Q

where are the most vulnerable fibres in the lens?

A

in the center because there is less O2 there.

37
Q

most of the proteins in the lens are what? what are the two other types that each make up 5%? having a high concentration of protein in the lens makes it what?

A

water soluble (90%)
urea soluble (cytoskeletal protein)
insoluble
osmotically active.

38
Q

more specifically, what types of water soluble proteins do we have?

A

alpha (type A and B) 40%, beta 35% and gamma 25% crystallins.

39
Q

more specifically, what types of urea proteins do we have in the lens? what types of insoluble proteins do we have?

A 
crystallin and cytoskeletal (i.e. actin)
membrane proteins (such as albuminoid, MIP 26, ATPases, N-cadherin) and crystallins.
40
Q

the alpha A and alpha B crystallins in the lens act as what? mutation in which type can cause cataracts and myopathy due to aggregation of misfolded proteins?

A

chaperones (which are a type of protein that help fold other proteins into correct orientation and prevent misfolding)
alpha B.

41
Q

in terms of location, alpha and beta crystallins are more prominent where? What about gamma and albuminoid (which is formed by the aggregation of alpha, beta and gamma)?

A

in the periphery, they decrease as we move toward the center.
they increase as we move toward the center, less concentrated in periphery

42
Q

albuminoid is thought to arise via what?

A

oxidation and disulfide bond formation.

43
Q

which surface of the lens is more permeable? therefore which side has more pumps and which side has more leaky channels?

A

posterior surface because there is only an epithelium layer on the anterior surface which acts as a barrier. therefore ant side has more pumps, post has more leaky channels.

44
Q

what controls water flow in the lens? higher osmotic gradient causes what? which surface of lens has a higher osmotic gradient?

A 
osmotic gradient. 
higher osmotic gradient draws more water into the lens. 
anterior surface (glucose concentration higher anteriorly).
45
Q

cataracts that are formed due to leaky membranes will form in which part of the lens? cataracts due to faulty pumps and osmotic gradients will be located in which portion?

A

posterior portion

anterior portion.

46
Q

movement of ions and water from the aqueous and vitreous enter the lens on which surface? which types of passing do they use?

A

will come through on anterior surface. therefore using the pumps in forms of passive diffusion, active transport and facilitated diffusion.

47
Q

lens capsule is completely permeable to most molecule EXCEPT what?

A

proteins! AA can enter and form proteins but proteins can not enter themselves.

48
Q

how does water enter lens? Na+? Cl-? K+? Ca2+? glucose?

A 
freely
active transport (from lens to aqueous humor)
diffusion (leak into lens)
action transport (aqueous humor into lens)
diffusion (leak into lens)
facilitated diffusion (leak into lens)
49
Q

lactic acid? glutathione (tripeptide)? ascorbic acid? inositol? AA? protein?

A

diffusion (leak out of lens)
synthesized in lens cant physically move in.
diffusion (leak into lens)
active transport (into lens)
active transport (into lens)
synthesized in lens cant physically move in.

50
Q

lens nucleus requires energy for pumps on anterior surface, what type of energy is used? the energy that is used is most concentration where? the highest protein content is located where?

A

creatine phosphate
highest in nucleus
highest in nucleus.

51
Q

in the lens, what percent of glucose is dedicated to glycolysis? (how much is anaerobic and aerobic?) where does the remaining percent go?

A

85% to glycolysis (80% anaerobic 2ATP made per molecule of glucose and 5% aerobic 36ATP made per molecule of glucose)
pentose shunt pathway (15%) which produces NADPH which helps reduce free radicals.

52
Q

in diabetes, when glucose is in excess what is made? is this good or bad for the lens?

A

sorbitol
bad, it has a high osmotic pressure therefore it likes to draw water in with it therefore lots of sorbitol, lots of water being drawn into lens.

53
Q

if there are changes in osmolarity in the lens, what can this cause in terms of refractive changes?

A

thickness, radius of curvature and Rx (i.e. increased glucose levels causes increased sorbitol, which causes increased water amount, causes increased IOP, increases power therefore causes myopic changes)

54
Q

unusualy changes in Rx may indicated what?

A

diabetes.

55
Q

oxidative stress in the lens is typically a result of?

A

formation of free radicals therefore activating oxidative systems.

56
Q

free radical production in the lens is due to what? free radical reduction in the lens is done by?

A 
superoxide synthetase (changes O2 to reactive species) and short wavelengths
superoxide dimutase (changes reactive species to H2O2 and in presence of catalase-Fe it will change H2O2 to H2O) and glutathione (once NADPH is reduced from pentose shunt path, glutatione is activated)
57
Q

How can free radicals cause damage?

A

cross linking of DNA (gene mutations)
cross linking of lipids (leaky membranes)
cross linking of proteins (non functional enzymes)

58
Q

as your age increases, what type of oxidative stress becomes more prevalent with respect to proteins?

A

polymerization of proteins occurs with increased age, increases in shorter wavelengths and Ca2+ build up in the lens. proteins can get to a point where they are too large and can no longer be broken down influencing cataracts.

Anatomy (18 decks)

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