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Neural Biology 1 > introduction to the uvea and structure of the lens > Flashcards

introduction to the uvea and structure of the lens Flashcards

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1
Q

what is the adnexa of eye ?

A
  • eyelid( muscles and glands )
  • lacrimal gland
  • tear film
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2
Q

what forms the outer coat of the eye ?

A

sclera and cornea

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3
Q

what does uvea consist of ?

A
  • choroid - middle coat of eye sandwiched between sclera and retina
  • ciliary body
  • iris
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4
Q

what is the lens attached to ?

A

lens is attached to ciliary body by thin fibres called suspensory ligaments/zonules fibres

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5
Q

what two surfaces does lens have ?

A

anterior and posterior surfaces which meet at equator

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6
Q

what is centre of anterior surface of lens known as ?

A

anterior pole- 3mm behind cornea

less convex than posterior

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7
Q

what is centre of posterior surface of lens known as ?

A

posterior pole

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8
Q

what is anterior chamber ?

A

vitreous filled cavity between cornea and front surface of lens

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9
Q

what does anterior of iris touch ?

A

anterior chamber

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10
Q

what is posterior to iris but anterior to lens ?

A

posterior chamber

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11
Q

what is posterior chamber ?

A

filled with aqueous humour

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12
Q

what is behind lens ?

A

vitreous chamber

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13
Q

what is axial diameter of lens ?

A

3.5 to 4mm at birth increase to 5mm in old age

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14
Q

describe the equator of lens ?

A
  • not smooth
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15
Q

how many layers does lens have ?

A

the lens consists of 3 concentric layers

  1. thin elastic capsule on the outside
  2. simple epithelium
  3. stroma ( made of lens fibres)
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16
Q

what is the lens capsule ?

A
  • surrounds the lens
  • basement membrane of the cells epithelial cells which lie inside of it
  • produced by epithelial cells
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17
Q

explain the structure of lens capsule ?

A
  • appears to lack structure
  • made up of lamellae ( 40 layers ) of superhelical collagen
  • very elastic ( no elastic tissue gets its elasticity from collagen )
  • thickness varies
    depending on location within the lens
  • thicker anteriorly
  • 16um at anterior pole
  • less than 3um at posterior pole
  • at age 22 capsule is thickest at equator
  • as we age maximal thickness is between pole and equator
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18
Q

explain Fincham lens capsule structure ?

A
  • at age 22 capsule is thickest at equator

- as we age maximal thickness is between pole and equator

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19
Q

what is lens capsule function ?

A
  • it’s elasticity plays an important role in accommodation
  • the capsule also forms a barrier stopping large particulate matter such as inflammatory cells entering the lens, while allowing smaller necessary metabolites through
  • plays an important role in cataract surgery
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20
Q

what happens in cataract surgery ?

A
  • the lens stroma is liquefied by an ultrasound probe and sucked out leaving the capsule empty
  • empty capsule is filled by an artificial lens
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21
Q

what is layer inside lens capsule ?

A

lens epithelium

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22
Q

how does the shape of lens epithelium vary ?

A
  • the shape of lens epithelium varies depending on where you are in lens
  • anterior pole - epithelial cells are squamous
  • between equator and pole - epithelial cells are cuboidal
  • at equator - cells are columnar
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23
Q

what are adjacent epithelial cells joined by in the lens ?

A

desmosomes- strong junction

gap junctions

24
Q

what is function of desmosomes in lens ?

A

connect epithelial cells to underlying lens fibres

25
Q

what other junction do you get between adjacent epithelial cells ?

A

gap junctions - allow ionic continuity from one epithelial cell to other

26
Q

what is different about posterior surface of lens ?

A

posterior lens surface has no epithelial cells

27
Q

what is lens stroma made off ?

A

made of lens fibres - long elongated cells which appear hexagonal

28
Q

what is fibre in lens stroma ?

A

long cells elongated cells which appear hexagonal

29
Q

what is significant about hexagonal shape ?

A

they tessellate together with no gaps

30
Q

where do lens fibres run from ?

A

lens fibres run from front surface of lens to back surface and join to one another at sutures

31
Q

how are sutures in young lens ?

A

in young lens sutures form a shape of a y

32
Q

what is suture ?

A

where lens fibres join to one another

33
Q

how are sutures in old lens ?

A

you have star like arrangement

- less space for sutures to from a y shape

34
Q

do lens fibers have organelles ?

A
  • lens fibres have few organelles

- nucleus is lost after fibre formation

35
Q

do lens fibers have proteins ?

A
  • lens fibres have the highest protein content of any cell in the body (>90% of their wet weight )
  • alpha , beta and gamma crystallins are what give the lens its high refractive index
36
Q

what are lens fibres joined by ?

A
  • ball and socket junctions are most abundant in the outer lens
  • tongue and groove junctions lie deeper
37
Q

what are different types of junctions between cells ?

A
  1. sticky glycoprotein on cell surface
  2. mechanical junctions
    - ball and socket
    - tongue and groove
  3. specialised cell-cell junction
    - occluding (tight)
    - anchoring ( desmosomes)
    - gap
38
Q

what is a ball and socket junction ?

A

. membrane of one cell bludges out to form a ball
. membrane of adjacent cell bludges in to form a socket
. ball fits into socket joining two cells together

39
Q

what is example of ball and socket ?

A
  • bone and hip

- between adjacent lens fibres

40
Q

what is tongue and groove junction ?

A
  • tongue and groove

- this what we know from woodwork

41
Q

what is example of tongue and groove ?

A

this is junction found between the cells within the lens

42
Q

why do we need many mechanical junctions within the lens ?

A
  • lens is only transparent because of regular arrangement of lens fibres which fit tightly together
  • lens is always changing shape , so lens fibres are always squeezed and pulled and they have to be tightly held together and forming gaps and loosing transparency of lens
43
Q

what are occluding junctions ? are they important in lens

A
  • adjacent protein molecules in opposing plasma membrane fuse , sealing the space between cells . this prevents the passage of molecules
  • occluding junction are not very important in lens
44
Q

what are desmosomes ? and where are they found in lens

A
  • adjacent cells are joined by fibres which form part of cytoskeleton
  • very robust and found in tissue to subject to severe mechanical stress
    e. g. lens epithelium
45
Q

what are gap junctions ?where are they found within lens

A
  • adjacent cells are joined by membrane protein, these allow cytoplasmic continuity between cells . this means that certain molecules/ions pass directly from one cell to next
  • very important in lens epithelium and lens fibres
46
Q

what are junctions between membrane proteins in gap junctions known as ?

A

connexons

47
Q

where does lens receive its nutrients from ?

A

lens has no blood supply . it receives its nutrients from the aqueous humour

48
Q

how do nutrients flow from aqueous humour to the centre of lens ?

A

via gap junctions

49
Q

what happens to epithelial cells in lens at the germinative zone ?

A
  • at the germinative zone epithelial cells undergo mitosis displacing cells towards the lens equator
  • when cells get to equator they become columnar
  • then they get pushed to lens stroma where they elongate and turn into lens fibres
50
Q

where do lens fibres that make up stroma of lens originate from ?

A

they originate from epithelium

51
Q

what do can be seen at lens equator ?

A
  • nuclear bow which is made up of residual nuclei of the most recently formed lens fibres
52
Q

how many new lens fibres shell do we lay every year ?

A
  • 5 layers every year
  • ## the older you get the more layers of cells you get
53
Q

what is the lens nucleus ?

A

lens nucleus contains the oldest cells

54
Q

what are the subdivisions of the lens ?

A

. embryonal nucleus
. foetal nucleus
. adult nucleus
. cortex

55
Q

why is lens unusual ?

A

you never loose any cells

Neural Biology 1 (58 decks)

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