Choroid, Iris and Lens Flashcards

1
Q

Why are both layers of the iris epithelium pigmented?

A

Absorb all the stray light

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2
Q

What sort of muscle is the iris dilator muscle and what is the orientation of the fibres?

A

It is a smooth muscle arranged radially and runs perpendicular to the pupil.

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3
Q

What is the effect of the contraction of the iris dilator muscle on pupil size?

A

Results in pupil dilation - widens the pupil

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4
Q

What is the orientation of the iris sphincter fibres and what is the effect of their contraction on pupil size?

A

It is a circular muscle and contraction leads to pupil constriction - decreases pupil size

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5
Q

What neurotransmitters are involved at the iris sphincter and dilator muscles?

A

Iris Sphincter = adrenaline

Iris Dilator =

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6
Q

Apart from muscle, what else do you expect to find in the iris stroma?

A

Loose connective tissue and widely spaced collagen fibres, fibroblasts and mast cells and blood vessels

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7
Q

What makes up the anterior border layer of the iris? How is this different to most other biological borders?

A

Fibroblasts

-There arent any epithelial cells lining the surface

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8
Q

What makes up the anterior border layer of the iris? How is this different to most other biological borders?

A

Fibroblasts

-There arent any epithelial cells lining the surface

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9
Q

What makes irises different colours?

A

The varying number and thickness of melanocytes

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10
Q

What is the nature and function of the pigment in the choroid?

A

To create a black box effect, minimising light scatter

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11
Q

To what structure do the choroidal capillaries supply nutrients?

A

RPE

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12
Q

How thick is Bruch’s membrane?

A

5 microns

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13
Q

To what structures to the short posterior ciliary arteries supply blood?

A

They supply blood to the choroid and iris

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14
Q

To what structures do the anterior ciliary arteries supply blood?

A

They supply blood to the superior, inferior and medial rectus as well as the conjunctiva and sclera

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15
Q

What is the compostition of the lens capsule?

A

It is a smooth transparent basement membrane composed of super helical collagen fibres

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16
Q

What gives the lens capsule its elasticity?

A

Due to superhelical (spring like structure) collagen

17
Q

What is the function of the lens capsule elasticity?

A

To allow the lens to change shape during accommodation

18
Q

How does the shape of the lens epithelium vary with location on the lens?

A

A the anterior pole, it is squamos, between the pole and the equator it is more cuboidal and at the equator its almost columnar

19
Q

What process accounts for the nuclear bow in the lens equator?

A

epithelial cells elongate to become lens fibres

20
Q

What happens to old lens fibres?

A

They remain in the lens, clump together and form opacities in the lens

21
Q

What structures do lens fibres form when they join together on the anterior and posterior surfaces?

A

Sutures

22
Q

Why is there a need for such a tight fitting organisation of the lens fibres?

A

So that all light passing through the lens is refracted

23
Q

Why the requirement for gap junctions in lens fibres?

A

To allow nutrients to pass from cell to cell in the lens - cytoplasmic continuity

24
Q

Whys is the stroma of the iris so insubstantial?

A

Widely spaced collagen fibres allow contraction