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Histology > Eye > Flashcards

Eye Flashcards

1
Q

How many structural layers is the eye composed of? Name them.

A

3 parts:
- cornoscleral coat
- vascular coat (uvea)
- retina

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2
Q

Name the structural layers of the eye, and what they include.

A
  • cornoscleral coat (sclera, cornea)
  • vascular coat (choroid, stroma of ciliary body, iris)
  • retina (outer pigment epithelium, inner neyral retina, iris, epithelium of the ciliary body)
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3
Q

What is the corneoscleral coat? What does it include?

A

outer fibrous layer, including:
- sclera (white portion)
- cornea (transparent portion)

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4
Q

What is the vascular coat? What is its different name? What does it contain?

A

middle layer= uvea
- choroid
- stroma of the ciliary body
- iris

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5
Q

What is the retina? What does it contain?

A

inner layer of the eye, includes:
- outer pigment epithelium
- inner neutral retina
- epithelium of the ciliary body
- iris

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6
Q

What is the white portion of the eye?

A

the sclera

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7
Q

What is the transparent portion of the eye?

A

the cornea

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8
Q

What does the optic nerve connect?

A

the neural retina with the central nervous system

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9
Q

What is the primary role of the corneoscleral coat?

A

protective layer (barrier from mechanical and chemical damage)

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10
Q

What is the primary function of the retina?

A

Transform light into nervous impulses, which travel to the CNS by the optic nerve.

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11
Q

Which part of the eye gives it ‘colour’?

A

the iris (in the vascular coat layer)

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12
Q

Why is the middle layer called the vascular coat?

A

It is highly vascularised (contains many blood vessels) giving nutrition to the outer and inner most eye layers.

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13
Q

How are nutrients supplied to the retina?

A

through the highly vascularized vascular coat

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14
Q

What is the location of the cornea?

A
  • covers the anterior 1/6 of the eye,
  • in this window like region, the surface of the eye has a prominence or convexity
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15
Q

What is the cornea continuous with? What is that thing composed of? What is its function?

A

continuous with the sclera.
- dense fibrous connective tissue
- provides attachment for the extrinsic muscles of the eye
- the white portion of the eye

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16
Q

What does the cornea consist of? How many layers?

A

5 layers:
- 2 non cellular layers (2 basement membranes (bowmans and descemets )
- 3 cellular layers ( 2 epitheliums (corneal epithelium and corneal endothelium) and 1 stroma (corneal))

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17
Q

What is the epithelium always positioned on?

A

the basement membrane
- bowman’s (anterior)
- descemet’s (posterior)

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18
Q

What is the core of the cornea made of?

A

connective tissue stroma:
- thickest part of the cornea
- “corneal stroma”

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19
Q

What are the three cellular layers of the cornea? What are they divided by?

A
  • corneal epithelium
  • corneal endothelium
  • corneal stroma

seperated by basement membranes:
- bowman’s membrane (anterior)
- descements membrane (posterior)

basement membranes are homogenous when viewed in the light microscope.

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20
Q

What is the corneal epithelium composed of?

A

nonkeratinized stratified squamous epithelium:
- 5-10 layes of cells
- continuous with the conjuctival epithelium that overlies the adjacent sclera
- regenerative capacity

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21
Q

How does the stratified epithelium look like (same as other)?

A

the cells proliferate from the basal layer and become squamous at the surface

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22
Q

What capacity does the corenal epithelium have? What is its approximate turnover?

A

regenerative capacity
7 day turnover

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23
Q

What does protects the DNA in corneal epithelial cells? From what?

A

nuclear ferritin
- from UV light

cancer is very rare (even though it is constntly exposed to UV light)

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24
Q

What is exceptional about the bowman’s basement membrane?

A

It is very thick as the corneal epithelium is very thin (5-10 layers).
- protects the entire eye from pathogens (infectious agents)

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25
Q

What are the two primary purposes of the epithelium cells of the cornea?

A
  • fast regeneration (top layer cells detatch very quickly) (1 week)
  • strong protection (nuclear ferritin)
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26
Q

What protein exists in the cornea?

A

nuclear ferritin

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27
Q

What does UV light cause?

A

cancer (melanoma)

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28
Q

State important properties of the bowman’s membrane.

A
  • anterior basement membrane
  • homogenous, faintly fibrillar lamina
  • b/w corneal epitheliuma and stroma
  • ends at the cornoscleral limbus
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29
Q

State the composition of the bowman’s membrane.

A

faintly fibrillar lamina:
- collagen fibril diameter - 18nm
- randomly oriented

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30
Q

What is the primary function of the bowmans membrane?

A

1) acts as a barrier to the spread of infections
2) imparts strength to the cornea

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31
Q

State the regenerative properties of the cornea.

A

does NOT regenerate:
- if damaged, an opaque scar forms impairing vision

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32
Q

What is another name for the corneal stroma?

A

substantia propria

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33
Q

What is the corneal stroma composed of? State the arrangement.

A
  • thin lamellae
  • each lamellae: parallel bundles of collagen fibrils
  • sheets of flattened fibroblasts between lamellae
  • ground substance= corneal proteoglycans
  • collagen fibrils are arranged at approximately right angles to theose in the adjacent lamellae.
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34
Q

What does the ground substance if the cornea contain?

A

corneal proteoglycans:
- sulfated glycosaminoglycan, keratan sulfate (lumican) and chondrpoitin sulfate (bound to protein decorin)

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35
Q

```

~~~

What is the function of lumican (keratan sulfate)?

A
  • regulates normal collagen fibril assembly in the cornea,
  • critical in the development of a highly organized collagenous matrix
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36
Q

What is responsible for the transparency of the lamellae?

A
  • uniform spacing of collagen fibrils and lamellae
  • orthogonal array (alternating layers at right angles)
37
Q

Why is the orthogonal array of the lamellae important in the eye?

A

light does not reflect. light goes through the alternating layers (like through glass). (corneal stroma is transparent)
- allows us to see coulours based on the extent of rfeflection (different wavelengths of light)

38
Q

Explain the regenerative properties of the cornea.

A

The frontal membrane (bowman’s) canNOT regenerate.

The posterior membrane (descemet’s) CAN regenerate.
- readily regenerates after injury
- produced continuously but slowly thickens with age

39
Q

What is the basal lamina of the the corneal endothelial cells? What does it seperate?

A

Descemet’s membrane
- seperates the corneal endothelium from the adjacent corneal stroma

40
Q

State the structure of the Descemet’s membrane.

A
  • felt-like appearance
  • interwoven meshwork of fibers and pores
41
Q

State the composition and name of the final layer of the cornea.

A

Endothelium:
- simple squamous epithelium

42
Q

State the composition of the sclera.

A

IRREGULAR DENSE CONNECTIVE TISSUE

  • thick fibrous layer
  • containing flat collagen bundles
  • pass in various directions in planes parallel to its surface
  • irregular in diameter and arrangement

interspersed between collagen fibers:
- fine networks of elastic fibers
- moderate amount of ground substance

interspersed between elastic fibers:
- fibroblasts

43
Q

How many parts is the sclera divided into? What are they?

A

3 ill-defined parts:
- EPISCLERAL LAYER (episclera): external layer, loose ct adjacent to the periorbital fat, (outer environment)
- SUBSTANTIA PROPRIA (sclera proper/Tenon’s capsule) investing fascia of the eye, dense network of thick collagen fibers (DENSE CONNECTIVE TISSUE)
- SUPRACHOROID LAMINA (lamina fusca): internal layer, adjacent to choroid, contains thinner collagen and elastic fibers and fibroblasts, melanocytes, macrophages, and other connective tissue cells. (highly vascularized)

BASE= dense ct –> loose ct OUTSIDE

44
Q

What is the second layer of the eye? What is its other name? What is it composed of?

A

Vascular coat= uvea
- choroid
- cilliary body
- iris

45
Q

What is the choroid? What is its function? What is it composed of?

A

the vascular layer
function: provides nutrients to the retina
composition:
- venous plexus and capillaries
- pigment
(2nd eye layer= uvea)

46
Q

How is the colour of the choroid determined?

A

blood vessels and melanin (intense dark brown colour)

47
Q

What does the pigment of the choroid do?

A

absorbs scattered and reflected light to minimize the glare within the eye

48
Q

What is the choroid firmly attached to?

A

the retina

49
Q

What does the anterior rim of the uveal layer form?

A
  • stroma of the ciliary body
  • iris
50
Q

What is the iris? What does it form?

A
  • the most anterior part of the vascular coat
  • forms a contractile diaphragm in front of the lens
51
Q

What is the pupil? How does it effect the iris?

A
  • the central aperture of the thin disc
  • pupil changes in size in response to light intensity –> iris is pushed forward
52
Q

What is the iris composed of?

A
  • highly vascularized connective tissue stroma
  • covered on the posterior surface by highly pigmented cells: posterior pigment epithelium
  • layer of myoepithelial cells: anterior pigment epithelium
53
Q

Why can neither the nucleus nor cytoplasm of the iris be seen in the light microscope?

A

high degree of pigmentation

54
Q

In general, what is the iris made of?

A
  • core of connective tissue
  • 2 epitheliums: posterior pigment epithelium & anterior pigment epithelium

pigmented epithelium + muscles

55
Q

State the composition of the anterior pigment epithelium.

A
  • myoepithelial cells
  • laden with melanin granules which effectively obscure their boundries with the posterior pigment epithelial cells.
56
Q

How does the anterior pigment epithelium differ from the posterior pigment epithelium?

A

Anterior pigment myoepithelial cells have processes forming dilator pupillae muscle which alters the pupil size in response to light intensity.

57
Q

What are the different muscles within the iris? What forms them? How are the cells oriented?

A

DILATOR pupillae muscle:
- anterior pigment myoepithelium posess processes which extend radially
- contractile processes are enclosed by a basal lamina seperating them from the adjacent stroma

SPHINCTER pupillae muscle:
- smooth muscle cells (cells in the connective tissue, forming a ring around the pupil (acting like a sphincter limiting the amount of light entering the eye)
- circumferentially oriented cells

58
Q

What is the ciliary body? Where is it located?

A
  • thickened anterior portion of the vascular coat
  • located between the iris and choroid
59
Q

Where does the cilliary body extend from?

A

the root of the iris postolaterally to the ora serrata

60
Q

What does teh cilliary body have a lot of? What arises from its grooves?

A

ciliary processes (~75 radial ridges)
- fibers of the zonule arise from the grooves between ciliarry processes.

61
Q

What is the stroma of the ciliary body divided into? How many layers? What are they?

A

1) CILIARY MUSCLE:
- outer layer of smooth muscle
- makes up the bulk of the ciliary body

2) inner VASCULAR REGION:
- extends into the ciliary processes

62
Q

What is the epithelial layer covering the internal surface of the ciliary body a direct continuation of?

A

the two layers of retinal epithelium,
- bilayer of epithelium
- COLUMNAR epithelium
- epithelium produces secrete
secrete fills the chamber ensuring that it is not dry

63
Q

What does the ciliary muscle do? How does it do that?

A

regulates the focal point of the lens by changing its shape.

64
Q

What directions do ciliary muscles go?

A

3 different directions:
- oblique
- linear
- longitudinal

65
Q

What do all structures in the second layer of the eye have in common?

A

The excessive amount of blood vessels

66
Q

What is the last portion of the uvea? What does it do?

A

choroid
- provides most of the nutrition (largest part in the vascular layer)

67
Q

What is the choroid? What is it composed of?

A
  • dark brown vascular sheet
  • lies between the sclera and retina
  • connective tissue
  • rich network of blood vessels (capillaries)

2 layers:
- choriocapillary layer (inner vascular layer)
- bruch’s membrane (thin, amorphous hyaline membrane)

68
Q

What is the function of the bruch’s membrane?

A
  • seperates the choroid from the retina (deeper)
  • also called “lamina vitea” runs from the optic nerve to the ora serrata
  • continues as the ciliary body
69
Q

What is the function of the choriocapillary layer? What is it composed of?

A

composition:
- highly vascularized
- fenestrated capillaries have lamina: large and irregular

function:
- provides nutrients to the cells

70
Q

What is the third, inner most part of the eye?

A

RETINA

71
Q

```

~~~

What is the retina composed of?

A

2 layers (visual and non visual)

1) NEURAL RETINA/RETINA PROPER:
- contains photoreceptors

2) RETINAL PIGMENT EPITHELIUM (RPE)
- attached to the choriocapillary layer through the bruch’s membrane

72
Q

What are the two regions of the retina?

A

1) nonphotosensitive region (non visual)
- light doesnt affect the cells in that portion behind teh retina (portion is hidden and light only goes in straight lines)
- no nervous impulses made from visual effects

2) photosensitive region (optic part)

73
Q

How many types of neurons and synapses are there in the retina?

A
  • 15 types of neurons
  • 38 different synapses
74
Q

What 4 groups of cells can neurons and supporting cells of the retina be divided into?

A

photoreceptor cells- retinal rods and cones
conducting neurons- bipolar neurons and ganglion cells
association neurons- horizontal, centrifugal, interplexiform, amacrine neurons
supporting (neuroglial) cells- muller cells, microglial cells, astrocytes

75
Q

What is the most important cells within the eye? Which group do they classify as? What do they do?

A

PHOTORECEPTOR CELLS: retinal rods and cones
function: generate impulses regarding colours

76
Q

What is the function of conducting neurons? State examples.

A

make nervous impulses and carry them to the brain
eg. ganglion cells and bipolar neurons

77
Q

What is the function of associated neurons?

A

make additional synapses in between of conducting neurons/rods and cones/ conductive neurons and photoreceptive cells.
- makes more nervous impulses which go through the entire structure
- amplifies nervous impulses
- plays minor role

78
Q

What is the function of supporting (neuroglial) cells?

A
  • retina is part of the nervous system (by way of development (not nervous system))
  • microglial cells: macrophages, fight pathogens & digest dead cell debris
  • astrocytes: communicate between neurons and blood vessels
  • muller cells: primary suporting neuroglial cell in the retina (metabolism of minerals, creates neurotransmitters)
79
Q

What is the primary supporting cell in the retina?

A

muller cells

80
Q

What are the layers of the retina from outside inwards?

A

1) retinal pigment epithelium (RPE)
2) layer of rods and cones (outer and inner segments of photoreceptor cells)
3) outer limiting membrane (apical membrane of muller cells)
4) outer nuclear layer (retinal rod and cone cell bodies)
5) outer plexiform layer (processes of rods and cones + cells that connect them)
6) inner nuclear layer
7) inner plexiform layer
8) ganglion cell layer
9) optic nerve fibers
10) inner limiting membrane

81
Q

What are the two most important layers of the retina?

A

1) RPE: Retinal Pigment Epithelium
- single cuboidal cell layer
- cells rest on bruch’s membrane
- contains melanin pigment
- absorbs scattered light
- blood-retina barrier
- restores photosensitivity to visual pigments
- phagocytoses membranous disks

2) Photoreceptor layer:
- layer of rods and cones
- rods (layer 1) = most numerous (120 million)= detect light intensity with their cylindrical outer segments
- cones (layer 2) = less numberous (7 million)= conical shape= detect 3 different wavelengths corresponding to three primary colours

82
Q

What do rods and cones contain?

A

rods: rhodopsin (visual pigment): opsin and retinal
cones: iodopsin (visual pigment)

83
Q

What is visual processing?

A

the conversion of light into nerve impulses in the photoreceptors

84
Q

What is the major function of rods and cones?

A

Transform electromagnetic waves into electrical impulses (mechanical signals).
(one form of energy to another)

rods: intensitivity (see without colour)
cones: see colour (cannot work properly in the dark environment)

rods > cones : less colour

85
Q

What is the importance of bipolar neurons?

A

connect rods and cones with ganglion neurons
(act as junctions)

86
Q

What is the optic nerve? Where does it lead?

A

A nerve made from the connection of multiple axons coming from all the** ganglion neurons** in the retina.
It leads to the brain for processing.

87
Q

What do the layers of the eye and the lens serve as boundries for?

A

the three chambers

88
Q

What are the three chambers of the eye?

A

1) anterior chamber (b/w cornea and iris)
2) posterior chamber (b/w iris and lens)
3) vitreous chamber (b/w lens and neural retina)

89
Q

What is the lens?

A
  • transparent, biconvex structure
  • helps (cornea) refract light to be focused on the retina
  • changes focal distance of the eye allowing a sharp real image to form on the retina
  • covered by simple cuboidal epithelium: made from lens fibers (not ct fibers= cells!! (have nucleus!) )
  • similar to onion (cells go circularily and singularily=transparent structure)

Histology (20 decks)

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