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APP4 > Cellular structure & innervation of the eye > Flashcards

Cellular structure & innervation of the eye Flashcards

1
Q

What is conjuctiva made out of?

A
  • epithelium
  • stroma
  • accessory lacrimal glands
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2
Q

what do lacrimal glands do?

A

secret aq. components of tears

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3
Q

how would you describe the conjunctiva epithelium?

A
  • non-keratinised epithelium (2 to 5 layers) - squamous and stratified
  • microvilli
  • globet cells
  • basement membrane
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4
Q

what do microvilli do?

A

secret glycoproteins that stabilises the tear film

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5
Q

what are globet cells?

A

mucin layer of tear film

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6
Q

which glycoprotein stabilises the tear film?

A

glycocalyx

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7
Q

where does glycocalyx come from?

A

glycoprotein that is secreted from the microvilli

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8
Q

what is the conjunctiva stroma made out of?

A
  • superficial lymphoid layer
  • deep fibrous layer (collagen & elastic layer)
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9
Q

what are the functions of the tear film?

A
  • protection
  • lubrication
  • vision
  • reduce infection risk by washing away foreign particles
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10
Q

what is the tear film composed of? and how are they produced?

A
  1. mucin layer produced by globet cells that secret mucin
  2. aq. layer produced by lacrimal glands and accessory lacrimal glands
  3. phospholipid layer produced by melibomian glands
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11
Q

describe the mucin layer

A

hydrophilic surface that stabilises the aq. with the hydrophobic epithelium

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12
Q

describe the aqueous layer

A

water, growth factors, lactoferrin, lysozymes, immunoglobins, cytokines

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13
Q

describe the phospholipid layer

A

reduces the evaporation of the aqueous layer
increases surface tension of the tear film, therefore increasing the stability.

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14
Q

whats the maximum volume of conjuctiva sac/tear volume?

A

7-30 microlitres

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15
Q

whats the maximum volume of an eye drop?

A

0.025 - 0.07mL
25 - 70 microlitres

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16
Q

how many drops can the conjuctiva support?

A

roughly one drop

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17
Q

what are the contributing factors of ocular absorption of eye drops?

A
  • Tear volume (7-30 microlitres)
  • Tear turnover time (0.5-2.2microlitres/min, may be higher if drug
    irritative)
  • Spontaneous blink rate (~15/min, may be higher if drug is
    irritative)
  • Corneal thickness
  • Lipophilic-hydrophilic-lipophilic nature of cornea
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18
Q

how long does drugs remain in the conjunctival sac for?

A

3 to 5 minutes

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19
Q

how can i increase the drug retention in the conjuctival sac?

A

apply eye ointment instead of drops - stay longer = better penetration

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20
Q

what is the rate of ocular absorption ?

A

1 to 7%

21
Q

what are the functions of the cornea?

A

mainly to refract to get clear vision
protect against infection and trauma aided by tear film

22
Q

what are the 5 layers of the cornea? in order

A
  1. epithelium
  2. bowmans layer
  3. stroma
  4. descemets membrane
  5. endothelium
23
Q

describe the cornea epithelium

A
  • non-keratinised- squamous
  • hemidesmosomes
  • microvilli
  • limbus - tight junctions between cells
24
Q

what are limbus known as ? and where are they?

A

epithelium stem cells

in the cornea epithelium

25
Q

describe the bowmans layer

A

superficial, strong layer of stromal collagen
avascular, unable to regenerate
scars produced when healing from trauma/injury

26
Q

describe the stroma

A

75% water
collagen 1 , 4, 5 and 6
proteoglycan
keratocytes - used to remodel from injuries

27
Q

describe the descemets membrane

A

produced and repaired by cornea endothelium

28
Q

describe the cornea endothelium

A

monolayer of hexagonal cells
unable to regenerate

29
Q

describe the cornea

A

provides nutrition from aqueous, limbus and tear film
transparency

30
Q

what does the transparency of the cornea depend on?

A

Correct amount of water in stroma
- Water + nutrients flow passively from aqueous into stroma
- Endothelium prevents overhydration - actively pumps Na+ back into aqueous (Na+/K+ ATPase), water follows Na+ passively

Regular orientation and spacing of collagen fibres

31
Q

what is the episclera?

A

loose connective tissue overlying the sclera
that provides the nutrition to sclera
also providing low friction to allow free movement of the eye

32
Q

what is the episclera composed of?

A
  1. inner layer
  2. intermediate loose connective tissue
  3. outer layer - muscle sheaths fused & conjuctiva at limbus

and heavily vascularised
- anterior and posterior plexus

33
Q

describe the stroma

A

Tough outer coat of eye
Continuous with cornea and optic nerve
Avascular but pierced by vessels
Collagen (mainly types I, III, V, also IV, VI, VIII)  Proteoglycans, glycoproteins, elastin

Layers:
1. Outer stroma – criss-cross arrangement collagen bundles
2. Inner lamina fusca – blends with uveal tract, separated from it by potential space (suprachoroidal space)

34
Q

what are the main functions of the sclera?

A
  1. protect
  2. maintain shape
  3. tolerance of intraocular pressure fluctuations
  4. blocking of light
35
Q

what are the three components of the uveal tract?

A
  1. iris
  2. choroid
  3. ciliary body
36
Q

what is the iris composed of?

A
  • Anterior surface - Connective tissue, incomplete border layer overlying
    stroma
  • Stroma
    • Contains vessels, nerves  Sphincter pupillae(circular)
    • Smooth muscle (short ciliary nerves – CNIII – parasympathetic)
    • Dilator pupillae (radial)
    • Smooth muscle (sympathetic supply, carried by long ciliary
      nerves (Va))
  • Posterior epithelium
    • Cuboidal, pigmented
37
Q

what is the function of the iris?

A

control the pupil size to regulate light, depth of focus, minimising optical aberrations
blood-aqueous barrier due to the tight junctions between the iris and endothelium cells

38
Q

what is the ciliary body composed of?

A

Ciliary epithelium
- Cuboidal bilayer, apex to apex, gap junctions
- Inner layer – nonpigmented, high metabolic activity
- Outer layer – pigmented
- Ciliary muscle

39
Q

whats the function of the ciliary body?

A
  1. Blood aqueous barrier (tight junctions between inner nonpigmented cells)
  2. Aqueous humour production (both epithelial layers)
  3. Accommodation (ciliary muscle)
    - Contracts => zonules relax => lens fattens =>
    enables focus on near objects
    - Parasympathetic (short ciliary nerves CNIII)
40
Q

whats the structure of the choroid? in order

A

bruchs membrane
choriocapillaries
stroma - larger blood vessels

41
Q

whats the function fo the choroid?

A

Vascular supply:
1. Nutrition
2. Waste removal
3. Heat dissipation
4. Ocular immunity

42
Q

describe the vitreous

A

80% ocular volume
99% water
Transparent “gel”
Hyaluronic acid
Collagen (II, IX, V/XI hybrid)

43
Q

describe the lens

A
  1. 30% refractive power of eye
  2. Capsule - Basement membrane
  3. Epithelium
    - Cuboidal and non-mitotic centrally
    - Columnar and mitotic peripherally
  4. Fibres
    - Cells elongate and lose organelles, become fibres.
    - Confer transparency
    - Nucleus – older fibres, cortex – newly formed fibres
  5. Zonules
    - Sheets of suspensory fibres
    - Made of fibrillin
    - Attach ciliary body to lens at and around its equator
44
Q

what are the contents of the lens?

A
  1. low water (65%)
  2. high protein (35%)
  3. relatively hypoxic
  4. clarity
    - Narrow lens fibre membranes
    - Small interfibre spaces
    - Tightly packed regular contents (crystallin)
    - Absence of blood cells
    - Loss of organelles from cells when they => fibres
45
Q

what is the structure of the retina?

A

RPE (pigment epithelium)
- Hexagonal monolayer epithelial cells
- Microvilli – envelop photoreceptor outer segments
- Tight junctions – outer blood-retinal barrier
- Rich in mitochondria
- Basement membrane – forms part of Bruchs membrane

46
Q

LOOK AT NOTES FOR MORE ON RETINA AND RPE

A
47
Q

describe the photoreceptors

A
  1. Rods - Low light vision, peripheral vision
  2. Cones - Bright/normal, central vision, colour vision
  3. Light perception by outer segments of photoreceptors
    - G proteins – “opsins”
    - Vitamin A derived molecules (chromophores)
48
Q

describe the ganglion cells

A

Optic nerve - produced a Light signal => brain
1. Parvocellular - Fine vision, colour,  Mainly in fovea
2. Magnocellular - Motion, coarse vision,  Peripheral

49
Q

what nerves are important to the eye?

A

APP4 (14 decks)

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