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OD1 - Integrated Ophthalmic Sciences & Preclinical Optometry > BS - Lacrimal Glands and Tear Flim - Week 2 > Flashcards

BS - Lacrimal Glands and Tear Flim - Week 2 Flashcards

1
Q

What 7 structures contribute to the lacrimal apparatus?

A 
Lacrimal gland
Accessory lacrimal glands
Goblet cells
Meibomian glands
Tear film
Drainage system
Eyelid surfaces
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2
Q

How many layers does the tear film have?

A

3

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3
Q

What two structures contribute to the aqueous component of the tear film?

A

Lacrimal and accessory lacrimal glands

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4
Q

What four structures contribute to the mucous component of the tear film?

A

Stratified squamous epithelia of the conjunctiva, cornea, the accessory lacrimal glands, and goblet cells within the conjunctiva

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5
Q

What structure contributes to the lipid component of the tear film?

A

Meibomian glands

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6
Q

How t h i c c is the tear film?

A

~10 microns

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7
Q

What percentage of the tear film is water? What about the rest?

A

95% water, rest are oil, mucins, salts, metabolites, immunoglobins, and antibachterials.

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8
Q

What kind of layer does the tear film form? Name each layer, and its purpose.

A

Trilaminar layer of:
Basal mucin - attachment
Central aqueous - hydration
Superficial lipid - anti-evaporation

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9
Q

What two purposes does blinking have regarding the tear film?

A

Distributes the tears, and expels excess tears

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10
Q

How does lid opening affect the tear film?

A

Smooths out the tear film to an appropriate thickness, creating surface conditions conducive to tear spreading.

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11
Q

What three functions does lid closure have on the tear film, and what does it aid in the secretion of (3, cell name and secretion)?

A 
Wipes the corneal surface clean
Assists in tear film drainage
Aids in fresh secretions by:
Goblet cells (mucins)
Krause/Wolfring glands (aqueous)
Meibomian (lipids)
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12
Q

Whaqt is the total volume of the tear film?

A

5-9 microlitres

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13
Q

What is the rate of tear film secretion?

A

1.2-1.3uL/min

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14
Q

What is the pH of the open eye vs closed eye, and why the difference (2)?

A

Oen - 7.45
Closed - 7.25
This is due to increased CO2 and lactic acid when closed, resulting in more acidic conditions.

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15
Q

Does the pH increase, decrease, or remain the same with crying?

A

Increases

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16
Q

Does the pH increase, decrease, or remain the same with infection? Give a possible reason for this.

A

Decreases, possibly due to corneal antibacterial response resulting in H+ release

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17
Q

Describe the structure of the lacrimal gland, which part is larger/smaller (name them), and what structure it can be found on either side of.

A

It has two portions, but is continuous:
Orbital (larger)
Palpebral (smaller)
They are found on either side of the aponeurosis of the levator palpebrae superioris

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18
Q

What kind of gland is the lacrimal gland?

A

Adenoid/glandular

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19
Q

Is the lacrimal gland richly or poorly vascularised?

A

Richly

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20
Q

Where in the orbit is the lacrimal gland situated?

A

Upper temporal orbit, under the rim

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21
Q

Where does the lacrimal gland extend to, and in which direction?

A

Extends anteriorly to the septum

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22
Q

Hoe mny secretory ducts does the lacrimal gland have and where do they empty into?

A

6-12 secretory ducts emptying into the superior fornix just above the tarsal plate.

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23
Q

For what percentage of aqueous production is the lacrimal gland responsible for?

A

90%

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24
Q

Where does the lacrimal gland receive its sympathetic innervation from? What effect does it have, including secretory roles?

A

From the superior cervical ganglion
Causes vasoconstriction
No apparent direct secretory role

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25
Q

Where does the lacrimal gland receive its parasympathetic innervation from? What effect does it have, including secretory roles?

A

From CNVII
-secretomotor and vasodilator
Explains reflex tearing with noxious smells

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26
Q

Where does the lacrimal gland receive its sensory innervation from? What effect does it have, including secretory roles?

A

Branches of CNV ophthalmic division

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27
Q

What are the smallest ducts within the lacrimal gland called, and what do they form when one or more merge?

A

Acinus
They merge to form intercalated ducts.
These merge to form larger ducts, eventually forming one of 6-12 large secretory ducts

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28
Q

What is the structure of a lacrimal gland, and what are these structures separated by?

A

It is lobulated, tubulo-acinar

Lobules are separated by loose connective tissue

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29
Q

Define acini

A

Round tube-shaped masses of columnar secretory cells that drain into small ducts

30
Q

Consider the epithelial cells of lacrimal gland ducts. Do they have tight or loose junctions?

A

Tight

31
Q

Which cells drive secretion, and where are they found?

A

Innervated myoepithelial cells around the duct

32
Q

What kind of immune cells can be found in the lacrimal glands, where are they exactly, and what do they produce?

A

Found in the loose connective tissue of the lacrimal glands, producing mostly IgA.

33
Q

On which eyelid are glands of krause mainly found? Give approximate numbers per eyelid.

A

Mostly superior, at 42

Inferior has 6-8

34
Q

On which eyelid are glands of wolfring mainly found? Give approximate numbers per eyelid.

A

Likely superior, 2-5

2 inferiorly

35
Q

What are accessory lacrimal glands like structurally?

A

Like a miniature-sized regular lacrimal gland

36
Q

What is basal tear secretion primarily mediated by?

A

Na+K+ATPase

37
Q

What is reflex tear secretion primarily mediated by?

A

Mostly parasympathetic innervation

38
Q

Name 3 stimulated production means of tear secretion.

A 
Conjunctival sensory (dust, wind, cold etc)
Retinal stimulation (light)
Psychological (emotions)
39
Q

What creates polarisation of the acinar cell, and what does this allow for?

A

Tight junctions separate the apical from the basolateral plasma membranes, polarising the acinar cells, and allowing secretion of elecrolytes, water, and proteins.

40
Q

Describe the biochemical basis of electrolyte and water secretion (4).

A
  • Driven by Na+K+ATPase-mediated efflux of Na+ and influx of K+ across the basolateral membrane
  • Net result is K+ and Cl- in the lumen
  • Negative potential difference results, causing Na+ to move by paracellular oathway
  • Water secreted into the lumen by aquaporins
41
Q

What is electrolyte and water secretion regulated by? Which system activates this system, and what effect does it have?

A

By M3 muscarinic receptors

Parasympathetic activation causes K+ and Cl- channels to open, leading to increased secretion.

42
Q

How t h i c c is the aqueous layer of the tear film? What percentage is water, and what is the rest composed of?

A

7um thick

98% water, the rest are inorganic cations and anions

43
Q 
Relative to plasma, compare the following in the aqueous layer of the tear flim:
Lactate
Potassium
Bicarbonate
Glucose
Calcium
Chloride
sodium
A

Increased
Chloride
Potassium
Lactate

Same
Sodium
Bicarbonate

Decreased
Calcium
Glucose

44
Q

What is the role of lysozyme, and in what percentage is it found within which tear film layer?

A

Antibacterial - 30-40%, in the aqueous layer

45
Q

What is the role of lactoferrin, and in what percentage is it found within which tear film layer?

A

Bacteriostatic, UV protection, 25%, in the aqueous layer

46
Q

What is the role of lactoferrin, and in which tear film layer is it found?

A

Antibacterial, in the aqueous layer

47
Q

What is the role of substance P, and in which tear film layer is it found?

A

Neuropeptide responsible for pain perception within the aqueous layer.

48
Q

Name 2 glycoproteins in the aqueous layer, and their roles.

A

Transferrin - iron transport

Caeruloplasmin - copper transport

49
Q

Name the three main immunoglobins found in the aqueous layer of the tear flim, and their role. Name which is the predominant Ig.

A

IgA for infection, predominant Ig in tears.
IgG for post-trauma
IgE for allergic conjunctivitis

50
Q

How t h i c c is the mucoid layer?

A

0.04um thick

51
Q

Where does most of the mucoid layer originate from?

A

Goblet cell secretion

52
Q

What 3 compounds contribute to form mucus?

A

Glycoprotein, protein. and lipoprotein

53
Q

Describe mucin, what happens when it dissolves in water, how it associates with carbohydrates, and the major sugar groups (3).

A

Dissolves in water to form mucus.
Has many short carbohydrate chains
Major sugar groups are sialic acid, galactose, and n-acetylglucosamine

54
Q

What are membrane mucins produced by? With what other structure do they form what?

A

Surface epithelial cells of the cornea and conjunctiva.

They form the glycocalyx with the microplicae

55
Q

What is the role of secreted mucins?

A

They move freely over the glycocalyx and move throughout the tear film collecting debris

56
Q

Describe the concentration gradient of mucins through the aqueous layer. What does this confer?

A

Gradually increases moving towards the cornea, but increases significantly very close to it.
Increases the wetting properties of the epithelium and increases aqueous adherence to the surface.

57
Q

What would the epithelium be like if there were no mucins in the tear flim?

A

Very hydrophobic

58
Q

What is an advantage of having the tear film as it is, in regards to the cornea’s surface?

A

Makes the corneal surface smooth by filling in irregularities.

59
Q

What is the glycocalyx formed by?

A

Membrane-bound mucins attaching to microplicae of the epithelium.

60
Q

What does the lipid layer bind to?

A

Lipocalin

61
Q

If the lipid layer is lost, how much more quickly does evaporation occur?

A

10-20 fold increase

62
Q

Describe the percentage composition of the lipid layer.

A

Non-polar lipids - 60-70%

Polar lipids - 30-40%

63
Q

Which eyelid dominates blinking?

A

Upper

64
Q

What is the normal tear break up time?

A

10-20 seconds

65
Q

Name 3 reasons why the tear film stays in place.

A

Thinness of the film
Mucins provide stability
Lipids prevent evaporation

66
Q

In what direction does eyelid closure occur?

A

Temporal to nasal

67
Q

What two structures form the lacrimal lake?

A

Plica semilunaris and caruncle

68
Q

What force draws tears into the lacrimal canaliculus?

A

Capillary action

69
Q

Where do the two canaliculi drain into?

A

The nasolacrimal sac, then to the nasolacrimal duct, then through the valve of hasner, into the nasal sinuses.

70
Q

When do the puncta in the eyes open?

A

Until up to 13 weeks of age

71
Q

Name 3 possible causes of dry eyes, and the disease name if applicable.

A

Lacrimal gland dysfunction/inflammation/tumour
Meibomian gland dysfunction
Goblet cell disease - xerophthalmia

72
Q

Name 3 possible causes of impaired tear drainage, and the disease name if applicable.

A

Eyelids - ectropian, causes epiphora
Nasolacrimal infection
Stenosis of puncta

OD1 - Integrated Ophthalmic Sciences & Preclinical Optometry (123 decks)

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