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OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry > Lacrimal system and Tear film - Week 2 > Flashcards

Lacrimal system and Tear film - Week 2 Flashcards

1
Q

Define lacrimal

A

Correlated with weeping or tears

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2
Q

Define lacrimal gland

A

An almond shaped gland that secretes tears into ducts that empty on the surface of the conjunctiva of the eye

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3
Q

Define lacrimal apparatus

A

A network of structures of the eye that secrete tears and drain them from the surface of the eyeball

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4
Q

List the structures of the lacrimal apparatus [7]

A
  • lacrimal gland
  • accessory lacrimal glands of Krause & wolfring
  • goblet cells
  • meibomian glands
  • tear film
  • drainage system
  • eyelid surface

*Tm dagel

Or * M’ Lag Ted – it’s like you’re a nice guy telling ted about the lag you’re getting

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5
Q

List the components of the drainage system [5] [lacrimal lecture]

A
  • plica semilunaris/caruncle
  • Puncta
  • canaliculae
  • lacrimal sac
  • nasolacrimal duct
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6
Q

List the functions of the lacrimal apparatus [8]

A
  • normal tear production
  • tear distribution
  • tear stability
  • tear drainage
  • keep optical surface patent
  • nutrition (O2 in, CO2 out)
  • lubrication
  • protection (antimicrobial, debris)

** way to remember
Normal tears keep protecting nutrients from lubrication

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7
Q

How many layers does the tear film have?

A
  1. Tri-laminar. Though recently it’s suggested that aqueous and mucous may be more like a gradient and not 2 separate layers.
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8
Q

What structure/s contribute to the aqueous component of the tear film?

A

Lacrimal gland and accessory lacrimal glands

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9
Q

What structures contribute to the mucous component of the tear film? [4]

A
  • Accessory lacrimal glands
  • Stratified squamous epithelia of Cornea …
  • and Conjunctiva
  • Goblet cells of conjunctiva
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10
Q

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

A

Meibomian Glands

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11
Q

What type of mucin is produced by:

  • stratified squamous epithelia of cornea + conjunctiva
  • goblet cells of conjunctiva
A

epithelia: special type of mucin that’s anchored to tissue
goblet: secretory mucin

These two types of mucins interact with each other and then interact with the aqueous to make a charged gel

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12
Q

How thick is the tear flim?

A

Around 10 microns - relatively thin

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13
Q

What percentage of the tear flim is water? What is the rest?

A

98% water

The rest is made from: oil, mucins, salts, metabolites, immunoglobulins, antibacterials

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14
Q

What is the baseline osmolarity of the tear flim vs with stimulation? How does it change in a patient with dry eye disease?

A

Basal: 0.90% NaCl, 285-295 mOsm/kg
Reflex: 0.97% NaCl, 310-334 mOsm/kg

In dry eye disease, osmolarity can get as high as 350 mOsm/kg

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15
Q

What are the 3 layers of the tear flim? What are they each important for?

A
  1. Basal Mucin Layer (mucous layer) = attachment of tear flim to cornea
  2. Central Aqeuous Layer = hydration of ocular surface
  3. Superficial Lipid Layer = creates a seal to stop evaporation
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16
Q

Out of the 3 tear film layers, which one would Phil Swift, of “flex seal” fame, approve of?

A

The Superficial lipid layer. It creates a “seal” to stop evaporation

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17
Q

What is the purpose of blinking in regards to tear film?

A
  • distributes tears

- expels excess tears

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18
Q

What is the purpose of lid opening in regards to tear film?

A
  • smooths out tear film to appropriate thickness

- creates surface conditions conducive to tear spreading

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19
Q

What is the purpose of lid closure in regards to tear film?

A
  • wipes clean corneal surface
  • assists drainage of tear lake
  • aids expression of fresh secretions of: goblet cells (by mucins), glands of Krause & Wolfring (aqueous), Meibomian glands (oily layer)
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20
Q

What is the total volume of the tear film (including meniscus)?

A

5-9ul

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21
Q

How is the volume of tear film affected in dry eye disease?

A

Decreases

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22
Q

How does pH differ between open and closed eyes? Why is this?

A

Open eye: pH = 7.45

Closed eye: pH = 7.25 – more acidic possibly due to CO2 and lactic acid build up

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23
Q

How does crying affect the level of pH? What about infection?

A

Crying: increases pH
Infection: decreases pH

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24
Q

Where do the secretory ducts empty their aqueous secretions?

A

into the superior-temporal part of your orbit

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25
Q

Describe the pathway of tear drainage across your general anatomy

A
  • Secretory ducts empty aqueous secretions into superior-temporal orbit
  • tears then spread across eyelid and drain into ‘puncta’
  • the 2 puncta then drain into the nose
26
Q

When blinking, how do the eyelids close? (describe the movement). What is the purpose of this?

A

Blink starts from the lateral side of your eyelids and then slowly closes towards the nasal side.
- this assists in pushing away old tear fluid towards the caruncle region (where your puncta are)

27
Q

Is the lacrimal gland continuous or discontinuous?

A

Continuous but in 2 portions that sit either side of the LPS (levator muscle)

28
Q

Name the 2 portions of the Lacrimal Gland. Which is larger?

A

Orbital portion - larger

Palpebral portion - smaller

29
Q

How much of the aqueous production is the lacrimal gland responsible for?

A

90% of aqueous production

30
Q

What kind of nerve fibres does the lacrimal gland receive? (innervation)

A

Receives both autonomic and sensory nerve fibres

31
Q

Where does the lacrimal gland’s parasympathetic supply come from?

A

CN VII nucleus (secretomotor and vasodilatory)

32
Q

What is the lacrimal gland’s parasympathetic innervation important for?

A

Reflex tearing with noxious smells

33
Q

Where does the lacrimal gland’s sympathetic supply come from?

A

Superior Cervical Ganglion

*(Sup Cerv Gang)

34
Q

What is the lacrimal gland’s sympathetic innervation important for?

A

Vasoconstriction of the vessels

35
Q

True or False: lacrimal gland sympathetic innervation has no apparent direct secretory role

A

True

36
Q

Where is the lacrimal gland’s sensory innervation?

A

Branches of CN V1 (ophthalmic division of CNV)

37
Q

Describe the appearance of Acinus

A

is like a grape with lots of cells in it

38
Q

What is the smallest functional unit of the lacrimal gland structure?

A

Acinus

39
Q

In the acinus secretory unit, where do the round nuclei usually sit?

A

towards the basal compartment of the cell

40
Q

In the acinus secretory unit, what portion gets secreted into the lumen?

A

Apical portion

41
Q

How many secretory ducts does the lacrimal gland have and where do they empty into?

A

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

42
Q

Is the lacrimal gland richly or poorly vascularised?

A

Richly

43
Q

Where in the orbit is the lacrimal gland located?

A

Upper-temporal orbit, under the rim

44
Q

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

A

Extends anteriorly to the septum

45
Q

In lacrimal gland structure, how are intercalated ducts formed?

A

By the merger of acini lumens

46
Q

Define acini

A

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

47
Q

Describe the structure of the lacrimal gland. What separates these structures?

A

Lobulated, tubulo-acinar

  • the lobules are separated by loose CT
48
Q

How does the structure of the lacrimal gland ensure that secreted fluid doesn’t get re-absorbed by the ducts?

A

Tight junctions between epithelial cells of duct

49
Q

What method of secretion is used to secrete into acini?

A

Apocrine secretion

50
Q

What type of cells sit around duct cells to help drive secretion?

A

Innervate myoepithelial cells

51
Q

How many glands of Krause are there? How are they distributed?

A

42 superior, 6-8 inferior

52
Q

How many glands of Wolfring are there? How are they distributed?

A

2-5 superior tarsus

2 inferior tarsus

53
Q

How much do the accessory glands of Krause and wolfring contribute to aqueous secretion?

A

10%

54
Q

What is the primary mediator for basal secretion of tears?

A

Na+/K+ ATPase

55
Q

What is the primary mediator for reflex (stimulated) secretion of tears?

A

Parasympathetic control

56
Q

Name the causes of reflex (stimulated) tears

A
  • Conjunctival sensory stimulation (e.g dust/wind/cold)
  • Retinal stimulation (light)
  • psychological (emotions)
57
Q

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

A

Tight junctions, which separate the apical from the basolateral plasma membranes

This enabled secretion of electrolytes, water, and proteins

58
Q

What does the basolateral membrane contain to help unregulate tearing rate?

A

Receptors for neurotransmitters

59
Q

What does the basolateral membrane contain to help initiate the secretory process?

A

Growth factors

60
Q

What does the basolateral membrane contain for initiating electrolyte and water secretion?

A

Ion transport proteins and ion channels

61
Q

Describe the biochemistry of electrolyte and water secretion

A
  • driven by Na+/K+ ATPase-mediated efflux of Na and K across basolateral membrane
  • net result: K+ and Cl- into lumen
  • result in negative potential difference causing Na+ to move by paracellular pathway
  • water secreted into lumen through aquaporins

OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry (49 decks)

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