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I. Ocular Physiology > Tear Film > Flashcards

Tear Film Flashcards

1
Q

What is the volume of an average tear film?

A

6.5μl

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2
Q

What is the volume of an average tear film for someone with dry eye?

A

4.8μl

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3
Q

What happens to the osmolality of tears when sleeping?

A

increases

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4
Q

Are tears hypo or hypertonic when the person has dry eye?

A

hypertonic

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5
Q

What is the equivalent percentage of NaCl in tears?

A

300 mOsm/kg

0.97% equiv. NaCl

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6
Q

What is the average pH of tears? 1. What is its range? 2

A
  1. 7.5

2. 3.0 -9.5

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7
Q

What is the pH of tears maintained by?

A

A carbonate-bicarbonate buffer system

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8
Q

Is the pH of tears lower of higher when sleeping?

A

lower

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9
Q

What generates the viscosity of tears?

A

The lipid layer

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10
Q

During blinks, is there more or less viscosity?

A

less

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11
Q

What is the index of refraction for tears?

A

1.33698

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12
Q

Where does mucin protein synthesis take place? 1. Where is it “sugar-coated”? 2. And how are they secreted? 3

A
  1. endoplasmic reticulum
  2. Golgi apparatus
  3. with vesicles
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13
Q

What are the functions of mucins?

A
  1. Lubricates globe/eyelid apposition during palpebral closure
  2. Traps exogenous debris
  3. Provides a physical barrier to pathogens
  4. Maintain smooth optical surface
  5. Aids in the maintenance of corneal hydration
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14
Q

What cells produce Membrane-Associated Mucins (MUC1, MUC4, MUC16)?

A

cornea and conjunctiva epithelial cells

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15
Q

What are proteins that bind to glycan side-chains of cell surface mucins and facilitate formation of mucosal barrier called? 1. Where are these located? 2

A
  1. Galectins

2. posterior mucin layer of cornea and conjunctival epithelia

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16
Q

What cells secrete Gel-Forming (MUC5AC)?

A

goblet cells in conjunctiva

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17
Q

What cells secrete Small Soluble Mucins (MUC7)?

A

lacrimal acinar cells

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18
Q

What is the major function of goblet cells?

A

secrete mucin

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19
Q

Where are goblet cells located?

A

In the conjunctiva

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20
Q

What are the afferent fibers involved in secretion of goblet cells?

A

Ophthalmic (cornea & conjunctiva) of Trigeminal and Maxillary (conjunctiva) branches of Trigeminal

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21
Q

What are the afferent fibers involved in secretion of goblet cells?

A

Parasympathetic and sympathetic nerves

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22
Q

What is the primary stimuli of goblet cell secretion?

A

parasympathetic nerves

23
Q

What are the neurotransmitters, receptors, and ions involved in parasympathetic stimulation of goblet cells?

A
  1. ACh
  2. muscarinic receptors
  3. Ca2+
  4. VIP and its receptors (VIPAC2)
24
Q

What regulates goblet cell proliferation?

A

EGF-dependent signaling pathways

25
Q

What cell types are found within the lacrimal gland?

A

Acinar and myoepithelial cells

26
Q

What neural pathways pathways regulate lacrimal secretion?

A

parasympathetic and sympathetic nerves

27
Q

Which ions are found in the tears, in order of most abundant?

A
  1. Na+
  2. Cl-
  3. K+
  4. HCO3-
  5. Ca+
  6. Mg2+
28
Q

What is transport of substances through the intercellular space between the cells called?

A

paracellular transport

29
Q

What is transport of substances through cells called?

A

transcellular transport

30
Q

What are the transport proteins involved in lacrimal gland secretion?

A
  1. Na+-K+-ATPase (NKA)
  2. Na+/H+ (NHE) and Cl-/HCO3- (AE) (Antiporters)
  3. Na+,K+,2Cl- Co-transporter (NKCC)
  4. Calcium-sensitive Cl- and K+ channels (uniporters)
  5. Aquaporins
31
Q

What transport proteins involved in lacrimal secretion use Na+ electrochemical gradient to drive influx of Cl- ?

A
  1. AE

2. KKCC

32
Q

What does a high intracellular Cl- drive?

A

Cl- efflux through apical calcium sensitive Cl- channels generating electro-potential difference

33
Q

What drives Na+ paracellular transport in lacrimal secretion?

A

electro-potential difference

34
Q

What drives water paracellular transport in lacrimal secretion?

A

solute concentration difference

35
Q

What transport proteins does the acinar end of lacrimal cells have that the ductal end does not?

A
  1. Na+-K+-ATPase (NKA)
  2. Na+/H+ (NHE) and Cl-/HCO3- (AE) (Antiporters)
  3. Na+,K+,2Cl- Co-transporter (NKCC)
36
Q

What nerves are involved in afferent stimulation of lacrimation in the bulbar conjunctiva (1), palpebral conjunctiva (2), and cornea (3)?

A
  1. long ciliary n, infratrochlear n
  2. frontal, lacrimal, infraorbital, and infratrochlear
  3. long ciliary and short ciliary
37
Q

What nerves are involved in efferent stimulation of lacrimation?

A
  1. sympathetic

2. parasympathetic

38
Q

What proteins found in the tear film came from blood vessels?

A
  1. albumin
  2. transferrin
  3. IgA
  4. IgG
  5. IgM
  6. Ceruloplasmin
39
Q

Where do most of the tear proteins come from?

A

lacrimal gland

40
Q

What tear protein is iron-complexing, 20-30% of proteins, bacteriostatic, and inhibits complement? 1. Where are these proteins from? 2

A
  1. lactoferrin

2. lacrimal gland

41
Q

What tear protein is 15-33% of proteins, a barrel structure, partially responsible for shear-thinning, helps stabilize the tear film by dec surface tension, and can inhibit bacterial growth? 1. Where are these proteins from? 2

A
  1. lipocalin

2. lacrimal gland

42
Q

What tear protein is 40% of proteins, decreases with age and with dry eye, and has a bacteriolytic effect on Gram + bacteria? 1. Where are these proteins from? 2

A
  1. lysozyme

2. lacrimal gland

43
Q

What tear protein increases with corneal hypoxia? 1. Where is this protein from? 2

A
  1. Lactate Dehydrogenase

2. Ocular surface epithelia

44
Q

What tear protein increases with epithelial injury? 1. Where is this protein from? 2

A
  1. Fibronectin

2. ocular surface epithelia

45
Q

What tear proteins does the ocular surface epithelia produce?

A
  1. lactate dehydrogenase
  2. fibronectin
  3. mucins
46
Q

What monosaccharideis found within the tear film?

A

glucose

47
Q

What structures produce the lipids of the lipid layer of the tear film?

A

Meibomian glands

48
Q

What are the non-polar lipids secreted by the meibomian glands? 1. What are the polar lipids? 2

A
  1. wax esters, cholesterol, cholesterol esters

2. phospho-lipids and hydroxy fatty acids

49
Q

What is the major enzyme in the production of meibomian gland lipids?

A

fatty acid synthase

50
Q

Where does biochemical synthesis of the Meibomian lipids occur?

A

cytoplasm

51
Q

What is the difference between a hordeolum and a chalazion?

A

hordeolum is an infection while chalazion is just a blocked meibomian gland

52
Q

What are the major factors affecting the tear film?

A
  1. age
  2. gender
  3. contact usage
53
Q

What are the major causes of Dry Eye, what are risk factors?

A
  1. Lack of quantity and composition of mucin
  2. Inadequate fluid volume
  3. Lack of sufficient blink frequency
  4. Lack of good lid-to-cornea apposition
  5. Lack of quantity and composition of lipid
54
Q

What conditions prevent lacrimal drainage?

A
  1. Dacryostenosis

2. Dacryocystitis

I. Ocular Physiology (20 decks)

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