Tear Film Flashcards by Tyler Dowdall

What is the volume of an average tear film?

6.5μl

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

4.8μl

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What happens to the osmolality of tears when sleeping?

increases

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

hypertonic

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What is the equivalent percentage of NaCl in tears?

300 mOsm/kg

0.97% equiv. NaCl

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

2. 3.0 -9.5

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What is the pH of tears maintained by?

A carbonate-bicarbonate buffer system

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Is the pH of tears lower of higher when sleeping?

lower

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What generates the viscosity of tears?

The lipid layer

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During blinks, is there more or less viscosity?

less

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What is the index of refraction for tears?

1.33698

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

endoplasmic reticulum
Golgi apparatus
with vesicles

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What are the functions of mucins?

Lubricates globe/eyelid apposition during palpebral closure
Traps exogenous debris
Provides a physical barrier to pathogens
Maintain smooth optical surface
Aids in the maintenance of corneal hydration

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

cornea and conjunctiva epithelial cells

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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

Galectins

2. posterior mucin layer of cornea and conjunctival epithelia

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What cells secrete Gel-Forming (MUC5AC)?

goblet cells in conjunctiva

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What cells secrete Small Soluble Mucins (MUC7)?

lacrimal acinar cells

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What is the major function of goblet cells?

secrete mucin

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Where are goblet cells located?

In the conjunctiva

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

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

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

Parasympathetic and sympathetic nerves

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What is the primary stimuli of goblet cell secretion?

parasympathetic nerves

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

ACh
muscarinic receptors
Ca2+
VIP and its receptors (VIPAC2)

What regulates goblet cell proliferation?

EGF-dependent signaling pathways

What cell types are found within the lacrimal gland?

Acinar and myoepithelial cells

What neural pathways pathways regulate lacrimal secretion?

parasympathetic and sympathetic nerves

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

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

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

paracellular transport

What is transport of substances through cells called?

transcellular transport

What are the transport proteins involved in lacrimal gland secretion?

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

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

1. AE | 2. KKCC

What does a high intracellular Cl- drive?

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

What drives Na+ paracellular transport in lacrimal secretion?

electro-potential difference

What drives water paracellular transport in lacrimal secretion?

solute concentration difference

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

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

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

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

What nerves are involved in efferent stimulation of lacrimation?

1. sympathetic | 2. parasympathetic

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

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

Where do most of the tear proteins come from?

lacrimal gland

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

1. lactoferrin | 2. lacrimal gland

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

1. lipocalin | 2. lacrimal gland

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

1. lysozyme | 2. lacrimal gland

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

1. Lactate Dehydrogenase | 2. Ocular surface epithelia

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

1. Fibronectin | 2. ocular surface epithelia

What tear proteins does the ocular surface epithelia produce?

1. lactate dehydrogenase 2. fibronectin 3. mucins

What monosaccharide is found within the tear film?

glucose

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

Meibomian glands

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

1. wax esters, cholesterol, cholesterol esters | 2. phospho-lipids and hydroxy fatty acids

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

fatty acid synthase

Where does biochemical synthesis of the Meibomian lipids occur?

cytoplasm

What is the difference between a hordeolum and a chalazion?

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

What are the major factors affecting the tear film?

1. age 2. gender 3. contact usage

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

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

What conditions prevent lacrimal drainage?

1. Dacryostenosis | 2. Dacryocystitis