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32 Cards in this Set
- Front
- Back
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Name 4 functions of tears.
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- provides smooth refractive surface
- lubricates corneal surface, palpebral and bulbar conj - oxygen exchange interface (avascular cornea) - flushes particles and contaminants - protects from infection (IgA) |
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Describe the structure of the tear film.
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- No distinct layers
- Inner middle and outer phases - Inner is aqueous/mucin phase - Middle is also aqueous/mucin phase but contains more aqueous content - Outer is lipid phase ---> gradual changes between mucin, aqueous and lipid. mucin/aqueous are present together |
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Glycocalyx is produced by ___________________ cells
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[corneal] epithelial cells
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What is the function of glycocalyx wrt ocular surface?
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Aids in binding mucins onto the corneal [irregular] surface
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what is the main function of the outer phase of the tear film?
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outer phase is lipid --> main fx is to prevent evaporation
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Lipid portion of tear film is secreted by which glands?
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Meibomian glands (main) along with glands of Zeis and Moll (modified sweat glands)
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Lacrimal secretions from where?
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lacrimal gland
glands of krause and wolfring (upper lid) |
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Mucin secretions from?
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goblet cells of conj
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Lacrimal gland innervation?
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cholinergic
adrenergic VIP(ie para and symp) |
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thermal, mechanical and optic nerve stimulation (Light) causes refelx tearing mainl bc of the fast response from
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lacrimal gland
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name some fxs of mucins wrt tear film/ocular surface
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1 - reduces surface tension (spreads evenly over hydrophobic epith))
2- physical barrier 3- lubrication 4- mucosal immunity 5- decreased amount of mucin makes people more susceptible to disease! |
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Which of the following does not affect mucous production?
a) Vitamin B deficiency b) age c) inflammation d) Vitamin A deficiency |
a
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viscous quality of mucous is produced by
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tangled molecular nature of highly glycosylated (HMW) mucins
--> less water = more viscous |
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describe the classification of ocular mucins
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either
a - membrane associated (MAMs)) or b - secretory mucins further divided into: b1 = gel forming b2 = soluble |
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glycocalyx layer is comprised of?
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MAMs
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Important MAMs?
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MUC 1, MUC 4 and MUC 16
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Important gel forming mucins?
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MUC 2, MUC 5AC, MUC 5B
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Important soluble mucins?
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MUC 7
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Which mucins are the largest? smallest?
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largest are gel forming
smallest are soluble |
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WHY is the MAM/glycocalyx important?
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since corneal surface is hydrophobic, mucin covering makes it hydrophilic and thus attracts the tear film
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Tonicity and tear production regulated by _________ feedback
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negative
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increase tonicity = ________ tear flow
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increaASE
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describe the neural pathway (BASIC) for tear production
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sensory: CN V
motor output: along VII as facial nerve |
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____ % of total tear volume is turned over every min
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16%
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REGULATION (NOTTT PRODUCTION!) of tears is mostly done by?
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parasympathetic
ACh released --> muscarinic receptor increases intra Ca2+, therefore causing exocytosis and release of tear components - parasymmpathtic also causes myoepithelial cells to squeeze forcing tears out of lacrimal glands |
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Why is Ca2+ important in tear regulation?
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- promotoes exocytosisso then lacrimal gland releases tear components
- activates K+ and Cl- channels which change tonicity |
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Regular blink rate = ___ blinks per minute or one blink every _____ sec
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12/min
1/5 sec |
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describe three types of blink
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- conscious closure - complete non spontaneous closure
- reflexive closure - resp to stim - spontaneous closure - usually imcomplete blinks |
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fx of blinking?
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re spreads tear film over cornea and sclera
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Which is correct wrt tear breakup time?
a) evaporation leads to lipid phase --> mucin phase because of an attraction, which disrupts tear film b) mucin rupture theory is the best theory to explain tear breakup time as mucin is wettable layer - contaminant disrupts the mucin creating a non-wettable area which forms a "hole" |
b
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main method of tear drainage?
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canalicular pump
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describe blink process & tear drainage
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- right after a blink, tears from lac lake enter canaliculi via puncta
- with ~1/3 closure, two puncta come into contact and beome blocked - as blink continues, canaliculi are squeezed by orb. m. which expells content into lac sac (Gravity and + pressure may also aid here) - when eye opens again, negative pressure builds and pull valve closed--> nld - completely open process starts again |
