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39 Cards in this Set
- Front
- Back
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what are three main fx of cornea?
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refraction - ~70%, n
transmission - smooth surface decreases scatter protection - stroma strx strength, descemet resistence to trauma, epithelium bio protection |
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layers of cornea
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epithelium (10% thickness) - has BM
bowman layer stroma (90% thickness) descemet membrane (BM of endothekium) endothelium |
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type of cells @ cornea epithelium?
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non-keratinized stratified squamous 5-7 layers
- NO goblet - Langerhan cells at periphery --> immune resp |
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what makes corneal epithelium hydrophillic?
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secretion of glycocalyx by squamous cells - anchors mucins to epith surface.
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which is not a correct wrt microplicae on the corneal epithelium?
a) enhances secretory functions b) decreases adherence of tear film c) enhances absorptive function d) patients wearing RGP lenses can damage these |
b
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the entire epithelium is replaced every __ days
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7
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_______ cells undergo mitosis (@epithelium). They come from the _______.
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basal cells
limbus (stem cells) - migrate twd center in a "swirl pattern" |
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most common location of ocular carcinoma?
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limbus
bc of rapid mitotic activity |
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main permeability barrier for epithelium?
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tight jxs
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what holds adjacent squamous cells tog at epitheiulm?
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desmosomes
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cicatricial pemphigoid occurs because of an autoimmune response to which of the following?
a) desmosomes of corneal epithelium b) gap junctions located between squamous cells c) hemidesmosomes of corneal epithelium d) dry eye |
c
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describe corneal innervation
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long ciliary and short ciliary nerves innervate stroma at periphery - enter from limbus ~2mm in - lose myelination & becone free nerve endings - ++ branching forms three main plexi:
- midstromal - subepithelial - epithelial |
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main reason for ++corneal sensitivity?
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density of corneal innervation is 3-4X greater - increases twd apex and more superficially - no innervation to descemet or endo!
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which doesnt affects corneal sensitivity?
a) O2 b) eye color c) age d) CN VII palsy |
d
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major reason for stroma tensile strength?
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collagen fibril arrangement (lamellae)
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approximately _________ lamellae are stacked in the corneal stroma. Proteoglycans in the ground substance are ________ and __________.
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200-300
keratan sulfate chondroitin sulfate |
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_______ H2O in the corneal stroma will decrease corneal transmittance.
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increased
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GAGs are _______ (+/-) charged and therefore _____________ (hydrophobic/hydrophillic).
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-
phillic |
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optimal optical clarity is produced with ______% H2O content.
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75-80%
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describe hydrolamellar light interactions @ stroma
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at 75-80% H2O content, spacing is optimal for destructive interference to occur (wavelenth/2) which decreases light scatter and increases transmission and maintains corneal clarity
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stromal turnover is controlled by ________ which produces _______ and ________.
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keratocytes
MMPs TIMPs |
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photorefractive keratectomy
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removes epithelium and anterior stroma
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haze after PRK may be because of
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- lamellae and fibrils at new weird angles
- keratocytes take on char of myofibroblasts in wound healing |
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endothelial _______________ protect against stromal hydration (maintain deturgescence)
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discontinuous tight jxs
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hexagonal shape of endothelial cells is optimal. If cells are damaged, what occurs?
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endothelium is non regenerative so if cells are damaged, others will spread and become bigger to fill the damaged area.
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The edge of Descemet membrane is ____________
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Schwalbe's line
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corneal hydration maintained by:
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- epithelial barrier to tears
- endothelial barrier to aqueous - active pump |
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describe epithelial pump process and fx
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fx is to maintain high stromal Na gradient. done by Na-K-ATPase pump at basal membrane of epithelium.
INFLUX of K+, EFFLUX of Na+/Cl-, Cl- exits --> tears* High ionic concentration outside the cornea draws water out of the cornea |
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what is poisoned with ouabain
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Na-K-ATPase pump endothelial
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________ is produced by carbonic anhydrase @ endothelial cells
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HCO3-
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describe endothelial pump for continually drawing ions out of stroma and into aqurous
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carbonic anhydrase rxn with H2O and CO2 roduces H+ and HCO3-. H+ is exchanged for 1 Na+ from the stroma. HCO3- and Na+ are both sent to aqueous
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most corneal ATP is generated __________, using 15% of available glucose.
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aerobically
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glucose for corneal ATP production is supplied from ___________.
a) aqueous b) tears c) vitreous |
a
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Highest glucose content can be found:
a) epithelium b) stroma c) tears d) aqueous |
b
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glucose is stored as ___________ in the corneal ____________.
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glycogen
epithelium - used in times of stress for anaerobic resp |
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What negative effect occurs with anaerobic respiration @ cornea?
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lactic acid production bc of accumulation of pyruvate
- alters cellular morphology |
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what are the sources of oxygen for the cornea?
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- air vis tears
- aqueous - limbal vessels - palpebral conj during sleep |
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What is Henry's Law
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The mass of the gas absorbed by a fixed volume of liquid
at a given temperature will be proportional to the pressure of the gas” |
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What is the critical oxygen tension?
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point at which O2 tension can be reduced before dysfunction occurs
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