Tears Flashcards
what is the outer layer made up of?
lipid (oil)
what is the middle layer made up of?
aqueous (water)
what is the inner layer made up of?
mucin layer
what issues would occur if no tear layer?
cornea epithelium is irregular (due to microvilli) and this disrupts the optical wavefront (blurry image on retina)
function of: lysozyme
degrades mucopeptides of bacterial cell wall
function of: B-lysin
disrupts integrity of bacterial plasma membranes
function of: immunoglobulin A
mediates antigen-specific humoral immunity, marks bacteria for destruction
where is aqueous mostly produced?
lacrimal gland in the superior temporal fornix
lipid layer contains:
many proteins
large aqueous and mucous layer contains:
various proteins and ions (Na+, K+, Cl-)
mucous layer subdivided into:
- mucous laye r
- glycocalyx
source of outer oily layer is:
meibomian glands
source of middle aqueous layer is:
lacrimal glands (a little by accessory lacrimal glands)
source of inner mucin layer is:
goblet cells
definition of glycocalyx:
layer of membrane bound mucin attached to epithelial cells
function of glycocalyx:
protects epithelium, prevents bacterial from reaching and attacking epithelium
where are goblet cells located and NOT located?
goblet cells only in conjunctiva and NOT in cornea
mucous reduces the surface tension of the epithelium from:
70 to 40 dynes/cm^2
mucin attaches to epithelium to make the surface:
hydrophilic
so water spreads out
sensory stimulation causes what affect on goblet cells?
causes goblet cells to release mucous
about how many goblet cells are in an eye?
about 1.5 million
most goblet cells are located
medially and inferiorly
sources (and %) of aqueous
- lacrimal gland (95%)
- accessory lacrimal glands (5%)
characteristics of aqueous
low protein concentration, isotonic solution
functions of aqueous:
- prevents desiccation of epithelium
- bacteriostatic function due to proteins it contains
what can increase aqueous tear production?
parasympathetic stimulation
meibomian glands produce what via what type of secretion?
oil produced by holocrine secretion
function of oil layer:
- provides a smooth refracting surface
- retards evaporation of aqueous
composition of the oil layer:
waxy esters, sterols, cholesterol, lipids (hundreds of different types of substances)
location and general appearance of oil layer:
on top of aqueous later and looks like oil slick in street (forms colored fringes)
thickness of tear film estimate via fine glass fibers was:
7-8 microns
thickness of tear film estimate via OCT was:
3.4 +/- 2.6 microns
which layer is thicker in the conjunctiva than in the cornea?
mucous layer
which layer is thicker in the cornea than in the conjunctiva?
aqueous
total tear volume
8 microns of fluid on the eye
entire eye and curl-de-sac can hold a max of ___ before blink
50-60 microns
tear volume in the superior and inferior cul-de-sac
4 microns (about 1/2 of all fluid)
tear volume in the tear prism
3 microns
tear volume in the exposed eye
1 micron
basal aqueous production rate:
1.2 microliters/min
aqueous production can go up to ___ microliters/min if stimulated
70 microliters/min (reflex-driven tear production)
what is a normal tear meniscus height test result?
> 0.1 mm
what is normal Schirmer tear strip findings?
> 10 mm in 5 minutes
what kind of skewed result does the sponge method give for tear production?
gives low aqueous production rates (0.5 ul/min) probably due to evaporation
what is an important finding about changes in tear production discovered in fluorophotometry studies?
showed tear production decreases with age
about 20% decrease in 40-53 age group
explain how age may affect tear production vs. tear volume
- tear volume on the eye does NOT decrease with age
- tear production does!
the most irritating test has the highest tear production rate: which test is this?
schirmer strip WITHOUT anesthesia has highest rate
performing tests with anesthesia will show ____ tear production rates
lower
since age dramatically decreases tear production, what is the normal wetting for age 20-29 group?
40-50 mL
list of medications that can cause dry eye
-antihypertensive, glaucoma (beta blockers), antidepressants, decongestants, antihistamines, birth control pills
what is unique about stimulated tears for aqueous secretion?
stimulated tears are all from the lacrimal gland (none from accessory)
in the parasympathetic pathway: receptors on the lacrimal gland are:
m3 muscarinic receptors
in the parasympathetic pathway: receptors in the lacrimal are located in the:
acinar and duct cells of the gland
increasing parasympathetic activity of lacrimal gland will ____ tear production
increase
sphenopalatine ganglion stimulation leads to _____ tear secretion
increase
increased tear secretion includes
water, electrolytes (Na+, K+, Cl-, bicarbonate), regulated protein
in the sympathetic pathway, what are the receptors?
alpha and beta adrenergic receptors on acinar cells
sympathetic stimulation causes and increase in what type of secretion in the tears?
increase in PROTEIN secretion
what is stage 1 of tear production?
acinus-intercalated duct region secretes fluid resembling an isotonic ultra filtrate of plasma
what is stage 2 of tear production?
ductal segments secrete additional K+ and Cl-
what is special about the type of control between the 2 stages of tear production?
ions in the tears remain constant regardless of tear production
what ion concentrations increase as ultra filtrate travels down duct?
K+ and Cl-
in tear production, what are the set affects of the Na/K pump and K channel?
increase Na+ in interstitial space
what does the net increase in Na+ drive?
the Na+/Cl- cotransport channel (brings Na+ and Cl- into cell)
net effect of Na+/Cl- cotransport is:
Cl- concentration in the cell increases
definition of constitutive protein secretion
proteins that require something external to the lacrimal gland to make it
example of a constitutive protein secretion?
IgA- dependent on plasma cells in interstitial space around lacrimal gland to make IgA
what are the stimuli for regulated protein secretion?
parasymp. or symp. results in 2nd messenger system(cAMP, Ca2+) to release stored proteins into the tears
definition of regulated protein secretion:
proteins made in cells of lacrimal gland are released when stimulus is given
about how many proteins in the tears have been identified?
200
in stimulated flow of tears there is an increase in what substances?
immunoglobulin and lysozyme
