Flashcards in Exam 1 Remington- Corneal Physiology Deck (106)
What are the 4 functions of the cornea?
Transmits light, absorbs short wavelength UV, refracts light, and proper corneal function requires minimal scattering and distortion
Cornea scatters less than __% incident light.
Cytoplasm of epi and endo cells in the cornea contain what?
Corneal crystallins, water soluble proteins
What do corneal crystallins do?
They make cytoplasm homogenous and decrease light scattering
What range does the cornea transmit?
UV 310 nm to IR 2500 nm
What is the reason for photokeratitis?
The cornea absorbs short wavelength UV
Inflammation caused by absorption of UV
What are causes of photokeratitis?
Welder's arc, tanning beds, and snowblindness
What is the refraction of light of the cornea determined by?
Curvatures of the various surfaces, interfaces between different indices of light, and length of pathway through the structures
Proper corneal function requires what?
Minimal scattering and distortion, no blood vessels, proper hydration
Relative corneal deturgescenes means the corneal is ___% water
Corneal hydration is dependent on what?
Temperature, swells when cooled and returns to normal at body temperature
What is the role of tears in maintaing proper hydration?
As tears evaporate the tear fluid becomes more concentrated, tear film osmolarity increases relative to the cornea, the hypertonicity of tear film draws water from cornea and the blink response is elicited because hypertonicity causes a slight sting and thus tear film is restored
What is the role of the epithelium in maintaining proper hydration?
ZO barrier prevents intercellular water influx from tears, ions move across both surfaces, aquaporins are water transport channels
What do channels of the epithelium allow?
Channels allows Na+ to pass into epi from tears and Cl- to pass into tears
What are major driving forces for water transport?
Cl- extrusion and Na+ influx
The co-transporter mechanism moves what ions in the cornea?
Na, K, and Cl ions
Na+/K+ ATPase pumps located in ______ ______ of the cornea actively move ions
Aquarporins are present where?
Epithelial cell membranes
There is a ________ flow of water across the plasma membrane in the cornea.
What is the role of the stroma in maintaining proper hydration?
GAGs are present in ground substance surrounding collagen fibers, increasing hydration leads to decreasing transparency
What is the role of GAGs in the stroma of the cornea?
Due to anionic characteristics they bind with water- there is an inherent tendency to imbibe water and to swell
Water content of the stroma should be approximately ___%
The normal water content of the sclera is ___%, if it falls below ___% or above ___% the sclera becomes lucent
68, 40, 80
What is the role of endothelium in the cornea in maintaining proper hydration?
These cells have high metabolic activity, apparent by large number of mitochondria and Golgi apparatus, slow leak of fluids and solutes from the aqueous, the Na+/K+ ATPase pump is located in the basolateral membrane of the endothelium
How does the Na+/K+ ATPase pump located in the basolateral membrane of the endothelium act?
Pumps act at a steady rate and the rate of leakage is dependent upon the pressure gradient across the endo
What are the ions that cotransporters move across membranes?
Na, K, Cl, HCO3
Where are aquaporins located in the endothelium?
In the endo cell membrane
What are 4 measures of endothelial function?
Coefficient of variation CV, cell density, polymegathism, and pleomorphism