Lecture 45 4/30/24 Flashcards
What are the characteristics of the uvea?
-vascular tunic of eye
-supplies blood and its nutrients to the eye and its constituent parts
How does the uvea work around not being able to directly supply the avascular components of the eye?
-relies on the creation of aqueous humor
-aqueous humor bathes the cornea and lens and provides them with nourishment
What are the characteristics of aqueous humor production?
-continuously created and drained
-results in a constant flow of fluid within the eye
-involves both passive and active transport
-active transport is most important
-occurs at the non-pigmented epithelium of the ciliary processes
Which two enzymes drive the production of aqueous humor?
-Na+/K+ ATPase
-carbonic anhydrase
What are the steps of ultrafiltration that lead to the production of aqueous humor?
-Na+/K+ ATPase exchanges sodium for potassium, creating an osmotic and electric gradient across cell membrane
-carbonic anhydrase catalyzes conversion of H2O and CO2 to HCO3- and H+ to maintain a neutral electrochemical gradient
-the two processes work together to create a concentration gradient that favors diffusion of water from the plasma within the stroma into the aqueous humor
How does passive transport contribute to aqueous humor production?
by creating a reservoir of fluid within the ciliary process stroma that will become aqueous humor via the active transport mechanism
How does conventional outflow of aqueous humor differ from unconventional outflow?
-conventional outflow involves a specific drainage mechanism
-unconventional outflow occurs from natural absorption of fluid into and around the uveal tissue
What are the anatomic components of the aqueous humor drainage system?
-iridocorneal angle
-pectinate ligaments
-trabecular meshwork
-angular aqueous plexus
What is the iridocorneal angle?
region within the anterior chamber that is comprised of the intersection of the iris and cornea at the periphery
What is the pectinate ligament?
-beginning of the aqueous drainage structure
-comprised of beams of iris tissue crossing from the iris to the cornea/sclera
What is the trabecular meshwork?
-second set of collagenous beams
-thinner, with collagenous material, elastin, and extracellular matrix protein components
-lined by endothelial cells that respond to pressure and outflow changes; also have phagocytic activity
What is the main function of the trabecular meshwork?
controlling the pressure within the eye
What is the angular aqueous plexus?
set of vessels where the aqueous humor begins its journey outside the eye
In which species is unconventional flow significant?
horses
Why is unconventional outflow important in inflamed eyes?
it allows for outflow in case inflammation and/or debris prevents drainage through the conventional pathway
What are the physiological differences between plasma and aqueous humor?
aqueous humor has:
-decreased protein
-increased ascorbate
Why is it important that the aqueous humor has low protein?
allows for a clear ocular media
What is the role of ascorbate in the aqueous humor?
prevents oxidative damage from light
What is the function of the blood-ocular barrier?
prevents optically dense material within the blood from entering the eye and causing opacity/decreased vision
What is the epithelial component of the blood-aqueous barrier?
tight junctions in the NPE of the ciliary body; prevent movement of molecules/cells into anterior chamber
What is the endothelial component of the blood-aqueous barrier?
tight junctions in the iris endothelial ells
What is the epithelial component of the blood-retinal barrier?
RPE that regulates diffusion of material from choroid to the retina
What is the endothelial component of the blood-retinal barrier?
retinal vessel capillary tight junctions and lack of fenestrations
What regulates constriction of the pupil?
-iris sphincter muscle
-parasympathetic system
What mediates the degree of constriction?
parasympathetic nucleus of CN3, based on the amount of light present
What regulates dilation of the pupil?
-dilator muscle
-sympathetic system
-inactivation of sphincter muscle
