Ocular: Aqueous Humor Dynamics Flashcards
What acid does aqueous humor transports into the anterior segment>
ascorbic acid
Ascorbic acid acts as an..
Antioxidative agent
During inflammation what does aqueous humor facilitate?
Local immune responses
Volume of AH?
250-315ul
Secretion rate of AH?
2.5ul/min
Turnover rate of AH/
100ul/min
What is the protein content of AH?
Less than one percent protein content of blood plasma
-protein causes light scattering
What is the first step in AH formation and where does it take place?
-elaboration of plasma filtrate
-Ciliary body microvasculature
What is the second step of AH formation and where does it occur?
-AH is formed from the plasma filtrate
-in ciliary epithelium
Where in the ciliary body are capillaries fenestrated and why?
The anterior arterioles are fenestrated to allowing plasma proteins, fluids, and ions to leak into the ciliary stroma.
What pushes the proteins, ions, and fluid into the surrounding ciliary stroma to make filtrate?
Hydrostatic pressure within the capillaries
Ions from the filtration are actively transported where in the ciliary epithelium?
Into the pigmented ciliary epithelium
Ions that are transported into the pigmented ciliary epithelium are moved to where? Via what type of junctions?
They are moved into intercellular clefts in the NPCE via GAP JUNCTIONS
The presence of the ions in the NPCE clefts causes..
Water to be drawn out of the cleft and AH formation
What type of junctions are in the NPE?
TIGHT JUNCTIONS
Tight junctions in the NPE restrict flows towards what?
Posterior chamber
The tight junctions the NPE create what barrier?
Blood aqueous barrier
What happens if the blood aqueous barrier breaks down?
Secretion of proteins into the posterior chamber
What happens if gap junctions are unable to communicate with adjacent cells?
Compromised and produce less AH which increase IOP
What is carbonic anhydrase used for?
Decreasing AH production in glaucoma therapy, inhibits movement of h2o out of NPCE
Na-K-ATPase and carbonic a hydrate are found along..
Basal enfolding of the ciliary epithelium
The presence of Na-K-ATPase and carbonic a hydrate on the basal enfolding suggest?
Active metabolic pumping and moving of fluids and ions
Explain the flow of AH?
-flows from posterior chamber through the pupil
-resting of iris on the anterior surface of the lens forming a one way valve
-AH enters anterior chamber and rises dues to iris vasculature(warm)
-AH falls near cooler corneal endothelium
What percentage of AH passes through the trabecular meshwork?
90%
What causes vertical orientation of Krukenburg Spindle?
Pigment from iris pigment epithelium deposits in a vertical line on corneal endothelium
The BAB blocks movements of what substances?
-Intermediate and high molecular weight substances such as protein
-toxic substances
What are the three Locations of the BAB?
-tight junctions between NPCE
-tight junctions between endothelial cells and the iris vasculature
-tight junctions between endothelial cells of inner wall of schlemms canal
Are tight junctions in the post iris epithelium part of the BAB?
NO, but important for preventing AH from ant. chamber from flowing back into post. chamber
Trabecular pathway of aqueous flow:
TM -> juxtacanalicular CT -> schlemm’s canal -> collector channels and aqueous veins -> scleral and episcleral venous plexus
What percentage of aqueous flows through the trabecular pathway?
90%
Flow through the TM is _________ dependent
Pressure
Where does teh bulk of the AH resistance reside? What structures contribute to it?
-juxtacanalicular CT
-contains fibroblasts, ECM material, elastic-like fibers
Pressure must be ______ in order to make it to the Schlemm’s canal
High
What happens to the TM in the accommodated state?
-scleral spur moves posteriorly
-flow enhances across TM by opening flow channels
-increase in effective filtration area
What happens t the TM when the ciliary muscle is relaxed?
-scleral spur moves forward into normal position
-closing flow channels in TM which decreases flow
-decreases in effective filtration area
What percentage of AH outflow takes the uveoscleral pathway?
10%
Uveoscleral pathway is pressure ___________
Pressure independent
What is the uveoscleral outflow pathway?
-AH enters CBB and iris root
-AH passes between bundles of muscle fibers of the ciliary body to enter the supraciliary space
-in supraciliary space the AH is pumped through sclera to the episclera (can also exit through vortex veins)
