Aqueous Humor Composition and Formation (M2) Flashcards
What secretes the aqueous humor?
ciliary epithelium lining the ciliary processes
What drives aqueous flow in the anterior chamber?
convection (heat and cod from iris vasculature)
What are the aqueous humor pathways?
- conventional route
2. Uveoscleral/unconventionial route
Describe the conventional route to aqueous outflow:
trabecular meshwork -> inner wall of Schlemm’s canal into its lumen -> collector channels -> deep scleral -> intrascleral -> episcleral plexus (aqueous veins) -> episcleral vein
Describe the uveoscleral/unconventional route to aqueous outflow
Across the iris root -> uveal meshwork -> anterior face of the ciliary muscle -> CT between muscle bundles -> suprachoroidal space -> through the sclera
What percentage of drainage is through the uveoscleral route? 1. Does it increase or decrease with age? 2
- 35-55%
2. decreases
What are the major sources of the blood-aqueous barrier?
- nonpigmented ciliary epithelium and posterior epithelium
2. nonfenestrated blood vessels of the iris
What are the major differences in composition of the blood plasma and the aqueous?
- protein content (plasma>AH)
- Ascorbic acid (AH>plasma)
- Lactate (AH>plasma)
What make up the majority of ions in the AH?
sodium and chloride
What are the organic molecules found in the AH?
- Urea
- ascorbic acid
- lactate
- amino acids/proteins
- glutathione
What is the average pO2 in the AH?
55mmHg
Which ions are greater in the AH than the plasma? 1. Lesser in the AH than plasma? 2
- H+ and Cl-
2. bicarbonate
What is the source of the proteins in the AH?
fenestrated capillaries of the ciliary body
What are the proteins found in the AH?
- Albumin
- IgGs
- cytokines
- carbonic anhydrase
What are the fibrinolytic and pro-coagulation proteins found in the AH?
- plasminogen
2. plasminogen proactivator
Where are the tight junctions in the ciliary processes epithelium?
non-pigmented epithelium
What is dialysis in the presence of hydrostatic pressure called?
ultrafiltration
What is when a solution of protein and salt is separated from plain water by a membrane permeable to the salt and water but not to the protein, there will be a net movement of water to the protein side by diffusion and a movement of salt away from the protein side called?
dialysis
What is the primary source of aqueous humor?
ultrafiltration of plasma from capillaries
What must occur in order for ultrafiltration to occur?
hydrostatic pressure must be larger than the sum of the IOP + Oncotic pressure
What drives the NKCC pump? 1. What is the location of this pump in the formation of aqueous? 2
- High Na+ in stroma
2. basolateral pigmented epithelium
What does the NKCC transport?
- 2 Cl-
- Na+
- K+
What converts available CO2 into hydrogen ions and bicarbonate? 1. What is the location of this in the formation of aqueous? 2
- carbonic anhydrase
2. pigmented epithelium cytoplasm
What causes NHE and AE2 transport to occur readily? 1 What is the location of these pumps in the formation of aqueous? 2
- build up of H+ and HCO3- AND the availability of Na+ and Cl- in the stroma
- basolateral pigmented epithelium
What does the NHE transport?
Na+ into cell and H+ out
What does the AE2 transport?
Cl- into cell and HCO3- out
What draws water through aquaporin water channels in aqueous production? 1. What is the location of the aquaporin? 2
- Build up of sodium and chloride ions in the PE
2. basolateral pigmented epithelium
What drives the NKA pump in aqueous formation? 1. What is the location of this pump in the formation of aqueous? 2
- ATP and the available intracellular sodium
2. basolateral nonpigmented epithelium
What does the NKA pump transport?
3 Na+ out and 2 K+ in
What facilitates basolateral transport of Cl- through chloride channels into the aqueous humor?
positive charge of Na+ in aqueous humor AND available intracellular Cl-
What drives water being drawn basolaterally and transcellularly into the aqueous humor?
Na+ AND Cl- in aqueous
What is the aqueous formation rate?
2.5 microliters/min
Is aqueous production increase or decreased during sleep?
decrease
What things regulate aqueous production?
- NKCC pump can moves ions both ways
- circadian rhythm
- autonomic/adrenergic (sympathetic) control
- Timolol (a β-adrenergic antagonist)
What transports glucose into cells from the ciliary process stroma? 1. What does it use to drive this process? 2
- SGLT/Sodium Glucose transporter
2. Na+ concentration gradient
What helps glucose exit cells through facilitated diffusion?
GLUT
What is ascorbate essential for? 1. What secretes it? 2. What inhibits ascorbic acid transport? 3
- limiting ultraviolet radiation (UVR) and anti-oxidant
- ciliary body epithelium
- Blocking sodium channels
What do Dorzolamide and brinzolamide do?
inhibit Carbonic anhydrase
Do SVCT/Sodium vitamin C transporter require ATP? 1. Where are these found? 2
- yes
2. pigmented epithelium
What are the afferent nerves found in the CB? 1. Efferent nerves? 2
- sensory peptidergic neurons
2. Sympathetic and Parasympathetic
What is the mechanism of increased secretion of AH with sympathetic innervation?
Catecholamine (NorE) bind to Beta receptor -> formation of cAMP -> indirectly activates chloride channels -> AH production
What is the mechanism of stimulation of A3 adenosine receptors increasing AH production?
A3 adenosine receptor activated -> cAMP increase -> indirectly activates chloride channels -> AH production
What can stimulate NKCC co-transporter?
Catecholamines that stimulate the β-adrenergic receptor
What is the mechanism of aproclonidine?
α2-adrenergic agonists to decrease aqueous humor formation and IOP
