Aqueous Humor Composition Study Guide | Biology Terms

What is the embryological source of the pigmented and non-pigmented epithelium of the ciliary body?

ectoderm

What is the embryological source of the vasculature of the ciliary body?

mesoderm

What is the embryological source of post/ant epithelial cells of the iris?

distal tip of the optic vesicle (ectoderm)

What is the embryological source of stroma of the iris?

neural crest/ectoderm

What is the embryological source of iris vasculature?

mesoderm

What is the embryological source of choroid vasculature?

mesoderm

What is the embryological source of ciliary muscle?

neural crest/ectoderm

What is the embryological source of trabecular meshwork?

neural crest/ectoderm

What is the embryological source of Schlemm's canal?

mesoderm

aniridia

congenital lack of the iris and disruption of anterior segment

most known cause is due to mutation of the Pax6 gene

at risk for developing

Why is aqueous humor composition different than that of blood plasma?

due to the blood-aqueous barrier

What are the differences between the aqueous humor composition and blood plasma?

protein content: blood plasma protein concentration is greater in the aqueous humor

ascorbic acid/ascorbate: concentration is greater in the aqueous humor than plasma

lactate: concentration is higher in aqueous humor than plasma

What are the major ions found in the aqueous humor?

sodium chloride

bicarbonate lactate

What is the most prevalent ion in the aqueous humor?

sodium

What organic molecules are present in aqueous humor?

ascorbate

urea

glucose

lactate

Which has lower pH: aqueous humor or plasma?

aqueous humor

What are the two processes that produce aqueous humor?

ultrafiltration

ion/water secretion

ultrafiltration

produces a reservoir of plasma in the ciliary process stroma

IOP sensitive

ion/water secretion

moves ions from plasma ultra filtrate to aqueous humor

transport of ions occurs bilayered ciliary epithelium

IOP sensitive

capillary hydrostatic pressure

pushes fluid from capillaries through fenestrations into the stromal space in a process called ultrafiltration

capillary derived solution is referred to as the "ultrafiltrate"

created by fenestrations of stroma

What causes ultrafiltration?

solution movement across a semi-permeable barrier due to pressure differential

balance between oncotic and hydrostatic pressures

What is ultrafiltration opposed by?

IOP and oncotic forces

What must happen for ultrafiltration to occur?

hydrostatic pressure must be larger than the sum of the IOP + oncotic pressure

Is ultrafiltration sensitive to IOP?

yes

as IOP rises ultrafiltration decreases

decrease in facility of inflow

a decrease in ultrafiltration due to IOP

What happens to ultrafiltration if capillary pressure drops below a critical level?

ultrafiltration will not occur because ultrafiltration cannot overcome both oncotic pressure and IOP

What happens to ultrafiltration if IOP increases to a critical level?

ultrafiltration will also be inhibited

What is the relationship between blood flow/aqueous humor production?

when the blood flow is in the range of normal to 75% below normal, production of aqueous humor is independent of bloodfloow

when blood flow is significantly below normal, production of aqueous humor is dependent on blood flow and is also reduced

What is aqueous humor production under physiological conditions?

2.5 ul/min

How is aqueous humor production affected by IOP at normal levels?

it is unaffected

How is aqueous humor production affected when IOP is very high?

aqueous humor production decreases due to exceeding ability of blood flow to be auto regulated

T/F: aqueous humor production is an energy dependent process

true, it is dependent on oxygen levels and therefore requires aerobic metabolism

What does the basolateral domain of the pigmented ciliary process epithelium face?

ciliary process stroma

What does the basolateral domino of the the non-pigmented ciliary process epithelium face?

faces the aqueous humor

Where are non-leaky tight junctions found in the ciliary processes?

found only in non-pigmented epithelium

Where are gap junctions are found in the ciliary processes?

found between the pigmented epithelium cells

between non-pigmented epithelium cells, and between pigmented epithelium and non-pigmented epithelial cells

What are the functions of gap junctions in aqueous humor secretion?

gap junctions allow free diffusion of ions and water between epithelial layers

What is the stroma ultra filtrate sodium concentration compared to that of intracellular concentrations?

ultra filtrate has a high sodium concentration relative to intracellular concentrations

What prevents paracellular transport in the ciliary processes?

tight junctions

Where are aquaporins found in the ciliary processes?

both in the non-pigmented and pigmented ciliary epithelium

How is glucose transported across the ciliary epithelia?

transported through sodium dependent SGLT and independent mechanisms

SGLT

transports glucose into cells from the ciliary process stroma using sodium concentration gradient

GLUT

glucose exits through facilitated diffusion

Where are GLUTs found in ciliary processes?

found in non-pigmented epithelial cells

What is the function of ascorbate in the aqueous humor?

absorb UV light

donates electrons to ROS

What two molecules scavenge for ROS in the aqueous humor?

ascorbate

urea

What is the rate of aqueous humor formation?

2.5 microliters/min

T/F: aqueous humor production is reduced at night?

true

How is the circadian rhythm of aqueous humor controlled?

controlled by autonomic/adrenergic control

Where are the cell bodies of the parasympathetic fibers that are associated with the ciliary epithelium and ciliary blood vessels?

cell bodies of postganglionic parasympathetic fibers originate in the pterygopalatine ganglion

What sympathetic fibers innervate the blood vessels of the ciliary body?

postganglionic fibers from the superior cervical ganglion

How does binding of agonists to B adrenergic receptors affect the ciliary epithelium,?

this triggers the formation of cAMP which in turn directly activates chloride channels

activation of chloride channels increases aqueous humor formation and increases IOP

What is the mechanism of action for timolol?

Beta receptor antagonist which prevents normal levels of stimulation which maintain the activation of chloride channels

lack of chloride channel activation decreases aqueous humor formation and decreases IOP

How does simulation of adenosine receptors cause a higher IOP?

stimulation of A3 adenosine receptors triggers the activation of chloride channels which lead to more aqueous humor production and a higher IOP

What are the two mechanisms by which alpha 2 agonists decrease aqueous humor formation?

1. presynaptic nerve inhibition (systemic application)

2. direct inhibition of non-pigmented cell secretion (topical application)

clonidine

alpha 2 agonist that inhibits presynaptic sympathetic nerves

Apraclonidine/brimonidine

alpha 2 agonist that directly inhibits NPE cell secretion

What is the mechanism of action of clonidine?

alpha 2 receptor present in the presynaptic sympathetic nerve inhibits further norepinephrine release and block further synaptic transmission

vasodilation ensues due to reduced smooth muscle contraction

lowers aqueous humor production

What is the mechanism of action of apraclonidine/brimonidine?

alpha 2 receptors are present in ciliary epithelium and stimulation of them causes reduction of intracellular cAMP

reduction in cAMP reduces basolateral ion transport (Cl-)

What is the mechanism of action of dorzolamide and brinzolamide?

inhibition of carbonic anhydrase which indirectly reduces ion transport and therefore reduces aqueous humor production