Physiology - Aqueous Humor

Question 1

What is the role of aqueous humor

Answer 1

• Provides oxygen & nutrients
• Contains high concentration of ascorbate (antioxidant)
• Contains bicarbonate to buffer the H+ produced by the cornea in anaerobic glycolysis

Question 2

Where is aqueous humor produced

Answer 2

The epithelial layer of the ciliary body

Question 3

Aqueous humor is an ultrafitarte of plasma - True or False

Answer 3

Unlike CSF the aqueous humor is not simply an ultrafiltate of plasma. It is produced by an energy dependant process.

Question 4

Describe the flow of aqueous humor

Answer 4

1. Epithelial layer of ciliary body =>
2. Posterior chamber of eye =>
3. Posterior segment of anterior chamber of eye =>
   Travels through the pupil =>
4. Anterior segment of anterior chamber of eye =>
   Travels through the trabecular meshwork =>
5. Canal of schlemm (in iridocorneal angle)

** tiny amount of aqueous humor travels through the vitreous humor and is absorbed across the retinal pigment epithelium

Question 5

Describe the production of aqueous humor

Answer 5

In the PE cells….
1. Carbonic anhydrase catalyses the hydration of CO2 in the PE. This produces HCO3- & H+ which is moved out of the cell into the interstitial fluid in exchange for Cl- & Na+

In the NPE cells…
2. The Cl- & Na+ is then moved from the PE into the NPE by gap junctions. The Na+ & Cl- is then transported out of the NPE cells into aqueous humor via Na/K/2Cl cotransporter

In the aqueous humor
3. Water follows the Cl- & Na+ into the aqueous humor via aquaporin channels. The K+ is moved back into the NPE cells via the Na/K pump.

Question 6

Describe the ciliary epithelium

Answer 6

Pigmented epithelial cells (basal) covered by non-pigmented epithelial cells (apical/ inner)

Question 7

What is the pathophysiology of glaucoma

Answer 7

raised intra-ocular pressure is caused by an imbalance between the rates of secretion and removal of aqueous humor

Question 8

Why can carbonic anhydrase inhibitors be used in glaucoma

Answer 8

They reduce production of aqueous humor & so reduce intra-ocular pressure

Question 9

name 2 carbonic anhydrase inhibitors

Answer 9

• Dorzolamide - administered as eye drops so avoids systemic side effects
• Acetazolomide -oral administration also targets kidney so can lead to acidosis