Physiology: Aqueous Humor

Question 1

what function does the bicarbonate in aqueous humor have

Answer 1

buffers the hydrogen ions produced in the cornea and lens by anaerobic glycolysis and ensures the pH is constant

Question 2

describe the layers of the ciliary epithelium

Answer 2

inner layer in transparent (NPE) and covers the vitreous body. it becomes pigmented when it reaches the iris

outer layer is highly pigmented (PE) and continuous with retinal pigmented epithelium

Question 3

describe the movement of ions in the PE and NPE cells

Answer 3

HCO₃^- and H⁺ are formed in the PE cells from the hydration of CO₂ catalysed by carbonic anhydrase, and are transported across the membranes of PE cells into interstitial fluid, in exchange for Cl and Na

the Cl and Na ions that enter the PE cells diffuse through gap junctions into NPE cells and are transported out of NPE cells into aqueous humor via Na/K/2Cl transporter

Question 4

outcome of ion movement in PE and NPE cells

Answer 4

net movement of Cl and Na through cells from interstitial fluid to aqueous humor is accompanied by water moving through aquaporins (AQP1 of NPE cell) down the osmotic gradient created by solute movement

Question 5

compare the rate of replacement of aqueous humor in posterior and anterior chamber

Answer 5

as the anterior chamber has a larger volume than the posterior (250ml and 60ml) it takes 4x the time to replace the aqueous humor in it

Question 6

what is the normal intraocular pressure

Answer 6

maintained by balance between secretion and drainage of aqueous humor maintains it between 12 and 22 mmHg

Question 7

what can be used to treat glaucomas

Answer 7

CA inhibitors - decrease production of aqueous humor and can therefore reduce pressure in glaucoma

eg Dorzolamide eye drops or Acetazolamide orally