Production of aqueous humour

Production of aqueous humour

The aqueous humour is formed by the ciliary epithelium, which transfers solute from the stroma of the ciliary processes into the posterior chamber. The mechanisms responsible for the secretion of Na+ and Cl into the aqueous humour are not clearly understood. Na+ and Cl probably enter the epithelium through counter-transport against HCO3 and H+, respectively. At the side of the posterior chamber, Na+ is actively excreted by the Na+-K+-ATPase pump. The resulting osmotic gradient drives water from the stroma into the aqueous humour.

Regulation of aqueous humor production

Once β-adrenergic receptors are stimulated by epinephrine, the activated receptor enhances the coupled adenyl cyclase enzyme in the cell membrane, which initiates synthesis of cyclic-AMP within the cell. cAMP in turn stimulates the Na+-K+-ATPase pump, which pumps sodium ions into the posterior chamber.

The α-adrenergic receptors are coupled to adenyl cyclase as well, but inhibit the enzyme and thus the synthesis of cyclic-AMP.

H+ (hydrogen ion) is needed for the counter transport of chloride ions into the epithelium. HCO3 is needed for the counter transport of sodium ions into the epithelium. CO2 and H2O are combined using the carbonic anhydrase enzyme to form carbonic acid, which immediately dissociates to form hydrogen and H+ and HCO3.