Aqueous-biochemistry , aqueous humor biochemical components

It describes about the biochemistry of aqueous humor,it is the fluid which is important for understanding the intra ocular pressure in eye . Any imbalance may lead to increased intra ocular pressure

1. Aqueous Humor biochemistry Rikta Paul Assistant Professor Department of optometry Swami Vivekananda University

2. Biochemical composition 1.Water: it constitute of 99.9% of normal A.H 2.Proteins (colloid content): in plasma it is of the order of 6-7gm/100ml In aqueous humor it is only 5-16mg/100ml ( about 1/500 that of plasma protein level) This is because of blood-aqueous barrier Any disruption of this barrier will increase protein influx

3. The albumin and globulin ratio is the same as plasma although there are less gamma globulins. Human aqueous has been found to contain IgG and IgM but no IgD and IgA.

4. Amino acids: concentration of amino acids varies with aqueous/plasma ranging from 0.08 to 3.14

5. Non-colloid constituents: Non-colloid are the dissolved solids that give an absolutely clear solution. Concentration of ascorbat , pyruvate and lactate are much higher than in plasma, while those of urea and glucose are much less.

6. Insulin and steroid this hormones are also present and enters the A.H by simple diffusion. Prostaglandins: they appears to be actively released into the aqueous by iris. Cyclic adenosine monophosphate (AMP): it has been detected in the aqueous at a level about the same as found in serum.

7. Composition of A.H of the ant.& post.Chamber Composition of aqueous humor in anterior chamber differs from posterior chamber. its depends not only on the nature of production but also on the constant metabolic interchange that occurs through out its intraocular course. Diffusional exchange across the iris is a significant factor in changing the composition. Vessels are permeable to aninons and non-electrolytes.

8. Continue… Bicarbonate concentration in posterior chamber aqueous is higher than in the anterior. This is because freshly secreted fluid has much higher concentration than in the plasma Diffusion due to the vitreous and into the blood from iris and decomposition by the acids formed by the lens and cornea metabolism, it’s level decreases in the ant. Aqueous.

9. Continue… The chloride concentration in the newly formed aqueous of the posterior chamber is lower than the plasma. Diffusion of chloride from the blood raises the chloride levels of anterior chamber aqueous

10. Ascorbate concentration in the posterior aqueous is much higher than the plasma. The gradient of diffusion for ascorbic acid from the anterior chamber to the blood reduces the concentration of ascorbic acid in the anterior aqueous.

11. Steps involved in aqueous humor formation Formation of stromal pool: By ultrafiltration most substances pass from the capillaries of the ciliary process, pass through stroma , then through gaps between the pigmented epithelium cells Accumulated behind the tight junctions of non pigmented epithelium Protein is the filtrate Semipermeable membrane is ciliary capillaries

12. Steps involved in aqueous humor formation Active transport of stromal filtrates: Tight junctions between non pigmented epithelium acts as blood aqueous barrier Active transport happens Evident because of presence of Na+K + active ATPase, glycolipids, glycoproteins Others – sodium(70%) by active secretion Carbonic anhydrase acts as a catalyst.

13. Steps involved in aqueous humor formation Passive transport across non pigmented ciliary epithelium Active transport of substances across tight non pigmented epithelium imbalance of osmotic and electrical forces To maintain balance water, chloride and few plasma constituents move into posterior chamber by ultrafiltration and diffusion. Sodium is responsible for movement of water into PC and major factor in the formation of aqueous

14. Functions