Biochemistry and Metabolism- Aqueous Humor, Iris, and Ciliary Body

Question 1

Where is aqueous humor secreted from

Answer 1

nonpigmented ciliary epithelium (NPE) from a substrate of blood plasma

Question 2

Composition of aqueous humour

Answer 2

low protein content and a high concentration of ascorbate

Question 3

Function of ascorbate

Answer 3

antioxidant properties, and its high concentration in the aqueous protects intraocular structures by blocking ultraviolet (UV) light

Question 4

What makes up blood-aqueous barrier

Answer 4

tight junctions of the NPE, the iris vasculature, and the inner wall endothelium of the Schlemm canal

Question 5

Function of ciliary body

Answer 5

produces the aqueous humor, regulates its composition, and contributes to uveoscleral outflow, thereby directly influencing the ionic environment and metabolism of the cornea, lens, and trabecular meshwork.

Question 6

Does ciliary body have a role in defending against oxidative stress

Answer 6

It has the highest concentration of redox (oxidation-reduction) enzymes in the anterior segment. The ciliary body also contains proteins of the cytochrome P450 family, though only a small number compared with the liver. These enzymes are involved in detoxification

Question 7

How is Timolol metabolised

Answer 7

CYP2D6 is one such enzyme that metabolizes timolol. It is expressed in low levels in ocular tissues but is abundant in the liver.

Question 8

What happens when blood mixes with ocular fluids

Answer 8

cause blood constituents to mix with ocular fluids; this mixing leads to plasmoid aqueous, retinal exudates, or retinal edema

Question 9

Which epithelium is leaky and which is tight

Answer 9

NPE has tight junctions proximal to the apical plasma membrane that form part of the blood–aqueous barrier, thereby preventing paracellular transport from the ciliary stroma into the posterior chamber. In contrast, the PE cell layer is considered a leaky epithelium because it allows solutes to move through the space be- tween the PE cells.

Question 10

Aqueous humour production rate

Answer 10

2–3 μL/min, but this rate varies according to our circadian rhythm, dropping to 1.0 μL/min at night.

Question 11

What is a symporter

Answer 11

membrane proteins that mediate the cotransport of molecules in the same direction

Question 12

What is an antiporter

Answer 12

mediate the cotransport of molecules in opposite directions

Question 13

Aqueous composition of components compared to plasma and vitreous

Answer 13

Highest in Na+, Cl- Ascorbate, Lactate and Inositol
Lowest in HCO3- and glucose

Question 14

Impact of diabetes mellitus on lens

Answer 14

In individuals with diabetes mellitus, glucose levels in the aqueous humor are increased.this leads to higher glucose concentrations in the lens, which has short- term refractive and longer-term cataract implications.

Question 15

Function of inositol

Answer 15

Inositol, which is important for phospholipid synthesis in the anterior segment, is found in the aqueous at a concentration approximately 10 times higher than that in plasma.

Question 16

What contains highest concentration of glutathione

Answer 16

Blood however, virtually all glutathione resides within the erythrocytes, and plasma has a low concentration of only 5 μmol/L or less.

Question 17

Function of glutathione

Answer 17

stabilizes the oxidation-reduction (redox) state of the aqueous by reconverting ascorbate to its functional form after oxidation, as well as by removing excess hydrogen peroxide

Question 18

Where is glutathione S transferase found

Answer 18

highly concentrated in the ocular ciliary epithelium

Question 19

Concentration of urea in aqueous

Answer 19

between 80% and 90% of that in plasma

Question 20

Concentration of protein in aqueous

Answer 20

Normal aqueous contains approximately 0.02 g of protein per 100 mL, as compared with the typical plasma level of 7 g per 100 mL

Question 21

Most abundant plasma protein in aqueous

Answer 21

albumin and transferrin, which together may account for 50% of the total protein content.

Question 22

Other proteins hypothesised to be made by ciliary body

Answer 22

• C4, a component of the classical complement pathway that participates in immune- mediated inflammatory responses
• α2-macroglobulin, a carrier protein that is involved in proteinase inhibition, clear- ance, and targeting, as well as the processing of foreign peptides
• apolipoprotein D, which binds and transports hydrophobic substances, including cholesterol, cholesteryl esters, and arachidonic acid (AA)
• selenoprotein P, which has antioxidant properties

Question 23

Growth factors found in aqueous

Answer 23

• transforming growth factor βs 1 and 2 (TGF-β1 and -β2)
• acidic and basic fibroblast growth factors (aFGF and bFGF) * insulin-like growth factor I (IGF-I)
• insulin-like growth factor binding proteins (IGFBPs)
• vascular endothelial growth factors (VEGFs)
• transferrin

Question 24

How many VEGF are there

Answer 24

VEGF-A, -B, -C, and -D,

Question 25

Function of VEGF-A

Answer 25

VEGF-A is a crucial regulator of vasculogenesis (embryologic blood vessel development from mesodermal elements) and a potent inducer of vascular permeability and angiogenesis (neovascularization). VEGF-C and VEGF-D regulate lymphangiogenesis. VEGF receptors (VEGFR) are tyro- sine kinases.

Question 26

Impact of oxygen concentration in aqueous humor

Answer 26

Oxygen concentration in the aqueous humor may increase with age-related vitreous degeneration or after surgical removal of vitreous. elevated oxygen concentration induces oxidative damage in the lens and trabecular meshwork and leads to an increased risk of nuclear sclerosis, cataract, and open-angle glaucoma after vitrectomy.