Flashcards in Chapter 9: Aqueous humor, Iris, and Ciliary Body Deck (23):
What is the function of the aqueous humor?
- provides nutrients to support the Anterior segment tissues
- removes metabolic waste products
- helps maintain appropriate IOP
Where is the aqueous humor produced? What is the flow rate?
It is secreted by the non-pigmented epithelium of the ciliary body from a substrate of blood plasma
Flow rate= 2-3 micro Liters per minute
How does the aqueous humor enter the posterior chamber from the ciliary body?
It enters via both active and passive mechanisms
Active= Carbonic Anhydrase II activity
Passive= diffusion and ultrafiltration
Which layer of the ciliary body has tight junctions? Which has leaky junctions?
The NPE of the ciliary body has tight junctions proximal to the apical plasma membrane, and helps to establish the blood-aqueous barrier
The PE is leaky, and allows solutes through intercellular spaces
How do Carbonic anhydrase inhibitors and beta blockers used to treat glaucoma?
they both decrease the rate of aqueous humor formation in the NPE of the ciliary body
Describe the process of aqueous formation by the ciliary body
1- solutes/h2O are taking in by the PE at their stromal surface
2- Transferred to NPE via gap junctions
3- Transferred from NPE into the posterior chamber
What are the components of the aqueous humor? What are the major Anions?
- Inorganic Ions - Organic anions - carbohydrates
- glutathione - urea - proteins
- growth modulatory factors - 02/CO2
Major anions= HCO3, CL
How do the ionic concentrations in the aqueous humor compare to serum?
NaK/Mg/Fe/Cu/Zn are similar to plasma concentrations
Ca+2 is 50% of plasma level
What organic anions are found in the aqueous humor?
vitamin C (ascorbic acid)
How does the glucose level of the aqueous compare to serum?
The aqueous has 70% of the glucose found in the serum
However, inosital is 10x greater than the serum levels, due to its importance for phospholipid synthesis ion the anterior segment
WHat is the function of glutathione in the aqueous humor?
It stabilizes the redox state of the aqueous by re-converting ascorbate to its functional form after oxidation, and removal of excess H202
Therefore, protects tissues from oxidative damage.
Is highly concentrated in the ocular ciliary epithelium
What is the urea concentration of the aqueous compared to plasma?
Its concentration is 80-90% of its plasma value
What is the protein concentration of the aqueous humor? What are the most abundant proteins found in the aqueous himor?
0.02 g of protein per 100 mL
Albumin and Transferrin are the most abundant proteins, accounting for 50% of total protein
What are the proteinases/inhibitors found in the aqueous humor?
Cathepsin D and O, which are synthesized in the ciliary epithelial cells.
Cathepsin D is involved in the degradation of neuropeptides and peptide hormones.
Cathepsin O function is unknown
How do the levels of growth modulatory factors in the aqueous change in patients with DM?
Levels of Insulin-Like growth Factor binding proteins (IGFBP) are 5x higher in patients without retinopathy
IGF-1 is increased in patients with diabetic retinopathy
What VEGFs are found in the aqueous humor? What is the significance of VEGF-A?
VEGF A-D, adn placental Growth factor are found in the aqueous.
VEGF A is the only member of its family induced by hypoxia--it is a crucial regulator of angiogenesis and a potent inducer of vascular permeability.
Levels of VEGF A increase in patients with active neovascularization from PDR, CRVO, and NVI
What are the partial pressures of 02 and CO2 in the aqueous humor? Where is the 02 in the aqueous derived from? What is the pH of the aqueous humor?
O2- 55 mm Hg CO2- 40-60 mm Hg
02 is derived from blood supply to ciliary body
How does the protein content of the aqueous humor change s/p blood-aqueous barrier breakdown? What consequences would it have?
There would be a 10-100x increase in protein
Could cause formation of fibrinous exudates, clot formation (with or without macrophage reaction and formation of cyclitic membrane), and synechiae formation (peripheral and posterior)
Chronic disruption of the blood-aqueous barrier has been implicated in several intraocular processes--what are they?
abnormal hypoplastic response of the lens epithelium, corneal endothelium, TM, Iris, and formation of complicated cataracts.
What embryologic tissues are the Iris and CB derived from?
They are both derived from Neuroectoderm
How does PGF2 agonists work to treat glaucoma?
Unlike BB's/CAIs/Alpha 2 agonists, PGF2 decrease IOP by increasing outflow.
Typically lowers IOP by 27-35%
What effect do Arachidonic Acid/PGE/PGF have on the eye when administered topically or intracamerally?
When administered intracamerally or topically at high concentrations, they cause miosis, increased IOP, increased aqueous protein content, and entry of WBS into the tear fluid and aqueous.