Flashcards in Exam 1 Koh- Aqueous Humor 1 Deck (82)
What is the function of aqueous?
A circulatory system to portions of the eye, provides nutrients (glucose and amino acids) to avascular lens, cornea, and trabecular meshwork; removes metabolic wastes (lactic acid, pyruvic acid), maintains normal IOP (7-21); maintains the shape of the eye
Why is the aqueous transparent?
Devoid of blood cells and of more than 99% of the plasma proteins, provides an optically clear medium for transmission of light
What is the ciliary epithelium?
A polarized bilayer lining surface of the ciliary body
What are the 2 layers the ciliary epithelium is composed of?
Nonpigmented, faces aqueous humor; pigmented, faces the ciliary stroma
Apical plasma membranes in the ciliary epithelium _____ each other
Gap junctions in the ciliary epithelium form a complex _______
Why are tight junctions important in the ciliary body?
Limits proteins in aqueous and cell polarity
_____ junctions are present between the apical borders of NPE cells
What is a major part of the blood-aqueous barrier?
PE cell layer has a _____ epithelium
Where is the aqueous humor formed from?
Ciliary epithelium (2-3 mililiters/min)
How is aqueous humor formed?
Formed by transport of water and electrolytes from leaky capillaries of ciliary processes to epithelial syncytium and thence across the plasma membrane of NPE
What is the flow of the aqueous humor?
Transferred solute from stroma of ciliary processes into PC, circulated through the pupil towards the AC, drained from AC via outflow apparatus into the episcleral veins, aqueous exchanges solutes with cornea, lens, iris, ciliary body and vitreous
What are 3 mechanisms of aqueous production?
Diffusion, ultrafiltration, and active secretion
What happens in diffusion of aqueous humor?
Solute moves across the ciliary epithelial barrier
What is ultrafiltration of the aqueous humor?
Passive movement of fluids across the plasma membrane exerted by the net hydrostatic and oncotic pressure difference
What active secretion occurs in regards to the aqueous humor?
Of solutes, primarily Na+ and Cl-, drives aqueous humor inflow from the stroma
What are the major ions in the aqueous?
Na+, Cl-, and to a lesser extent HCO3-; participate in transeptihelial secretion across the ciliary epithelium
What are the 3 transport steps of cations?
1. ion uptake by the PE cells 2. diffusion of ion from PE to the NPE cells through gap junctions 3. ion release from the NPE cells into posterior chamber
Where are the Na/K-ATPase pumps predominantly localized? Where is it more highly expressed?
At the basolateral infoldings and interdigitations of both PE and NPE cells; more highly expressed in the NPE cells
What is ouabain?
Cardiac glycoside, blocks Na/K-ATPase, lowers IOP in experimental animals, primarily by reducing the rate of aqueous inflow
What are the anions involved in the aqueous?
Bicarbonate and chloride
HCO3- constitues only __- ___% of the total anion
Cations secreted are predominantly accompanied by what anion?
What is the major driving force of AH secretion?
What are the other transports for chlorides?
Na+-K+/2Cl- symport and parallel Cl-/HCO3- and Na+/H+ antiports
How does Cl- uptake occur into pigmented epithelial cells?
Na+K+/2Cl- cotransporter along the basolateral border of PE cells, parallel Cl-/HCO3- and Na+/H+ antiports regulate pH and Cl- secretion across the ciliary epithelium
What plays a central role in aqueous humor formation?
What type of aquaporin is abundant in the aqueous epithelium?