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?
How much molecules/second does AQP1 transport?
~3 billion water molecules per second
Water transport is _____ based on an _____ gradient
What is the aquaporin structure?
28 kD tetramer, each subunit consists of 6 TM helices with 2 short helices
Short helices form a major portion of the ___ of an aquaporin
Inner part of the pore of an aquaporin excludes _____ species including ____
What enzymes attack reactive oxygen species?
Catalase, superoxide dismutase, and glutathione peroxidase
What is the amount of ascorbic acid in the AH?
0.6- 1.5 mM, 10-50x higher than in the plasma
Ascorbic acid in a diurnal mammal is ___x higher than in nocturnal mammals
Ascorbic acid is actively transported from what?
Stroma to posterior chamber via Na+- dependent- vitamin C transporter
What types of antioxidants are in the AH?
Enzymes, ascorbic acid, glutathione, Cys, Uric acid and tyrosine
How much glutathione is in the AH?
An important tripeptide, 1-10 micometers (plasma
What does glutathione do?
Removes excess H2O2, reactivates ascorbate, serves as a substrate in enzymatic conjugation from blood lens, and cornea
What are 3 molecules in the AH?
Glucose, urea, and inositol
Glucose makes up what percentage of plasma?
Glucose passes across the ciliary epithelium by ____ _____
Glucose is _____ of insulin and ______ in diabetes
Urea makes up what percentage of plasma?
Urea moves _____ across membranes and is a ____ _____ for glaucoma
Passively, hyperosmotic agent
What is inositol important for?
Phospholipid synthesis in anterior segment
Concentration of inositol in AH is how many times that in plasma?
How is oxygen important in the AH?
From blood supply, corneal endothelium uses aqueous oxygen, the lens and endothelial lining of trabecular meshwork also use aqueous oxygen
The lens contributes what percentage of total bicarbonate?
What determines aqueous pH (7.5-7.6)?
Relative proportions of CO2 and HCO3-
Why is CO2 continuously lost from the aqueous?
Diffusion across the cornea into the tear film
Proteins are what percentage of plasma?
How much protein is in aqueous and plasma?
0.02 mg/100mL, plasma 7 mg/100mL
The ___ ___ can secrete proteins directly
What types of proteins are in the AH?
Albumin and transferrin account for 50%, local Igs via iris lymphocytes or plasma cells, small amounts of local fibronectin
How many nonredundant proteins are in the AH?
What is pigemented epithelium derived factor?
Secreted by ciliary nonpigmented cells, a serine proteinase inhibitor, exhibits neuroprotective activities on neurons
What do growth factors do in the AH?
Proliferation, differentiation, functional viability, and wound healing; perform diverse, synergistic or opposite biological activities
What are some growth factors in the AH?
Acidic and basic fibroblast growth factor (aFGF and bFGF), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor (VEGF), epidermal growth facotr (EGF), IL-6 (anti-inflam)
What are some trace molecules in low abundance in the aqueous humor?
Steroid hormone, catecholamines (epinephrine, norepinephrine, dopamine), prostaglandins 2 ng/mL
Prostaglandins are ___x higher in the inflamed eye
What second messangers are in the AH?
Cyclic nucleotides (cA/GMP), atrial natriuretic peptide
How do second messangers alter aqueous secretion?
Via transport of the HCO3- ion across the cells
Which molecules are more abundant in the aqueous?
Lactate, ascorbate, Cl-
Which molecules are more abundant in the plasma?
Glucose, albumin, transferrin, fibronectin, IgG, and Ca2+
What is the dominant cation in the aqueous?
What is the dominant anion in the aqueous?
What molecules have similar concentration in aqueous and plasma?
Na+, K+, Mg2+, Cl-, HCO3-
What fraction are lipids in the plasma?
Oxygen concentration is what percentage of the plasma value?
How is IOP determined?
By the rate of aqueous production and flow, outflow resistance, and episcleral venous pressure
What happens to steady- state IOP?
Aqueous inflow is equal to outflow
What are the outflow paths of IOP?
Trabecular and uveoscleral outflow
How do you lower IOP?
By reducing inflow, or by increasing outflow, or a combination of both
IOP change is ____ in glaucoma patients with progressive visual fields
What are the diurnal fluctuations of IOP?
Increased variation in daytime (diurnal) IOP than healthy control, no difference between the groups in nocturnal IOP fluctuation
Transient IOP spikes may induce what?
Optic nerve damage
What is the IOP in cornea?
>/= 40 mm Hg
What happens if the IOP in the cornea is too high?
Megalocornea, photophobia, Haab's striae