BS - Aqueous Humour - Week 4 Flashcards
What volume does the aqueous humour have? What percentage is in the anterior/posterior chamber?
~250μL
Anterior - 80%
Posterior - 20%
What makes the aqueous humour?
Ciliary processes
Describe the path aqueous humour takes in the eye.
Begins at the ciliary processes, passes over and in front on the lens, through the pupil, out towards the cornea, to the angle.
Name 6 functions of the aqueous humour.
- Provides O2 and nutrients to the lens/cornea
- Removes waste products
- Removes tissue debris
- Assists with corneal and lens pump mechanisms
- Maintains intraocular pressure
- Maintains eye shape
What is the composition of aqueous humour like?
Like plasma, but a lot less protein.
What molecule is particular is present in high concentrations in the aqueous humour, and why?
Ascorbate, for antioxidation.
What is the pH of aqueous humour?
7.4
What is the production rate of aqueous humour?
~1 -3 μL/min
Define ultrafiltration of aqueous humour, where it occurs, what its driven by, and the percentage it accounts for.
It is the movement of water and soluble substances across a fenestrated cell membrane.
Occurs mainly between capillaries and the stroma of ciliary processes.
Driven by hydrostatic forces.
Accounts for 15% max.
Describe the three steps of active transport in aqueous humour production.
For steps 1 and 3, name the three and two channels responsible respectively.
1 - Na+ and Cl- transferred from the stroma into the pigmented epithelium
Channels
-Na+/H+ antiport
-Cl-/HCO3- antiport
-Na+/K+/2Cl- symport
2 - Solutes pass into the non-pigmented epithelium through gap junctions
3 - Non-pigmented epithelium releases Na+ and Cl- into the posterior chamber
Channels
-Na+/K+-ATPase
-Cl- channels
Define the following: Electroneutral transport Uniport Symport Antiport
Electroneutral - no net change in charge
Uniport - passage on one molecule
Symport - molecules transported in the same direction at the same time, often utilising a charge potential
Antiport - Molecules transported in opposite directions
Describe the adrenergic modification of aqueous humour formation, and what is results in. Describe which receptors are stimulatory and inhibitory.
Adrenergic receptors coupled to G-protein cascades. Alpha receptors are inhibitory Beta receptors are stimulatory They both regulate adenyl cyclase Adenyl cyclase converts ATP to cAMP cAMP binds to Protein Kinase A PKA phosphorylates Na/K-ATPase This increases the Na+ gradient, and thus icreases unidirectional secretion.
Describe the action of an alpha agonist on aqueous humour formation.
Increases the inhibitory effects of alpha receptors, decreasing PKA activity, reducing aqueous humour production.
Describe the action of a beta antagonist on aqueous humour formation.
Decreases the excitatory effects of the beta receptors, decreasing PKA activity, reducing aqueous humour production.
What effect does a muscurinic agonist have on the aqueous humour, and what kind of pathway is this, and why?
Results in the contraction of ciliary muscles, opening trabecular pores, and increasing outflow of aqueous humour.
What effect do alpha agonists and beta antagonists have on trabecular meshwork? What happens despite this?
They cause contraction of trabecular meshwork, decreasing drainage.
However, their decreasing effect of aqueous humour production outweighs this, and IOP decreases.
What percentage of drainage does uveoscleral outflow account for? What about trabecular drainage?
Uveoscleral - 15%
Trabecular - 85%
Which of the two outflow pathways is enhanced by prostanoid receptor agonists? What effect does it have? What percentage outflow can it result in?
Uveoscleral outflow.
It relaxes ciliary muscles.
Up to 35% outflow increase can occur.
Name 4 means of resistance in closed angle glaucoma.
A narrow angle
Reduced anterior angle with age
Iridocorneal adherance
Iridolenticular adherance
Name 3 means of resistance in open angle glaucoma.
Increased aqueous production
Increased venous pressure
Increased resistance to outflow (debris)
What two agents reduce aqueous humour production?
alpha adrenergic agonist
beta adrenergic antagonist
What is the effect of carbonic anhydrase inhibitors?
Reduced aqueous humour production
What is the effect of muscurinic agonists?
Increased trabecular outflow
What is the effect of prostanoid agonists?
Increased unveoscleral and trabecular outflow
How do prostanoid agonists increase TM outflow?
It causes enlarged tissue space in the TM
