BS - Aqueous Humour - Week 4

Question 1

What volume does the aqueous humour have? What percentage is in the anterior/posterior chamber?

Answer 1

~250μL
Anterior - 80%
Posterior - 20%

Question 2

What makes the aqueous humour?

Answer 2

Ciliary processes

Question 3

Describe the path aqueous humour takes in the eye.

Answer 3

Begins at the ciliary processes, passes over and in front on the lens, through the pupil, out towards the cornea, to the angle.

Question 4

Name 6 functions of the aqueous humour.

Answer 4

• 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

Question 5

What is the composition of aqueous humour like?

Answer 5

Like plasma, but a lot less protein.

Question 6

What molecule is particular is present in high concentrations in the aqueous humour, and why?

Answer 6

Ascorbate, for antioxidation.

Question 7

What is the pH of aqueous humour?

Answer 7

7.4

Question 8

What is the production rate of aqueous humour?

Answer 8

~1 -3 μL/min

Question 9

Define ultrafiltration of aqueous humour, where it occurs, what its driven by, and the percentage it accounts for.

Answer 9

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.

Question 10

Describe the three steps of active transport in aqueous humour production.
For steps 1 and 3, name the three and two channels responsible respectively.

Answer 10

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

Question 11

Define the following:
Electroneutral transport
Uniport
Symport
Antiport

Answer 11

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

Question 12

Describe the adrenergic modification of aqueous humour formation, and what is results in. Describe which receptors are stimulatory and inhibitory.

Answer 12

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.

Question 13

Describe the action of an alpha agonist on aqueous humour formation.

Answer 13

Increases the inhibitory effects of alpha receptors, decreasing PKA activity, reducing aqueous humour production.

Question 14

Describe the action of a beta antagonist on aqueous humour formation.

Answer 14

Decreases the excitatory effects of the beta receptors, decreasing PKA activity, reducing aqueous humour production.

Question 15

What effect does a muscurinic agonist have on the aqueous humour, and what kind of pathway is this, and why?

Answer 15

Results in the contraction of ciliary muscles, opening trabecular pores, and increasing outflow of aqueous humour.

Question 16

What effect do alpha agonists and beta antagonists have on trabecular meshwork? What happens despite this?

Answer 16

They cause contraction of trabecular meshwork, decreasing drainage.
However, their decreasing effect of aqueous humour production outweighs this, and IOP decreases.

Question 17

What percentage of drainage does uveoscleral outflow account for? What about trabecular drainage?

Answer 17

Uveoscleral - 15%

Trabecular - 85%

Question 18

Which of the two outflow pathways is enhanced by prostanoid receptor agonists? What effect does it have? What percentage outflow can it result in?

Answer 18

Uveoscleral outflow.
It relaxes ciliary muscles.
Up to 35% outflow increase can occur.

Question 19

Name 4 means of resistance in closed angle glaucoma.

Answer 19

A narrow angle
Reduced anterior angle with age
Iridocorneal adherance
Iridolenticular adherance

Question 20

Name 3 means of resistance in open angle glaucoma.

Answer 20

Increased aqueous production
Increased venous pressure
Increased resistance to outflow (debris)

Question 21

What two agents reduce aqueous humour production?

Answer 21

alpha adrenergic agonist

beta adrenergic antagonist

Question 22

What is the effect of carbonic anhydrase inhibitors?

Answer 22

Reduced aqueous humour production

Question 23

What is the effect of muscurinic agonists?

Answer 23

Increased trabecular outflow

Question 24

What is the effect of prostanoid agonists?

Answer 24

Increased unveoscleral and trabecular outflow

Question 25

How do prostanoid agonists increase TM outflow?

Answer 25

It causes enlarged tissue space in the TM