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Ocular Physiology Exam 2 > Aqueous Humor > Flashcards

Aqueous Humor Flashcards

1
Q

Aqueous humor comes from

A

Circulation from the major circle of the iris by an ultrafiltration mechanism
(Similar to CSF)

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2
Q

Aqueous humor is produced by

A

Ciliary processes

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3
Q

Aqueous humor is necessary for

A

Maintaining the proper shape of the eye and its optical properties

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4
Q

What part of ciliary body is AH facing?

A

Non pigmented epithelium (NPE) faces the posterior chamber (it crosses from the pigmented epithelium that is facing circulation)

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5
Q

Fenestrated capillaries allow for transportation of AH because

A

Capillaries are lined by endothelium with PORES and NO TIGHT JUNCTIONS, so they are very permeable to macromolecules. Allows for the passing of nutrients

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6
Q

Blood flows from ____ to _____ and drains through _____.

A

Anterior to posterior and drains through the choroidal veins

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7
Q

3 physiological processes contribute to the formation and composition of AH:
Which is more relied on?

A

1.Diffusion
2. Ultrafiltration
3. Active secretion
Mostly relying on active secretion

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8
Q

Ultrafiltration needs

A

Pressure

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9
Q

Diffusion and ultrafiltration are ___ processes requiring______.

A

Passive

No active cellular participation

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10
Q

How does diffusion across cell membranes happen? What is more likely to go through?

A

It moves down the concentration gradient.

Substances with high lipid solubility move readily through membranes in this way.

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11
Q

What does ultrafiltration depend on

A

Pressure

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12
Q

Ultrafiltration is due to bulk flow of blood plasma across fenestrated ciliary capillary endothelium into the ciliary stroma, down

A

A pressure gradient across a semipermeable membrane (hydrostatic pressure)

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13
Q

If you have a pressure gradient and your IOP increases what will happen to the ultrafiltration

A

It will decrease because the gradient is made smaller

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14
Q

Relationship between IOP and ultrafiltration?

A

Lower IOP, higher ultrafiltration into the eye because of pressure gradient

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15
Q

Relation between hydrostatic force and ultrafiltration?

A

Increasing hydrostatic force will increase the ultrafiltration

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16
Q

Active secretion requires ____ provided by ____.

A

Requires energy normally provided by hydrolysis of ATP.

AGAINST THE CONCENTRATION GRADIENT

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17
Q

What does active secretion transport?

A

Na+ is actively transported into the posterior chamber by NPE of the ciliary body. Results in H2O following

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18
Q

Major mechanism for making the AH is

A

Secretion (not pressure)

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19
Q

Active secretion is pressure ____ at near physiologic IOP (normal IOP)

A

Insensitive

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20
Q

Ultrafiltration of AH formation is ____ to changes in IOP

A

Sensitive

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21
Q

As IOP increases _____ decreases

A

Ultrafiltration

22
Q

Pseudofacility

A

When IOP decrease = more filtration
When IOP increases= grading smaller, less filtration

Pressure induced decrease in inflow appears as an increase in outflow when measuring outflow by tonography and constant pressure perfusion

23
Q

In healthy eyes the area of AH formation is

A

2.5 ul/min

24
Q

The rate of AH formation and drainage is 1% per min.

Drainage can go through

A

Trabecular meshwork or uveal scleral pathway (most through TM)

25
Q

Enzymes needed for active process

A

Na+/K+ ATPase
Carbonic anhydride

Can be targeted for modification to the formation of AH

26
Q

Where is Na+/K+ ATPase located? Where is Na+ and K+ transported to?

A

Basolateral infoldings of the NPE
Na+ towards aqueous
K+ toward stroma

27
Q

Na+/K+ ATPase inhibitors like ouabain, vanadate are

A

Cardiac glycosides

28
Q

When you you block Na+/K+ ATPase in the ciliary processes

A

It will significantly decrease the rate of AH formation and IOP

But not usually used to block production of AH because of effects

29
Q

Inhibition of Na+/K+ ATPase topically will cause

A

No effect on IOP and may cause corneal edema by interfering with epithelial Na+/K+ ATPase pump

30
Q

Na+/K+ ATPase inhibiter administered systemically will cause

A

So many side effects seen in eyes and cardiovascular

31
Q

Carbonic anhydrase found in the eye

A

II (aqueous) & IV

32
Q

CA inhibitor administered systemically will cause

A

Decrease in AH secretion by as much of 50%

33
Q

CA inhibition will block

A

HCo3- and H+

Both affect Na+ transport

34
Q

Blocking CA will decrease HCO3

A

transport of Na+ from the cytosol of the NPE to the aqueous wont happen

-decreases intracellular pH, inhibiting Na+/K+ ATPase

Altering formation

35
Q

Inhibiting CA will decrease H+ formation

A

Resulting in a decrease in the Na+ & H+ exchange

36
Q

Inhibition of CA systemically will cause

A

Systemic acidosis -> decreasing AH formation

37
Q

CAI in low doses (methazolamide)

A

Will inhibit ocular enzyme without affecting erythrocytes and renal enzymes and avoiding systemic acidosis.

Will suppress AH formation

38
Q

To achieve adequate suppression AH secretion using CAI it is required to have

A

More than 99% of ciliary CA suppressed

39
Q

Rate of production of AH in a glaucoma person

A

Is the same as in a normal person

40
Q

How do we measure the rate of AH formation

A

Fluorophotometry

Flourescein is given to the pt. A subsequent decline in anterior chamber concentration is used to calc aqueous flow

41
Q

How does AH production vary during the day

A

Drops during sleep

But IOP increases during sleep (supine position)

42
Q

Affect of Age on AH

A

Production decreases

Decreased outflow facility

43
Q

What are some anti glaucoma drugs that will increase drainage?

A

Alpha 2 adrenergic agonist

Prostaglandin analogs

44
Q

What are some glaucoma drugs that will affect AH production

A

Alpha 2 agonist
Beta antagonist
Cholinergic (muscarinic) agonist
CAI

45
Q

Antoglaucoma medication that will reduce formation of HCO3- which in turn reduces AH secretion?

A

CAI

46
Q

What causes AH to be different from plasma (2)

A

BAB

Active transport of substances by the ciliary epithelium

47
Q

Protein:

AH vs plasma

A

200x «< protein in AH

48
Q

CL- ions and A.A.:

AH vs plasma

A

More in the AH than plasma

49
Q

Ascorbic acid in AH

A

20X more in AH than plasma
ANTIOXIDANT
It has to stop the oxidation that occurs when UV light goes across

50
Q

Lactate

AH vs plasma

A

More in AH
Metabolic products accumulated way more
Increases when getting closer to the lens

51
Q

How does uveitis affect the AH?

How will it look in the slit lamp?

A

Uveitis = inflammation

Inflammation will increase permeability and leak protein

Tyndall effect will be seen in slit lamp exam: flare/light scatter in anterior chamber

52
Q

Classic Model of BAB

A

Tight junctions are present between non pigmented ciliary epithelial cells.
And in between endothelial cells if iris vascularture

The proteins present ate actively transported from ciliary epithelium into the AH

Ocular Physiology Exam 2 (4 decks)

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