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Neuroanatomy Exam 1 > Biochemistry - Metabolic Profile of the Eye > Flashcards

Biochemistry - Metabolic Profile of the Eye Flashcards

1
Q

Where can there be no oxidative metabolism in the eye?

A

In the path of light, therefore the lens and fovea are out.

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2
Q

What are 4 functions of the cornea?

A

1) Structure
2) Ion transport
3) energy production
4) Anti-oxidant system

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3
Q

What lies between collagen fibers keeping them in orderly arrays.

A

Keratan sulphate I (GAG). Fiber array minimizes light scattering

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4
Q

Glaucoma treatment:

what does prostaglandin analogs do?

A

Increase outflow (ex. Latanoprost -xalatan)

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5
Q

Glaucoma treatment:

What do B-blockers do?

A

Reduce secretion ( Timolol - Timoptic)

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6
Q

Glaucoma treatment:

What do cholinergic agonists do?

A

Restore outflow after an acute attack.

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7
Q

Glaucoma treatment:

What does Carbonic Anhydrase inhibitors do?

A

Reduce secretion
Systemically via acetazolamide (diamox)
Topical via dorzolamide (trusopt)

**Cosopt is a comb of timolol and dorzolamide

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8
Q

What is posterior Vitreous Detachment?

A

-Common in elderly it can result in seeing flashing lights and “floaters” due to shrinkage and collapse of vitreous. Normally with age vitreous becomes more liquid and falls aways from the retina.

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9
Q

What are the 2 main ingratiates in the composition of the cornea?

A
  • Water (78%) critical to transparency

- collagen (15%) type I

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10
Q

What transport system in the cornea protects the eye from GAG’s natural tendency to uptake water?

A

Active transport of bicarbonate out into aqueous humour counteracts this and keeps the aqueous humour hypertonic with respect to teh cornea and maintains corneal transparency
***requires ATP

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11
Q

What is the main metabolic process of glucose in the eye?

A
  • 60% foes to HMP shunt and 35% anaerobic glucolysis, and 5% goes to aerobic glycolysis + TCA cycle
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12
Q

What can occur with prolonged wearing of contact lenses?

A
  • hypoxia:
    • -> increased lactate production
    • -> decreased corneal pH
    • -> Corneal swelling
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13
Q

What are the main functions of the anti-oxidant system in the cornea?

A
  • Removes superoxide
  • Removes peroxide
  • Reduces disulphide bridges (in proteins)
  • Maintains reduced (active form of glutathione.
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14
Q

What is the main energy producing system that supports the anti-oxidant system?

A
  • pentose phosphate pathway
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15
Q

What are the main functions of the Aqueous humor?

A
  • Secreted by the ciliary processes into the posterior chamber
  • Drains out through the canal of Schlem
  • Brings nutrients to the cornea and lens
  • Removes metabolic end products from the cornea and lens.
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16
Q

What is the main composition of Aqueous humor?

A
  • Glucose (80% plasma), lactate (3-4x plasma), Ascorbic acid (10-50x)
  • *High glucose and ascorbic acid due to anaerobic activity.
17
Q

What is the leading cause of preventable blindness?

  • What are the two types of the above disease?
  • What is the leading cause of non-preventable blindness.
A
  • Glaucoma
  • decrease in drainage (most common) or overproduction
  • Macula degeneration
18
Q

What are the 3 types of glaucoma that results in a decrease in drainage?

A
  • Primary open angle glaucoma (blockage in drainage canals)
  • narrow angle glaucoma (Angle closure - outer edge of iris blocks entrance to canals, chronic and acute forms)
  • Normal tension glaucoma - optic nerve damage despite normal IOP
19
Q

What are some risk factor for Glaucoma?

A
  • African ancestry
  • Family history
  • Diabetes
  • Severe myopia
  • Age > 45 years
  • Prolonged use of steroids
  • Previous eye injury
20
Q

Trace the circulation of aqueous humor in the eye?

A
  • Aqueous humor is secreted at the ciliary body circulates through the posterior and anterior chambers before it is reabsorbed through the canal of Achlemm
21
Q

What are the functions of the vitreous humor in the eye?

A
  • Support function
  • metabolic “carrier” for retina
  • Gelatinous mass (not fluid)
  • Low Concentration of macromolecules
  • Fibrillar network - largely proteoglycans, hyaluronic acid, and collagen
22
Q

What is the composition mainly composed of?

A
  • Water (99%)
  • Collagen (mostly type II) - form sparse network
  • Proteoglycans (especially chondroitin sulphate)
  • Hyaluronic acid
  • Ascorbic acid (10 x plasma)
23
Q

In the vitresous humour structure what holds the collagen fibrils apart?
- What holds these apart?

A
  • proteoglycan bridges

- hyaluronic acid holds bridges apart while maintaining sparse meshwork

24
Q

What is the makeup of the lens?
Is there blood supply to the lens?
What are some other feature of the lens?

A
  • Mostly water (66%) and proteins (33%)
  • No blood supply (low in oxygen)
  • High glutathione content, high cholesterol content, grows throughout life and cells don’t turn over, receives nutrients and voids wastes via aqueous humor.
25
Q

In what direction do lens grow?

What is the problem with increases in weight and thickness?

A
  • Lens grow from the periphery

- decreased elasticity

26
Q

What is the main source of energy production at the lens?

A
  • Largely anaerobic glycolysis. High level of pentose phostphate pathway, Anti-oxidant system is especially important since the lens does not turnover
27
Q

In the lens what is glucose converted to during periods of high glucose concentrations?

A
  • Sorbitol which also depletes NADPH
28
Q

What is the only known disease of the lens and what is its is the reason for the manifestation of vision impairment?

A
  • Cataracts ( 2 types- Diabetic cataracts and senile cataracts)
  • Aggregation of lens proteins
29
Q

What are risk factors for cataract formation?

A
  • diabetes
  • galactosemia
  • Radiation
  • smoking
  • high fat diet
  • certain drugs
  • genetic
30
Q

What is the mechanisms of cataract formation?

A
  • osmotic damage
  • oxidative damage
  • Damage by radiation
  • protein modification
31
Q

How does osmotic damage occur during diabetic cataracts?

A
  • Increased [glucose] leads to increased production of sorbitol
  • Osmotic uptake of water
  • Crystallins become hydrated and aggregate, scattering light.
  • Analogous mechanism in galactosemia
32
Q

With cataracts how does oxidative damage occur?

A
  • oxidation of sugars to dicarbonyl compounds that may cause :
    • oxidation of glutathione
    • oxidation of protein -SH groups
    • Inhibition of pentose phosphate pathway
33
Q

With cataract formation what damage does ionizing radiation do?

A
  • [Glutathione] decrease
  • [Calcium] increase
  • Promotes binding of 43 kD protein to plasma membrane
  • Crystallins bind to protein forming light scattering aggregates
34
Q

What are the main features of senile cataract formation?

A
  • reduced glutathione levels
  • modification of lens permeability
  • modification of lens proteins
35
Q

What is the main features that protect the environment of the retina?

  • What is the main form of energy production for the retina?
  • There are high levels of mitochondria in the retina except where?
A
  • Blood-retinal barrier
  • Anaerobic glycolysis and oxidative metabolism
  • The fovea
36
Q

What anti-oxidants are popular in high levels in the retina?

A
  • Vitamins A and C
37
Q

What is the difference between dry and wet age- related macular degeneration?

A
  • Dry and (more common)
    • -> slow progression, and cells of the macula slowly break down.
  • Wet AMD:
    • -> Rapid progression, blood vessels grow beneath macula- fragile and leak
38
Q

What are the treatments of dry vs. wet age related macular degeneration?

A
  • Dry AMD: no treatments
  • Wet AMD: Injection of VEGF inhibitors - good data shows arrest of progression - stops angiogenesis. Laser treatment to arrest or retard progression

Neuroanatomy Exam 1 (4 decks)

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