Biochem- Metabolic Eye Flashcards
(198 cards)
1
Q
What 2 subtances composes the cornea?
A
Collagen type I and proteoglycans
2
Q
What if there is an accumulation of GAGs in the cornea?
A
Cleauding
3
Q
What type of metabolism does the corneea use to get energy (aerobic or anaerobic)?
A
Anaerobic mainly
4
Q
Energy comes from which substance since the cornea is anaerobic?
A
Aqueous humor
5
Q
What are the 2 things that make up the lens?
A
water and crystallin proteins
6
Q
What is the fxn of crystallin proteins?
A
increase transparency
7
Q
What type of metabolism does the lens use to get energy (aerobic or anaerobic)?
A
Anaerobic
8
Q
Is the retina part of the CNS or PNS?
A
CNS
9
Q
The retina has a pretty good vascular supply except where?
A
The fovea
10
Q
What type of metabolism does the retina use to get energy (aerobic or anaerobic)?
A
Mostly anaerobic metabolism but also oxidative metabolism because it is much more efficient
11
Q
Wearing contacts cuts off what supply?
A
Oxygen diffusion to the cornea
12
Q
Cutting off O2 supply causes what metabolic changes?
A
increase in lactate and decrease in pH
13
Q
The increase in lactate and decrease in pH cause what changes to the cornea?
A
lactate causes corneal swelling –> increased thickness and disruption of fiber arrangement –> cloudiness
(lol great thing I wore contacts for 10 years)
14
Q
What is the chemical composition of aqueous humor?
A
Na+, bicarbonate, Cl-, glucose, amino acids, and ascorbic acid
15
Q
Is aqueous humor free flowing?
A
yes
16
Q
What are the 2 roles of aqueous humor?
A
Brings: nutrients to the cornea and lens
Removes: end products from the cornea and lens to the blood stream
17
Q
What is the chemical composition of vitreous humor?
A
99% water, type II collagen, proteoglycans (chondroitin sulphate), and hyaluronic acid
18
Q
Is vitreous humor free flowing?
A
Nope
19
Q
What is the role of vitreous humor?
A
Keep the retina in palce
20
Q
What 2 things does the eye depend on for antioxidants?
A
The eye depends on both ascorbic acid (vitamin C) and reduced glutathione to prevent and/or reverse photo-oxidation
21
Q
How do we get vitamin C?
A
;-)
22
Q
Which molecule is needed to regenerate reduced glutathione?
A
NADPH
23
Q
True or False: Glaucoma is an increase in intra-ocular pressure, causing damage to the eye.
A
FALSE
24
Q
So what is glaucoma?
A
Glaucoma is an eye disease in which the optic nerve is damaged. It is NOT synonymous with increased intra-ocular pressure because there can be normal or low tension glaucomas as well. Increased intra-ocular pressure, however, is the most common cause of glaucoma.
25
What causes an increase in intra-ocular pressure?
a decrease in drainage (as seen with primary open angle glaucoma, the most common form)
26
Who are the patient populations most prone to cataract formation?
Diabetics and galactosemic infants
27
What are the 3 mechanisms to cataracts?
osmotic, oxidation, and modification of proteins.
28
What causes formation of cataracts through osmotic changes?
. Sugars are reduced to sorbitol --> sorbitol causes osmotic uptake of water which hydrates crystallins (which are normally dehydrated and found on the surface of the lens in order to increase transparency) --> hydrated crystallins aggregate (cataract formation) and scatter light.
29
What causes formation of cataracts through oxidation changes?
sugars are oxidized to produce dicarbonyl compounds which oxidizes glutathione and inhibits the pentose pathway which is used to produce NADPH, a coenzyme of glutathione reductase --> protein aggregation
30
What causes "wet" AMD?
caused by the growth of blood vessels underneath the macula and then rupturing because they are fragile
31
What causes "dry" AMD?
a slow break down of the macula and yellow deposits known as drusens are left behind
32
So what are the main differences between wet and dry AMD on clinical exam?
Wet AMD is acute, more serious, and rapidly progressing. It can also cause complete vision loss within a few days. Although it is the more serious form of AMD, it can be treated with an injection of VEGF inhibitors.
Dry AMD on the other hand progresses very slowly and generally only impairs vision. It cannot be treated
33
I'm now gonna copy/paste some Q&A's from ray's section of the module. There are repeats.
What is the major fuel of the eye?
Glucose
34
In the lens and cornea, how is most of the ATP produced?
By anaerobic glycolysis
35
In the retina, how is ATP produced?
By both anaerobic glycolysis and oxidative metabolism.
36
Why is there little or no oxidative metabolism in the lens or cornea?
Blood vessels and mitochondria absorb light and interfere with vision.
37
What are the layers of the cornea?
From the outermost layer to innermost: ABCDE (Anterior (corneal) epithelium, Bowman’s layer, Corneal stroma, Descemet’s membrane, and Corneal Endothelium)
38
What syndromes cause corneal clouding?
Hurler (MPS I) and Sly (MPS VII) syndromes due to the accumulation of glycosaminoglycans.
39
What is the normal water content of the cornea?
78%
40
How is this water content maintained?
Active pumping of HCO3- out of the cornea.
41
How do GAGs cause clouding?
GAGs increase water uptake disrupt fiber arrangement
42
How is clarity sustained in the cornea?
Large amounts of VEGFR-3 in the anterior epithelial layer
43
What is the function of VEGFR-3?
Prevents growth of blood vessels by binding to and neutralizing growth factors that stimulate angiogenesis.
44
Why is ATP important?
Mainly ion transport for transparency.
45
How is glucose used in the cornea?
40% glycolysis (35% anaerobic, 5% oxidative glycolysis) 60% pass through the pentose phosphate pathway to produce NADPH (used to prevent or reverse photo-oxidation w/ reduced gluthathione).
46
Why do we need an anti-oxidant system?
Large amounts of oxygen via diffusion allows for photo-oxidation in the cornea and lens.
47
What is the function of NADPH in this anti-oxidant system?
NADPH is the coenzyme of glutathione reductase which is used to keep glutathione reduced.
48
Why are tears important?
It provides the cornea (which is avascular) with oxygen via diffusion.
49
What is the effect of prolonged wearing of contact lenses?
Hypoxic conditions underneath the lens (↑lactate and ↓corneal pH)
50
What is the effect of increased lactate?
It will diffuse from the epithelium into the stroma and cause corneal swelling due to osmosis.
51
What is the function of the aqueous humour?
It maintains the intra-ocular pressure, brings nutrients (mostly glucose, amino acids, and ascorbic acid via facilitated diffusion or active transport) to the cornea and lens, and removes end products to the blood stream.
52
Where does the aqueous humour come from?
Secreted by ciliary processes into the posterior chamber.
53
How does the aqueous humour flow?
Posterior chamber pupil anterior chamber trabecular meshwork Schlemm’s canal.
54
What is the vitreous humour?
Non free flowing gelatinous mass made up of 99% water held together by collagen type II, proteoglycans (mainly sulphate), and hyaluronic acid.
55
What is the function of the vitreous humor?
To keep the retina in place.
56
What is posterior vitreous detachment (PVD)?
A common and normal cause of occasional flashing lights and floaters in the visual field.
57
What causes PVD?
With age, the vitreous humour becomes more liquid-like increasing the risk of separation from the retina.
58
When is PVD serious?
Frequent flashing and floaters indicate retinal detachment and requires immediate attention.
59
What is glaucoma?
Optic nerve damage.
60
What is the main cause of glaucoma?
Increased intra-ocular pressure.
61
What normally causes an increase in intra-ocular pressure, increased aqueous humor production or a decrease in drainage?
Decrease in drainage.
62
What is the most common form of glaucoma?
Primary open angle glaucoma
63
Africans are most susceptible to which form of glaucoma, open angle or closed?
Open.
64
What is it most commonly treated with?
Prostaglandin analogs which increase drainage (latanoprost (XALATAN) or B-blockers which reduces the secretion of aqueous humour (timolol (TIMOPTIC) or betaxolol.
65
What is used to treat acute attacks?
Cholinergic agonists such as pilocarpine which restores resorption and outflow of aqueous humour.
66
How do carbonic anhydrase inhibitors work?
They decrease the rate of bicarbonate production decrease aqueous humour secretion.
67
What are some carbonic anhydrase inhibitors?
Acetazolamide (DIAMOX), methazolamide (NEPTAZANE), and dorzolamide (TRUSOPT, used topically only).
68
What is a combination of B-blocker and carbonic anhydrase inhibitor used frequently?
COSOPT which is timolol and dorzolamide.
69
What is closed-angle glaucoma?
Less common form of glaucoma in which the outer edge of the iris protrudes over the drainage canal.
70
How is closed-angle glaucoma treated?
By surgically removing the outer edge of the iris.
71
What are risk factors for glaucoma?
Africans (primary open angle), family history, diabetes, myopia, >45 y/o, prolonged steroid use, eye injury (secondary glaucoma).
72
What is secondary glaucoma?
Glaucoma with an identifiable cause of increased optic pressure (injury, steroid use)
73
What is the lens made up of?
Mostly water and proteins
74
What separates the aqueous humor from the vitreous humor?
The lens.
75
What brings the avascular lens nutrients and removes wastes?
The aqueous humor.
76
Where does protein synthesis take place on the lens?
The periphery
77
Are these proteins, , and crystallins, normally hydrated or dehydrated?
Dehydrated.
78
What is the function of these proteins?
They increase transparency with increased concentration but too much decreases transparency (cataract formation).
79
Besides reduced glutathione (~20mM), what is another important anti-oxidant?
Ascorbic acid (~2 mM)
80
What is the major source of cholesterol in the lens membrane?
De novo synthesis.
81
What is cataract formation?
An opacity of the lens due to aggregation of lens proteins.
82
Who is prone to cataracts?
Diabetic patients and galactosemic infants.
83
What happens to monosaccharides in the lens?
They are oxidized and reduced.
84
What are the effects of sugar reduction?
The reduction of sugar produces sorbitol and depletes NADPH (part of the anti-oxidation system)
85
What does sorbitol do to the lens?
It causes osmotic uptake of water which hydrates crystallins.
86
What are the consequences of hydrated crystallins?
Aggregation and scattering of light.
87
What are the effects of sugar oxidation?
Production of dicarbonyl compounds oxidizes gluthathione and inhibits the pentose phosphate pathway (used to produce NADPH).
88
How do X-rays increase the risk of cataract formation?
Decreased concentration of reduced glutathione increase in cellular calcium calcium ions promote binding of a protein to the membrane creates a focus for aggregation of crystallins.
89
What is the cause of senile cataracts?
Age-related modification and breakdown of lens proteins. This is thought to indirectly reduce glutathione levels.
90
What is the cause of “premature” cataracts?
Inherited mutations; mutated chaperones misfold lens proteins.
91
Which of the following is an extension of the brain: cornea, lens, or retina?
Retina.
92
Which part of the retina is not vascularized?
The area where visual acuity is greatest.
93
Which two vitamins are present in high levels in the retina?
Vitamin A (visual cycle) and vitamin C (prevention/reversal of photo-oxidation).
94
What is the leading cause of blindness in the elderly?
Age-related macular degeneration (AMD)
95
What is dry AMD?
Cells of the macula slowly breaks down and gets characteristic yellow deposits known as drusen.
96
What is wet AMD?
As its name suggests, blood vessels growth under the macula, rupture, and leak blood.
97
How is wet AMD different from dry AMD?
Wet AMD is acute; vision can be lost within days. Dry AMD progresses very slowly and generally only reduces vision.
98
Which AMD cannot be treated?
Dry.
99
What is the treatment for wet AMD?
Injection of VEGF inhibitors.
100
What is the treatment for wet AMD?
Injection of VEGF inhibitors.
101
What if there is an accumulation of GAGs in the cornea?
Cleauding
102
What type of metabolism does the corneea use to get energy (aerobic or anaerobic)?
Anaerobic mainly
103
Energy comes from which substance since the cornea is anaerobic?
Aqueous humor
104
What are the 2 things that make up the lens?
water and crystallin proteins
105
What is the fxn of crystallin proteins?
increase transparency
106
What type of metabolism does the lens use to get energy (aerobic or anaerobic)?
Anaerobic
107
Is the retina part of the CNS or PNS?
CNS
108
The retina has a pretty good vascular supply except where?
The fovea
109
What type of metabolism does the retina use to get energy (aerobic or anaerobic)?
Mostly anaerobic metabolism but also oxidative metabolism because it is much more efficient
110
Wearing contacts cuts off what supply?
Oxygen diffusion to the cornea
111
Cutting off O2 supply causes what metabolic changes?
increase in lactate and decrease in pH
112
The increase in lactate and decrease in pH cause what changes to the cornea?
lactate causes corneal swelling --> increased thickness and disruption of fiber arrangement --> cloudiness
(lol great thing I wore contacts for 10 years)
113
What is the chemical composition of aqueous humor?
Na+, bicarbonate, Cl-, glucose, amino acids, and ascorbic acid
114
Is aqueous humor free flowing?
yes
115
What are the 2 roles of aqueous humor?
Brings: nutrients to the cornea and lens
Removes: end products from the cornea and lens to the blood stream
116
What is the chemical composition of vitreous humor?
99% water, type II collagen, proteoglycans (chondroitin sulphate), and hyaluronic acid
117
Is vitreous humor free flowing?
Nope
118
What is the role of vitreous humor?
Keep the retina in palce
119
What 2 things does the eye depend on for antioxidants?
The eye depends on both ascorbic acid (vitamin C) and reduced glutathione to prevent and/or reverse photo-oxidation
120
How do we get vitamin C?
;-)
121
Which molecule is needed to regenerate reduced glutathione?
NADPH
122
True or False: Glaucoma is an increase in intra-ocular pressure, causing damage to the eye.
FALSE
123
So what is glaucoma?
Glaucoma is an eye disease in which the optic nerve is damaged. It is NOT synonymous with increased intra-ocular pressure because there can be normal or low tension glaucomas as well. Increased intra-ocular pressure, however, is the most common cause of glaucoma.
124
What causes an increase in intra-ocular pressure?
a decrease in drainage (as seen with primary open angle glaucoma, the most common form)
125
Who are the patient populations most prone to cataract formation?
Diabetics and galactosemic infants
126
What are the 3 mechanisms to cataracts?
osmotic, oxidation, and modification of proteins.
127
What causes formation of cataracts through osmotic changes?
. Sugars are reduced to sorbitol --> sorbitol causes osmotic uptake of water which hydrates crystallins (which are normally dehydrated and found on the surface of the lens in order to increase transparency) --> hydrated crystallins aggregate (cataract formation) and scatter light.
128
What causes formation of cataracts through oxidation changes?
sugars are oxidized to produce dicarbonyl compounds which oxidizes glutathione and inhibits the pentose pathway which is used to produce NADPH, a coenzyme of glutathione reductase --> protein aggregation
129
What causes "wet" AMD?
caused by the growth of blood vessels underneath the macula and then rupturing because they are fragile
130
What causes "dry" AMD?
a slow break down of the macula and yellow deposits known as drusens are left behind
131
So what are the main differences between wet and dry AMD on clinical exam?
Wet AMD is acute, more serious, and rapidly progressing. It can also cause complete vision loss within a few days. Although it is the more serious form of AMD, it can be treated with an injection of VEGF inhibitors.
Dry AMD on the other hand progresses very slowly and generally only impairs vision. It cannot be treated
132
What is the major fuel of the eye?
Glucose
133
In the lens and cornea, how is most of the ATP produced?
By anaerobic glycolysis
134
In the retina, how is ATP produced?
By both anaerobic glycolysis and oxidative metabolism.
135
Why is there little or no oxidative metabolism in the lens or cornea?
Blood vessels and mitochondria absorb light and interfere with vision.
136
What are the layers of the cornea?
From the outermost layer to innermost: ABCDE (Anterior (corneal) epithelium, Bowman’s layer, Corneal stroma, Descemet’s membrane, and Corneal Endothelium)
137
What syndromes cause corneal clouding?
Hurler (MPS I) and Sly (MPS VII) syndromes due to the accumulation of glycosaminoglycans.
138
What is the normal water content of the cornea?
78%
139
How is this water content maintained?
Active pumping of HCO3- out of the cornea.
140
How do GAGs cause clouding?
GAGs increase water uptake disrupt fiber arrangement
141
How is clarity sustained in the cornea?
Large amounts of VEGFR-3 in the anterior epithelial layer
142
What is the function of VEGFR-3?
Prevents growth of blood vessels by binding to and neutralizing growth factors that stimulate angiogenesis.
143
Why is ATP important?
Mainly ion transport for transparency.
144
How is glucose used in the cornea?
40% glycolysis (35% anaerobic, 5% oxidative glycolysis) 60% pass through the pentose phosphate pathway to produce NADPH (used to prevent or reverse photo-oxidation w/ reduced gluthathione).
145
Why do we need an anti-oxidant system?
Large amounts of oxygen via diffusion allows for photo-oxidation in the cornea and lens.
146
What is the function of NADPH in this anti-oxidant system?
NADPH is the coenzyme of glutathione reductase which is used to keep glutathione reduced.
147
Why are tears important?
It provides the cornea (which is avascular) with oxygen via diffusion.
148
What is the effect of prolonged wearing of contact lenses?
Hypoxic conditions underneath the lens (↑lactate and ↓corneal pH)
149
What is the effect of increased lactate?
It will diffuse from the epithelium into the stroma and cause corneal swelling due to osmosis.
150
What is the function of the aqueous humour?
It maintains the intra-ocular pressure, brings nutrients (mostly glucose, amino acids, and ascorbic acid via facilitated diffusion or active transport) to the cornea and lens, and removes end products to the blood stream.
151
Where does the aqueous humour come from?
Secreted by ciliary processes into the posterior chamber.
152
How does the aqueous humour flow?
Posterior chamber pupil anterior chamber trabecular meshwork Schlemm’s canal.
153
What is the vitreous humour?
Non free flowing gelatinous mass made up of 99% water held together by collagen type II, proteoglycans (mainly sulphate), and hyaluronic acid.
154
What is the function of the vitreous humor?
To keep the retina in place.
155
What is posterior vitreous detachment (PVD)?
A common and normal cause of occasional flashing lights and floaters in the visual field.
156
What causes PVD?
With age, the vitreous humour becomes more liquid-like increasing the risk of separation from the retina.
157
When is PVD serious?
Frequent flashing and floaters indicate retinal detachment and requires immediate attention.
158
What is glaucoma?
Optic nerve damage.
159
What is the main cause of glaucoma?
Increased intra-ocular pressure.
160
What normally causes an increase in intra-ocular pressure, increased aqueous humor production or a decrease in drainage?
Decrease in drainage.
161
What is the most common form of glaucoma?
Primary open angle glaucoma
162
Africans are most susceptible to which form of glaucoma, open angle or closed?
Open.
163
What is it most commonly treated with?
Prostaglandin analogs which increase drainage (latanoprost (XALATAN) or B-blockers which reduces the secretion of aqueous humour (timolol (TIMOPTIC) or betaxolol.
164
What is used to treat acute attacks?
Cholinergic agonists such as pilocarpine which restores resorption and outflow of aqueous humour.
165
How do carbonic anhydrase inhibitors work?
They decrease the rate of bicarbonate production decrease aqueous humour secretion.
166
What are some carbonic anhydrase inhibitors?
Acetazolamide (DIAMOX), methazolamide (NEPTAZANE), and dorzolamide (TRUSOPT, used topically only).
167
What is a combination of B-blocker and carbonic anhydrase inhibitor used frequently?
COSOPT which is timolol and dorzolamide.
168
What is closed-angle glaucoma?
Less common form of glaucoma in which the outer edge of the iris protrudes over the drainage canal.
169
How is closed-angle glaucoma treated?
By surgically removing the outer edge of the iris.
170
What are risk factors for glaucoma?
Africans (primary open angle), family history, diabetes, myopia, >45 y/o, prolonged steroid use, eye injury (secondary glaucoma).
171
What is secondary glaucoma?
Glaucoma with an identifiable cause of increased optic pressure (injury, steroid use)
172
What is the lens made up of?
Mostly water and proteins
173
What separates the aqueous humor from the vitreous humor?
The lens.
174
What brings the avascular lens nutrients and removes wastes?
The aqueous humor.
175
Where does protein synthesis take place on the lens?
The periphery
176
Are these proteins, , and crystallins, normally hydrated or dehydrated?
Dehydrated.
177
What is the function of these proteins?
They increase transparency with increased concentration but too much decreases transparency (cataract formation).
178
Besides reduced glutathione (~20mM), what is another important anti-oxidant?
Ascorbic acid (~2 mM)
179
What is the major source of cholesterol in the lens membrane?
De novo synthesis.
180
What is cataract formation?
An opacity of the lens due to aggregation of lens proteins.
181
Who is prone to cataracts?
Diabetic patients and galactosemic infants.
182
What happens to monosaccharides in the lens?
They are oxidized and reduced.
183
What are the effects of sugar reduction?
The reduction of sugar produces sorbitol and depletes NADPH (part of the anti-oxidation system)
184
What does sorbitol do to the lens?
It causes osmotic uptake of water which hydrates crystallins.
185
What are the consequences of hydrated crystallins?
Aggregation and scattering of light.
186
What are the effects of sugar oxidation?
Production of dicarbonyl compounds oxidizes gluthathione and inhibits the pentose phosphate pathway (used to produce NADPH).
187
How do X-rays increase the risk of cataract formation?
Decreased concentration of reduced glutathione increase in cellular calcium calcium ions promote binding of a protein to the membrane creates a focus for aggregation of crystallins.
188
What is the cause of senile cataracts?
Age-related modification and breakdown of lens proteins. This is thought to indirectly reduce glutathione levels.
189
What is the cause of “premature” cataracts?
Inherited mutations; mutated chaperones misfold lens proteins.
190
Which of the following is an extension of the brain: cornea, lens, or retina?
Retina.
191
Which part of the retina is not vascularized?
The area where visual acuity is greatest.
192
Which two vitamins are present in high levels in the retina?
Vitamin A (visual cycle) and vitamin C (prevention/reversal of photo-oxidation).
193
What is the leading cause of blindness in the elderly?
Age-related macular degeneration (AMD)
194
What is dry AMD?
Cells of the macula slowly breaks down and gets characteristic yellow deposits known as drusen.
195
What is wet AMD?
As its name suggests, blood vessels growth under the macula, rupture, and leak blood.
196
How is wet AMD different from dry AMD?
Wet AMD is acute; vision can be lost within days. Dry AMD progresses very slowly and generally only reduces vision.
197
Which AMD cannot be treated?
Dry.
198
What is the treatment for wet AMD?
Injection of VEGF inhibitors.
