Biochem- The eye Flashcards
Where is anaerobic glycolysis the main source of energy in the eye? How about oxidative metabolism?
- Anaerobic in the lens
- Aerobic in the retina and cornea (but only slightly)
An accumilation of what substance will cause corneal clouding?
Glycosaminoglycans
(Hurler and Sly syndromes)
How is water balance within the cornea maintained?
-by the hypertonic nature of the aqueous humor and active pumping of HCO3- out of the cornea
What is the purpose of VEGFR-3 on the anterior epithelial layer of the cornea?
-prevents the growth of blood vessels into the cornea by neutilizing growth factors
Why is NADPH so important in the cornea?
-to prevent or reduce photo-oxidation through the GSH (glutathione) reductase pathway
How does glucose get to the cornea> How about oxygen?
- Glucose diffuses through the aqueous humor
- Oxygen diffuses through the anterior surface through the tears
How does prolonged contact lens wear cause corneal swelling?
-causes hypoxia beneath the lens which results in increased lactate production and decreased corneal pH
What is the main purpose of the aqueous humor?
-to bring nutients to the cornea and lense and remove end products to the blood stream
How is aqueous humor secreted? Reabsorbed?
- Secreted by ciliary process through secretion of Na, Cl and bicarb which water follows. Glucose, AA, and ascorbic acid are actively transported into the aqueous humor.
- it drains into the blood stream through the canal of schlemm
Is the vitreous humor a free flowing fluid?
no. it is a gelatinous mass
What is the major makeup of the vitreous humor?
99% water
-mostly Type II collagen, proteoglycans, and hylauronic acid
What is posterior vitreous attachment?
-with old age the vitreous becomes more liquid like and can separate from the retina
(floaters and flashes of light)
What is the most common cause of glaucoma?
-increased IOP due to a decrease in the drainage of the aqueous humor
Can glaucome result from someone who has a normal IOP?
Yes, it is called normal tension glaucoma
What is the most common form of glaucoma?
primary open angle glaucoma–> decrease in the rate of drainage of aqueous humor
How is open angle glaucoma most commonly treated?
With the use of:
- protaglandin analogues (Xalantan)
- ß-blockers (Timolol)
- and Cholinergic agonists for acute attacks (Pilocarpine)
How would a carbonic anhydrase inhibior help in the treatment of open angle glaucoma?
-Decreased secretion of bicarb results in decreased aqueous humor production
What is the cuase of closed angle glaucoma? How is it treated?
- the outer edge of the iris protrudes over the drainage canals
- surgical removal of that part of the iris
What are som erisk factors for glaucoma?
- African
- family history
- diabetes
- severe myopia
- steroid use
- previous eye injury
How does the lens receieve nutients/dump waste?
-through the aqueous humor
What is a cataract? What are some risk factors?
- opacity of the lense caused by an aggregation of proteins
- diabetes, galactosemia, radiation, smoking, high fat dies, genetic
How does excess sugar in the lense contribute to cataracts?
- Glucose is reduced to sorbitol
- sorbitol accumilation leads to an increased uptake of water–> when the crystallins become more hydrated they become less soluble in the lens
What causes cataract formation in a galactosemic infant?
- galactose is reduced to galactitol
- Galactitol has the same effect as sorbitol and draws water into the lense–> reduced crystalline solubility
What is the first sign of cataract formation in an individual who has recieved radiation (x-ray)?
-Sharp decrease in reduced glutathione
How does oxidative damage lead to the formation of cataracts?
Oxidation of sugars produces compound that can cause the oxidation of glutathione and other proteins and inhibit the pentose phosphate pathway.
What is the cause of senile cataracts?
- Old-ness
- modification and breakdown of proteins, reduction in glutathione levels and changes in membrane permeabilities.
What is the major inherited mutation leading to cataract formation?
-premature formation from mutations in chaperone proteins which results in misfolded lens proteins
What areas of the retina are involved with oxidative metabolism? How about anaerobic metabolism?
- The vascular portions (oxidative)
- Fovea has no vessels as well as the outer segments of rods and cones (anaerobic)
What is the leading cause of blindness in the eldery?
-Age related macular degeneration (AMD)
What are the two forms of AMD?
Wet and Dry
What is Dry AMD?
-cells of the macula slowly breakdown and develop yellow deposits called Drusen
What is wet AMD?
blood vessels grow in beneath the macula and leak blood
What is the treatment for Dry AMD? how about Wet AMD?
-Dry: no effective treatment (some antioxidant vitamins and minerals may help)
Wet: injections of VEGF inhibitors may arrest the progression of the disease (also Laser)
