L47 Biochem of the Eye

Question 1

structures in the eye and patterns

Answer 1

Cornea, Aqueous Humor, Lens, Retina

—»» more mitochondria, more respiration, less anaerobic glycolysis

Question 2

Cornea and Carb Metabolism

Answer 2

Cornea is transparent external protective layer as a window for light

bathed by tears and aqueous humor

epithelial cells are non keratinized cells
-healthy tissue maintained by Retinol (vitamin A and its derivatives)

glucose metabolism:

• 65% HMP shunt: highest in body (perm to O2 leading to formation of ROS)
• 30% anaerobic glycolysis
• 5% complete oxidation to CO2 and H2O (TCA/ETC)

CC: severe vitamin A def implies lack of mucous secretion and drying of epithelieal cells

• Bitots spotsL keratinized surface with excess keratin synthesis
• Xeropthalmia: pathological dryness of conjunctiva and cornea. (common cause of blindness in dev countries)

Question 3

Lens and carb metabolism

2 CC

Answer 3

brings images to focus on retina

grows from the periphery throughout life and differentiates new fibers, so older les fibers are in the central nucleus

• composed of H2O and protiens (35%)
• alpha, beta and gamma crystalin are chaperones assisting with folding. Gamma is temp sensitive precipitating to form cold cataracts
• AVASCULAR-nutrients and waste from aqueous humor
• 85% anaerobic glycolysis
• 10% HMP shunt
• 5% complete oxidation ot CO2 and H2O-TCAETC

Polyl pathway (minor path of glucose since aldose reductase has much higher Km than hexokinase)

• in diabetics hyperglycemia increases production of sorbitol via aldose reductase and consumes NADPH.
• sorbitol is osmotically active (increases osmotic pressure)-> precipitation of lens crystalline leading to diabetic cataracts

cataracts: lens opacities, lens protiens need to maintain their native state
- #1 cause of blindness worldwide. Senile of diabetic

CCL human lens increases in weight and thickness with age, leading to a loss of near vision, called PRESBYOPIA

Question 4

Aqueous humor and intraocular pressure

Answer 4

clear watery liquid in anterior and posteror chambers

• generates intraocular pressure
• supplies nutrients to and carris away wastes from (cornea, lens, trabecular meshwork, anterior vitrious.

continutally processed every two hours by ciliarry processes

DRAW CYCLE
-into posterior chamber –> anterior chamber –> trabecular meshwork –> schlemms canal (exit)

ciliary epithelium covers the surface of siliary process: formed by pigmented and non pigmented epithelial cells.
-tight junctions between Non Pig Ep cells form the antior blood aqueous barrier. Keeps large molecules out and maintains clarity of AH

AH formed by ultrafiltration of plasma, mod in NPE and active secretion of soluntes into the post chamber through the NPE

NaK ATPase pump is MOST IMPORTANT PROCESS in the formation of aqueous humor. Active transport of Na balances with HCO3- produced by carbonic anhydrase within NPE
-that was ultrafiltration

CC: aq humor prod balanced with drainage from ant chaber to ensure constant intraocular P

• GlaucomaL failure of ad drainage, high intraocular P,and retinal neuron damage
• treat: Acetazolamide is potent inhibitor of carbonic anhydrase. Lowers concentration of HCO3- in the aq humaor , therefore lower Na and decreased P

Question 5

Retina and Carb met

Answer 5

Retina: innermost layer of the eye, contains light sensitive neurons (photoreceptors)
-multilayered, multicell typed

lighe enters eye and passes optic nerve fiber, ganglion neurons, bipolar neurons before it come to outer segment of photoreceptors

pigemented epithelial layerL rods and cones

• different photopigment
• distribution across retina, sensitiveity to light, pattern oneuronal connection
• AVASCULAR
• lots os MITOCHONDRIA active resp. aerobic and anaerobic glycolysis

outer segmentL 100 membranous discs, densely packed with light sensitive photoreceptors pigement (start of signal trans)

inner segmentL nucleus and mito

sunaptic terminal: contacting withtoer neurons by releaseing GLUTAMATE

Question 6

photoreceptors

Answer 6

pigment= protein=opsin + 11 cis retinal

rods: rhodopsin: night, peripheral

cons, color, acute
-red blue or green, similar but different from opsin in rhodopsin

Question 7

color blindness

Answer 7

protanopia (red cone)
deuteranopia/daltism (green cone)
tritanopia (blue cone)
-red and green cone encoded on x chromosome

retinitis pigmentosumL group of hereditary eye disorders, with gradual deg of photoreceptors
-initial diff seeing at night followd by loss of puerperal and then color

mutations in 30 or more genes (most common in rhodopsin)

Question 8

light and dard states or rod phototransduction cascade

Answer 8

resting: darkL inactive -30mV

activeL lightL active: cascade!!inward flow of Na and Ca, Rods become hyperpolarized in light@
-65mV
release of NT Glutamate is dependant of the Ca channels

HYPERPOLARIZATION REDUCSES TEH NUMBER OF OPEN CHANNELS AND DECREASES RATE OF GLUTAMATE RELEASE

changes in light are changes in membrane P

Question 9

Lutein and zeaxanthin

Answer 9

macula is most sensitiveL center of macula is fovea centralisL million of tightly packed cones

macula degeneration leads to blindess…NO CURE

age increases MD risk

high levels of lutein and zeanthin are gound in macula or retina
-carotenoids-Xanthophylls, leutin and zeaxanthin

Carotenoids cannot be produced by humans must be in diet,.

higher intake of lutein and zeaxanthin associates with low risk of AMD
-they protect against photodamage by fildering out glue light, high engery visible light,
protect photoreceptor membraes from oxidation
protect blood vessels