Quiz 1 (Introduction, Ocular Fluids, Crystallins, & Collagen)

What is the best way to describe the effects of post-translational modifications in the lens?

They can have both protective and degenerative effects

When comparing normal lens proteins to cataractous lens proteins, what is seen?

Major increase in insoluble proteins in the cataractous lens

When examining the corneal stroma and scleral collagen, what is difference that accounts for the differed light opacities?

The corneal stroma collagen is highly uniformly arranged and organized, allowing it to be totally clear

In the cornea, the size of primary type I collagen...

depends on the amount of type V fibers that are present (if there's more type V, type I will be smaller)

The lattce structure of Descemet's membrane is attributed to

Type VIII Collagen

What percentage of our bodies are water?

60%

What percentage of an infant's body is water?

75%

How much blood does an adult have?

around 5L

How much blood does an 8 lb. baby have?

around 2.7L

How much blood does a pregnant woman have?

around 30-50% more than an average adult

What are the ocular-specific fluids?

Aqueous, vitreous, precorneal tears

How much of the eye is fluid?

about 80%

Is there normal metabolic activity in cells with 50% water?

No, there must be at least 60-65% water for normal activity to occur

What are the "nearest neighbors" of water?

Ammonia (NH3), hydrogen fluoride (HF), dihydrogen sulfide (H2S)

T/F: Water has a high boiling point

True

T/F: Water has a high melting point

True

T/F: Water has a high heat of vaporization

True

T/F: Water has high surface tension

True

Is water's dielectric constant high or low?

Relatively high for a molecule of its size

What compound has the highest dielectric constant?

Calcium copper titanate (CCTO) - over 10,000

What is dielectric constant?

A measure of a substance/material's ability to store electrical energy

What is another name for dielectric constant?

Relative permittivity

Are hydrogen bonds strong or weak?

Strong when there are many together, relatively weak alone

How much stronger is a covalent bond than a hydrogen bond?

About 25x

Are non-polar substances soluble in water?

No

What is the normal physiologic pH of blood?

7.33-7.45

What gases are carried in blood?

O2, N2, and CO2

What are the functions of blood in the eye?

Nourishment, waste disposal, generation of IOP, homeostasis of retinal functions

T/F: The lens has a direct supply of blood

False

Where is aqueous fluid produced?

Ciliary body

How is the retina nourished?

The choroid and the central retinal artery

The pumping activity of what two ATPases generates the aqueous fluid?

Na/K-ATPase and bicarbonate-ATPase

How many Na/K-ATPases are in each ciliary body cell?

800K-30M

What portion of the aqueous fluid is water?

99.9%

The aqueous is a source of _____________ for the lens

antioxidants

What nourishes the corneal endothelium, stromal keratocytes, corneal epithelium, and the lens?

The aqueous fluid

What is the IOP?

The balance between production and drainage of the aqueous fluid

Is the concentration of ascorbic acid in the aqueous fluid higher or lower than in blood?

higher

Is the concentration of bicarbonate in the aqueous fluid higher or lower than in blood?

unchanged

Is the concentration of globulin in the aqueous fluid higher or lower than in blood?

unchanged

What percentage of the vitreous fluid is water?

98-99.7%

As we age, does the vitreous get more or less gel-like?

Less

What causes the gel-like composition of the vitreous fluid?

Type II collagens and proteoglycans (hyaluronic acid)

What causes the vitreous to become less gel-like as we age?

Degredation of collagens

Is the concentration of bicarbonate in the vitreous fluid higher or lower than in blood?

unchanged

Is the concentration of glucose in the vitreous fluid higher or lower than in blood?

slightly lower

Is the concentration of potassium in the vitreous fluid higher or lower than in blood?

lower

What are the 4 functions of the precorneal tears?

wetting the corneal epithelium, creating a smooth surface, supplying oxygen to the cornea, and destroying bacteria via lysozyme

What are the 3 layers of the precorneal tears?

outer oily layer, aqueous layer, inner mucus layer

What area produces the surface oily layer of the precorneal tears?

The Meibomian glands

The aqueous layer makes up how much of the precorneal tears?

60%

What area produces the aqueous portion of the precorneal tears?

The lacrimal gland

Is the concentration of bicarbonate in the tear film higher or lower than in blood?

unchanged

Is the concentration of sodium in the tear film higher or lower than in blood?

slightly lower

Is the concentration of potassium in the tear film higher or lower than in blood?

MUCH higher (nearly 7x)

What is the average thickness of the adult human lens?

5mm

What is the average diameter of the adult human lens?

9mm

How many layers of epithelial cells are found in the outer edge of the lens?

one

Do the lens epithelia divide normally?

No, only when undergoing repair

What is the lens capsule composed of?

Type IV collagen and sulfated GAGs

Which portion of the lens regulates most of the homeostatic functions?

The lens epithelium

What are the average diameters of the lens fiber cells?

4-7 microns

What are the average lengths of the lens fiber cells?

up to 12mm

How are the lens fibers arranged?

Lengthwise from posterior to anterior poles

What protein makes up more than 90% of the lens?

Crystallins

What type of proteins are crystallins?

Water soluble

Do crystallins increase or decrease the index of refraction of the lens?

Increase

What type of proteins are ⍺-crystallins related to?

Heat shock proteins

What type of proteins are β-crystallins related to?

Bacterial spore coat proteins

Where all have crystallins been found?

Heart, brain, lung, retina, and cornea

What are the largest crystallins?

⍺-crystallins

What is the molecular wright of ⍺-crystallins?

750,000 d

What is the molecular weight of β-crystallins?

70,000 d

What is the molecular weight of γ-crystallins?

20,000 d

What type of crystallins are found in the lens epithelium?

Only ⍺-crystallins

What two types of crystallins have N-terminus acetylation?

⍺- and β-crystallins

What is the secondary structure of ⍺-crystallins?

⍺ helices and β pleated sheets

What is the secondary structure of β- and γ-crystallins?

β pleated sheets

What is the simplest form of crystallins?

γ-crystallins

What type of crystallin has chaperone activity?

⍺-crystallins

What are the age-related cataracts?

Cortical cataracts, nuclear cataracts, and posterior subcapsular cataracts

What is the "repeating triplet" of collagen?

Glycine-Proline-Hydroxyproline

What are class I collagens?

banded, fibrillar collagens

What are class II collagens?

FACIT collagen

What are class III collagens?

Those that are not attached to fibers such as anchoring rods

What is the most abundant type of collagen in the human body?

Type I

What type of collagen is the basis for cartilage?

Type II

Which GAG is found primarily in the central cornea?

Keratan sulfate

Which GAG is found primarliy in the peripheral cornea?

Dermatan sulfate

Are type V fibers acidic at the N- or C- terminus?

N-terminus

What types of collagen makes up Bowman's membrane?

types I, III, and VII

What types of collagen makes up Descemet's membrane?

types V, VIII, IX, and XII

Where are type II collagen fibers attached the strongest in the vitreous fluid?

The ciliary body and the posterior retina

Is there more collagen in the vitreous fluid or in the corneal stroma?

The corneal stroma

What GAG is found in the vitreous?

Hyaluronic acid

What is the non-collagenous area that associates with hyaluronate?

NC4