Quiz 4 Old Quiz Questions

In spite of ionic activity of stroma and aqueous (see table), effective osmolarity of Na+ is less in stroma than aqueous. This is because...

Most Na+ is bound to GAG in stroma

Colloidal osmotic pressure in cytoplasm is about 50% greater than that caused by proteins alone. this is because...

Proteins are negatively charged. To balance this, large number of cations (mainly Na+) are held by proteins on the same side of membrane as proteins

The tear is -30mV compared to stroma (0 mV) because of:

Cl- transport from stroma to tears

Epinephrine increases the transport of Cl- from stroma to tear via epithelial cells by

Forming Cl- conductance channels on apical membrane

Stroma is 75% water, which means

3.75 parts of water, 1 part of solid materials

One of the following is true: a. Ability for fluid to flow (to even out differences in hydration) is greatest in a tissue that has near dehydrated and less for tissue with near normal hydration b. Ability for fluid to flow (to even out differences in hydration) is in greatest in a tissue that has near normal hydration and less for swollen and dehydrated tissues

b. Ability for fluid to flow (to even out differences in hydration) is in greatest in a tissue that has near normal hydration and less for swollen and dehydrated tissues

One of the following statements is true: a. Ability of stroma to swell increases as hydration increases b. Ability of stroma to swell decreases as hydration increases

b. Ability of stroma to swell decreases as hydration increases

Swelling pressure is defined as

The pressure that must be exerted on the cornea to prevent it from increasing its volume when placed in saline solution.

The major stromal collagen of type I forms heterotypic fibrils with type V collagen. The postulated function of type V collagen in the fibril is:

1. The amino-terminal domains of the type V collagen regulates heterotypic collagen fibril diameter. 2. Type V collagens project externally to the fibril surface and block further accretion of collagen molecules.

Mouse corneal studies suggest that 5-10% of total cells in stroma are:

Three types of bone-marrow derived immune cells

One of the major stromal glycosaminoglycan is keratin sulfate. It is a polymer of repeating units of:

Galactose and N-acetyl glucosamine

The figure below shows the in vivo confocal microscopy back-scattered light intensity profile from central and temporal portions of a 25 year old normal cornea. The light scatter in the stromal region (between C and D) is due to:

Wavelength of light passing through is greater in nm relative to diameter (in nm) of collagen fibrils

Which statement is true: a. Dermatan sulfate is a polymer of repeating units of galactose and N-acetyl glucosamine. b. Keratan sulfate is polymer of repeating units of iduronic acid and N-acetylgalactosamine c. Keratan sulfate is a polymer of repeating units of galactose and N-acetyl glucosamine

Keratan sulfate is a polymer of repeating units of galactose and N-acetyl glucosamine

The regional differences in the corneal stroma for the proportion of the two types of corneal GAGs and the water-absorbing properties in these regions show:

Compared to anterior stroma, the posterior stroma contains more keratan sulfate relative to dermatan sulfate and water per gram dry weight

Corneas collapse 20% if proteoglycan is precipitated out with cetylpyridinium. This observation suggests that:

One function of proteoglycans is to provide volume to cornea and these are mostly space filling molecules Another function of proteoglycans is to provide viscoelastic property to cornea

The diagram is significant to demonstrate the contribution of stromal components (collagen and proteoglycans) to minimize light scatter to maintain corneal transparency. Which plays a major role in reducing the light scatter?

Equidistance arrangement of scatter from equidistance collagen fibers

Among different glycosaminoglycans, the two major ones that are found in the corneal stroma are:

Dermatan sulfate and keratan sulfate

Highest area of light scatter occurs in the temporal cornea (lower graph) where the indices of refraction is high. Identify that highest area in the lower graph

Air-tear interface of epithelium

On recording of voltage during [Cl-] transport in the cornea, it will show

Negative voltage in tear layer compared to stroma/epithelium

The active Cl- transport occurs from stroma to tears. This transport is under the influence of

1. Beta adrenergic agonists 2. cAMP production

Ability of fluid to flow at the most rapid rate in stroma (stromal fluid facility) to even out differences in hydration is maximum when stroma is

Near normal hydration

The swelling pressure in stroma is about 55 mmHg when stroma has

Normal hydration of 78%

Donnan's equilibrium causes

Greater osmotic pressure of proteins because of association of large number of cations

The active Cl- transport occurs from stroma to tears. When an enzyme inhibitor was used, the Cl- transport was reduced along with cAMP levels. This indicated that the inhibitor caused inhibition of

Adenylate cyclase

The swelling pressure in stroma shows an exponential drop when cornea has

Overhydration (150% of its normal hydration)

At an average stromal hydration of 3.45, the stromal pressure is estimated to be 55mmHg. At a higher stromal hydration above 3.45, the swelling pressure will be

Lower than 55 mmHg

If IOP is 15 mm Hg and swelling pressure is 55 mm Hg, the imbibition pressure in the stroma will be

-40 mmHg (IP = IOP -SP or IP = 15-55)

One of the characteristics of collagen is that

Gly as every third residue in its structure

Swelling pressure of cornea at 150% of its normal thickness is 15 mmHg, whereas at the normal thickness of cornea, it'll be

Higher than 15 mmHg

When stroma is dehydrated below normal condition, the driving force of fluid flow (swelling pressure gradient) increases exponentially. One of the following factors also plays an important role: a. Ability of stroma to swell increases as hydration increases b. Ability for fluid to flow (to even out differences in hydration) is in greatest in a tissue that has near normal hydration and less for swollen and dehydrated tissues. c. Ability for fluid to flow (to even out differences in hydration) is less for swollen and dehydrated tissues. d) Both B and C

d) Both B and C b. Ability for fluid to flow (to even out differences in hydration) is in greatest in a tissue that has near normal hydration and less for swollen and dehydrated tissues. c. Ability for fluid to flow (to even out differences in hydration) is less for swollen and dehydrated tissues.

The active Cl- transport occurs from stroma to tears. This transport is under the influence of

beta-adrenergic agonists (serotonin and dopamine are beta-adrenergic agonists)

The graph below shows stromal fluid flow facility as a function of stromal hydration (x axis: hydration [mg H2O/mg of dry weight], and y axis: stromal flow facility [1x10^8 cm^3/cm^2 per sec]). Identify (a), (b), and (c) during stromal hydration (hint: stroma is 78% water)

(a) dehydrated, (b) normal hydration and (c) fully hydrated