Ocular Fluids

Is water nonpolar or polar

polar

What does the polar property of water allow it to do?

solubilize simple and complex molecules (proteins)

Solubilization in water

weak interactions between the water and solute molecules

What are the weak interactions that are observed in water?

• hydrogen bonds
• ionic bonds
• van deer waals forces

How does oxygen affect electrons

it pulls oxygen towards it, very electronegative

ionic bonds

involves electrostatic attraction between 2 ionic species that are oppositely charged

Van Der Waals forces

attraction involving neutral molecules in gases, liquids and solids

Hydrogen bonds

a IMF that is present between hydrogen and a second EN molecule

Water has the ability to __ with __ atoms

1. associate
2. charged

In solvation, what element of water would surround Na+?

Oxygen

In solvation, what element of water would surround Cl-?

Hydrogen

When water associated with other polar molecules, what can be observed?

hydrogen bonding

When water is fluid, are hydrogen bonds permanent?

No, constantly made and broken

When water is frozen, are hydrogen bonds permanent?

Yes, this gives ice its ordered structure as it expands

Are hydrogen bonds between water and protein permanent?

No, they are weak and often break

Number of hydrogen bones formed between a protein and water is…?

High

What is the equation of pH

pH = -log [H+]

([H+] = hydrogen concentration)

Why must pH be tightly controlled?

preserving tissue structure and cell viability

What happens to a cell if pH is too high or too low?

Apoptosis - programmed cell death

What is a buffer system?

reaction system that maintains pH in a certain range

What is hydrogen ion concentration (pH) controlled by?

partial ionization of weak electrolytes

What are the 3 types of buffer systems?

1. phosphate
2. bicarbonate
3. protein

How is pH measured in fluids?

pH meter

How is pH measured mathematically?

Henderson-Hasselbach equation

What is the Henderson-Hasselbach equation?

What is a weak electrolyte?

A weak acid that does not fully dissociate in water

What is a dissociation constant?

How much a weak electrolyte ionizes

What is the equation for calculation a weak electrolyte’s dissociation constant?

How do you solve for pKa?

pKa = -log [Ka]

What does a pKa value represent?

It is equivalent to the pH value of a solution when it is 50% ionized

Buffer capacity

how much acid or base can be added to the buffer for it to still maintain its intended pH

Range of buffer

the range of which the buffer can neutralize an added acid or base

What is the range of a buffer system dependent on?

pKa

what does log [salt]/[acid] represent?

log of the ration of the ionized anion to the non ionized acid of the weak electrolyte

What is the equation for a phosphate buffer?

What is the most common buffer present within cells?

phosphate buffer

What is the pKa and buffer range of a phosphate buffer?

• pKa = 6.86
• range of: 5.86-7.86

What is the equation for a bicarbonate buffer?

Why is a bicarbonate buffer more complex?

CO2 can be removed with expired air

What can your breathing influence?

• HCO3-/H2CO3 ration
  • extracellular pH of blood and ocular fluids

What can happen when you are hyperventilating?

respiratory alkalosis, blood pH can raise to 7.9

What is the equation of a protein buffer

Why are protein buffers important?

They are present both inside and outside of cells

Ionizable groups n proteins have __ pKa values

altered

prediction of exact buffering tendencies and capacities of proteins are __

difficult

Ocular fluids include:

1. aqueous fluids
2. vitreous
3. precorneal tears

What two blood vessels make the major circle of iris?

1. anterior ciliary artery
2. branch of LPCA

What vein is draining the blood from the eye?

vortex veins

What are the ocular physiological functions of blood

1. nourishment and removal of waste components of ocular cells
2. a source of generation for IOP
3. a source of information of aqueous and vitreous fluid
4. homeostasis of retinal functions

What is the pH of blood?

7.4, (can vary from 7.33-7.45)

Gases carried in the blood

1. oxygen
2. nitrogen
3. CO2

Partial pressure of O2 in Ocular capillary bed

only 50mmHg

Partial pressure of O2 in Arterial blood

83-108mmHg

Partial pressure of CO2 in venous blood

38-50mmHg

Albumin

Protein that carries water-insoluble components

Calcium

Soluble ion that is responsible for: blood clotting, enzyme activation, hormone activity and muscle contraction

Cholesterol

Lipid that is not soluble in blood

Globulin

Water-soluble protein involved in immunological functions

Glucose

Water-soluble sugar that has great importance as a nutrient

Hemoglobin

Protein that carries O2 to cells

Phosphate

Water-soluble, important for phosphate buffer, protein function and cellular energy

Potassium

Principal cation of intracellular fluid, important for enzyme function

Triglycerides

lipid class, not soluble in blood

Aqueous humor

a controlled filtrate of blood produced by ciliary body (non-pigmented ciliary epithelium)

What drains aqueous humor from the AC?

episcleral veins

What is the importance of aqueous humor?

• only source of nourishment for cells of corneal endothelium and epithelium
• stroma keratocytes
• lens
• source of antioxidants

Processes involved in aqueous humor production

• diffusion
• ultrafiltration
• active secretion

Does aqueous humor have RBCs?

NO, it is a filtrate of blood

What does aqueous humor give rise to in the eye?

IOP, which maintains the shape of the eye

• it also protects to some extent from the physical shock

How is aqueous humor different from blood?

1. decreased protein component, no cellular components

   1. reduced buffering capacity due to this

2. ascorbic acid concentration is higher

Why is aqueous humor still able to maintain pH even though it has a decreased buffering capacity?

due to comparable amounts of phosphate and bicarbonate

Vitreous humor

a mixture of fluid and gel

How much of vitreous is water?

98%

What are the ratios of gel/fluid initially, and with age?

1. Initially: 80%gel/20%fluid
2. With age: 40%gel/60%fluid

Describe the gel portion of vitreous humor

a stiff, semi-rigid precipitate having collagens and proteoglycans

What causes a retinal detachment to occur?

1. increase in proportion of fluid with age
2. breakdown of type 2 collagen
3. destabilization of retinal surface
4. retinal detachment

What causes thee viscoelasticity of the vitreous?

due to proteoglycans (hyaluronic acid) and collagens

What are special properties of the vitreous gel?

capability to reform its original shape, and has some flow property

Comparisons of vitreous to blood

1. ascorbate levels are high
2. protein and hyaluronic acid is high
3. sodium and glucose content is lower
4. potassium level is low
5. vitreous is clear

Precorneal tears

a film between the inside of lids and the cornea

Role for tears

• lubricating fluid
• protects the eyes from microorganisms
• temporary disposition for topical drugs
• comprised of 3 layers

What are the 3 layers of tear film?

1. lipid
2. aqueous
3. mucin

How can tears protect from Gram+ bacteria?

tears have enzyme called lysozyme

Comparison of tears to blood

1. tears are more dilute

2. potassium concentration is 7x higher than blood

3. ascrobate and glucose levels are lower

   1. not a source of nourishment for corneal and conjunctival cells

Where does the cornea get its nutrients from?

aq. humor

Where do conjunctival cells receive nourishment from?

interstitial fluid and local blood supply

Globulin range

2.3-3.5 gm/mL

Cholesterol range

140-250 mg/100mL

Glucose range

70-105 mg/100mL

13-16 g/100mL

3-4.5 mg/100mL

Potassium range

~ 105mmol/liter in red blood cells

Triglycerides range

35-140 mg/100mL