Corneal Hydration (M1) Flashcards
What is the relationship between hydration and corneal thickness?
linear positive relationship
When the pump rate exceeds the leak rate what is the result in the cornea?
Corneal Deturgescence
When the leak rate exceeds the pump rate what is the result in the cornea?
Corneal Swelling
What are the five factors that determine corneal hydration?
- Stromal swelling pressure (SP)
- Intraocular pressure (IOP)
- barrier function of the epithelium and endothelium/ imbibing pressure (IP) (“leak”)
- endothelium pump
- tear evaporation (minor)
What is equal to the force necessary to prevent stromal swelling at a given hydration? 1. What is the normal value of this? 2
- Stromal swelling pressure (SP)
2. 55 mmHg (at 78% [H2O])
What happens to the swelling pressure when there is an increased corneal thickness?
decrease because GAGs are further apart
What is the negative imbibition pressure caused by? 1. What does this draw in? 2. What is a normal value for this? 3
- negatively charged glycosaminoglycans (GAGs)
- Na+
- -40 mmHg
What is more permeable: corneal epithelium or corneal endothelium?
corneal epithelium
What is corneal epithelial permeability mediated by?
Claudins (tight junctions)
What is corneal epithelial permeability mediated by?
Claudins (tight junctions)
Where is the NKA pump located? 1. What does it move? 2
- stromal end of epithelial cell
2. 3 Na+ out, 2 K+ in
Where is the NBCe1 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell
- 1 Na+ in, 2 HCO3- out
- Na+ stromal concentration
Where is the NHE1 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell
- 1 Na+ in, 1 H+ out
- Na+ stromal concentration
What does increasing the intracellular pH favor?
reversible reaction of carbonic anhydrase (CAII) toward HCO3-
Where is the AE2 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell
- 1 HCO3- out, 1 Cl- in
- High [HCO3-]
Where is the NKCC pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell
- 1 Na+ in, 1 K+ in, 2 Cl- in
- high stromal [Na+]
Where is the NKA pump located? 1. What does it move? 2
- stromal end of epithelial cell (basolateral membrane)
2. 3 Na+ out, 2 K+ in
Where is the NBCe1 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell (basolateral membrane)
- 1 Na+ in, 2 HCO3- out
- Na+ stromal concentration
Where is the NHE1 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell (basolateral membrane)
- 1 Na+ in, 1 H+ out
- Na+ stromal concentration
Where is the AE2 pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell (basolateral membrane)
- 1 HCO3- out, 1 Cl- in
- High [HCO3-]
Where is the NKCC pump located? 1. What does it move? 2. What drives it? 3
- stromal end of epithelial cell (basolateral membrane)
- 1 Na+ in, 1 K+ in, 2 Cl- in
- high stromal [Na+]
Where is the CaCC and CFTR pump located? 1. What does it move? 2. What drives it? 3
- aqueous end of epithelial cells (Apical membrane)
- 1 HCO3- out, 1 Cl- out
- High intracellular [HCO3-] and [Cl-]
What drives Na+ paracellularly into the aqueous?
High negative charge
What draws water paracellularly into the aqueous?
Osmotic pressure of high Na+, Cl- and HCO3-
Secreted ATP and adenosine can stimulate receptors to increase intracellular cAMP, which causes what?
CFTR (efflux of Cl-)
What does GABA stimulate?
HCO3- efflux
Where is Aquaporin 1 highly expressed?
corneal endothelium
When is corneal thickness greatest?
during sleep (less evaporation of tears so lower osmolarity)
What is permanent swelling of cornea due to loss of endothelial pump function?
Bullous Keratopathy (BK) (~-30 mmHg)
What is permanent swelling of cornea due to loss of endothelial pump function?
Bullous Keratopathy (BK) (~-30 mmHg)
How does age dependent loss of endothelial cells normally affect endothelial pump function?
It doesn’t
What is corneal guttata (local thickening of descemet’s membrane) that can cause overlaying endothelial cells to thin and slow pump function?
Fuch’s Endothelial Dystrophy
