1. Water and Ions Membranes surround cells Epithelia surround tissues
Epithelia separate an organism from its environment
At each level ion and water movement is controlled so volume and ion concentration can be maintained

2. Cell
Blood

4. The Nernst Equation
Chemical and charge gradients determine whether an ion is in equilibrium across a membrane
The Nernst equation predicts the potential difference at equilibrium
The equilibrium potential for sodium = RT/zF ln [Concentration out]/[Concentration in]
R is the gas constant, T is the absolute temperature, z is the charge on the ion and F is Faradays’ constant 96,500 couloumbs/mole

5. Nernst Equation
Vm = RT ln [Co]
zF [Ci]
R = joules/Ko/mole
T = Temperature
F = Faraday’s constant 96,500 coulombs/mole

6. Frog Skin Model Developed by Ussing Tested in “Ussing” Chamber
Uptake occurs against and electrical and a concentration gradient.
Inhibited by specific inhibitors
Temperature Dependent
Ion specific
Saturation Kinetics

8. The Frog Skin Model
Hans Ussing worked on one of the first models of epithelia transport
The skin of a frog is able to absorb sodium from a fresh water pond against a considerable concentration gradient
Using the Na gradient provided by the active pumping of sodium at the basolateral(serosal) surface of the cell, Na is drawn across the apical(mucosal) surface
Transport requires serosal K and displays saturation kinetics

10. Patterns of Osmoregulation
Marine Invertebrates and Osmoconformers
Regulation is Marine Elasmobranchs
Seawater Fishes and Ion Balance

11. Osmoregulation in Marine Invertebrates
Most marine invertebrates are osmoconformers, they do not regulate the NaCl concentration of the blood
Inside the cell amino acids provide osmotic currency
Proto kidneys do regulate calcium and magnesium

12. Once Upon a Time . . . In Biscayne Bay. . . There were three copepods.
Blood p = External Medium p = 1000 mOs = Cell p
Cell
Blood

13. And then the rains came down .
The osmolality of the external medium falls, and initially the organism swells until ions reach equilibrium

14. Recovery
In recovery blood = external medium = 800 mOs, but cells cannot reduce ion concentrations -- so free amino acids are extruded

15. Marine Elasmobranchs
Marine Elasmobranchs are in osmotic equilibrium with sea water
p in blood = p medium
Ion concentrations of the blood are below sea water
Urea and TMAO increase blood osmolality

16. Gills and Kidneys retain Urea
Drinking Rates are low %body water/hr
Toxic Effects of Urea are lessened by the presence of trimethylamine oxide
Urea = 350 mOs; TMAO = 50 mOs
The Rectal Gland of sharks actively extrudes chloride
The rectal gland is a model Cl extruding system used in study of cystic fibrosis
One FW elasmobranch of the Orinoco has lost the ability to produce and retain urea, salt uptake mechanisms are unknown.

17. Na,K,Cl Cl Na
Lumen K
Blood
Rectal Gland Transport

18. Water Loss
Ion Gain

19. Marine Teleosts
Osmotic Water Loss Across Gills
Drink Sea Water to Replace Osmotic Loss, approximatley 2% of body weight/hour
Extrude Ions at Gills with Active Chloride Transport
Kidneys Excrete Sulfate and Magnesium, but can’t produce a hypertonic urine.

20. Fish Gills in Seawater
Fish gills extrude Na and Cl gained diffusively across the body surface and taken in via the gut
The chloride cell is packed with mitochondria and uses the active Na/K ATPase and a linked Na/K/Cl channel to move Chloride from the blood to the seawater against a gradient

24. Migrating Fishes
In salmon, the vector of transport and the anatomy of the gill chganges as the fish moves from FW to SW
Cortisol and Growth Hormone mediate the movement from FW to SW; Prolactin stimulates the SW to FW alteration

25. Marine Birds and Turtles
Nasal and lacrimal transport of salt
Mechanisms Similar to Rectal Gland Model

26. Malpighian Tubule in Insects
Act as the kidney of insects, but form a “urine” by the secretion of potassium from the hemolymph
Using a counter current movement of ions and water, insects are able to reabsorb water from the hindgut and prevent water loss in dry environments