Water and Electrolytes Flashcards
Water Balance
the balance between water intake and output
Electrolyte
compound that dissociates into ions when dissolved in water
They conduct electric current
Most abundant ions of electrolytes in most animals
Sodium (Na+)
Chloride (Cl-)
Potassium (K+)
Calcium (Ca 2+)
Electrolyte ion imbalances can lead to…
muscle spasms, confusion, irregular heart rhythms, fatigue, paralysis and even death
Osmolarity
the total concentration of all solute particles in a solution
measured in osmoles per lire
osmotic stress
occurs when the concentration of dissolved substances in a cell or tissue is abnormal
Osmoregulation
regulation of solute concentrations and water balance by a cell or organism
Osmoconformers
marine animals which maintain the osmolarity of their body fluids such that it is always equal to the surrounding seawater.
(sharks, jellyfish, dogfish)
Osmoregulators
An organism that controls its internal salt concentration
(most fish, vertebrates and terrestrial invertebrates
hyperosmotic
the solution outside the body has a higher solute concentration than solution inside
hyposomotic
A term describing organisms with body fluids with a higher concentration of water and lower solute concentration than the external environment.
Hyperosmotic Sea Creatures…
Live in seawater, Higher concentration outside than inside
Water tends to flow out by osmosis (cells will shrivel)
Drink water to regain balance, but Gain excess electrolytes.
use Membrane proteins to actively pump out ions
and Excrete small # of electrolytes through urine to achieve balance
Hyposomotic Sea Creatures…
Live in freshwater, Higher concentration inside than outside
Water tends to flow in by osmosis (cell will lyse)
Excrete water to regain balance, but Lose electrolytes.
Actively transport ions in from the environment to gain electrolytes (through gills)
epithelial cells
skin cells that cover the outside of the body and line the internal surfaces of organs
primary active transport
source of energy like ATP is used to move ions against their concentration gradient
Ex. Sodium-Potassium Pump
secondary active transport (cotransport)
relies on membrane proteins that use an electrochemical gradient established by a pump during primary active transport
symporter
cotransporter that carries two different ions or small molecules, both in the same direction
antiporter
cotransporter that carries two ions or small molecules in different directions
Aquaporins
A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane
cells use pumps to set up an osmotic gradient that allows this.
Ammonia (NH3)
toxic to cells because at high concentrations it can raise the pH of intracellular fluids enough to inactivate enzymes.
(made by the breakdown of excess amino and nucleic acids)
How is electrolyte balance maintained?
What drives the movement of ions across membranes?
Ions are moved either by active transport or passive transport (ion pumps, co- transporters, ion channels)
How is water balance maintained?
What drives the movement of water across membranes?
Water movement is driven by osmosis (differences in osmolarity). Water movement is facilitated through some proteins (aquaporins) that make the membrane more permeable to water.
How is nitrogenous waste eliminated?
What is the reason for the different elimination products (ammonia, uric acid, urea)?
The removal strategy depends on water availability.Ammonia: easy to make, but is toxic and requires lots of water
Uric acid: most energy-consuming synthesis; minimal water (solid waste)
Urea: some energy required; water soluble but harmless; contributes to osmolarity
What are the advantages of urea in sharks to help maintain salt balance?
Urea is a very inert substance that doesn’t really do any damage to proteins or cells therefore you can accumulate very high concentrations without any negative effects
What happens if you starve a shark or dogfish?
if you starve dogfish or sharks they will not get enough food to create enough nitrogenous waste to maintain the urea concentration
as a consequence, they will actively break down their own proteins and they will break down their muscles,
because it’s better for them to be skinny and weak than to have the wrong osmolarity
How do sharks secrete concentrated salt solutions?
The rectal gland
What are the steps involved in salt excretion through the rectal gland in sharks? (4)
ABC
AB
AB
A
- A) Na+/K+ - ATPase pump actively pumps Na+ ions out of the epithelial cells and into the interstitial fluid. (3 out, 2 in)
B) This creates an electrochemical gradient which allows Na+ ions to enter the cell.
C) This gradient also allows for other ions to enter the cell w/o the expenditure of extra energy.
2.
A) Due to Na+ master gradient, Na+, Cl- and K+ all move into the cell via a cotransporter (secondary transport)
B) Na+ moves ALONG its chemical gradient, whereas, Cl- and K+ move AGAINST their chemical gradients
(with Na+ through cotransporter)
- A) As Cl- build-ups inside the cell, it exists through chloride channels in the APICAL membrane; into the rectal gland lumen (down its concentration gradient)
B) K+ diffuses back into the interstitial fluid through potassium channels in the BASOLATERAL membrane - A) Access amount of Na+ diffuses into the lumen along its chemical gradient from the interstitial fluid through SPACES in between the cells.
Where is the Na+/K+ - ATPase pump located in freshwater fish? Why?
It is located in the APICAL membrane instead of the Basolateral membrane.
This is because freshwater fish need to bring salt in not remove salt.
How do terrestrial (not marine) animals maintain water and electrolyte balance?
What are the advantages and disadvantages of uric acid
The big advantage of uric acid is it’s water-insoluble so you don’t lose any water or very little water if you excrete it
However,
the big disadvantage is that it’s a very complex molecule making this compound requires a lot of ATP and energy
Which of the following mechanisms contributes to osmoregulation in both marine and freshwater bony fish?
gain of water through food
The intercellular concentration of three electrolytes is compared with the concentration of these electrolytes in fluid eliminated from the shark rectal gland in the Table. Based on the data, which of the following is a likely function of the rectal gland?
The rectal gland is able to concentrate Na+, K+, and Cl-.
Why do birds secrete uric acid as their nitrogenous waste? Because uric acid…
requires little water for nitrogenous waste disposal, thus conserving water and reducing body mass.
