Osmoregulation Flashcards
What is osmoregulation?
The maintenance of constant osmotic pressure in internal fluids in the face of a different or varying external concentration
What is ionic regulation?
The maintenance of a constant ratio of ions within internal fluids- this ratio will invariably be different than that of the external environment
What is excretion?
The elimination of nitrogenous waste
What is osmosis?
The movement of water molecules through a semi-permeable membrane-cannot be actively pumped across said membrane but instead relies on changing the ionic concentration
Why do organisms have to osmoregulate?
The concentration of solutes needs to be maintained between narrow limits
How is the concentration of solutes in organisms maintained?
Changing the membrane permeability
Decreasing the concentration gradients between body fluids
Active transport of ions
What is an osmoconformer?
An organism whose body fluid osmolarity is similar to that of the external environment
What is an osmoregulator?
An organism which can maintain their body fluid osmolarity different from that from the external environment
How is an organism hypo-osmotic?
Their body fluid osmolarity is < external conditions
How is an organism hyper-osmotic?
Their body fluid osmolarity is > external conditions
What type of osmoregulation do most marine invertebrates undertake?
Osmoconformers
Describe the problems and solutions faced by the marine invertebrate- shore crab
Have a lower internal ionic concentration than the external environment thus face water loss and salt gain Solutions; Reduce permeability Low urine excretion rate Drink more water Actively excrete salt
Describe the problems and solutions faced by all freshwater invertebrates
All have internal ionic concentrations that are higher than that in the external environment thus face water gain and salt loss
Solutions;
Reduce permeability
Excrete excess water via urine
Produce a dilute enough urine to conserve salts
Active absorption of Na+ and Cl- ions from the dilute external medium (freshwater)
Describe osmoregulation in hagfish
They are the only vertebrate with extracellular NaCl similar to that in saltwater and thus are an osmoconformer
Describe osmoregulation in elasmobranchs (sharks/rays)
They are iso-osmotic but have low [NaCl] ~30% of seawater, and their iso-osmotic extracellular fluid evolved secondarily
They also have high [urea]
TMAO is actively reabsorbed
Na+ is excreted by the rectal gland, kidneys and gills
