What are the intracellular and the extracellular fluids?
-intracellular fluids are cytoplasm and extracellular fluids are blood/hemolymph
Why do intracellular fluids have different composition than extracellular fluids?
-the organism has specific needs and keeps their internal fluid at the optimal conditions for their survival
What are the major ions in seawater, and their concentrations?
Cl- (510 mOsm)
Na+ (440 mOsm)
K+ (10 mOsm)
Mg2+, Ca2+, SO42- (100 mOsm)
What is the osmolarity of a solution with 250 mM NaCl? And of a solution with 250 mM glucose?
- 500 mOsm NaCl
- 250 mOsm glucose
What is the osmolarity of a solution with 300 mM NaCl, 100 mM urea, 50 mM glycine, and 50 mM protein?
800 mOsm
How do cells regulate their volume when they swell or shrink?
-they have a semipermeable membrane that allows water and some ions to cross in order to keep concentrations balanced across it (osmosis)
What was the composition of the extracellular fluids of the most ancient animals?
-similar composition to seawater
What is the osmotic gap?
- the difference in mOsm of solute between intracellular fluids and extracellular/external fluids
- causes large amount of osmosis, requiring lots of energy to offset, if not filled
How do marine invertebrates make up for the osmotic gap, and why is this important?
- marine invertebrates are osmoconformers, so their internal composition is very similar to the composition of seawater
- osmotic balance with seawater
- indicates that they did not leave marine environment
- accumulate amino acids to make up for the osmotic gap
Why is the composition of the extracellular fluids of marine elasmobranchs different from that of marine bony fishes?
- have different mechanisms of handling osmotic gap
- elasmobranchs accumulate urea and TMAO to make up osmotic gap while fish just drink SW and excrete NaCl (sharks excrete NaCl through rectal gland)
- elasmobranchs have similar osmolarity to SW while bony fish have lower osmolarity, both have lower ionic concentrations
