Physiology 5: Water balance Flashcards
Why do we regulate water?
The conc. of bodily fluids is usually different to that of the external environment
What happens a cell when there’s a lower water conc. & higher solute conc. outside
Cell lose water and shrivel (crenation)
What happens to a cell when there’s a higher water conc. & lower solute conc. inside
Cell will take up water and burst (lysis)
What is osmoregulation?
process that balances the uptake and loss of water
homeostatic control
Describe passive transport
along a conc. gradient (high to low)
Describe active transport
against a conc. gradient → requires energy (low to high)
Name 4 factors that influence the rate of passive transport (and how they do it)
Temperature
- Higher temp = faster rate
Size of particles
- Smaller particles = faster rate
Electrical charge of the ion
- Can prevent passage
Conc. gradient
- Greater gradient → faster rate
What is osmolarity?
measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane compared to pure water
What is the osmolarity of pure water?
0
What is the equation for osmolarity?
(no. particles/ molecules of solute) X (moles/ litres)
What are the units for osmolarity
osmoles/litre (Osm/L)
Define hypo-osmotic
low solute conc. High water conc.
Define hyperosmotic
high solute conc. Low water conc.
The net flow will be from ____osmotic to ____osmotic
The new flow will be from hypo-osmotic to hyperosmotic
What does iso-osmotic mean?
2 solutions have equal osmolarity
What is saying ‘the cell is hyperosmotic to the extracellular fluid’ the same as?
‘the extracellular fluid is hypo-osmotic to the cell’
What is tonicity?
effect of a solution on cell volume
What can tonicity depend on?
- Solutes
- Membrane permeability
What’s the difference between osmolarity and tonicity?
Osmolarity → measure of solute conc.
Tonicity → effect of a solution on cell volumes
Describe a hypertonic solution
- Higher solute conc. outside the cell
- Water leaves the cell via osmosis
= cell shrivels
Describe a hypotonic solution
- Lower solute conc. outside the cell
- Water enters the cell via osmosis
= cell swells and eventually bursts
Describe an isotonic solution
- Same solute conc. inside and outside the cell
- No net gain/loss of water
Describe osmoregulators
→ Osmolarity of body fluids regulated to within a set range
Give some examples of osmoregulators
mammals, birds, most marine and freshwater teleosts
Describe osmoconformers
Osmolarity of body fluids matches that of the external environ
- Osmolarity still in a set range though → would not be 0
Give some examples of osmoconformers
some fish and amphibians, freshwater and brackish invertebrates
Describe limited osmoregulation
Regulate osmolarity within a certain range, but in other ranges will adjust to the external environ
- But their osmolarity is never quite the same as the external environ
Give some examples of limted osmoregulators
some fish and amphibians, freshwater and brackish invertebrates
What are the challenges of freshwater for osmoregulation?
Freshwater is hypo-osmitic compared to organism
What are the challenges of saltwater for osmoregulation?
Saltwater is hyperosmotic compared to organism
Marine teleosts are ____osmotic to their environ
Marine teleosts are hypo-osmotic to their environ
Describe the problem marine telosts face in terms of osmoregulation
Too much salt:
- Due to gills high surface area, salt is gained by diffusion
- Water lost by osmosis through gills
- Water also lost because skin is permeable
How do marine teleosts balance water loss?
Water (+ salt) ingested and when eating
Produce small amounts of high conc. urine to get rid of salt
Active transport of salt out through the gills
What specialised cell do marine teleosts use to activley transport salt out of their gills?
Chloride cell
- lots of mitochondria
Describe how marine teleosts activley transport salt out of their gills (7)
- Actively pump Na+ out of cell and into extracellular fluid
= conc. gradient of Na+ - Na+ moves down a conc. gradient into cell
- Cl- is symported into the cell
- Na+ pumped out again, Cl- build up in the cell channels so Cl- can diffuse out passively
- charge is built up at the basolateral surface where there’s lots of Na+
- charge built up at the apical surface where there’s lots of Cl-
- Change gradient means Na+ can be pulled out through ‘leaky’ junctions between the cells
= Net movement of Na+ and Cl- from inside the fish into the seawater
What is the basolateral surface?
Faces the inside
What is the apical surface?
Faces external environment or lumen of a tube (that is often invloved in absorption or secretion)
Freshwater teleosts are ____osmotic to their environment
Freshwater teleosts are hyperosmotic to their environment
Describe the problem freshwater telosts face in terms of osmoregulation
need more salt:
Water uptake by osmosis
Salts lost through diffusion from the gills
How do freshwater teleosts retain/gain salt?
Large amounts of dilute urine
Gain salt through food
Salts and water lost in faeces
Active transport salt in through gills
Describe how freshwater teleosts actively transport salt in via their gills
Basolateral Na/K ATPase pumps
→ pump Na out of the cell
Super-high affinity NA+ & Cl- transporter on apical surface
→ pumps Na+ and Cl- ions into cell from freshwater environ
Don’t have leaky junctions between cells
→ ensures little salt is lost to environ
How are some fish able to move between marine / freshwater environs? E.g salmon
Close off leaky junctions between cells
Reverse ion uptake (able to switch position of pumps and symporters)
Take up more water
