Physiology 5: Water balance

Question 1

Why do we regulate water?

Answer 1

The conc. of bodily fluids is usually different to that of the external environment

Question 2

What happens a cell when there’s a lower water conc. & higher solute conc. outside

Answer 2

Cell lose water and shrivel (crenation)

Question 3

What happens to a cell when there’s a higher water conc. & lower solute conc. inside

Answer 3

Cell will take up water and burst (lysis)

Question 4

What is osmoregulation?

Answer 4

process that balances the uptake and loss of water
homeostatic control

Question 5

Describe passive transport

Answer 5

along a conc. gradient (high to low)

Question 6

Describe active transport

Answer 6

against a conc. gradient → requires energy (low to high)

Question 7

Name 4 factors that influence the rate of passive transport (and how they do it)

Answer 7

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

Question 8

What is osmolarity?

Answer 8

measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane compared to pure water

Question 9

What is the osmolarity of pure water?

Answer 9

0

Question 10

What is the equation for osmolarity?

Answer 10

(no. particles/ molecules of solute) X (moles/ litres)

Question 11

What are the units for osmolarity

Answer 11

osmoles/litre (Osm/L)

Question 12

Define hypo-osmotic

Answer 12

low solute conc. High water conc.

Question 13

Define hyperosmotic

Answer 13

high solute conc. Low water conc.

Question 14

The net flow will be from ____osmotic to ____osmotic

Answer 14

The new flow will be from hypo-osmotic to hyperosmotic

Question 15

What does iso-osmotic mean?

Answer 15

2 solutions have equal osmolarity

Question 16

What is saying ‘the cell is hyperosmotic to the extracellular fluid’ the same as?

Answer 16

‘the extracellular fluid is hypo-osmotic to the cell’

Question 17

What is tonicity?

Answer 17

effect of a solution on cell volume

Question 18

What can tonicity depend on?

Answer 18

• Solutes
• Membrane permeability

Question 19

What’s the difference between osmolarity and tonicity?

Answer 19

Osmolarity → measure of solute conc.
Tonicity → effect of a solution on cell volumes

Question 20

Describe a hypertonic solution

Answer 20

• Higher solute conc. outside the cell
• Water leaves the cell via osmosis
  = cell shrivels

Question 21

Describe a hypotonic solution

Answer 21

• Lower solute conc. outside the cell
• Water enters the cell via osmosis
  = cell swells and eventually bursts

Question 22

Describe an isotonic solution

Answer 22

• Same solute conc. inside and outside the cell
• No net gain/loss of water

Question 23

Describe osmoregulators

Answer 23

→ Osmolarity of body fluids regulated to within a set range

Question 24

Give some examples of osmoregulators

Answer 24

mammals, birds, most marine and freshwater teleosts

Question 25

Describe osmoconformers

Answer 25

Osmolarity of body fluids matches that of the external environ - Osmolarity still in a set range though → would not be 0

Question 26

Give some examples of osmoconformers

Answer 26

some fish and amphibians, freshwater and brackish invertebrates

Question 27

Describe limited osmoregulation

Answer 27

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

Question 28

Give some examples of limted osmoregulators

Answer 28

some fish and amphibians, freshwater and brackish invertebrates

Question 29

What are the challenges of freshwater for osmoregulation?

Answer 29

Freshwater is hypo-osmitic compared to organism

Question 30

What are the challenges of saltwater for osmoregulation?

Answer 30

Saltwater is hyperosmotic compared to organism

Question 31

Marine teleosts are ____osmotic to their environ

Answer 31

Marine teleosts are hypo-osmotic to their environ

Question 32

Describe the problem marine telosts face in terms of osmoregulation

Answer 32

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

Question 33

How do marine teleosts balance water loss?

Answer 33

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

Question 34

What specialised cell do marine teleosts use to activley transport salt out of their gills?

Answer 34

Chloride cell - lots of mitochondria

Question 35

Describe how marine teleosts activley transport salt out of their gills (7)

Answer 35

1. Actively pump Na+ out of cell and into extracellular fluid = conc. gradient of Na+ 2. Na+ moves down a conc. gradient into cell 3. Cl- is symported into the cell 4. Na+ pumped out again, Cl- build up in the cell channels so Cl- can diffuse out passively 5. + charge is built up at the basolateral surface where there's lots of Na+ 6. - charge built up at the apical surface where there's lots of Cl- 7. 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

Question 36

What is the basolateral surface?

Answer 36

Faces the inside

Question 37

What is the apical surface?

Answer 37

Faces external environment or lumen of a tube (that is often invloved in absorption or secretion)

Question 38

Freshwater teleosts are ____osmotic to their environment

Answer 38

Freshwater teleosts are hyperosmotic to their environment

Question 39

Describe the problem freshwater telosts face in terms of osmoregulation

Answer 39

need more salt: Water uptake by osmosis Salts lost through diffusion from the gills

Question 40

How do freshwater teleosts retain/gain salt?

Answer 40

Large amounts of dilute urine Gain salt through food Salts and water lost in faeces Active transport salt in through gills

Question 41

Describe how freshwater teleosts actively transport salt in via their gills

Answer 41

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

Question 42

How are some fish able to move between marine / freshwater environs? E.g salmon

Answer 42

Close off leaky junctions between cells Reverse ion uptake (able to switch position of pumps and symporters) Take up more water