lec 18

Question 1

kangaroo rats live in dry environments. scientists put some in a lab and fed it dried barley. compared to regular rats, what were its adaptations? (4 things to note)

Answer 1

• metabolic water prod was about the same
• respiratory water loss was about the same
• kangaroo rat urine was a lot more concentrated (retains water)
• fecal water loss was virtually nothing

Question 2

stingrays are hyperosmotic even in saltwater. how do they stay this way? what are some complications along the way, and the consequent adaptations to overcome it?

Answer 2

stingrays stay hyperosmotic by retaining urea in blood.

problem! urea is toxic in high levels bc it fucks up enzyme affinities (seen in pyruvate kinase).

stingrays counteract this with trimethyl amine oxide (TMAO) which significantly decreases Km

the ratio is about 2:1 TMAO:urine to keep a normal enzyme affinity

Question 3

crayfish are freshwater fish, and retain abnormally high internal osmotic pressure. what do they do about this?

Answer 3

hyperosmotic = water wants to move inward
crayfish are constantly pissing dilute urine

Question 4

do a quick recap of how freshwater fish bring in salts

Answer 4

H+ and HCO3- byproducts of metabolism

fish ejects H+ to take in Na+ and then active transports HCO3- in to bring Na+ into blood
switch up H+ and HCO3- for bringing in Cl-

Question 5

what are lamellae? why are they shaped like that?

Answer 5

lamellae are sites for O2 uptake; they are shaped super thin to maximize O2 exchange

Question 6

mitochondria rich cells surround pavement cells that plate the gills. what is their purpose?

Answer 6

[SOMETHING IN THERE IDK] has pores which were thought to be for Cl- excretion. however, we have figured out that lamellae are also for Ca uptake, which req active transport

Question 7

if u take trout from FW to SW, do they die or adapt? what about SW to FW

Answer 7

they can go both ways, but it does take time to acclimate. chloride cells become filled with MRR cells in FW (take up salts) and less filled in SW

Question 8

how do fish undergo NaCl secretion?

Answer 8

CHLORIDE CELLS

1. NaK pump does its thing –> 3 Na in the blood
   Na now has a diffusion gradient favoured going into the cell
2. NKCC channel provides a channel for Na to enter into cell from blood, taking K and 2 Cl along with it (active))
3. K returns back to the blood through a channel
   2 Cl- leave the cell through channels (cell is hyperosmotic –> natural diffusion gradient)
   Na+ leaves straight from the blood (paracellular) to maintain electroneutrality