Nitrogen Excretion and Osmoregulation

Question 1

protein in diet… excretion

Answer 1

NH2 (amine groups) –> ammonia, urea, uric acid

usually excrete primary nitrogenous waste, may produce all 3 nitrogen compounds

ammonotelism, uricotelism, ureotelism

NH3 toxic to cells (aqueous NH4OH - ammonium hydroxide)

• cell necrosis (membrane lipid destruction)
• glucose 80% more likely to be metabolized anaerobically

So eliminate NH3 with much water or convert to nontoxic waste

Question 2

number of nitrogen per molecule

Answer 2

ammonia - 1
urea - 2
uric acid - 4

Question 3

ammonotelism

Answer 3

most fishes, many amphibians

advantages:

• no energy to excrete
• very water soluble
• eliminated across any permeable membrane bathed by water

disadvantages:

• toxic
• water loss

Question 4

ureotelism

Answer 4

mammals, terrestrial amphibians, lungfishes, chondrichthyeans

advantages:

• less toxic
• less water loss
• may counter osmotic dehydration (chondrichthyes)

disadvantages:

• energy to assemble
• some water loss

Question 5

uricotelism

Answer 5

reptilia

advantages:

• least toxic
• minimal water loss

disadvantage:
-most energy to assmeble

transported to cloaca
joins with ions and forms precipitate (sodium urate)
water absorbed by cloacal wall
“sludge” eliminated

Question 6

osmoregulation

Answer 6

maintenance of relative constant osmotic concentration of body fluids (water and solute balance)

general kidney function across taxa

• nitrogen removal
• osmoregulation

Question 7

osmoconformers

Answer 7

isosmotic to surrounding seawater

hagfishes only (craniates - not verts)

Question 8

osmoregulators

Answer 8

maintain relative constant osmotic conditions via physiologic adjustments

general challenges:
water loss/gain
solute loss/gain

marine challenge: osmotic loss of water and gain of salt

freshwater challenge: osmotic gain of water and loss of salt

Question 9

Freshwater Teleosts

Answer 9

hyperosmotic - more salt in blood compared to surrounding water

gain water = flooding, lose salt

kidneys eliminate excess water (and lose Na, Ca, Cl, K ions)

Cl cells (ionocytes) in gills, active transport

Question 10

Aquatic Amphibians

Answer 10

similar challenges to freshwater teleosts; flooding and salt loss

kidneys eliminate extra water, lose salt; chloride cells in skin

acid rain: impairs ionocyte function; can’t osmoregulate

Question 11

Marine Teleosts

Answer 11

hyposmostic to seawater - more water less salt per unit volume

lose water

solution: drink sea water
70-80% water absorbed by gut
much salt absorbed
kidneys can't eliminate excess salt
chloride cells in gills, active transport again

Question 12

Marine chondrichthyes

Answer 12

blood/tissue salt concentration ~ 1/2 to 1/3 sea water

but blood/tissues are slightly less hyperosmotic to sea water because of urea

blood urea concentration 100x of mammals

so, slight flooding, kidneys eliminate excess water

no salt elimination with gill ionocytes

salt elimination via kidney and digitform gland (rectal gland)

collects and delivers salt to rectum (and then to cloaca) - excess salt eliminated with feces

Question 13

extra renal salt elimination common in marine taxa

Answer 13

marine turtles: orbital gland

marine lizard: nasal gland

sea birds: nasal glands

sea snakes: sublingual glands

salt water crocodiles: lingual glands

Question 14

stenohaline

Answer 14

most fishes are stenohaline

meaning freshwater or saltwater only

Question 15

euryhaline

Answer 15

diadromous fishes

Question 16

diadromous (“between running”) conditions:

Answer 16

1. anadramous

2. catadramous

Question 17

anadromous

Answer 17

“up running”

salmon, striped bass, lampreys

“ascend freshwater to spawn”

adults spawn in freshwater, juveniles leave freshwater and mature in oceans

Question 18

catadramous

Answer 18

“down running”

American and European eels

adults spawn in mid-Atlantic, juveniles return to freshwater to mature

descend freshwater and spawn in oceans

females provide eggs with suitable osmotic environment

Question 19

diadromous fishes experience osmotic transitions…. freshwater marine

Answer 19

at any life stage, adjusted to either freshwater or saltwater

adjustments seem genetically determined physiological changes

EX: salmon can’t enter saltwater until certain stage in development (for ionocytes to become salt eliminating units)