Water Balance in Animals

Osmolarity is an easily measurable characteristic, by e.g. freezing point depression. In simple terms it is the total concentration of solutes (including ions) in a solution, and this does not depend on whether the solutes can cross cell membranes or not. Tonicity relates to the osmotic GRADIENT due to solutes that affects a semi-permeable membrane ( i.e. a membrane that is permeable to water); ONLY solutes that do not cross the membrane contribute to this effect.

The mouth and nose will always be permeable

Reg. Est. a body where everything inside is kept at a certain level Osmoregulator or conformer keeps blood at certain levelMost marine invertebrates equilibrate their extracellular fluid osmolarity with the ocean water and are therefore called osmoconformers. Other marine animals maintain extracellular fluid osmolarities much lower than seawater and are therefore called osmoregulators

1. Marine- salt water about 1000 mOsm

Animal life probably evolved hereish is constantly losing water through osmosis This can be minimized by waterproofing the fish through skin, mucous layer, scales Cannot minimize water loss through gills, skin, digestive system How can we gain water back? Eating, drinking but gain salt Fish has to find a way to get rid of salt Don't produce very much urine b/cuz Constantly dehydrated

2. Fresh water- about 100 mOsm

Vertebrates evolved hereDon't drink water Produce copious dilute urine Main problem is loss of ions Use gills to get ions back

3. Terrestrial- Land
3. Losing air and water through mouth

Lose salt through the gills; pumps send salt outThey drink the water and they have salt glands or pumps which pump salt out of the creature and on to the skinMarine mammal - exceedingly good kidney to get rid of salt or it never drinks; dietary water; very good at conserving water
Water uptake by osmosis and ion active uptake in gills

PICTURE

1. Filtration- push fluid out of blood into capsule
1. Water, ions, and sugar
1. Capillary pressure may change and that would change the whole system Filtration is critically dependant on pressure

2. Reabsorption- take back what you need
2. Epithelial membrane and red blood cellConvince blood to come into the epithelial by placing more ions inside of the Cell and H2O would follow it in Want to resorp things in the proximal tubule
3. Secretion- actively get rid of some things
3. active exclusion of some things -H+ ions (acid) -kidneys have a critical role in blood pH -hormones and drugs -antibiotics, pain killer, anti depressants, birth control hormones…..

Normal amount of glucose in a normal adults urine 0 Things in kidneys resorp glucoseDiabetes mellitus Sugar in the urine Caused by excessive sugar in the blood

Loop of henle allows us to retain water (highly permeable) Use counter current exchanger (ensures that water leaves the kidney tubules and come back into the blood); loop of henle Fluid that is going to the collecting duct is more concentrated 4x as concentrated

If you have an amino acid you can uses it for energy or other purposes NH2 is difficult to let go of because it may produce nh3 in the blood which is toxic Plants can turn nh3 back into amino acids To get rid of ammonia dissolve it in water to get rid of itFish: to get rid of 1 g of ammonia 300 ml of h2o is needed Mammal: to get rid of 1 g N 50 ml of h2o is needed (needs ATP) Uric acid is really toxic and not soluble in water To excrete 1g N takes less than 10 ml water