Osmosis Osmosis and Terminology Ion and Osmotic Balance Across Aquatic Habitats and Animal Groups 2/19 and 2/25/08

2 Osmosis Defined  Movement of some solvent across a selectively permeable membrane usually refers to the movement of water  cause most solutes can’t pass through the membrane across a cell membrane down a concentration gradient (for solvent) 2

3 Terminology  Isosmotic Equal osmolarity But may still result in a change in cell volume Due to differences in the electrochemical gradient Or membrane permeability to particular solutes  Isotonic Reference is cell response Solution that does not cause shrinking or swelling 3

4 Terminology (cont) 4 Hypotonic solution

5 Overview  Osmoregulation: solute and H20 balance  Animals use different combinations of tissues to control ion and water balance  Representatives of most animal phyla live in direct association with water Greater pressure for water/salt exchange than terrestrial habitats  Point: Animals cope with the ionic concentration of the external environment using different mechanisms 5

6 Obligatory Exchanges  Is there a gradient between the extracellular compartment and the external environment? Greater the gradient, greater tendency for NET DIFFUSION  Surface-to-volume ratio, higher for smaller animals Larger surface area = greater exchange Evaporative water loss, ion exchange, etc. 6

7 Obligatory Exchanges (2)  Permeability of the integument or portions of the integument, esp. respiratory surfaces Covering external surfaces with hydrophobic molecules, e. g. mucous, keratin, chitin More aquaporin proteins increase water permeability 7

8 Obligatory Exchanges (3)  Feeding Gain water and solutes from food In marine enviro. salt gain is a problem Will have special means for excreting excess salt  Metabolic factors End products of metabolism that cannot be used must be eliminated (nitrogenous waste) and this requires WATER ! 8

9 Ionic and Osmotic Regulation  Strategies Ionoconformer  exert little control over the solute profile within the extracellular space; exclusively marine Ionoregulator  control the ion profile of the extracellular space Osmoconformer  internal and external osmolarity are similar; marine invertebrates Osmoregulator  osmolarity is constant regardless of the external environment 9

10 Ionic and Osmotic Regulation Very similar to Figure and Table 11.9 Willmer, 2/e 10

11 Ionic and Osmotic Regulation (Cont.)  Ability to cope with changes in external osmolarity Stenohaline – tolerate a narrow range  Generally conformers Euryhaline – tolerate a wide range  Generally regulators 11

12 Marine Invertebrates  Marine inverts: internal osmotic concentration similar to seawater Tend to be osmoconformers Exception is arthropods!  May regulate solute COMPOSITION to differ from their enviro, requires extensive regulation (= energy) Echinoderms – no significant regulation Jellyfish – regulate select ions  Lg size, active cells on outer surface Crustaceans – variable, but regulate ions  See Tables 11.3 and 11.4 in Willmer, 2/e

13 Marine Invertebrates  Osmoregulation accomplished via: impermeable body surface thin surface membrane of the gills (rapid exchange)  Salt gained via: INCOMPLETELY impermeable body surface thin surface membrane of the gills food and seawater (both containing some solutes)

14 Invasion of Other Habitats  Marine inverts, both conformers and regulators, can inhabit brackish water Oysters – tolerate dilution, even before closing shell Various crabs (again) – fairly successful regulators, although extremes may be too much  No FW Echinoderms or Cephalopods

Brackish Inverts + Fish  Solid lines arthropods  Dashed lines molluscs  Black dotted lines worms  Teleosts shaded area 15 Figure 12.13

Freshwater Inverts + Fish  Solid lines arthropods  Dashed green lines molluscs  Black dotted lines worms  Teleosts shaded area 16 Figure 13.9

Extreme Habitats - cryptobiosis  Adaptation to extreme enviro change  Drying in enviro can lead to increased osmotic conc  Response may be extreme = cryptobiosis 17 Figure 14.4

Extreme Habitats – regulation!  Regulation of internal conc over wide range of salinities!!!  Also see Figure 14.7 structures/mechanisms used by Artemia at different life stages 18 Figure 14.6

19 Marine bony fishes  Marine bony fishes Few same or slightly above the conc. of the external medium (hagfish), most about 1/3 the conc. of seawater  General Osmotic Tendencies Osmotic efflux of water Influx of ions

20 Marine bony fishes (2)  Active secretion of monovalent ions at the gills  Produce small amount of urine isosmotic to the blood but high in Mg++ and SO4=  Drink water  Compare/contrast w/ freshwater bony fish, see summary handout of vertebrates (slide 15) Osmotic issues are loss of ions/salts and water gain!

21 Bony fishes: marine vs freshH2O Figure Saltwater teleost Figure Freshwater teleost

22 Freshwater Vertebrates Figure Compare To Figure 11.5

23 Marine Vertebrates -elasmobranchs/chondrichthyes  Sharks and rays almost exclusively marine  Solve problem of water efflux by being slightly hyperosmotic (to the environment)  However, salt conc. about 1/3 that of SW  High osmolarity from organic compounds in a ratio of 2 urea: 1 TMAO Urea is an end-product of protein metabolism and is known to destabilize many proteins (= ENZYMES)!! TMAO has an inhibitory effect on the action of the urea

24 Marine Vertebrates -elasmobranchs/chondrichthyes v(2)  Hyperosmotic internal environment solves problem of water efflux actually slight influx via gills! No need to drink SW (w/ additional salt load)  But salt conc. about 1/3 that of SW means that there is still an ion regulation issue  Solutions include- Excretion of salts in urine Excretion of Na+ and Cl- (hyperosmotic to SW) via the rectal gland

25 Marine Vertebrates -birds and reptiles  Salt glands  May eliminate excess salt load by using an extrarenal salt gland  Salt gland produces a highly concentrated solution of salt Seawater = 470 mmol Na + /L Seabird salt gland excretion = mmol Na + /L  Also produce uric acid Combines with ions Precipitates from solution (H2O) conservation

26 Marine Vertebrates -mammals  Marine mammals have a HIGHLY EFFICIENT KIDNEY that can produce urine more conc. than SW  Some pinnipeds can live without drinking water on a diet of fish Remember that marine fish are NOT as conc. as SW or MARINE INVERTS!!

27 Marine Vertebrates -reptiles, bird, and mammals Figure 11.38

28 Moist Skinned Animals  Back to regulatory issues, these animals will have less control over water loss than others Worms, various phyla Gastropod molluscs, esp. slugs Amphibians (only vertebrates here)  Evaporation rates are 1-2 orders of magnitude higher than other animals (Table 8.8 and Fig 8.12 in Schmidt-Nielsen, 5 th Ed)

29 Moist Skinned Animals (2)  Solutions to minimize water loss include Live near water Humid habitats, soil or mud Active at night (lower evaporation rate) Active during or immediate following precipitation

30 Less Permeable Terrestrial Animals  These animals will have more control over water loss than moist skinned animals Arthropods  exoskeleton and cuticle Most higher vertebrates, except amphibians  epidermis, hair, scales, feathers

31 Additional Information from Text  Willmer (2/e) Table 5.1, extracellular fluid concentration of various animals Figure 5.2, responses to changing environmental concentrations Table 5.2, tolerance to water loss Table 5.3, permeability across various surfaces Figure 5.6, chloride cells of fish