HomeostasisChapter 7Zoology 1450

TopicsOsmoregulationEndocrine regulationThermal regulationImmune Response (briefly)

Part 1: Osmoregulatory Systems in FishesMaintaining homeostasis with respect to solute concentrations and water content

IntroductionMaintaining steady-state equilibrium in the internal environment of aquatic and marine organisms is challenging.

Much is done involuntarily (hormones, enzymes, osmoregulation, etc.) so little physical action is required, however

Pick-up-and-move still an option! (Poor environment.)

DefinitionsHomeostasis = maintaining steady state equilibrium in the internal environment of an organismsSolute homeostasis = maintaining equilibrium with respect to solute (ionic and neutral solutes) concentrations (i.e. salts)Water homeostasis = maintaining equilibrium with respect to the amount of water retained in the body fluids and tissues

Definitions, continuedOsmotic concentration - Total concentration of all solutes in an aqueous solution.Unitsosmolals = 1 mole of solute/liter of water milliosmolals = 1/1000th of one osmolal

Osmoregulation in different environmentsChallenge to homeostasis depends on

Solute concentration of body fluids and tissuesconcentration of environmental solutes marine: ~34 ppt salinity = 1000 mosm/lfreshwater: < 3 ppt salinity = 1 - 10 mosm/l

Osmoregulation in different environmentsEach species has a range of environmental osmotic conditions in which it can function:stenohaline - tolerate a narrow range of salinities in external environment euryhaline - tolerate a wide range of salinities in external environmentshort term changes: estuarine - 10 - 32 ppt, intertidal - 25 - 40long term changes: diadromous fishes (salmon)

Four osmoregulatory strategies in fishes1. Isosmotic (nearly isoionic, osmoconformers)2. Isosmotic with regulation of specific ions3. Hyperosmotic (fresh H20 fish)4. Hyposmotic (salt H2O fish)

Osmoregulation StrategiesOsmoconforming (no strategy) Hagfish internal salt concentration = seawater. However, since they live IN the ocean....no regulation required!

Osmoregulation StrategiesElasmobranchs (sharks, skates, rays, chimeras)

Maintain internal salt concentration ~ 1/3 seawater, make up the rest of internal salts by retaining high concentrations of urea & trimethylamine oxide (TMAO).

Bottom linetotal internal osmotic concentration equal to seawater!

How is urea retained? Gill membrane has low permeability to urea so it is retained within the fish. Because internal inorganic and organic salt concentrations mimic that of their environment, passive water influx or efflux is minimized.

ionic conc. approx 1/3 of seawaterdrink copiously to gain waterChloride cells eliminate Na+ and Cl- kidneys eliminate Mg++ and SO4=

advantages and disadvantages?Osmotic regulation by marine teleosts...

Saltwater teleosts:chloride cellskidneys

Chloride Cell fig 6.2: sea waterinternalmitochondriatubular systemNa+K+Na+ K+ ATPaseNa+Cl-+

Ionic conc. Approx 1/3 of seawaterDont drinkChloride cells fewer, work in reverse Kidneys eliminate excess water; ion lossAmmonia & bicarbonate ion exchange mechanisms

advantages and disadvantages?Osmotic regulation by FW teleosts

Freshwater teleosts:kidneysIon exchangepumps; beta chloride cells

Ion Exchange MechanismsfreshwaterinterioractivepumpactivepumpATPATP

Freezing Resistance:What fishes might face freezing?

hagfishes?isotonicmarine elasmobranchs?isotonicfreshwater teleosts?hypertonicmarine teleosts?hypotonic

Solution for Antarctic fishMacromolecular compounds peptides (protein) glycopeptides (carbohydrate/protein)molecules adsorb (attach) to ice crystal surface

interfere with ice crystal growth (disrupt matrix)

Why is this important???ice ruptures cells; hinders osmoregulation

What about rapid ion flux?EuryhalineShort-term fluctuations in osmotic state of environment, e.g. in intertidal zone or in estuaries where salinity can range from 10 to 34 ppt with the daily tidal cycle:these fish have both kinds of chloride cellswhen salinity is low, operate more like FW fisheswhen salinity is high, operate like marine fisheskidneys function only under low salinity conditions

EuryhalineDiadromous fishes (spend part of life in salt water, part in freshwater catadromous (migrate seaward) or anadromous (migrate up river)hormone-mediated changes associated with metamorphosis - convert from FW adaptations to SW or vice versa, depending on direction of migration

What about stress??Stressors (handling, sustained exercise such as escape from predator pursuit) cause release of adrenaline (epinephrine) - for mediating escape, etc.

Adrenaline causes diffusivity of gill epithelium to increase, i.e. leaky cell membranes water & ions)

This accentuates the normal osmoregulatory challenge for FW or marine fishes

How to reduce stress in stressed fishes?Minimize the osmotic challenge by placing fish in conditions that are isosmoticadd salt to freshwater, e.g. in transporting fish or when exposing them to some other short-term challengedilute saltwater for same situation with marine species

Thermoregulation in Fishes

Temperature effects on fishTemperature exhibits the greatest influence on fishs lives!Affects metabolismAffects digestionSignals reproductive maturation and behavior

Fish are conformers (well, sort of...)Body temperature is that of the environment (poikilothermic ectothermy)

Each species has particular range of temperatures that they can tolerate and that are optimal

Big difference!

Behavioral Thermoregulation in FishesAlthough fish are ectotherms, they can alter their body temperature by moving to habitats with optimal temperature

Hot FishesSome fish can maintain body temperature greater than ambient - tunas, billfishes, relatives (nearly endothermic)

Tuna use retia (similar to rete mirable) in muscles to conserve heat & exchange O2.

Also, red muscle is medial rather than distal

Billfishes have warm brains - heat organ from muscles around eye

Practical applicationYoure management decisions and actions must account for fish responses to temperature gradients and limitations

Endocrine Systems of Fishes

Pituitary Gland - Master GlandLinked with hypothalamus of brainProduces hormones that affect other endocrine tissues - indirect influenceProduces hormones that affect non-endocrine tissues directly

Pituitary GlandIndirect influenceACTH - adrenocorticotrophic hormonestimulates interrenal tissue production of cortisol, stress responseTH - thyrotrophic hormonestimulate thyroid production of thyroxin (growth, metamorphosis-i.e. flounder)GTH- gonadotrophic hormonestimulates gonads to produce androgens/estrogens

Pituitary GlandEffects non-endocrine tissues directlypigmentation - melanophore stimulating hormone (MSH)affects long-term control of colorosmoregulation - prolactin, vasotocincontrols fresh/saltwater systemsgrowth somatotrophic hormonestimulates > length, cell multiplication

Thyroid Glandisolated follicles distributed in connective tissue along ventral aortacontrols metabolic rateaffects metamorphosis, maturationfacilitates switch between fresh & salt water

Gonadsgamete and sex hormone productioncontrols gametes maturationcause formation of secondary sex characteristics: color, shape, behaviorin fish, several sex hormones also serve as pheromones - e.g. goldfish males respond to hormones released with ovulation

Other endocrine tissues in fisheschromaffin tissues-located near kidneys & heartproduce adrenaline/noradrenaline fight or flightincreases blood flow through gills, ventilation rate

interrenal (inside kidney) tissuesproduce cortisol, cortisone - stress response hormones (reduce inflamation)

Other endocrine tissues in fishespancreatic isletsproduce insulin - controls glucose, glycogen metabolism (glucagon production)

corpuscles of Stanniusproduce stanniocalcin - controls Ca2+ uptake at gills

Immune System

IntroductionObviously, the immune system is important in homeostatic processes.

Immune systems of fish have two components: non-specific and specific.

As we will see, both are involved in protecting fish from visible as well as invisible disease causing agents.

Non-specific immunitySkin & Scalesspecific solid layers of protection from pathological and chemical stressors.

Mucus secretiontraps microorganisms; preventing entry into body cavity or circulation

Macrophages (phagcytes) and cytotoxic cellspart of the inflamatory response which destroy pathogens within the body before they can do harm.

Specific Immune ResponseMore of an active response where an invader is detected and destroyed.

Primary organs: kidney, thymus, spleen, intestine.

Antigensinvading compounds which provoke an immune response.

Source: Cancer Research Institute (2002) www.cancerresearch.org/immhow.html

Specific immune response: What if something does get in??White blood cells called B lymphocyte cells (B cells) and T lymphocyte cells (T cells)bind to foreign cells and begin replication and attachement to antigens (sort of markers for things to come...).

Occasionally, invader actually goes trough a macrophage first...then B cell responds...

Once B cells replicate, antibodies are produced which bind specifically to pathogens and tag them for destruction (eating) by macrophages!

Looks like meats back on the menu boys!!!

Questions???