HomeostasisHomeostasis

Chapter 7Chapter 7

Zoology 1450Zoology 1450

TopicsTopics

OsmoregulationOsmoregulation Endocrine regulationEndocrine regulation Thermal regulationThermal regulation Immune Response (briefly)Immune Response (briefly)

Part 1: Osmoregulatory Part 1: Osmoregulatory Systems in FishesSystems in Fishes

Maintaining homeostasis with Maintaining homeostasis with respect to solute concentrations respect to solute concentrations

and water contentand water content

IntroductionIntroduction

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

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

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

DefinitionsDefinitions

HomeostasisHomeostasis = maintaining steady state = maintaining steady state equilibrium in the internal environment of an equilibrium in the internal environment of an organismsorganisms

Solute homeostasisSolute homeostasis = maintaining equilibrium = maintaining equilibrium with respect to solute (ionic and neutral solutes) with respect to solute (ionic and neutral solutes) concentrations (i.e. salts)concentrations (i.e. salts)

Water homeostasisWater homeostasis = maintaining equilibrium = maintaining equilibrium with respect to the amount of water retained in with respect to the amount of water retained in the body fluids and tissuesthe body fluids and tissues

Definitions, continuedDefinitions, continued

Osmotic concentrationOsmotic concentration - Total - Total concentration of all solutes in an aqueous concentration of all solutes in an aqueous solution.solution.

UnitsUnits

osmolalsosmolals = 1 mole of solute/liter of water = 1 mole of solute/liter of water

milliosmolalsmilliosmolals = 1/1000th of one osmolal = 1/1000th of one osmolal

Osmoregulation in different environmentsOsmoregulation in different environments

Challenge to homeostasis depends onChallenge to homeostasis depends on

Solute concentration of body fluids and Solute concentration of body fluids and tissues…tissues…

……concentration of environmental solutes concentration of environmental solutes marine: ~34 ppt salinity = 1000 mosm/lmarine: ~34 ppt salinity = 1000 mosm/l freshwater: < 3 ppt salinity = 1 - 10 mosm/lfreshwater: < 3 ppt salinity = 1 - 10 mosm/l

Osmoregulation in different environmentsOsmoregulation in different environments

Each species has a range of environmental Each species has a range of environmental osmotic conditions in which it osmotic conditions in which it cancan function: function: stenohalinestenohaline - tolerate a - tolerate a narrow rangenarrow range of of

salinities in external environment salinities in external environment euryhalineeuryhaline - tolerate a - tolerate a wide rangewide range of salinities of salinities

in external environmentin external environment short term changes: estuarine - 10 - 32 ppt, short term changes: estuarine - 10 - 32 ppt,

intertidal - 25 - 40intertidal - 25 - 40 long term changes: diadromous fishes long term changes: diadromous fishes

(salmon)(salmon)

Four osmoregulatory strategies in fishesFour osmoregulatory strategies in fishes

1. Isosmotic (nearly isoionic, osmoconformers)1. Isosmotic (nearly isoionic, osmoconformers)

2. Isosmotic with regulation of specific ions2. Isosmotic with regulation of specific ions

3. Hyperosmotic (fresh H3. Hyperosmotic (fresh H220 fish)0 fish)

4. Hyposmotic (salt H4. Hyposmotic (salt H22O fish)O fish)

Osmoregulation StrategiesOsmoregulation Strategies

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

Osmoregulation StrategiesOsmoregulation Strategies

Elasmobranchs (sharks, skates, rays, chimeras)Elasmobranchs (sharks, skates, rays, chimeras)

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

Bottom line…total internal osmotic concentration Bottom line…total internal osmotic concentration equal to seawater! equal to seawater!

How is urea retained? How is urea retained? Gill membrane has low permeabilityGill membrane has low permeability to urea so it is to urea so it is

retained within the fish. Because internal inorganic retained within the fish. Because internal inorganic and organic salt concentrations mimic that of their and organic salt concentrations mimic that of their environment, passive water influx or efflux is environment, passive water influx or efflux is minimized.minimized.

ionic conc. approx 1/3 of seawaterionic conc. approx 1/3 of seawater drink copiously to drink copiously to gaingain water water Chloride cellsChloride cells eliminate Na eliminate Na++ and Cl and Cl-- kidneys eliminate Mgkidneys eliminate Mg++++ and SO and SO44

==

advantages and disadvantages?advantages and disadvantages?

Osmotic regulation by marine teleosts...Osmotic regulation by marine teleosts...

Saltwater teleosts:Saltwater teleosts:

drinkdrink

active tran.active tran.

passive diff.passive diff.

NaNa++, Cl, Cl--

MgMg++++, SO, SO44==

HH22OO

NaNa++, Cl, Cl--

NaNa++, Cl, Cl--

chloride cellschloride cells

MgMg++++, SO, SO44==

kidneyskidneys

Chloride Cell Chloride Cell fig 6.2fig 6.2: :

pavementpavementcellcell PCPCPCPC

activeactive

passivepassive

chloride cellchloride cell

accessory accessory cellcell

sea watersea water

internalinternalmitochondriamitochondria

tubular systemtubular system

NaNa++

KK++ NaNa+ + KK+ + ATPaseATPase

NaNa++, , ClCl--

NaNa++

ClCl--

ClCl--

ClCl--ClCl--

gutgut

carriercarrier

NaNa++

NaNa++

NaNa++

pumppump

++

Ionic conc. Approx 1/3 of seawaterIonic conc. Approx 1/3 of seawater Don’t drinkDon’t drink Chloride cellsChloride cells fewer, work in reverse fewer, work in reverse Kidneys eliminate excess water; ion lossKidneys eliminate excess water; ion loss Ammonia & bicarbonate ion exchange mechanismsAmmonia & bicarbonate ion exchange mechanisms

advantages and disadvantages?advantages and disadvantages?

Osmotic regulation by FW teleostsOsmotic regulation by FW teleosts

Freshwater teleosts:Freshwater teleosts: activeactive

passivepassive

HH22OO

NaNa++, Cl, Cl--

NaNa++, Cl, Cl--

don’tdon’tdrinkdrink

waterwater

kidneyskidneysIon exchangeIon exchange

pumps; beta chloride cellspumps; beta chloride cells

Ion Exchange MechanismsIon Exchange Mechanisms

gill membranegill membrane

freshwaterfreshwater interiorinterior

activeactive

pumppump

activeactive

pumppump

NaNa++

ClCl--

NHNH44++ or H or H++

HCOHCO33--

ATPATP

ATPATP

Freezing Resistance:Freezing Resistance: What fishes might face freezing?What fishes might face freezing?

hagfishes?hagfishes?

isotonicisotonic

marine elasmobranchs?marine elasmobranchs?

isotonicisotonic

freshwater teleosts?freshwater teleosts?

hypertonichypertonic

marine teleosts?marine teleosts?

hypotonichypotonic

Solution for Antarctic fishSolution for Antarctic fish

Macromolecular compoundsMacromolecular compounds peptides (protein)peptides (protein)

glycopeptidesglycopeptides

(carbohydrate/protein)(carbohydrate/protein){rich in alaninerich in alanine

molecules adsorb (attach) to ice crystal surfacemolecules adsorb (attach) to ice crystal surface

interfere with ice crystal growth (disrupt matrix)interfere with ice crystal growth (disrupt matrix)

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

What about rapid ion flux?What about rapid ion flux?

EuryhalineEuryhaline Short-term fluctuations in osmotic state of Short-term fluctuations in osmotic state of

environment, e.g. in intertidal zone or in environment, e.g. in intertidal zone or in estuaries where salinity can range from 10 to estuaries where salinity can range from 10 to 34 ppt with the daily tidal cycle:34 ppt with the daily tidal cycle: these fish have both kinds of chloride cellsthese fish have both kinds of chloride cells

when salinity is low, operate more like FW fisheswhen salinity is low, operate more like FW fishes when salinity is high, operate like marine fisheswhen salinity is high, operate like marine fishes kidneys function only under low salinity conditionskidneys function only under low salinity conditions

EuryhalineEuryhaline

DiadromousDiadromous fishes (spend part of life in salt fishes (spend part of life in salt water, part in freshwater – water, part in freshwater – catadromouscatadromous (migrate seaward) or (migrate seaward) or anadromousanadromous (migrate (migrate up river)up river)

hormone-mediated changes associated hormone-mediated changes associated with metamorphosis - convert from FW with metamorphosis - convert from FW adaptations to SW or vice versa, depending adaptations to SW or vice versa, depending on direction of migrationon direction of migration

What about stress??What about stress??

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

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

This accentuates the normal osmoregulatory This accentuates the normal osmoregulatory challenge for FW or marine fisheschallenge for FW or marine fishes

How to reduce stress in stressed fishes?How to reduce stress in stressed fishes?

Minimize the osmotic challenge by placing Minimize the osmotic challenge by placing fish in conditions that are fish in conditions that are isosmoticisosmotic add salt to freshwater, e.g. in transporting fish add salt to freshwater, e.g. in transporting fish

or when exposing them to some other short-or when exposing them to some other short-term challengeterm challenge

dilute saltwater for same situation with marine dilute saltwater for same situation with marine speciesspecies

Thermoregulation in FishesThermoregulation in Fishes

Temperature effects on fishTemperature effects on fish

Temperature exhibits the greatest influence on Temperature exhibits the greatest influence on fish’s lives!fish’s lives!

Affects metabolismAffects metabolism Affects digestionAffects digestion Signals reproductive maturation and behaviorSignals reproductive maturation and behavior

Fish are conformers (well, sort of...)Fish are conformers (well, sort of...)

Body temperature is that of the environment Body temperature is that of the environment ((poikilothermic ectothermypoikilothermic ectothermy))

Each species has particular range of Each species has particular range of temperatures that they can temperatures that they can toleratetolerate and that and that are are optimaloptimal

Big difference!Big difference!

Behavioral Thermoregulation in FishesBehavioral Thermoregulation in Fishes

Although fish are Although fish are ectothermsectotherms, they can , they can alter their body temperature by moving to alter their body temperature by moving to habitats with optimal temperaturehabitats with optimal temperature

Hot FishesHot Fishes

Some fish can maintain body temperature greater than Some fish can maintain body temperature greater than ambient - tunas, billfishes, relatives (nearly ambient - tunas, billfishes, relatives (nearly endothermicendothermic))

Tuna use Tuna use retiaretia (similar to rete mirable) in muscles to (similar to rete mirable) in muscles to conserve heat & exchange Oconserve heat & exchange O22..

Also, red muscle isAlso, red muscle is medial medial rather than distal rather than distal

Billfishes have warm brains - heat organ from muscles Billfishes have warm brains - heat organ from muscles around eyearound eye

Practical applicationPractical application

You’re management decisions and actions You’re management decisions and actions must account for fish responses to must account for fish responses to temperature gradients and limitationstemperature gradients and limitations

Endocrine Systems of FishesEndocrine Systems of Fishes

Pituitary Gland - Master GlandPituitary Gland - Master Gland

Linked with hypothalamus of brainLinked with hypothalamus of brain Produces hormones that affect other Produces hormones that affect other

endocrine tissues - indirect influenceendocrine tissues - indirect influence Produces hormones that affect non-Produces hormones that affect non-

endocrine tissues directlyendocrine tissues directly

Pituitary GlandPituitary Gland

Indirect influenceIndirect influence ACTH - adrenocorticotrophic ACTH - adrenocorticotrophic

hormonehormone stimulates interrenal tissue production stimulates interrenal tissue production

of cortisol, stress responseof cortisol, stress response

TH - thyrotrophic hormoneTH - thyrotrophic hormone stimulate thyroid production of thyroxin stimulate thyroid production of thyroxin

(growth, metamorphosis-i.e. flounder)(growth, metamorphosis-i.e. flounder)

GTH- gonadotrophic hormoneGTH- gonadotrophic hormone stimulates gonads to produce stimulates gonads to produce

androgens/estrogensandrogens/estrogens

Pituitary GlandPituitary Gland

Effects non-endocrine tissues directlyEffects non-endocrine tissues directly pigmentation - melanophore stimulating hormone (MSH)pigmentation - melanophore stimulating hormone (MSH)

affects long-term control of coloraffects long-term control of color osmoregulation - prolactin, vasotocinosmoregulation - prolactin, vasotocin

controls fresh/saltwater systemscontrols fresh/saltwater systems growth – somatotrophic hormonegrowth – somatotrophic hormone

stimulates > length, cell multiplicationstimulates > length, cell multiplication

Thyroid GlandThyroid Gland

isolated follicles distributed in connective tissue isolated follicles distributed in connective tissue along ventral aortaalong ventral aorta

controls metabolic ratecontrols metabolic rate affects metamorphosis, maturationaffects metamorphosis, maturation facilitates switch between fresh & salt waterfacilitates switch between fresh & salt water

GonadsGonads

gamete and sex hormone productiongamete and sex hormone production controls gametes maturationcontrols gametes maturation cause formation of cause formation of secondary sex secondary sex

characteristicscharacteristics: color, shape, behavior: color, shape, behavior in fish, several sex hormones also serve as in fish, several sex hormones also serve as

pheromonespheromones - e.g. goldfish males respond - e.g. goldfish males respond to hormones released with ovulationto hormones released with ovulation

Other endocrine tissues in fishesOther endocrine tissues in fishes chromaffin tissueschromaffin tissues-located near kidneys & heart-located near kidneys & heart

produce adrenaline/noradrenaline – “fight or flight”produce adrenaline/noradrenaline – “fight or flight” increases blood flow through gills, ventilation rateincreases blood flow through gills, ventilation rate

interrenal (inside kidney) tissuesinterrenal (inside kidney) tissues produce cortisol, cortisone - stress response produce cortisol, cortisone - stress response

hormones (reduce inflamation)hormones (reduce inflamation)

Other endocrine tissues in fishesOther endocrine tissues in fishes pancreatic isletspancreatic islets

produce insulin - controls glucose, glycogen produce insulin - controls glucose, glycogen metabolism (glucagon production)metabolism (glucagon production)

corpuscles of Stanniuscorpuscles of Stannius produce stanniocalcin - controls Caproduce stanniocalcin - controls Ca2+2+ uptake at gills uptake at gills

Immune SystemImmune System

IntroductionIntroduction

Obviously, the immune system is important in Obviously, the immune system is important in homeostatic processes.homeostatic processes.

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

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

Non-specific immunityNon-specific immunity

Skin & ScalesSkin & Scales—specific solid layers of protection —specific solid layers of protection from pathological and chemical stressors.from pathological and chemical stressors.

Mucus secretionMucus secretion—traps microorganisms; preventing —traps microorganisms; preventing entry into body cavity or circulationentry into body cavity or circulation

MacrophagesMacrophages (phagcytes) and cytotoxic cells—part (phagcytes) and cytotoxic cells—part of the inflamatory response which destroy of the inflamatory response which destroy pathogens within the body before they can do harm.pathogens within the body before they can do harm.

Specific Immune ResponseSpecific Immune Response

More of an active response More of an active response where an “invader” is detected where an “invader” is detected and destroyed.and destroyed.

Primary organs: kidney, Primary organs: kidney, thymus, spleen, intestine.thymus, spleen, intestine.

AntigensAntigens—invading —invading compounds which provoke an compounds which provoke an immune response.immune response.

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

Specific immune response: What if something does get in??Specific immune response: What if something does get in??

White blood cells called White blood cells called B lymphocyte cells (B lymphocyte cells (B cellsB cells) and T ) and T lymphocyte cells (lymphocyte cells (T cellsT cells)—bind to foreign cells and begin )—bind to foreign cells and begin replication and attachement to antigens (sort of markers replication and attachement to antigens (sort of markers for things to come...). for things to come...).

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

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

“Looks like meat’s back on the menu

boys!!!”

Questions???Questions???