Homeostasis

Dr. G. Nugroho Susanto, M. Sc.Department of BiologyFaculty of Mathematics and Natural SciencesUniversity of Lampung

Homeostasis

Homeostasis refers to maintaininginternal stability within an organism andreturning to a particular stable state aftera fluctuation.

Homeostasis refers to maintaininginternal stability within an organism andreturning to a particular stable state aftera fluctuation.

Homeostasis

Changes to the internal environmentcome from: Metabolic activities require a supply of

materials (oxygen, nutrients, salts, etc) thatmust be replenished.

Waste products are produced that must beexpelled.

Changes to the internal environmentcome from: Metabolic activities require a supply of

materials (oxygen, nutrients, salts, etc) thatmust be replenished.

Waste products are produced that must beexpelled.

Homeostasis

Systems within an organism function inan integrated way to maintain a constantinternal environment around a setpoint. Small deviations in pH, temperature,

osmotic pressure, glucose levels, & oxygenlevels activate physiological mechanisms toreturn that variable to its setpoint. Negative feedback

Systems within an organism function inan integrated way to maintain a constantinternal environment around a setpoint. Small deviations in pH, temperature,

osmotic pressure, glucose levels, & oxygenlevels activate physiological mechanisms toreturn that variable to its setpoint. Negative feedback

Osmoregulation & Excretion

Osmoregulation regulates soluteconcentrations and balances the gainand loss of water.

Excretion gets rid of metabolic wastes.

Osmoregulation regulates soluteconcentrations and balances the gainand loss of water.

Excretion gets rid of metabolic wastes.

Osmosis

Cells require a balance between osmoticgain and loss of water.

Water uptake and loss are balanced byvarious mechanisms of osmoregulationin different environments.

Cells require a balance between osmoticgain and loss of water.

Water uptake and loss are balanced byvarious mechanisms of osmoregulationin different environments.

Osmosis

Osmosis is the movement of wateracross a selectively permeablemembrane. If two solutions that are separated by a

membrane differ in their osmolarity, waterwill cross the membrane to bring theosmolarity into balance (equal soluteconcentrations on both sides).

Osmosis is the movement of wateracross a selectively permeablemembrane. If two solutions that are separated by a

membrane differ in their osmolarity, waterwill cross the membrane to bring theosmolarity into balance (equal soluteconcentrations on both sides).

Osmotic Challenges

Osmoconformers, which are onlymarine animals, are isoosmotic withtheir surroundings and do not regulatetheir osmolarity.

Osmoregulators expend energy tocontrol water uptake and loss in ahyperosmotic or hypoosmoticenvironment.

Osmoconformers, which are onlymarine animals, are isoosmotic withtheir surroundings and do not regulatetheir osmolarity.

Osmoregulators expend energy tocontrol water uptake and loss in ahyperosmotic or hypoosmoticenvironment.

Osmotic Regulation

Most marine invertebrates are osmoticconformers – their bodies have thesame salt concentration as the seawater. The sea is highly stable, so most marine

invertebrates are not exposed to osmoticfluctuations.

These organisms are restricted to a narrowrange of salinity – stenohaline. Marine spider crab

Most marine invertebrates are osmoticconformers – their bodies have thesame salt concentration as the seawater. The sea is highly stable, so most marine

invertebrates are not exposed to osmoticfluctuations.

These organisms are restricted to a narrowrange of salinity – stenohaline. Marine spider crab

Osmotic Regulation

Conditions along thecoasts and in estuariesare often more variablethan the open ocean. Animals must be able to

handle large, often abruptchanges in salinity.

Euryhaline animals cansurvive a wide range ofsalinity changes by usingosmotic regulation. Hyperosmotic regulator

(body fluids saltier thanwater)

Shore crab.

Conditions along thecoasts and in estuariesare often more variablethan the open ocean. Animals must be able to

handle large, often abruptchanges in salinity.

Euryhaline animals cansurvive a wide range ofsalinity changes by usingosmotic regulation. Hyperosmotic regulator

(body fluids saltier thanwater)

Shore crab.

Osmotic Regulation

The problem of dilution is solved bypumping out the excess water as diluteurine.

The problem of salt loss is compensatedfor by salt secreting cells in the gills theactively remove ions from the water andmove them into the blood. Requires energy.

The problem of dilution is solved bypumping out the excess water as diluteurine.

The problem of salt loss is compensatedfor by salt secreting cells in the gills theactively remove ions from the water andmove them into the blood. Requires energy.

Osmotic Regulation - Freshwater

Freshwater animals face an even moreextreme osmotic difference than thosethat inhabit estuaries.

Freshwater animals face an even moreextreme osmotic difference than thosethat inhabit estuaries.

Osmotic Regulation - Freshwater

Freshwater fishes have skin covered with scales andmucous to keep excess water out.

Water that enters the body is pumped out by thekidney as very dilute urine.

Salt absorbing cells in the gills transport salt ions intothe blood.

Freshwater fishes have skin covered with scales andmucous to keep excess water out.

Water that enters the body is pumped out by thekidney as very dilute urine.

Salt absorbing cells in the gills transport salt ions intothe blood.

Osmotic Regulation - Freshwater

Invertebrates andamphibians alsosolve theseproblems in a similarway.

Amphibians activelyabsorb salt from thewater through theirskin.

Invertebrates andamphibians alsosolve theseproblems in a similarway.

Amphibians activelyabsorb salt from thewater through theirskin.

Osmotic Regulation – Marine

Marine bony fishes are hypoosmotic regulators. Maintain salt concentration at 1/3 that of seawater. Marine fishes drink seawater to replace water lost by

diffusion. Excess salt is carried to the gills where salt-secreting cells

transport it out to the sea. More ions voided in feces or urine.

Marine bony fishes are hypoosmotic regulators. Maintain salt concentration at 1/3 that of seawater. Marine fishes drink seawater to replace water lost by

diffusion. Excess salt is carried to the gills where salt-secreting cells

transport it out to the sea. More ions voided in feces or urine.

Osmotic Regulation – Marine

Sharks and rays retain urea (a metabolicwaste usually excreted in the urine) intheir tissues and blood.

This makes osmolarity of the shark’sblood equal to that of seawater, so waterbalance is not a problem.

Sharks and rays retain urea (a metabolicwaste usually excreted in the urine) intheir tissues and blood.

This makes osmolarity of the shark’sblood equal to that of seawater, so waterbalance is not a problem.

Osmotic Regulation – Terrestrial

Terrestrial animalslose water byevaporation fromrespiratory and bodysurfaces, excretion(urine), andelimination (feces).

Water is replaced bydrinking water, waterin food, and retainingmetabolic water.

Terrestrial animalslose water byevaporation fromrespiratory and bodysurfaces, excretion(urine), andelimination (feces).

Water is replaced bydrinking water, waterin food, and retainingmetabolic water.

Osmotic Regulation – Terrestrial

The end-product of protein metabolism isammonia, which is highly toxic. Fishes can excrete ammonia directly

because there is plenty of water to wash itaway.

The end-product of protein metabolism isammonia, which is highly toxic. Fishes can excrete ammonia directly

because there is plenty of water to wash itaway.

Osmotic Regulation – Terrestrial

Terrestrial animals must convertammonia to uric acid. Semi-solid urine – little water loss. In birds & reptiles, the wastes of developing

embryos are stored as harmless solidcrystals.

Terrestrial animals must convertammonia to uric acid. Semi-solid urine – little water loss. In birds & reptiles, the wastes of developing

embryos are stored as harmless solidcrystals.

Osmotic Regulation – Terrestrial

Marine birds andturtles have a saltgland capable ofexcreting highlyconcentrated saltsolution.

Marine birds andturtles have a saltgland capable ofexcreting highlyconcentrated saltsolution.

Excretory Processes

Most excretorysystems produceurine by refining afiltrate derived frombody fluids (blood,hemolymph, orcoelomic fluid).

Most excretorysystems produceurine by refining afiltrate derived frombody fluids (blood,hemolymph, orcoelomic fluid).

Excretory Processes

Key functions of most excretory systemsare: Filtration, pressure-filtering of body fluids

producing a filtrate. Reabsorption, reclaiming valuable solutes

from the filtrate. Secretion, addition of toxins and other

solutes from the body fluids to the filtrate. Excretion, the filtrate leaves the system.

Key functions of most excretory systemsare: Filtration, pressure-filtering of body fluids

producing a filtrate. Reabsorption, reclaiming valuable solutes

from the filtrate. Secretion, addition of toxins and other

solutes from the body fluids to the filtrate. Excretion, the filtrate leaves the system.

Invertebrate Excretory Structures

Contractile vacuoles are found inprotozoans and freshwater sponges. An organ of water balance – expels excess

water gained by osmosis.

Contractile vacuoles are found inprotozoans and freshwater sponges. An organ of water balance – expels excess

water gained by osmosis.

Invertebrate Excretory Structures

The most common type ofinvertebrate excretory organis the nephridium. The simplest arrangement

is the protonephridium ofacoelomates and somepseudocoelomates.

Fluid enters through flamecells, moves through thetubules, water andmetabolites are recoveredand wastes are excretedthrough pores that openalong the body surface. Highly branched due to

lack of circulatory system.

The most common type ofinvertebrate excretory organis the nephridium. The simplest arrangement

is the protonephridium ofacoelomates and somepseudocoelomates.

Fluid enters through flamecells, moves through thetubules, water andmetabolites are recoveredand wastes are excretedthrough pores that openalong the body surface. Highly branched due to

lack of circulatory system.

Invertebrate Excretory Structures

The metanephridium isan open system found inannelids, molluscs, andsome smaller phyla. Tubules are open at

both ends. Water enters through

the ciliated, funnelshaped nephrostome.

The metanephridium issurrounded by bloodvessels that assist inreclaiming water andvaluable solutes.

The metanephridium isan open system found inannelids, molluscs, andsome smaller phyla. Tubules are open at

both ends. Water enters through

the ciliated, funnelshaped nephrostome.

The metanephridium issurrounded by bloodvessels that assist inreclaiming water andvaluable solutes.

Invertebrate Excretory Structures

In arthropods,antennal glands arean advanced form ofthe nephridial organ. No open

nephrostomes,hydrostatic pressureof the blood formsan ultrafiltrate in theend sac.

In the tubule,selective resorptionof some salts andactive secretion ofothers occurs.

In arthropods,antennal glands arean advanced form ofthe nephridial organ. No open

nephrostomes,hydrostatic pressureof the blood formsan ultrafiltrate in theend sac.

In the tubule,selective resorptionof some salts andactive secretion ofothers occurs.

Invertebrate Excretory Structures

Insects and spiders haveMalpighian tubules thatare closed and lack anarterial supply.

Salts (especiallypotassium) are secretedinto the tubules from thehemolymph (blood). Water & other solutes

(including uric acid)follow.

Water & potassium arereabsorbed.

Uric acid is expelled infeces.

Insects and spiders haveMalpighian tubules thatare closed and lack anarterial supply.

Salts (especiallypotassium) are secretedinto the tubules from thehemolymph (blood). Water & other solutes

(including uric acid)follow.

Water & potassium arereabsorbed.

Uric acid is expelled infeces.

Vertebrate Kidneys

Kidneys, the excretory organs ofvertebrates, function in both excretionand osmoregulation.

Kidneys, the excretory organs ofvertebrates, function in both excretionand osmoregulation.

Vertebrate Kidneys

Nephrons and associated blood vesselsare the functional unit of the mammaliankidney.

The mammalian excretory systemcenters on paired kidneys which are alsothe principal site of water balance andsalt regulation.

Nephrons and associated blood vesselsare the functional unit of the mammaliankidney.

The mammalian excretory systemcenters on paired kidneys which are alsothe principal site of water balance andsalt regulation.

Vertebrate Kidneys

Each kidney issupplied withblood by a renalartery anddrained by arenal vein.

Each kidney issupplied withblood by a renalartery anddrained by arenal vein.

Vertebrate Kidneys

Urine exits each kidney through a ductcalled the ureter.

Both ureters drain into a common urinarybladder.

Urine exits each kidney through a ductcalled the ureter.

Both ureters drain into a common urinarybladder.

Structure and Function of the Nephronand Associated Structures

The mammalian kidney has two distinctregions: An outer renal cortex An inner renal medulla

The mammalian kidney has two distinctregions: An outer renal cortex An inner renal medulla

(b) Kidney structure

UreterSection of kidney from a rat

Renalmedulla

Renalcortex

Renalpelvis

Structure and Function of the Nephronand Associated Structures

The nephron, thefunctional unit ofthe vertebratekidney consists ofa single longtubule and a ballof capillariescalled theglomerulus.

The nephron, thefunctional unit ofthe vertebratekidney consists ofa single longtubule and a ballof capillariescalled theglomerulus.

Filtration of the Blood

Filtration occurs asblood pressureforces fluid from theblood in theglomerulus into thelumen of Bowman’scapsule.

Filtration occurs asblood pressureforces fluid from theblood in theglomerulus into thelumen of Bowman’scapsule.

Pathway of the Filtrate

From Bowman’scapsule, the filtratepasses through threeregions of the nephron: Proximal tubule Loop of Henle Distal tubule

Fluid from severalnephrons flows into acollecting duct.

From Bowman’scapsule, the filtratepasses through threeregions of the nephron: Proximal tubule Loop of Henle Distal tubule

Fluid from severalnephrons flows into acollecting duct.

From Blood Filtrate to Urine: ACloser Look

Filtrate becomes urine as it flows throughthe mammalian nephron and collectingduct. The composition of the filtrate is modified

through tubular reabsorption and secretion. Changes in the total osmotic concentration

of urine through regulation of waterexcretion.

Filtrate becomes urine as it flows throughthe mammalian nephron and collectingduct. The composition of the filtrate is modified

through tubular reabsorption and secretion. Changes in the total osmotic concentration

of urine through regulation of waterexcretion.

From Blood Filtrate to Urine: ACloser Look

Secretion and reabsorption in the proximaltubule substantially alter the volume andcomposition of filtrate.

Reabsorption of water continues as the filtratemoves into the descending limb of the loop ofHenle.

Secretion and reabsorption in the proximaltubule substantially alter the volume andcomposition of filtrate.

Reabsorption of water continues as the filtratemoves into the descending limb of the loop ofHenle.

From Blood Filtrate to Urine: ACloser Look

As filtrate travels through the ascendinglimb of the loop of Henle salt diffuses outof the permeable tubule into the interstitialfluid.

The distal tubule plays a key role inregulating the K+ and NaCl concentration ofbody fluids.

The collecting duct carries the filtratethrough the medulla to the renal pelvis andreabsorbs NaCl.

As filtrate travels through the ascendinglimb of the loop of Henle salt diffuses outof the permeable tubule into the interstitialfluid.

The distal tubule plays a key role inregulating the K+ and NaCl concentration ofbody fluids.

The collecting duct carries the filtratethrough the medulla to the renal pelvis andreabsorbs NaCl.

Conserving Water

The mammalian kidney’s ability toconserve water is a key terrestrialadaptation.

The mammalian kidney can produceurine much more concentrated than bodyfluids, thus conserving water.

The mammalian kidney’s ability toconserve water is a key terrestrialadaptation.

The mammalian kidney can produceurine much more concentrated than bodyfluids, thus conserving water.

Solute Gradients and WaterConservation

In a mammalian kidney, the cooperativeaction and precise arrangement of theloops of Henle and the collecting ductsare largely responsible for the osmoticgradient that concentrates the urine.

In a mammalian kidney, the cooperativeaction and precise arrangement of theloops of Henle and the collecting ductsare largely responsible for the osmoticgradient that concentrates the urine.

Solute Gradients and WaterConservation

The collecting duct, permeable to waterbut not salt conducts the filtrate throughthe kidney’s osmolarity gradient, andmore water exits the filtrate by osmosis.

The collecting duct, permeable to waterbut not salt conducts the filtrate throughthe kidney’s osmolarity gradient, andmore water exits the filtrate by osmosis.

Solute Gradients and WaterConservation

Urea diffuses out of the collecting ductas it traverses the inner medulla.

Urea and NaCl form the osmotic gradientthat enables the kidney to produce urinethat is hyperosmotic to the blood.

Urea diffuses out of the collecting ductas it traverses the inner medulla.

Urea and NaCl form the osmotic gradientthat enables the kidney to produce urinethat is hyperosmotic to the blood.

Regulation of Kidney Function

The osmolarity of the urine is regulatedby nervous and hormonal control ofwater and salt reabsorption in thekidneys.

The osmolarity of the urine is regulatedby nervous and hormonal control ofwater and salt reabsorption in thekidneys.

Regulation of Kidney Function

Antidiuretichormone (ADH)increases waterreabsorption in thedistal tubules andcollecting ducts ofthe kidney.

Antidiuretichormone (ADH)increases waterreabsorption in thedistal tubules andcollecting ducts ofthe kidney.

Temperature Regulation

Animals must keep their bodies within arange of temperatures that allows fornormal cell function.

Each enzyme has an optimumtemperature. Too low and metabolism slows. Too high and metabolic reactions become

unbalanced. Enzymes may be destroyed.

Animals must keep their bodies within arange of temperatures that allows fornormal cell function.

Each enzyme has an optimumtemperature. Too low and metabolism slows. Too high and metabolic reactions become

unbalanced. Enzymes may be destroyed.

Temperature Regulation

Poikilothermic animals’ bodytemperatures fluctuate withenvironmental temperatures.

Homeothermic animals’ bodytemperatures are constant.

Poikilothermic animals’ bodytemperatures fluctuate withenvironmental temperatures.

Homeothermic animals’ bodytemperatures are constant.

Temperature Regulation

All animals produce heat from cellularmetabolism, but in most this heat is lostquickly. Ectotherms – lose metabolic heat quickly,

so body temperature is determined by theenvironment. Body temp may be regulated environmentally.

Endotherms – retain metabolic heat andcan maintain a constant internal bodytemperature.

All animals produce heat from cellularmetabolism, but in most this heat is lostquickly. Ectotherms – lose metabolic heat quickly,

so body temperature is determined by theenvironment. Body temp may be regulated environmentally.

Endotherms – retain metabolic heat andcan maintain a constant internal bodytemperature.

Ectothermic TemperatureRegulation

Many ectotherms regulate body temperaturebehaviorally. Basking to increase temperature. Shelter in shade or coolness of a burrow to

decrease temperature.

Many ectotherms regulate body temperaturebehaviorally. Basking to increase temperature. Shelter in shade or coolness of a burrow to

decrease temperature.

Ectothermic TemperatureRegulation

Most ectotherms can also adjust theirmetabolic rates to the environmentaltemperature. Activity levels can remain unchanged over a

wider range of temperatures.

Most ectotherms can also adjust theirmetabolic rates to the environmentaltemperature. Activity levels can remain unchanged over a

wider range of temperatures.

Endothermic TemperatureRegulation

Constant temperature in endotherms ismaintained by a delicate balancebetween heat production and heat loss. Heat is produced by the animal’s

metabolism. Producing heat requires energy – supplied

by food. Endotherms must eat more in cold weather.

Constant temperature in endotherms ismaintained by a delicate balancebetween heat production and heat loss. Heat is produced by the animal’s

metabolism. Producing heat requires energy – supplied

by food. Endotherms must eat more in cold weather.

Endothermic TemperatureRegulation If an animal is too

cool, it cangenerate heat byincreasingmuscular activity(exercise orshivering). Heat isretained throughinsulation.

If an animal is toowarm it decreasesheat productionand increases heatloss.

If an animal is toocool, it cangenerate heat byincreasingmuscular activity(exercise orshivering). Heat isretained throughinsulation.

If an animal is toowarm it decreasesheat productionand increases heatloss.

Adaptations for Hot Environments

Small desert mammals are mostlyfossorial (living underground) ornocturnal. Burrows are cool and moist.

Adaptations to derive water frommetabolism and produce concentratedurine & dry feces.

Small desert mammals are mostlyfossorial (living underground) ornocturnal. Burrows are cool and moist.

Adaptations to derive water frommetabolism and produce concentratedurine & dry feces.

Adaptations for Hot Environments

Larger desert mammals(camels, desertantelopes) have differentadaptations. Glossy, pallid color

reflects sunlight. Fat tissue is

concentrated in ahump, rather thanbeing evenly distributedin an insulating layer.

Sweating and pantingare ways of dumpingheat.

Larger desert mammals(camels, desertantelopes) have differentadaptations. Glossy, pallid color

reflects sunlight. Fat tissue is

concentrated in ahump, rather thanbeing evenly distributedin an insulating layer.

Sweating and pantingare ways of dumpingheat.

Adaptations for Cold Environments

In cold environments,mammals reduce heatloss by having a thickinsulating layer of fat,fur, or both.

Heat production isincreased.

Extremities are allowedto cool. Heat loss is prevented

throughcountercurrent heatexchange.

In cold environments,mammals reduce heatloss by having a thickinsulating layer of fat,fur, or both.

Heat production isincreased.

Extremities are allowedto cool. Heat loss is prevented

throughcountercurrent heatexchange.

Adaptations for Cold Environments

Small mammals are not as wellinsulated. Many avoid direct exposure to the cold by

living in tunnels under the snow. Subnivean environment. This is where food is located.

Small mammals are not as wellinsulated. Many avoid direct exposure to the cold by

living in tunnels under the snow. Subnivean environment. This is where food is located.

Adaptive Hypothermia

Endothermy is energetically expensive. Ectotherms can survive weeks without

eating. Endotherms must always have energy

supplies.

Endothermy is energetically expensive. Ectotherms can survive weeks without

eating. Endotherms must always have energy

supplies.

Adaptive Hypothermia

Some very smallmammals & birds(bats orhummingbirds)maintain high bodytemperatures whenactive, but allowtemperatures to dropwhen sleeping. Daily torpor

Some very smallmammals & birds(bats orhummingbirds)maintain high bodytemperatures whenactive, but allowtemperatures to dropwhen sleeping. Daily torpor

Adaptive Hypothermia

Hibernation is a way to solvethe problem of lowtemperatures and the scarcityof food. True hibernators store fat,

then enter hibernationgradually. Metabolism & body slows to a

fraction of normal. Body temperature decreases. Shivering helps increase

temperatures when they arewaking up.

Hibernation is a way to solvethe problem of lowtemperatures and the scarcityof food. True hibernators store fat,

then enter hibernationgradually. Metabolism & body slows to a

fraction of normal. Body temperature decreases. Shivering helps increase

temperatures when they arewaking up.

Adaptive Hypothermia

Other mammals, such as bears,badgers, raccoons and opossums entera state of prolonged sleep, but bodytemperature does not decrease.

Other mammals, such as bears,badgers, raccoons and opossums entera state of prolonged sleep, but bodytemperature does not decrease.

Adaptive Hypothermia

Adverse conditions can also occur duringthe summer. Drought, high temperatures.

Some animals enter a state of dormancycalled estivation. Breathing rates and metabolism decrease. African lungfish, desert tortoise, pigmy

mouse, ground squirrels.

Adverse conditions can also occur duringthe summer. Drought, high temperatures.

Some animals enter a state of dormancycalled estivation. Breathing rates and metabolism decrease. African lungfish, desert tortoise, pigmy

mouse, ground squirrels.