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Chapter 44Chapter 44
Osmoregulation and Osmoregulation and Excretion.Excretion.
Salvin’s AlbatrossSalvin’s Albatross
Concept 44.1Concept 44.1
The ability to regulate the intake and The ability to regulate the intake and loss of water and solutes is called loss of water and solutes is called OsmoregulationOsmoregulation. .
Based on the controlled movement of Based on the controlled movement of solutes between the internal fluids solutes between the internal fluids and external environment. and external environment.
Concept 44.1Concept 44.1
Osmoregulation is a problem that all Osmoregulation is a problem that all animals, including humans, face. animals, including humans, face.
Water is one of the most important Water is one of the most important compounds in an organism and must compounds in an organism and must be balanced in order for the be balanced in order for the organism to survive. organism to survive.
Concept 44.1Concept 44.1
Osmoregulation is how animals Osmoregulation is how animals regulate solute concentrations and regulate solute concentrations and balance the gain/loss of water. balance the gain/loss of water.
Since animals don’t have cell walls, Since animals don’t have cell walls, the cells may: swell and burst, if the cells may: swell and burst, if there’s a constant net gain, or may there’s a constant net gain, or may shrivel and die, if there’s a significant shrivel and die, if there’s a significant amount of water loss. amount of water loss.
OsmosisOsmosis
OsmosisOsmosis- the movement of aqueous - the movement of aqueous substances across a semi permeable substances across a semi permeable membrane. membrane.
This is the basis of Osmoregulation!!!This is the basis of Osmoregulation!!!
Types of osmosisTypes of osmosis
OsmolarityOsmolarity- a difference in osmotic - a difference in osmotic pressure. pressure.
The total solute concentration The total solute concentration expressed as molarity, or moles of expressed as molarity, or moles of solute per liter of solution;solute per liter of solution;
Osmosis and organisms Osmosis and organisms
If an organism is:If an organism is: IsoosmoticIsoosmotic,, it has the same solute it has the same solute
concentration as the surrounding concentration as the surrounding environment.environment.
HypoosmoticHypoosmotic,, it has a more diluted it has a more diluted solution concentration than the solution concentration than the surrounding environment. surrounding environment.
HyperosmoticHyperosmotic, it has a greater , it has a greater concentration of solutes than its concentration of solutes than its surrounding environment.surrounding environment.
Osmotic challenges. Osmotic challenges.
Two basic solutions to water balancing Two basic solutions to water balancing problem!problem!
One is to be isoosmotic with the One is to be isoosmotic with the surroundings. surroundings.
This is only available for marine This is only available for marine animals.animals.
Since it can’t adjust its osmolarity it Since it can’t adjust its osmolarity it would be consider an Osmoconformer.would be consider an Osmoconformer.
OsmoconformersOsmoconformers
Are marine animalsAre marine animals Have stable compositionHave stable composition Are isoosmotic and do not need to Are isoosmotic and do not need to
regulate their osmolarityregulate their osmolarity Often have a very constant internal Often have a very constant internal
osmolarityosmolarity Therefore they must be……Therefore they must be……
Simple organisms!!!Simple organisms!!!
Osmotic challengesOsmotic challenges
The other way an organism can The other way an organism can regulate their osmotic problem is to regulate their osmotic problem is to control the osmolarity of its bodily control the osmolarity of its bodily fluids. fluids.
An An osmoregulatorosmoregulator must discharge must discharge excess water if it lives in a excess water if it lives in a hypoosmotic environment.hypoosmotic environment.
It must take in the water if it lives in It must take in the water if it lives in a hyperosmotic environment. a hyperosmotic environment.
Osmotic challengesOsmotic challenges
Osmoregulation Osmoregulation allows an animal allows an animal to live in an environment that would to live in an environment that would otherwise be uninhabitable for otherwise be uninhabitable for osmoconformers. osmoconformers.
This would be freshwater and This would be freshwater and terrestrial habitats.terrestrial habitats.
Allows many marine animals to Allows many marine animals to maintain internal osmolarities maintain internal osmolarities different than that of saltwater. different than that of saltwater.
The costs of being complexThe costs of being complex
ENERGY!!!!ENERGY!!!! In order to maintain the osmolarity In order to maintain the osmolarity
difference between the body and the difference between the body and the external environment, the organism must external environment, the organism must extend energy. extend energy.
They use active transportation to move the They use active transportation to move the solute concentrations in their bodily fluids.solute concentrations in their bodily fluids.
The amount of energy used depends on the The amount of energy used depends on the gradient of the organism’s solute to the gradient of the organism’s solute to the evironment’s solute concentration. evironment’s solute concentration.
Environmental changesEnvironmental changes
Most organisms, both osmoconformers Most organisms, both osmoconformers and osmoregulators, cannot survive and osmoregulators, cannot survive substantial changes in the environment. substantial changes in the environment.
These organisms are called These organisms are called StenohalinesStenohalines..
Derived from the Greek words Derived from the Greek words stenosstenos, , meaning narrow, and meaning narrow, and halinehaline referring to referring to salt. salt.
Environmental changes.Environmental changes.
Some animals, however, can survive large Some animals, however, can survive large fluctuations in solution concentration. fluctuations in solution concentration.
These are referred to as These are referred to as EuryhalinesEuryhalines.. Which is derived from the Greek words Which is derived from the Greek words
Eurys, meaning broad and of course Eurys, meaning broad and of course haline. haline.
Examples are some species of Salmon and Examples are some species of Salmon and Tilapia. Tilapia.
Tilapia can adjust to any salt concentration Tilapia can adjust to any salt concentration between fresh water and 2,000 mosm/L, between fresh water and 2,000 mosm/L, twice that of saltwater.twice that of saltwater.
AdaptationsAdaptations
Most marine invertebrates are Most marine invertebrates are isoosmoticisoosmotic Means their solute concentration is the Means their solute concentration is the
same as their surrounding environment. same as their surrounding environment. However they differ considerably However they differ considerably
from seawater in their concentrations from seawater in their concentrations of most specific solutes. of most specific solutes.
Thus even an osmoconformer has to Thus even an osmoconformer has to regulate its concentrations. regulate its concentrations.
Adaptations Adaptations
Sharks have a slighter higher Sharks have a slighter higher osmolarity than that of the sea water osmolarity than that of the sea water because they retain urea. because they retain urea.
Marine bony fishes are hypoosmotic to Marine bony fishes are hypoosmotic to the seawater and therefore must obtain the seawater and therefore must obtain solutes through diffuse and their food. solutes through diffuse and their food.
They (marine bony fishes) excrete their They (marine bony fishes) excrete their excess salt through rectal glands, gills, excess salt through rectal glands, gills, salt-excreting glands, or kidneys. salt-excreting glands, or kidneys.
Adaptations Adaptations Unlike bony fish and despite having a relatively low Unlike bony fish and despite having a relatively low
internal salt concentration, marine sharks do not internal salt concentration, marine sharks do not experience a large and continuous osmotic water experience a large and continuous osmotic water loss. loss.
Why?Why? Sharks maintain high concentrations of urea.Sharks maintain high concentrations of urea. An organic solute called trimethylamine oxide or An organic solute called trimethylamine oxide or
TMAO protects proteins from damage by the urea. TMAO protects proteins from damage by the urea. The sharks total osmolaric concentration would add The sharks total osmolaric concentration would add
up to just slightly above that of saltwater so therefore up to just slightly above that of saltwater so therefore a shark is actually a shark is actually hyperosmotic hyperosmotic to the saltwater. to the saltwater.
Consequently, water slowly enters a shark and is Consequently, water slowly enters a shark and is disposed of in the urine produced by the kidneys. disposed of in the urine produced by the kidneys.
LE 44-3aLE 44-3a
Gain of water andsalt ions from foodand by drinkingseawater
Osmotic water lossthrough gills and other partsof body surface
Excretion ofsalt ionsfrom gills
Osmoregulation in a saltwater fish
Excretion of salt ions and small amountsof water in scantyurine from kidneys
AdaptationsAdaptations
Would freshwater fish have the same Would freshwater fish have the same problem as marine fish?problem as marine fish?
No. Freshwater fish have the opposite No. Freshwater fish have the opposite problem than marine fish. problem than marine fish.
Since the seawater is hyperosmotic to the Since the seawater is hyperosmotic to the marine fish, then they are constantly marine fish, then they are constantly losing water and gaining salt, conversely losing water and gaining salt, conversely since fresh water is hypoosmotic to since fresh water is hypoosmotic to freshwater fish then they are constantly freshwater fish then they are constantly gaining water and losing salt. gaining water and losing salt.
LE 44-3bLE 44-3b
Excretion oflarge amounts ofwater in diluteurine from kidneys
Osmotic water gainthrough gills and other partsof body surface
Osmoregulation in a freshwater fish
Uptake ofsalt ionsby gills
Uptake ofwater and someions in food
Figure 44-2Figure 44-2
AdaptationsAdaptations
One way to prevent this salt loss is to One way to prevent this salt loss is to excrete diluted urine. excrete diluted urine.
The salt that is lost by diffusion and The salt that is lost by diffusion and in the urine are replaced by salts in in the urine are replaced by salts in food and by picking up chloride cells food and by picking up chloride cells in the gills. in the gills.
Some fish, like salmon will exhibit Some fish, like salmon will exhibit traits of both marine and freshwater traits of both marine and freshwater fish depending on the environment fish depending on the environment that they are in. that they are in.
Life without water.Life without water.
Most animals cannot survive dehydration.Most animals cannot survive dehydration. However some animals can survive the However some animals can survive the
dehydrated conditions by undergoing a dehydrated conditions by undergoing a dormant phase. dormant phase.
This adaptation is called This adaptation is called anhydrobiosisanhydrobiosis (life without water)(life without water)
Researchers believe that these animals Researchers believe that these animals have a sugar called trehalose that in the have a sugar called trehalose that in the absence of water will provide the cell with absence of water will provide the cell with membranes and proteins. membranes and proteins.
LE 44-4LE 44-4
Hydrated tardigrade Dehydrated tardigrade
100 µm
100 µm
AdaptationsAdaptations
Did you know that a human dies if they lose Did you know that a human dies if they lose only 12% of their body water. only 12% of their body water.
The threat of dehydration for terrestrial The threat of dehydration for terrestrial animals is great and offers a challenge to animals is great and offers a challenge to get around. get around.
Some animals develop waxy coverings Some animals develop waxy coverings called…called… CUTICLECUTICLE
Some desert dwelling animals have become Some desert dwelling animals have become nocturnal to avoid the dehydrating heat. nocturnal to avoid the dehydrating heat.
LE 44-5LE 44-5Water
balance in a kangaroo rat(2 mL/day)
Waterbalance ina human
(2,500 mL/day)
Watergain
Waterloss
Derived frommetabolism (1.8 mL)
Ingestedin food (0.2 mL)
Derived frommetabolism (250 mL)
Ingestedin food (750 mL)
Ingestedin liquid (1,500 mL)
Evaporation (900 mL)
Feces (100 mL)Urine(1,500 mL)
Evaporation (1.46 mL)
Feces (0.09 mL)Urine(0.45 mL)
Land adaptationsLand adaptations
Even with these adaptations animals Even with these adaptations animals still lose water through their gas still lose water through their gas exchange organs, in their urine and exchange organs, in their urine and feces, and across their skin. feces, and across their skin.
Land animals replenish their water Land animals replenish their water balance by drinking water and balance by drinking water and obtaining it in their food. obtaining it in their food.
Transport EpitheliaTransport Epithelia In most animals there are one or more In most animals there are one or more
different kinds of transport epithelium or a different kinds of transport epithelium or a layer/layers of specialized epithelial cells layer/layers of specialized epithelial cells that regulate solute movements.that regulate solute movements.
These are essential components of osmotic These are essential components of osmotic regulation and metabolic waste disposal. regulation and metabolic waste disposal.
They move specific solutes in controlled They move specific solutes in controlled amounts in specific directions.amounts in specific directions.
Some epithelia face outward towards the Some epithelia face outward towards the environment while others line channels environment while others line channels connected to the outside by an opening on connected to the outside by an opening on the body’s surface.the body’s surface.
LE 44-6LE 44-6
Control group(Unclipped fur)
Experimental group(Clipped fur)
Wat
er l
ost
per
day
(L/1
00 k
g b
od
y m
ass) 4
3
2
1
0
EpitheliaEpithelia
Are joined by impermeable tight Are joined by impermeable tight junctionsjunctions
Form a barrier at the tissue-Form a barrier at the tissue-environment boundaryenvironment boundary
Are arranged into complex tubular Are arranged into complex tubular networks with extensive surface networks with extensive surface areas. areas.
LE 44-7bLE 44-7b
Vein
Capillary
Secretorytubule
Transportepithelium
Directionof saltmovement
Centralduct
Artery
Bloodflow
Lumen ofsecretory tubule
NaCl
Secretory cellof transportepithelium
Nitrogenous waste and Nitrogenous waste and phylogeny/habitat.phylogeny/habitat.
The type and quantity of an animal’s The type and quantity of an animal’s waste may have a large impact on its waste may have a large impact on its water balance. water balance.
Metabolic processes of an organism Metabolic processes of an organism produces a nitrogenous waste ammonia. produces a nitrogenous waste ammonia.
Most mammals convert ammonia to urea, Most mammals convert ammonia to urea, which is less toxic to the body.which is less toxic to the body.
The urea is carried to the kidneys and The urea is carried to the kidneys and concentrated it is excreted with a minimal concentrated it is excreted with a minimal loss of water.loss of water.
Ammonia Ammonia
In fish the ammonia is lost as In fish the ammonia is lost as ammonium ions, while the kidneys ammonium ions, while the kidneys only excrete a minor amount of only excrete a minor amount of nitrogenous waste.nitrogenous waste.
The gill epithelium takes up NaThe gill epithelium takes up Na+ + in in exchange for the ammonium ionsexchange for the ammonium ions
This helps to maintain a higher This helps to maintain a higher amount of Na in the body fluids than amount of Na in the body fluids than in the surrounding waters.in the surrounding waters.
UreaUrea
Transferring through the skin is good for Transferring through the skin is good for fish but not so beneficial for land fish but not so beneficial for land animals because ammonia has to be animals because ammonia has to be transported in large amounts of diluted transported in large amounts of diluted solutions.solutions.
The reason why land dwelling organisms The reason why land dwelling organisms don’t use this type of excretion is that it don’t use this type of excretion is that it requires a huge amount of water and requires a huge amount of water and most land animals simply do not have a most land animals simply do not have a sufficient amount of water. sufficient amount of water.
LE 44-8LE 44-8
Nitrogenous bases
Nucleic acids
Amino acids
Proteins
—NH2
Amino groups
Most aquatic animals, including most bony fishes
Mammals, most amphibians, sharks, some bony fishes
Many reptiles (including birds), insects, land snails
Ammonia Urea Uric acid
UreaUrea
Mammals, sharks and some Mammals, sharks and some amphibians produce urea by a amphibians produce urea by a metabolic process in the liver that metabolic process in the liver that combines ammonia with carbon combines ammonia with carbon dioxide. dioxide.
Main advantagesMain advantages
Less toxic; about 100,000 times less Less toxic; about 100,000 times less toxic than ammoniatoxic than ammonia
This allows urea to be transported This allows urea to be transported safely at high concentrations.safely at high concentrations.
Little water is lost in the excretionLittle water is lost in the excretion
Main disadvantagesMain disadvantages
ENERGY!!! ENERGY!!!
It takes energy to convert the It takes energy to convert the ammonia to urea. ammonia to urea.
Many amphibians produce ammonia in Many amphibians produce ammonia in their aqueous stage and then produce their aqueous stage and then produce urea in their terrestrial phase. urea in their terrestrial phase.
Uric AcidUric Acid
Insects, land snails, and many reptiles Insects, land snails, and many reptiles including birds excrete uric acid. including birds excrete uric acid.
Similarly uric acid is less toxic than Similarly uric acid is less toxic than ammoniaammonia
Unlike urea and ammonia, uric acid is Unlike urea and ammonia, uric acid is insoluble in water and can be excreted in a insoluble in water and can be excreted in a semi-solid form. semi-solid form.
High energy cost!!! More so than making High energy cost!!! More so than making urea. Requires a considerable amount of urea. Requires a considerable amount of ATP for synthesis from ammoniaATP for synthesis from ammonia
Nitrogenous wastesNitrogenous wastes In general the kind of nitrogenous waste depends In general the kind of nitrogenous waste depends
on the organism’s evolutionary history, habitat on the organism’s evolutionary history, habitat and availability of water.and availability of water.
In some species individuals can change forms of In some species individuals can change forms of nitrogenous wastes when environmental nitrogenous wastes when environmental conditions change. conditions change.
Over time evolution determines the limits of Over time evolution determines the limits of physiological responses for a species, but during physiological responses for a species, but during their lives, individual organisms make their lives, individual organisms make physiological adjustments within these physiological adjustments within these evolutionary constraints. evolutionary constraints.
Finally the amount of waste produced is coupled Finally the amount of waste produced is coupled with the amount and what the animal consumes. with the amount and what the animal consumes.
Diverse excretory Diverse excretory systems are variations systems are variations
on a tubular theme.on a tubular theme.
Excretory systemsExcretory systems
Excretory systems produce urine by Excretory systems produce urine by refining a filtrate derived from body refining a filtrate derived from body fluids.fluids.
The key functions of excretory systems The key functions of excretory systems are filtration and the production of are filtration and the production of urine from the filtrate by selective urine from the filtrate by selective reabsorption, and secretion. reabsorption, and secretion.
Key functionsKey functions
FiltrationFiltration- pressure-filtering of body - pressure-filtering of body fluids, producing a filtrate.fluids, producing a filtrate.
Production of urine form the filtrate by Production of urine form the filtrate by selective selective reabsorptionreabsorption- reclaiming - reclaiming valuable solutes from the filtratevaluable solutes from the filtrate
SecretionSecretion- addition of toxins and other - addition of toxins and other solutes from the body fluids to the filtrate.solutes from the body fluids to the filtrate.
LE 44-9LE 44-9
Filtration
Reabsorption
Secretion
Excretion
Excretorytubule
Capillary
Filtrate
Urin
e
Excretory varieties of FlatwormsExcretory varieties of Flatworms
A A ProtenephridiumProtenephridium is a network of dead is a network of dead end tubules lacking internal openings.end tubules lacking internal openings.
The tubules branch throughout the body The tubules branch throughout the body and the smallest branches are capped by and the smallest branches are capped by a cellular unit called a flame bulb.a cellular unit called a flame bulb.
The flame bulb has cilia that draw water The flame bulb has cilia that draw water and solutes from the interstitial fluid and solutes from the interstitial fluid through the flame bulb and then moves through the flame bulb and then moves the urine outward through the tubules the urine outward through the tubules until they empty into the environment until they empty into the environment through pores called through pores called nephridiopores.nephridiopores.
Flame bulbsFlame bulbs
The tubules reabsorb most solutes The tubules reabsorb most solutes before the urine exits the body.before the urine exits the body.
Function mainly in osmoregulationFunction mainly in osmoregulation
Most metabolic wastes diffuse out of Most metabolic wastes diffuse out of the animal through the body surface the animal through the body surface or are excreted into the gastrovascular or are excreted into the gastrovascular cavity and eliminated through the cavity and eliminated through the mouth. mouth.
LE 44-10LE 44-10
Protonephridia(tubules)
Tubule
Nephridioporein body wall
Flamebulb
Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)
Tubule cell
Cilia
Nucleusof cap cell
MetaphridiaMetaphridia
Another type of excretory system is Another type of excretory system is called Metanephridia.called Metanephridia.
Found in most annelidFound in most annelid Each segment of an earthworm Each segment of an earthworm
contains a pair of metaphridia, which contains a pair of metaphridia, which are emmersed in coelomic fluid and are emmersed in coelomic fluid and enveloped by a capillary network. enveloped by a capillary network.
The internal opening is surrounded by The internal opening is surrounded by a ciliated funnel called the a ciliated funnel called the nephrostome.nephrostome.
LE 44-11LE 44-11
Collectingtubule
Nephridio-pore
Capillarynetwork
Coelom
Bladder
MetanephridiumNephrostome
Malipighian tubulesMalipighian tubules
Malpighian tubules- organs in insects Malpighian tubules- organs in insects and other terrestrial arthropods. and other terrestrial arthropods.
Malpighian tubules open into the Malpighian tubules open into the digestive tract and dead end at tips digestive tract and dead end at tips that are immersed in hemolymph that are immersed in hemolymph (circulatory fluid)(circulatory fluid)
Water -> tubules-> rectumWater -> tubules-> rectum Some of the solutes are transferred Some of the solutes are transferred
back into the hemolymph. back into the hemolymph. Highly effective in conserving water. Highly effective in conserving water.
LE 44-12LE 44-12
Salt, water, andnitrogenous
wastes
Digestive tract
Midgut(stomach)
Malpighiantubules
RectumIntestine Hindgut
Reabsorption of H2O,ions, and valuableorganic molecules
Malpighiantubule
HEMOLYMPH
Anus
Rectum
Feces and urine
Vertebrate kidneysVertebrate kidneys
Built out of tubules in an organized Built out of tubules in an organized network waynetwork way
Function in both osmoregulation and Function in both osmoregulation and excretoryexcretory
Compacted and nonsegmentary Compacted and nonsegmentary organsorgans
Ducts and other structures carry Ducts and other structures carry urine out of the body. urine out of the body.
KidneysKidneys Blood enters the kidneys Blood enters the kidneys
by the Renal artery.by the Renal artery. It’d drained by the Renal It’d drained by the Renal
vein.vein. Urine leaves the kidneys Urine leaves the kidneys
through a duct called the through a duct called the ureter and both drain into ureter and both drain into a urinary bladder.a urinary bladder.
During urination, the urine During urination, the urine leaves through a canal leaves through a canal called the urethra. called the urethra.
Two distinct region, an Two distinct region, an outer renal cortex and an outer renal cortex and an inner cortex. inner cortex.
The nephron, the The nephron, the functional unit of the functional unit of the vertebrate kidney, consists vertebrate kidney, consists of a single long tubule and of a single long tubule and a ball of capillaries called a ball of capillaries called the glomerulus. the glomerulus.
The blind end of the tubule The blind end of the tubule froms a cup shaped froms a cup shaped swelling called the swelling called the Bowman’s capsule which Bowman’s capsule which surrounds the glomerulus. surrounds the glomerulus.
LE 44-13LE 44-13
Excretory organs and major associated blood vessels
RenalmedullaRenalcortex
Renalpelvis
Section of kidney from a ratKidney structure
Ureter
Kidney
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Afferentarteriolefrom renalartery
Efferentarteriole from glomerulus
Distaltubule
Collectingduct
SEM20 µm
Branch ofrenal vein
Filtrate and blood flow
Vasarecta
DescendinglimbAscendinglimb
LoopofHenle
Renalmedulla
Nephron
Torenalpelvis
Renalcortex
Collectingduct
Juxta-medullarynephron
Corticalnephron
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
Pathway to FiltrationPathway to Filtration From the bowman’s capsule the urine moves to From the bowman’s capsule the urine moves to
the proximal tubule the loop of henle and the the proximal tubule the loop of henle and the distal tubule. distal tubule.
the distal tubule empties into a collecting duct the distal tubule empties into a collecting duct which is processed and filtered from many which is processed and filtered from many nephrons. nephrons.
This filtrate flows from the many collecting ducts This filtrate flows from the many collecting ducts of the kidney into the renal pelvis.of the kidney into the renal pelvis.
80% of the nephrons the cortical nephrons have 80% of the nephrons the cortical nephrons have reduced loops of Henle and are almost entirely reduced loops of Henle and are almost entirely confined to the renal cortex. confined to the renal cortex.
The other 20% have well developed loops that The other 20% have well developed loops that extend deeply into the renal medulla. extend deeply into the renal medulla.
LE 44-16bLE 44-16b
Distaltubule
Aldosterone
Homeostasis:Blood pressure,
volume
STIMULUS:The juxtaglomerular
apparatus (JGA) respondsto low blood volume or
blood pressure (such as due to dehydration or
loss of blood)
Increased Na+
and H2O reab-sorption in
distal tubules
Reninproduction
Arterioleconstriction
Adrenal gland
Angiotensin II
Angiotensinogen
JGA
Renin
LE 44-16aLE 44-16a
Osmoreceptorsin hypothalamus
Hypothalamus
ADH
Pituitarygland
Increasedpermeability
Distaltubule
Thirst
Drinking reducesblood osmolarity
to set point
Collecting duct
H2O reab-sorption helpsprevent further
osmolarityincrease
Homeostasis:Blood osmolarity
STIMULUSThe release of ADH istriggered when osmo-receptor cells in the
hypothalamus detect anincrease in the osmolarity
of the blood
STIMULUSThe release of ADH istriggered when osmo-receptor cells in the
hypothalamus detect anincrease in the osmolarity
of the blood
The kidneyThe kidney
The maintenance of osmotic The maintenance of osmotic differences and the production of differences and the production of hyperosmotic urine are possible only hyperosmotic urine are possible only because considerable energy is because considerable energy is expended for the active transport of expended for the active transport of solutes against concentration gradientssolutes against concentration gradients
The functions of the nephron can be The functions of the nephron can be thought of as small machines thought of as small machines producing a region of high osmolarity producing a region of high osmolarity in the kidney. in the kidney.
UreaUrea
Urea which diffuses out of the collecting duct Urea which diffuses out of the collecting duct as it traverses the inner medulla forms along as it traverses the inner medulla forms along with NaCl the osmotic gradient that enables with NaCl the osmotic gradient that enables the kidney to produce urine that is the kidney to produce urine that is hyperosmotic to the blood. hyperosmotic to the blood.
The osmolarity of the urine is regulated by The osmolarity of the urine is regulated by nervous system and hormonal control of nervous system and hormonal control of water and salt reabsorption in the kidneys. water and salt reabsorption in the kidneys. This regulation involves the actions of This regulation involves the actions of antidiuretic hormone (adh) the renin-antidiuretic hormone (adh) the renin-aldosterone system and atrial natriuretic aldosterone system and atrial natriuretic factor. factor.
AdaptationsAdaptations
The form and function of nephrons in The form and function of nephrons in various vertebrates are related primarily various vertebrates are related primarily to the requirements for osmoregulation in to the requirements for osmoregulation in the animal’s habitatthe animal’s habitat
The more hyperosmotic the excretion the The more hyperosmotic the excretion the longer the loops of Henle. longer the loops of Henle.
In conclusion the evolution of the In conclusion the evolution of the organism and the habitat of the organism organism and the habitat of the organism plays a huge part in the organism’s plays a huge part in the organism’s excretion. excretion.
