osmosis and osmolarity cells require a balance between uptake and loss of water osmolarity, the...
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Osmosis and Osmolarity
• Cells require a balance between uptake and loss of water
• Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane
• If two solutions are isoosmotic, the movement of water is equal in both directions
• If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution
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Figure 44.2
Selectively permeablemembrane
Solutes Water
Net water flow
Hyperosmotic side: Hypoosmotic side:
Lower free H2Oconcentration
•
Higher soluteconcentration
•
Higher free H2Oconcentration
•
Lower soluteconcentration
•
Osmotic Challenges
• Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity
• Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment
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Figure 44.3
(a) Osmoregulation in a marine fish (b) Osmoregulation in a freshwater fish
Gain of waterand salt ionsfrom food
Excretionof salt ionsfrom gills
Osmotic waterloss through gillsand other partsof body surface
Gain of waterand salt ionsfrom drinkingseawater
Excretion of salt ions andsmall amounts of water inscanty urine from kidneys
Gain of waterand some ionsin food
Uptake ofsalt ionsby gills
Osmotic watergain throughgills and otherparts of bodysurface
Excretion of salt ions andlarge amounts of water indilute urine from kidneys
Key
Water
Salt
Water balance ina kangaroo rat(2 mL/day)
Water balance ina human(2,500 mL/day)
Ingestedin food (0.2)
Ingestedin food (750)
Ingestedin liquid(1,500)Water
gain(mL)
Waterloss(mL)
Derived frommetabolism (1.8)
Derived frommetabolism (250)
Feces (0.09)
Urine(0.45)
Feces (100)
Urine(1,500)
Evaporation (1.46) Evaporation (900)
Figure 44.6
Figure 44.7
Nasal saltgland
Ducts
Nostril with saltsecretions
(a) Location of nasal glandsin a marine bird
(b) Secretorytubules
(c) Countercurrentexchange
Key
Salt movementBlood flow
Nasal gland
CapillarySecretory tubuleTransportepithelium
Vein Artery
Central duct
Secretory cellof transportepithelium
Lumen ofsecretorytubule
Saltions
Blood flow Salt secretion
Figure 44.8Proteins Nucleic acids
Aminoacids
Nitrogenousbases
—NH2
Amino groups
Most aquaticanimals, includingmost bony fishes
Mammals, mostamphibians, sharks,
some bony fishes
Many reptiles(including birds),
insects, land snails
Ammonia Urea Uric acid
Concept 44.3: Diverse excretory systems are variations on a tubular theme
• Excretory systems regulate solute movement between internal fluids and the external environment
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Excretory Processes
• Most excretory systems produce urine by refining a filtrate derived from body fluids
• Key functions of most excretory systems– Filtration: Filtering of body fluids
– Reabsorption: Reclaiming valuable solutes
– Secretion: Adding nonessential solutes and wastes from the body fluids to the filtrate
– Excretion: Processed filtrate containing nitrogenous wastes, released from the body
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Figure 44.10
CapillaryFiltration
Excretorytubule
Reabsorption
Secretion
Excretion
Filtrate
Urin
e
2
1
3
4
Figure 44.11
Tubules ofprotonephridia
Tubule
Flamebulb
Nucleusof cap cell
Cilia
Interstitialfluid flow
Opening inbody wall
Tubulecell
Figure 44.12
Components of a metanephridium:
Collecting tubule
Internal opening
Bladder
External opening
Coelom Capillarynetwork
Digestive tract
Midgut(stomach)
Malpighiantubules
RectumIntestine
Hindgut
Salt, water, andnitrogenous
wastes
Feces and urine
Malpighiantubule
To anus
Rectum
Reabsorption
HEMOLYMPH
Figure 44.13
Figure 44.14-a
Excretory Organs Kidney Structure Nephron Types
Posteriorvena cava
Renalarteryand vein
Aorta
Ureter
Urinarybladder
Urethra
Kidney
RenalcortexRenalmedulla
Renal artery
Renal vein
Ureter
Cortical nephron
Juxtamedullarynephron
Renal pelvis
Renalcortex
Renalmedulla
Nephron Organization
Afferent arteriolefrom renal artery Glomerulus
Bowman’scapsule
Proximaltubule
PeritubularcapillariesDistal
tubule
Efferentarteriolefrom glomerulus
Collectingduct
Branch ofrenal vein
Vasarecta
Descendinglimb
Ascendinglimb
Loopof
Henle20
0
m
Blood vessels from a humankidney. Arterioles and peritubularcapillaries appear pink; glomeruliappear yellow.
Figure 44.14-b
Concept 44.4: The nephron is organized for stepwise processing of blood filtrate
• The filtrate produced in Bowman’s capsule contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules
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From Blood Filtrate to Urine: A Closer Look
Proximal Tubule
• Reabsorption of ions, water, and nutrients takes place in the proximal tubule
• Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries
• Some toxic materials are actively secreted into the filtrate
• As the filtrate passes through the proximal tubule, materials to be excreted become concentrated
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Animation: Bowman’s Capsule and Proximal Tubule Right-click slide / select “Play”
Proximal tubule Distal tubule
Filtrate
CORTEX
Loop ofHenle
OUTERMEDULLA
INNERMEDULLA
Key
Active transportPassive transport
Collectingduct
NutrientsNaCl
NH3
HCO3 H2O K
H
NaClH2O
HCO3
K H
H2ONaCl
NaCl
NaCl H2O
Urea
Figure 44.15
Descending Limb of the Loop of Henle• Reabsorption of water continues through
channels formed by aquaporin proteins• Movement is driven by the high osmolarity of
the interstitial fluid, which is hyperosmotic to the filtrate
• The filtrate becomes increasingly concentrated
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Ascending Limb of the Loop of Henle• In the ascending limb of the loop of Henle, salt
but not water is able to diffuse from the tubule into the interstitial fluid
• The filtrate becomes increasingly dilute
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Distal Tubule• The distal tubule regulates the K+ and NaCl
concentrations of body fluids• The controlled movement of ions contributes
to pH regulation
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Animation: Loop of Henle and Distal TubuleRight-click slide / select “Play”
Collecting Duct• The collecting duct carries filtrate through the
medulla to the renal pelvis• One of the most important tasks is reabsorption
of solutes and water• Urine is hyperosmotic to body fluids
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Animation: Collecting DuctRight-click slide / select “Play”
The Two-Solute Model
• In the proximal tubule, filtrate volume decreases, but its osmolarity remains the same
• The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney
• This system allows the vasa recta to supply the kidney with nutrients, without interfering with the osmolarity gradient
• Considerable energy is expended to maintain the osmotic gradient between the medulla and cortex
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• The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosis
• Urea diffuses out of the collecting duct as it traverses the inner medulla
• Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood
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Osmolarityof interstitial
fluid(mOsm/L)
1,200
900
600
400
300
Key
Activetransport
Passivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEX H2O
H2O
H2O
H2O
H2O
H2O
H2O
1,200
900
600
400
300
300300
Figure 44.16-1
Osmolarityof interstitial
fluid(mOsm/L)
1,200
900
600
400
300
Key
Activetransport
Passivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXNaClH2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
1,200
100
100
200
400
700900
600
400
300
300300
Figure 44.16-2
Osmolarityof interstitial
fluid(mOsm/L)
Key
Activetransport
Passivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXNaClH2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Urea
Urea
Urea
1,200
1,2001,200
900
600
400
300300
400
600
100
100
200
400
700900
600
400
300
300300
Figure 44.16-3
Adaptations of the Vertebrate Kidney to Diverse Environments
• The form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animal’s habitat
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Mammals
• The juxtamedullary nephron is key to water conservation in terrestrial animals
• Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops
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Antidiuretic Hormone
• The osmolarity of the urine is regulated by nervous and hormonal control
• Antidiuretic hormone (ADH) makes the collecting duct epithelium more permeable to water
• An increase in osmolarity triggers the release of ADH, which helps to conserve water
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Figure 44.19-2
ThirstHypothalamus
ADH
Pituitarygland
Osmoreceptors inhypothalamus trigger
release of ADH.
STIMULUS:Increase in blood
osmolarity (forinstance, after
sweating profusely)
Homeostasis:Blood osmolarity
(300 mOsm/L)
Drinking reducesblood osmolarity
to set point.
H2O reab-sorption helpsprevent further
osmolarityincrease.
Increasedpermeability
Distaltubule
Collecting duct
© 2011 Pearson Education, Inc.
Animation: Effect of ADHRight-click slide / select “Play”
Collectingduct
ADHreceptor
COLLECTINGDUCT CELL
LUMEN
Second-messengersignaling molecule
Storagevesicle
Aquaporinwater channel
Exocytosis
H2O
H2O
ADH
cAMP
Figure 44.20
• Mutation in ADH production causes severe dehydration and results in diabetes insipidus
• Alcohol is a diuretic as it inhibits the release of ADH
© 2011 Pearson Education, Inc.
Figure 44.21
Prepare copies of humanaquaporin genes: twomutants plus wild type.
Synthesize mRNA.
Inject mRNA into frogoocytes.
Transfer to 10-mOsmsolution and observeresults.
2
1
3
4
EXPERIMENT
RESULTS
Aquaporingene
PromoterMutant 1 Mutant 2 Wild type
Aquaporinproteins
H2O(control)
Injected RNA Permeability (m/sec)
196
20
17
18
Wild-type aquaporin
None
Aquaporin mutant 1
Aquaporin mutant 2
AngiotensinogenLiver
JGAreleasesrenin.
Renin
Distaltubule
Juxtaglomerularapparatus (JGA)
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
More Na and H2Oare reabsorbed in
distal tubules,increasing blood volume.
Arteriolesconstrict,increasing
blood pressure.
STIMULUS:Low blood volumeor blood pressure(for example, dueto dehydration or
blood loss)
Homeostasis:Blood pressure,
volume
Figure 44.22-3
Homeostatic Regulation of the Kidney
• ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume
• Another hormone, atrial natriuretic peptide (ANP), opposes the RAAS
• ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin
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pH regulation by Kidney
Figure 44.UN01
Animal Inflow/Outflow Urine
Freshwaterfish. Lives inwater lessconcentratedthan body fluids; fishtends to gainwater, lose salt
Does not drink waterSalt in(active trans-port by gills)
H2O in
Salt out
Marine bony fish. Lives inwater moreconcentratedthan bodyfluids; fishtends to losewater, gain salt
Terrestrialvertebrate.Terrestrialenvironment;tends to losebody waterto air
Drinks water
Drinks water
Salt in H2O out
Salt out (activetransport by gills)
Salt in(by mouth)
H2O andsalt out
Large volume of urine
Urine is lessconcentratedthan bodyfluids
Small volumeof urine
Urine isslightly lessconcentratedthan bodyfluids
Moderatevolumeof urine
Urine ismore concentratedthan bodyfluids