Osmoregulation and excretion systems allow animals to balance water and solute levels. Freshwater animals gain water and lose salts, while marine animals deal with water loss and salt gain. Land animals conserve water. Kidneys and other tubular systems filter, reabsorb, and secrete materials to produce urine for nitrogen waste excretion. The form of nitrogenous waste, such as ammonia, urea, or uric acid, depends on an animal's habitat and phylogeny. Diverse excretory organs, including protonephridia, metanephridia, Malpighian tubules, and kidneys, regulate solute levels through tubular networks. Kidneys consist of nep

1. LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
Osmoregulation and Excretion
Chapter 44

2. Overview: A Balancing Act
• Physiological systems of animals operate in a
fluid environment
• Relative concentrations of water and solutes
must be maintained within fairly narrow limits
• Osmoregulation regulates solute
concentrations and balances the gain and loss
of water
© 2011 Pearson Education, Inc.

3. • Freshwater animals show adaptations that
reduce water uptake and conserve solutes
• Desert and marine animals face desiccating
environments that can quickly deplete body
water
• Excretion gets rid of nitrogenous metabolites
and other waste products
© 2011 Pearson Education, Inc.

4. Figure 44.1

5. Concept 44.1: Osmoregulation balances the
uptake and loss of water and solutes
• Osmoregulation is based largely on controlled
movement of solutes between internal fluids
and the external environment
© 2011 Pearson Education, Inc.

6. 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
© 2011 Pearson Education, Inc.

7. Figure 44.2
Selectively permeable
membrane
Solutes Water
Net water flow
Hyperosmotic side: Hypoosmotic side:
Lower free H2O
concentration
•
Higher solute
concentration
•
Higher free H2O
concentration
•
Lower solute
concentration
•

8. 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
© 2011 Pearson Education, Inc.

9. • Most animals are stenohaline; they cannot
tolerate substantial changes in external
osmolarity
• Euryhaline animals can survive large
fluctuations in external osmolarity
© 2011 Pearson Education, Inc.

10. Marine Animals
• Most marine invertebrates are osmoconformers
• Most marine vertebrates and some invertebrates
are osmoregulators
• Marine bony fishes are hypoosmotic to sea
water
• They lose water by osmosis and gain salt by
diffusion and from food
• They balance water loss by drinking seawater
and excreting salts
© 2011 Pearson Education, Inc.

11. Figure 44.3
(a) Osmoregulation in a marine fish (b) Osmoregulation in a freshwater fish
Gain of water
and salt ions
from food
Excretion
of salt ions
from gills
Osmotic water
loss through gills
and other parts
of body surface
Gain of water
and salt ions
from drinking
seawater
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
Gain of water
and some ions
in food
Uptake of
salt ions
by gills
Osmotic water
gain through
gills and other
parts of body
surface
Excretion of salt ions and
large amounts of water in
dilute urine from kidneys
Key
Water
Salt

12. (a) Osmoregulation in a marine fish
Gain of water
and salt ions
from food
Excretion
of salt ions
from gills
Osmotic water
loss through gills
and other parts
of body surface
Gain of water
and salt ions
from drinking
seawater
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
Key
Water
Salt
Figure 44.3a

13. Freshwater Animals
• Freshwater animals constantly take in water by
osmosis from their hypoosmotic environment
• They lose salts by diffusion and maintain water
balance by excreting large amounts of dilute
urine
• Salts lost by diffusion are replaced in foods and
by uptake across the gills
© 2011 Pearson Education, Inc.

14. Figure 44.3b
(b) Osmoregulation in a freshwater fish
Gain of water
and some ions
in food
Uptake of
salt ions
by gills
Osmotic water
gain through
gills and other
parts of body
surface
Excretion of salt ions and
large amounts of water in
dilute urine from kidneys
Key
Water
Salt

15. Figure 44.4

16. Animals That Live in Temporary Waters
• Some aquatic invertebrates in temporary ponds
lose almost all their body water and survive in a
dormant state
• This adaptation is called anhydrobiosis
© 2011 Pearson Education, Inc.

17. Figure 44.5
(a) Hydrated tardigrade (b) Dehydrated
tardigrade
50 µm
50 µm

18. Figure 44.5a
(a) Hydrated tardigrade
50 µm

19. Figure 44.5b
(b) Dehydrated
tardigrade
50 µm

20. Land Animals
• Adaptations to reduce water loss are key to
survival on land
• Body coverings of most terrestrial animals help
prevent dehydration
• Desert animals get major water savings from
simple anatomical features and behaviors such
as a nocturnal life style
• Land animals maintain water balance by eating
moist food and producing water metabolically
through cellular respiration
© 2011 Pearson Education, Inc.

21. Water balance in
a kangaroo rat
(2 mL/day)
Water balance in
a human
(2,500 mL/day)
Ingested
in food (0.2)
Ingested
in food (750)
Ingested
in liquid
(1,500)Water
gain
(mL)
Water
loss
(mL)
Derived from
metabolism (1.8)
Derived from
metabolism (250)
Feces (0.09)
Urine
(0.45)
Feces (100)
Urine
(1,500)
Evaporation (1.46) Evaporation (900)
Figure 44.6

22. Energetics of Osmoregulation
• Osmoregulators must expend energy to
maintain osmotic gradients
• The amount of energy differs based on
– How different the animal’s osmolarity is from
its surroundings
– How easily water and solutes move across
the animal’s surface
– The work required to pump solutes across the
membrane
© 2011 Pearson Education, Inc.

23. Transport Epithelia in Osmoregulation
• Animals regulate the solute content of body
fluid that bathes their cells
• Transport epithelia are epithelial cells that
are specialized for moving solutes in specific
directions
• They are typically arranged in complex tubular
networks
• An example is in nasal glands of marine birds,
which remove excess sodium chloride from
the blood
© 2011 Pearson Education, Inc.

24. Figure 44.7
Nasal salt
gland
Ducts
Nostril with salt
secretions
(a) Location of nasal glands
in a marine bird
(b) Secretory
tubules
(c) Countercurrent
exchange
Key
Salt movement
Blood flow
Nasal gland
Capillary
Secretory tubule
Transport
epithelium
Vein Artery
Central duct
Secretory cell
of transport
epithelium
Lumen of
secretory
tubule
Salt
ions
Blood flow Salt secretion

25. Figure 44.7a
Nasal salt
gland
Ducts
Nostril with salt
secretions
(a) Location of nasal glands
in a marine bird
Nasal gland

26. Figure 44.7b
(b) Secretory tubules
Capillary
Secretory tubule
Transport
epithelium
Vein Artery
Central duct
Nasal gland
Key
Salt movement
Blood flow

27. Figure 44.7c
(c) Countercurrent exchange
Secretory cell
of transport
epithelium
Lumen of
secretory
tubule
Salt
ions
Blood flow Salt secretion

28. Concept 44.2: An animal’s nitrogenous
wastes reflect its phylogeny and habitat
• The type and quantity of an animal’s waste
products may greatly affect its water balance
• Among the most significant wastes are
nitrogenous breakdown products of proteins
and nucleic acids
• Some animals convert toxic ammonia (NH3)
to less toxic compounds prior to excretion
© 2011 Pearson Education, Inc.

29. Figure 44.8
Proteins Nucleic acids
Amino
acids
Nitrogenous
bases
—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

30. Figure 44.8a
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

31. Forms of Nitrogenous Wastes
• Animals excrete nitrogenous wastes in different
forms: ammonia, urea, or uric acid
• These differ in toxicity and the energy costs of
producing them
© 2011 Pearson Education, Inc.

32. Ammonia
• Animals that excrete nitrogenous wastes as
ammonia need access to lots of water
• They release ammonia across the whole body
surface or through gills
© 2011 Pearson Education, Inc.

33. Urea
• The liver of mammals and most adult
amphibians converts ammonia to the less toxic
urea
• The circulatory system carries urea to the
kidneys, where it is excreted
• Conversion of ammonia to urea is energetically
expensive; excretion of urea requires less
water than ammonia
© 2011 Pearson Education, Inc.

34. Uric Acid
• Insects, land snails, and many reptiles, including
birds, mainly excrete uric acid
• Uric acid is relatively nontoxic and does not
dissolve readily in water
• It can be secreted as a paste with little water
loss
• Uric acid is more energetically expensive to
produce than urea
© 2011 Pearson Education, Inc.

35. Figure 44.9

36. The Influence of Evolution and
Environment on Nitrogenous Wastes
• The kinds of nitrogenous wastes excreted
depend on an animal’s evolutionary history and
habitat, especially water availability
• Another factor is the immediate environment of
the animal egg
• The amount of nitrogenous waste is coupled to
the animal’s energy budget
© 2011 Pearson Education, Inc.

37. Concept 44.3: Diverse excretory systems
are variations on a tubular theme
• Excretory systems regulate solute movement
between internal fluids and the external
environment
© 2011 Pearson Education, Inc.

38. 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
© 2011 Pearson Education, Inc.

39. Figure 44.10
Capillary
Filtration
Excretory
tubule
Reabsorption
Secretion
Excretion
FiltrateUrine
2
1
3
4

40. Survey of Excretory Systems
• Systems that perform basic excretory functions
vary widely among animal groups
• They usually involve a complex network of
tubules
© 2011 Pearson Education, Inc.

41. Protonephridia
• A protonephridium is a network of dead-end
tubules connected to external openings
• The smallest branches of the network are
capped by a cellular unit called a flame bulb
• These tubules excrete a dilute fluid and function
in osmoregulation
© 2011 Pearson Education, Inc.

42. Figure 44.11
Tubules of
protonephridia
Tubule
Flame
bulb
Nucleus
of cap cell
Cilia
Interstitial
fluid flow
Opening in
body wall
Tubule
cell

43. Metanephridia
• Each segment of an earthworm has a pair of
open-ended metanephridia
• Metanephridia consist of tubules that collect
coelomic fluid and produce dilute urine for
excretion
© 2011 Pearson Education, Inc.

44. Figure 44.12
Components of a
metanephridium:
Collecting tubule
Internal opening
Bladder
External opening
Coelom Capillary
network

45. Malpighian Tubules
• In insects and other terrestrial arthropods,
Malpighian tubules remove nitrogenous
wastes from hemolymph and function in
osmoregulation
• Insects produce a relatively dry waste matter,
mainly uric acid, an important adaptation to
terrestrial life
• Some terrestrial insects can also take up water
from the air
© 2011 Pearson Education, Inc.

46. Digestive tract
Midgut
(stomach)
Malpighian
tubules
Rectum
Intestine
Hindgut
Salt, water, and
nitrogenous
wastes
Feces
and urine
Malpighian
tubule
To anus
Rectum
Reabsorption
HEMOLYMPH
Figure 44.13

47. Kidneys
• Kidneys, the excretory organs of vertebrates,
function in both excretion and osmoregulation
© 2011 Pearson Education, Inc.

48. Figure 44.14-a
Excretory Organs Kidney Structure Nephron Types
Posterior
vena cava
Renal
artery
and vein
Aorta
Ureter
Urinary
bladder
Urethra
Kidney
Renal
cortex
Renal
medulla
Renal artery
Renal vein
Ureter
Cortical
nephron
Juxtamedullary
nephron
Renal pelvis
Renal
cortex
Renal
medulla

49. Nephron Organization
Afferent arteriole
from renal artery Glomerulus
Bowman’s
capsule
Proximal
tubule
Peritubular
capillaries
Distal
tubule
Efferent
arteriole
from
glomerulus
Collecting
duct
Branch of
renal vein
Vasa
recta
Descending
limb
Ascending
limb
Loop
of
Henle
200µm
Blood vessels from a human
kidney. Arterioles and peritubular
capillaries appear pink; glomeruli
appear yellow.
Figure 44.14-b

50. Figure 44.14a
Excretory Organs
Posterior
vena cava
Renal
artery
and vein
Aorta
Ureter
Urinary
bladder
Urethra
Kidney

51. Figure 44.14b
Kidney Structure
Renal
cortex
Renal
medulla
Renal
artery
Renal
vein
Ureter
Renal pelvis

52. Figure 44.14c
Nephron Types
Cortical
nephron
Juxtamedullary
nephron
Renal
cortex
Renal
medulla

53. Figure 44.14d
Nephron Organization
Afferent arteriole
from renal artery Glomerulus
Bowman’s capsule
Proximal
tubule
Peritubular
capillaries
Distal
tubule
Efferent
arteriole
from
glomerulus
Collecting
duct
Branch of
renal vein
Vasa
recta
Descending
limb
Ascending
limb
Loop
of
Henle

54. 200µm
Blood vessels from a human kidney.
Arterioles and peritubular capillaries
appear pink; glomeruli appear yellow.
Figure 44.14e

55. 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
© 2011 Pearson Education, Inc.

56. 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.

57. © 2011 Pearson Education, Inc.
Animation: Bowman’s Capsule and Proximal Tubule
Right-click slide / select “Play”

58. Proximal tubule Distal tubule
Filtrate
CORTEX
Loop of
Henle
OUTER
MEDULLA
INNER
MEDULLA
Key
Active transport
Passive transport
Collecting
duct
NutrientsNaCl
NH3
HCO3
−
H2O K+
H+
NaCl
H2O
HCO3
−
K+ H+
H2O
NaCl
NaCl
NaCl H2O
Urea
Figure 44.15

59. 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
© 2011 Pearson Education, Inc.

60. 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
© 2011 Pearson Education, Inc.

61. 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.

62. © 2011 Pearson Education, Inc.
Animation: Loop of Henle and Distal Tubule
Right-click slide / select “Play”

63. 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.

64. © 2011 Pearson Education, Inc.
Animation: Collecting Duct
Right-click slide / select “Play”

65. Solute Gradients and Water Conservation
• The mammalian kidney’s ability to conserve
water is a key terrestrial adaptation
• Hyperosmotic urine can be produced only
because considerable energy is expended to
transport solutes against concentration
gradients
• The two primary solutes affecting osmolarity are
NaCl and urea
© 2011 Pearson Education, Inc.

66. 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
© 2011 Pearson Education, Inc.

67. • 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
© 2011 Pearson Education, Inc.

68. Osmolarity
of interstitial
fluid
(mOsm/L)
1,200
900
600
400
300
Key
Active
transport
Passive
transport
INNER
MEDULLA
OUTER
MEDULLA
CORTEX
H2O
H2O
H2O
H2O
H2O
H2O
H2O
1,200
900
600
400
300
300
300
Figure 44.16-1

69. Osmolarity
of interstitial
fluid
(mOsm/L)
1,200
900
600
400
300
Key
Active
transport
Passive
transport
INNER
MEDULLA
OUTER
MEDULLA
CORTEX
NaClH2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
1,200
100
100
200
400
700900
600
400
300
300
300
Figure 44.16-2

70. Osmolarity
of interstitial
fluid
(mOsm/L)
Key
Active
transport
Passive
transport
INNER
MEDULLA
OUTER
MEDULLA
CORTEX
NaClH2O
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
1,200
1,200
900
600
400
300300
400
600
100
100
200
400
700900
600
400
300
300
300
Figure 44.16-3

71. 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
© 2011 Pearson Education, Inc.

72. 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
© 2011 Pearson Education, Inc.

73. Birds and Other Reptiles
• Birds have shorter loops of Henle but
conserve water by excreting uric acid instead
of urea
• Other reptiles have only cortical nephrons but
also excrete nitrogenous waste as uric acid
© 2011 Pearson Education, Inc.

74. Figure 44.17

75. Freshwater Fishes and Amphibians
• Freshwater fishes conserve salt in their distal
tubules and excrete large volumes of dilute
urine
• Kidney function in amphibians is similar to
freshwater fishes
• Amphibians conserve water on land by
reabsorbing water from the urinary bladder
© 2011 Pearson Education, Inc.

76. Marine Bony Fishes
• Marine bony fishes are hypoosmotic compared
with their environment
• Their kidneys have small glomeruli and some
lack glomeruli entirely
• Filtration rates are low, and very little urine is
excreted
© 2011 Pearson Education, Inc.

77. Concept 44.5: Hormonal circuits link kidney
function, water balance, and blood pressure
• Mammals control the volume and osmolarity of
urine
• The kidneys of the South American vampire bat
can produce either very dilute or very
concentrated urine
• This allows the bats to reduce their body weight
rapidly or digest large amounts of protein while
conserving water
© 2011 Pearson Education, Inc.

78. Figure 44.18

79. 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
© 2011 Pearson Education, Inc.

80. © 2011 Pearson Education, Inc.
Animation: Effect of ADH
Right-click slide / select “Play”

81. Figure 44.19-1
Thirst
Hypothalamus
ADH
Pituitary
gland
Osmoreceptors in
hypothalamus trigger
release of ADH.
STIMULUS:
Increase in blood
osmolarity (for
instance, after
sweating profusely)
Homeostasis:
Blood osmolarity
(300 mOsm/L)

82. Figure 44.19-2
Thirst
Hypothalamus
ADH
Pituitary
gland
Osmoreceptors in
hypothalamus trigger
release of ADH.
STIMULUS:
Increase in blood
osmolarity (for
instance, after
sweating profusely)
Homeostasis:
Blood osmolarity
(300 mOsm/L)
Drinking reduces
blood osmolarity
to set point.
H2O reab-
sorption helps
prevent further
osmolarity
increase.
Increased
permeability
Distal
tubule
Collecting duct

83. • Binding of ADH to receptor molecules leads to
a temporary increase in the number of
aquaporin proteins in the membrane of
collecting duct cells
© 2011 Pearson Education, Inc.

84. Collecting
duct
ADH
receptor
COLLECTING
DUCT CELL
LUMEN
Second-messenger
signaling molecule
Storage
vesicle
Aquaporin
water
channel
Exocytosis
H2O
H2O
ADH
cAMP
Figure 44.20

85. • 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.

86. Figure 44.21
Prepare copies of human
aquaporin genes: two
mutants plus wild type.
Synthesize mRNA.
Inject mRNA into frog
oocytes.
Transfer to 10-mOsm
solution and observe
results.
2
1
3
4
EXPERIMENT
RESULTS
Aquaporin
gene
Promoter
Mutant 1 Mutant 2 Wild type
Aquaporin
proteins
H2O
(control)
Injected RNA Permeability (µm/sec)
196
20
17
18
Wild-type aquaporin
None
Aquaporin mutant 1
Aquaporin mutant 2

87. Prepare copies of human
aquaporin genes: two
mutants plus wild type.
Synthesize mRNA.
Inject mRNA into frog
oocytes.
Transfer to 10-mOsm
solution and observe
results.
2
1
3
4
EXPERIMENT
Aquaporin
gene
Promoter
Mutant 1 Mutant 2 Wild type
Aquaporin
proteins
H2O
(control)
Figure 44.21a

88. Figure 44.21b
RESULTS
Injected RNA Permeability (µm/sec)
196
20
17
18
Wild-type aquaporin
None
Aquaporin mutant 1
Aquaporin mutant 2

89. The Renin-Angiotensin-Aldosterone System
• The renin-angiotensin-aldosterone system
(RAAS) is part of a complex feedback circuit
that functions in homeostasis
• A drop in blood pressure near the glomerulus
causes the juxtaglomerular apparatus (JGA)
to release the enzyme renin
• Renin triggers the formation of the peptide
angiotensin II
© 2011 Pearson Education, Inc.

90. • Angiotensin II
– Raises blood pressure and decreases blood
flow to the kidneys
– Stimulates the release of the hormone
aldosterone, which increases blood volume
and pressure
© 2011 Pearson Education, Inc.

91. Figure 44.22-1
JGA
releases
renin.
Renin
Distal
tubule
Juxtaglomerular
apparatus (JGA)
STIMULUS:
Low blood volume
or blood pressure
(for example, due
to dehydration or
blood loss)
Homeostasis:
Blood pressure,
volume

92. AngiotensinogenLiver
JGA
releases
renin.
Renin
Distal
tubule
Juxtaglomerular
apparatus (JGA)
Angiotensin I
ACE
Angiotensin II
STIMULUS:
Low blood volume
or blood pressure
(for example, due
to dehydration or
blood loss)
Homeostasis:
Blood pressure,
volume
Figure 44.22-2

93. AngiotensinogenLiver
JGA
releases
renin.
Renin
Distal
tubule
Juxtaglomerular
apparatus (JGA)
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
More Na+
and H2O
are reabsorbed in
distal tubules,
increasing blood volume.
Arterioles
constrict,
increasing
blood
pressure.
STIMULUS:
Low blood volume
or blood pressure
(for example, due
to dehydration or
blood loss)
Homeostasis:
Blood pressure,
volume
Figure 44.22-3

94. 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
© 2011 Pearson Education, Inc.

95. Figure 44.UN01
Animal Inflow/Outflow Urine
Freshwater
fish. Lives in
water less
concentrated
than body
fluids; fish
tends to gain
water, lose salt
Does not drink water
Salt in
(active trans-
port by gills)
H2O in
Salt out
Marine bony
fish. Lives in
water more
concentrated
than body
fluids; fish
tends to lose
water, gain salt
Terrestrial
vertebrate.
Terrestrial
environment;
tends to lose
body water
to air
Drinks water
Drinks water
Salt in H2O out
Salt out (active
transport by gills)
Salt in
(by mouth)
H2O and
salt out
Large volume
of urine
Urine is less
concentrated
than body
fluids
Small volume
of urine
Urine is
slightly less
concentrated
than body
fluids
Moderate
volume
of urine
Urine is
more
concentrated
than body
fluids

96. Figure 44.UN01a
Animal Inflow/Outflow Urine
Freshwater
fish. Lives in
water less
concentrated
than body
fluids; fish
tends to gain
water, lose salt
Does not drink water
Salt in
(active trans-
port by gills)
H2O in
Large volume
of urine
Urine is less
concentrated
than body
fluids
Salt out

97. Figure 44.UN01b
Animal Inflow/Outflow Urine
Marine bony
fish. Lives in
water more
concentrated
than body
fluids; fish
tends to lose
water, gain salt
Drinks water
Salt in H2O out
Salt out (active
transport by gills)
Small volume
of urine
Urine is
slightly less
concentrated
than body
fluids

98. Figure 44.UN01c
Animal Inflow/Outflow Urine
Terrestrial
vertebrate.
Terrestrial
environment;
tends to lose
body water
to air
Drinks water
Salt in
(by mouth)
H2O and
salt out
Moderate
volume
of urine
Urine is
more
concentrated
than body
fluids

99. Figure 44.UN02