Download Chapter 32- Part 2 Excretory

CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
32
Homeostasis and
Endocrine Signaling
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
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What is osmosis?
Why is it important in cells?
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Concept 32.3: A shared system mediates
osmoregulation and excretion in many animals
 Osmoregulation is the general term for the
processes by which animals control solute
concentrations in the interstitial fluid and balance
water gain and loss
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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 32.15
(a) Osmoregulation in a marine fish
Gain of water and Excretion of
salt ions from food salt ions
Osmotic water loss
from gills
through gills and
other parts of body
surface
SALT WATER
Gain of water
and salt ions from
drinking seawater
Excretion of salt ions and
small amounts of water in
scanty urine from kidneys
(b) Osmoregulation in a freshwater fish
Gain of water and
some ions in food
FRESH WATER
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Uptake of
salt ions Osmotic water gain
through gills and
by gills
other parts of body
surface
Excretion of salt
ions and large
amounts of water
in dilute urine
from kidneys
Key
Water
Salt
 Marine and freshwater organisms have opposite
challenges
 Marine fish drink large amounts of seawater to
balance water loss and excrete salt through their
gills and kidneys
 Freshwater fish drink almost no water and replenish
salts through eating; some also replenish salts by
uptake across the gills
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What do you think the difference
between osmoregulators and
osmoconformers might be?
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Osmoregulatory Challenges and Mechanisms
 Osmoconformers, consisting 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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What are the 3 different ways you can
excrete nitrogenous wastes?
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Figure 32.16
Proteins
Nucleic acids
Amino
acids
Nitrogenous
bases
Amino groups
Most aquatic
animals, including
most bony fishes
Ammonia
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Mammals, most
amphibians, sharks,
some bony fishes
Urea
Many reptiles
(including birds),
insects, land snails
Uric acid
Nitrogenous Wastes
 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
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 Ammonia excretion is most common in aquatic
organisms
 Vertebrates excrete urea, a conversion product of
ammonia, which is much less toxic
 Insects, land snails, and many reptiles including
birds excrete uric acid as a semisolid paste
 It is less toxic than ammonia and generates very
little water loss, but it is energetically more
expensive to produce than urea
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Figure 32.18
Nucleus
of cap cell
Cilia
Flame
bulb
Interstitial
fluid filters
through
membrane.
Tubule
Tubules of
protonephridia
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Opening
in body
wall
Tubule
cell
Invertebrates
 Flatworms have excretory systems called
protonephridia, networks 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
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 In insects and other terrestrial arthropods, Malpighian
tubules remove nitrogenous wastes from hemolymph
without a filtration step
 Insects produce a relatively dry waste matter, mainly
uric acid
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Vertebrates
 In vertebrates and some other chordates, the kidney
functions in both osmoregulation and excretion
 The kidney consists of tubules arranged in an
organized array and in contact with a network of
capillaries
 The excretory system includes ducts and other
structures that carry urine from the tubules out of the
body
Animation: Nephron Introduction
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In humans, how do we remove
these wastes?
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Figure 32.19a
Excretory Organs
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
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Kidney
Figure 32.19b
Kidney Structure
Renal cortex
Renal medulla
Renal artery
Nephron Organization
Renal vein
Afferent arteriole
from renal artery
Ureter
Proximal
tubule
Renal pelvis
Nephron Types
Peritubular
capillaries
Distal
tubule
Cortical
nephron
Efferent
arteriole
from
glomerulus
Branch of
renal vein
Renal
cortex
Collecting
duct
Renal
medulla
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Glomerulus
Bowman’s
capsule
Juxtamedullary
nephron
Vasa
recta
Descending
limb
Loop
of
Henle
Ascending
limb
What are the steps in urine
formation?
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 Many animal species 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: Releasing processed filtrate containing
nitrogenous wastes from the body
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Figure 32.17
Filtration
Capillary
Filtrate
Excretory
tubule
Reabsorption
Secretion
Urine
Excretion
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Concept 32.4: Hormonal circuits link kidney
function, water balance, and blood pressure
 The capillaries and specialized cells of Bowman’s
capsule are permeable to water and small solutes
but not blood cells or large molecules
 The filtrate produced there 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
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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 all
along its journey down the descending limb
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Ascending limb of the loop of Henle
 The ascending limb has a transport epithelium that
lacks water channels
 Here, salt but not water is able to move from the
tubule into the interstitial fluid
 The filtrate becomes increasingly dilute as it moves
up to the cortex
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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
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Collecting duct
 The collecting duct carries filtrate through the
medulla to the renal pelvis
 Most of the water and nearly all sugars, amino acids,
vitamins, and other nutrients are reabsorbed into the
blood
 Urine is hyperosmotic to body fluids
Animation: Bowman’s Capsule
Animation: Collecting Duct
Animation: Loop of Henle
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Figure 32.20
1 Proximal tubule
NaCI Nutrients
HCO3− H2O
K
H
CORTEX
NH3
4 Distal tubule
H2O
NaCI
K
HCO3−
H
Interstitial
fluid
3 Thick segment
Filtrate
H2O
Salts (NaCI and others)
HCO3−
H
Urea
Glucose, amino acids
Some drugs
2 Descending limb
of loop of
Henle
of ascending
limb
NaCI
H2O
OUTER
MEDULLA
NaCI
3 Thin segment
of ascending
limb
5 Collecting
duct
Urea
NaCI
Key
Active transport
Passive transport
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INNER
MEDULLA
H2O
Figure 32.20a
1 Proximal tubule
NaCI Nutrients
HCO3− H2O
K
H
Filtrate
CORTEX
NH3
4 Distal tubule
H2O
NaCI
K
HCO3−
H
Interstitial
fluid
Active transport
Passive transport
© 2014 Pearson Education, Inc.
Figure 32.20b
3 Thick segment
2 Descending limb
of loop of
Henle
of ascending
limb
NaCI
H2O
OUTER
MEDULLA
Active transport
Passive transport
NaCI
3 Thin segment
of ascending
limb
5 Collecting
duct
Urea
NaCI
INNER
MEDULLA
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H2O
Concentrating Urine in the Mammalian Kidney
 The mammalian kidney’s ability to conserve water is
a key terrestrial adaptation
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Figure 32.21-1
300
mOsm/L
300
300
300
CORTEX
Active
transport
Passive
transport
OUTER
MEDULLA
H2O
H2O
400
400
H2O
H2O
600
600
900
900
H2O
H2O
INNER
MEDULLA
H2O
1,200
1,200
© 2014 Pearson Education, Inc.
Figure 32.21-2
300
mOsm/L
300
100
300
100
CORTEX
Active
transport
Passive
transport
OUTER
MEDULLA
H2O
H2O
NaCI
400
NaCI
H2O
NaCI
600
H2O
INNER
MEDULLA
NaCI
H2O
H2O
H2O
200
400
400
600
700
900
NaCI
900
NaCI
NaCI
1,200
1,200
© 2014 Pearson Education, Inc.
300
Figure 32.21-3
300
mOsm/L
300
100
300
100
CORTEX
Active
transport
Passive
transport
H2O
H2O
NaCI
400
NaCI
300
300
400
400
H2O
200
H2O
NaCI
H2O
H2O
NaCI
NaCI
OUTER
MEDULLA
H2O
NaCI
H2O
H2O
INNER
MEDULLA
H2O
400
600
NaCI
NaCI
700
H2O
Urea
600
900
H2O
Urea
1,200
1,200
© 2014 Pearson Education, Inc.
600
H2O
Urea
NaCI
900
H2O
1,200
 Water and salt are reabsorbed from the filtrate
passing from Bowman’s capsule to the proximal
tubule
 In the proximal tubule, filtrate volume decreases, but
its osmolarity remains the same
 As filtrate flows down the descending limb of the loop
of Henle, water leaves the tubule, increasing
osmolarity of the filtrate
 Salt diffusing from the ascending limb maintains a
high osmolarity in the interstitial fluid of the renal
medulla
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 The loop of Henle and surrounding capillaries act
as a type of countercurrent system
 This system involves active transport and thus an
expenditure of energy
 Such a system is called a countercurrent
multiplier system
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 The filtrate in the ascending limb of the loop of Henle
is hypoosmotic to the body fluids by the time it
reaches the distal tubule
 The filtrate descends to the collecting duct, which is
permeable to water but not to salt
 Osmosis extracts water from the filtrate to
concentrate salts, urea, and other solutes in the
filtrate
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Adaptations of the Vertebrate Kidney to Diverse
Environments
 Variations in nephron structure and function equip
the kidneys of different vertebrates for
osmoregulation in their various habitats
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 Desert-dwelling mammals excrete the most
hyperosmotic urine and have long loops of Henle
 Birds have shorter loops of Henle but conserve
water by excreting uric acid instead of urea
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 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
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Figure 32.22
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Homeostatic Regulation of the Kidney
 A combination of nervous and hormonal inputs
regulates the osmoregulatory function of the kidney
 These inputs contribute to homeostasis for blood
pressure and volume through their effect on amount
and osmoregulatory of urine
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Antidiuretic Hormone
 Antidiuretic hormone (ADH) makes the collecting
duct epithelium temporarily more permeable to water
 An increase in blood osmolarity above a set point
triggers the release of ADH, which helps to conserve
water
 Decreased osmolarity causes a drop in ADH
secretion and a corresponding decrease in
permeability of collecting ducts
Animation: Effect of ADH
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Figure 32.23-1
Osmoreceptors
trigger release
of ADH.
ADH
STIMULUS:
Increase
in blood
osmolarity
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Figure 32.23-2
Thirst
Osmoreceptors
trigger release
of ADH.
ADH
Increased
permeability
Distal
tubule
STIMULUS:
Increase
in blood
osmolarity
Collecting duct
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Figure 32.23-3
Osmoreceptors
trigger release
of ADH.
Thirst
Drinking
of fluids
ADH
Increased
permeability
Distal
tubule
STIMULUS:
Increase
in blood
osmolarity
H2O
reabsorption
Collecting duct
Homeostasis
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The Renin-Angiotensin-Aldosterone System
 The renin-angiotensin-aldosterone system (RAAS)
also regulates kidney function
 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
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Figure 32.24-1
Distal
tubule
JGA
releases
renin.
Renin
Juxtaglomerular
apparatus (JGA)
STIMULUS:
Low blood
pressure
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Figure 32.24-2
Liver
Distal
tubule
Angiotensinogen
JGA
releases
renin.
Renin
Angiotensin I
Juxtaglomerular
apparatus (JGA)
ACE
Angiotensin II
STIMULUS:
Low blood
pressure
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Figure 32.24-3
Liver
Distal
tubule
Angiotensinogen
JGA
releases
renin.
Renin
Angiotensin I
Juxtaglomerular
apparatus (JGA)
ACE
Angiotensin II
STIMULUS:
Low blood
pressure
Arterioles
constrict.
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Figure 32.24-4
Liver
Distal
tubule
Angiotensinogen
JGA
releases
renin.
Renin
Angiotensin I
Juxtaglomerular
apparatus (JGA)
ACE
Angiotensin II
STIMULUS:
Low blood
pressure
Adrenal gland
Aldosterone
Na and H2O
reabsorbed.
Arterioles
constrict.
Homeostasis
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 Angiotensin II
 Raises blood pressure and decreases blood flow to
capillaries in the kidney
 Stimulates the release of the hormone aldosterone,
which increases blood volume and pressure
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Coordination of ADH and RAAS Activity
 ADH and RAAS both increase water reabsorption
 ADH responds to changes in blood osmolarity
 RAAS responds to changes in blood volume and
pressure
 Thus, ADH and RAAS are partners in homeostasis
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