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HOMEOSTASIS:
THERMOREGULATION &
OSMOREGULATION
CHAPTER 4.1
Outline





Overview: Form and Function
Hierarchical Organization of the Body Plane
Homeostasis and Feedback loops
Thermoregulation
Osmoregulation
 Mammalian
Kidney
Overview: Diversity in Form and Function



Anatomy is the study of the biological form of an
organism
Physiology is the study of the biological functions an
organism performs
The comparative study of animals reveals that form
and function are closely correlated
Fig. 40-1
Physical Constraints on Animal Size and
Shape



The ability to perform certain actions depends on an
animal’s shape, size, and environment
Evolutionary convergence reflects different species’
adaptations to a similar environmental challenge
Physical laws impose constraints on animal size and
shape
Exchange with the Environment



An animal’s size and shape directly affect how it
exchanges energy and materials with its
surroundings
Exchange occurs as substances dissolved in the
aqueous medium diffuse and are transported across
the cells’ plasma membranes
A single-celled protist living in water has a sufficient
surface area of plasma membrane to service its
entire volume of cytoplasm
Fig. 40-3
Mouth
Gastrovascular
cavity
Exchange
Exchange
Exchange
0.15 mm
1.5 mm
(a) Single cell
(b) Two layers of cells




Multicellular organisms with a sac body plan have body
walls that are only two cells thick, facilitating diffusion of
materials
More complex organisms have highly folded internal
surfaces for exchanging materials
In vertebrates, the space between cells is filled with
interstitial fluid, which allows for the movement of material
into and out of cells
A complex body plan helps an animal in a variable
environment to maintain a relatively stable internal
environment
Fig. 40-4
External environment
CO2
Food
O2
Mouth
Respiratory
system
0.5 cm
50 µm
Animal
body
Lung tissue
Nutrients
Heart
Cells
Circulatory
system
10 µm
Interstitial
fluid
Digestive
system
Excretory
system
Lining of small intestine
Kidney tubules
Anus
Unabsorbed
matter (feces)
Metabolic waste products
(nitrogenous waste)
Fig. 40-4a
External environment
CO2 O
Food
2
Mouth
Animal
body
Respiratory
system
Nutrients
Heart
Cells
Circulatory
system
Interstitial
fluid
Digestive
system
Excretory
system
Anus
Unabsorbed
matter (feces)
Metabolic waste products
(nitrogenous waste)
Hierarchical Organization of Body Plans



Most animals are composed of specialized cells
organized into tissues that have different functions
Different tissues have different structures that are
suited to their functions
Tissues make up organs, which together make up
organ systems
Table 40-1
Feedback control loops maintain the
internal environment in many animals



Animals manage their internal environment by
regulating or conforming to the external environment
A regulator uses internal control mechanisms to
moderate internal change in the face of external,
environmental fluctuation
A conformer allows its internal condition to vary with
certain external changes
Fig. 40-7
40
River otter (temperature regulator)
Body temperature (°C)
30
20
Largemouth bass
(temperature conformer)
10
0
10
20
30
Ambient (environmental) temperature (ºC)
40
Homeostasis


Organisms use homeostasis to maintain a “steady
state” or internal balance regardless of external
environment
In humans, body temperature, blood pH, and glucose
concentration are each maintained at a constant
level of equilibrium.
Mechanisms of Homeostasis



Mechanisms of homeostasis moderate changes in the
internal environment
For a given variable, fluctuations above or below a
set point serve as a stimulus; these are detected by
a sensor and trigger a response
The response returns the variable to the set point
Fig. 40-8
Response:
Heater
turned
off
Room
temperature
decreases
Stimulus:
Control center
(thermostat)
reads too hot
Set
point:
20ºC
Stimulus:
Control center
(thermostat)
reads too cold
Room
temperature
increases
Response:
Heater
turned
on
Homeostasis: Organ Systems

The organ systems of the human body contribute to
homeostasis

The digestive system



The respiratory system



Adds oxygen to the blood
Removes carbon dioxide
The liver and the kidneys




Takes in and digests food
Provides nutrient molecules that replace used nutrients
Store excess glucose as glycogen
Later, glycogen is broken down to replace the glucose used
The hormone insulin regulates glycogen storage
The kidneys

Under hormonal control as they excrete wastes and salts
Feedback Loops in Homeostasis





The dynamic equilibrium of homeostasis is maintained by negative
feedback, which helps to return a variable to either a normal range
or a set point
Most homeostatic control systems function by negative feedback,
where buildup of the end product shuts the system off
Positive feedback loops occur in animals, but do not usually
contribute to homeostasis
Set points and normal ranges can change with age or show cyclic
variation
Homeostasis can adjust to changes in external environment, a process
called acclimatization
Negative Feedback

Homeostatic Control
 Partially
controlled by hormones
 Ultimately

controlled by the nervous system
Negative Feedback is the primary homeostatic
mechanism that keeps a variable close to a set value

Sensor detects change in environment

Regulatory Center activates an effector

Effector reverses the changes
Positive Feedback

During positive feedback, an event increases
the likelihood of another event
 Childbirth
process
 Urge to urinate

Positive Feedback
 Does
not result in equilibrium
 Does not occur as often as negative feedback
Positive Feedback
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2. Signals cause pituitary gland to
release the hormone oxytocin.
As the level of oxytocin increases,
so do uterine contractions
until birth occurs.
pituitary gland
+
+
1. Due to uterine contractions,
baby’s head presses on
cervix, and signals are
sent to brain.
uterus
Homeostasis: Bioenergentics






Bioenergetics is the overall flow and transformation of
energy in an animal
It determines how much food an animal needs and
relates to an animal’s size, activity, and environment
Animals harvest chemical energy from food
Energy-containing molecules from food are usually used
to make ATP, which powers cellular work
After the needs of staying alive are met, remaining
food molecules can be used in biosynthesis
Biosynthesis includes body growth and repair, synthesis
of storage material such as fat, and production of
gametes
Homeostasis: Thermoregulation





Thermoregulation is the process by which animals
maintain an internal temperature within a tolerable
range
Endothermic animals generate heat by metabolism;
birds and mammals are endotherms
Ectothermic animals gain heat from external sources;
ectotherms include most invertebrates, fishes,
amphibians, and non-avian reptiles
In general, ectotherms tolerate greater variation in
internal temperature, while endotherms are active at a
greater range of external temperatures
Endothermy is more energetically expensive than
ectothermy
Fig. 40-9
(a) A walrus, an endotherm
(b) A lizard, an ectotherm
Homeostasis: Thermoregulation
Radiation
Convection
Evaporation
Conduction
Thermoregulatory General
Adaptations

Insulation (major)



mammals and birds
Skin, feathers, fur, and blubber reduce heat flow between an animal
and its environment
Circulatory adaptations





Regulation of blood flow near the body surface significantly affects
thermoregulation
Many endotherms and some ectotherms can alter the amount of blood
flowing between the body core and the skin
In vasodilation, blood flow in the skin increases, facilitating heat loss
In vasoconstriction, blood flow in the skin decreases, lowering heat loss
countercurrent gas exhangers like geese and bottleneck dolpins
Thermoregulatory General
Adaptations



Cooling by evaporative heat loss
 Panting increases the cooling effect in birds and many mammals
 Sweating or bathing moistens the skin, helping to cool an animal down
Behavioral responses
 Both endotherms and ectotherms use behavioral responses to control
body temperature
 Some terrestrial invertebrates have postures that minimize or maximize
absorption of solar heat
Adjusting metabolic heat production
 Some animals can regulate body temperature by adjusting their rate of
metabolic heat production
 Heat production is increased by muscle activity such as moving or
shivering
 Some ectotherms can also shiver to increase body temperature
Homeostasis: Mammalian Thermoregulation
Hair
Epidermis
Sweat
pore
Muscle
Dermis
Nerve
Sweat
gland
Hypodermis
Adipose tissue
Blood vessels
Oil gland
Regulation of Body Temperature
Homeostasis: Osmoregulation






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
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
Fig. 44-1
Homeostasis: Osmoregulation



Osmoregulation is based largely on controlled
movement of solutes between internal fluids and the
external environment
Cells require a balance between osmotic gain and
loss of water
Osmolarity, the solute concentration of a solution,
determines the movement of water across a
selectively permeable membrane
Fig. 44-2
Selectively permeable
membrane
Solutes
Net water flow
Water
Hyperosmotic side
Hypoosmotic side
Osmotic Challenges



Marine and land animals manage differently
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
 Osmoregulators
gradients
must expend energy to maintain osmotic
Transport Epithelia in Osmoregulation




Animals regulate the composition of body fluid that
bathes their cells
Transport epithelia are specialized epithelial cells
that regulate solute movement (water-salt balance)
They are essential components of osmotic regulation
and metabolic waste disposal
They are arranged in complex tubular networks
Nitrogenous Waste Products



The type and quantity of an animal’s waste products
may greatly affect its water balance
Among the most important wastes are nitrogenous
breakdown products of proteins and nucleic acids
into ammonia (NH3)
Some animals convert toxic ammonia (NH3) to less
toxic compounds prior to excretion
Fig. 44-9
Proteins
Nucleic acids
Amino
acids
Nitrogenous
bases
Amino groups
Most aquatic
animals, including
most bony fishes
Ammonia
Mammals, most
amphibians, sharks,
some bony fishes
Urea
Many reptiles
(including birds),
insects, land snails
Uric acid
Nitrogenous Waste Products

Ammonia:
 Animals
that excrete need lots of water
 They release ammonia across the whole body surface or
through gills

Urea
 The
liver of mammals and most adult amphibians
converts ammonia to less toxic urea
 Excreted via circulatory system to kidney
 Energetically expensive but requires less water than
ammonia
Nitrogenous Waste Products

Uric Acid
Insects, land snails, and many reptiles, including birds, mainly
excrete uric acid
 Largely insoluble in water and can be secreted as a paste
with little water loss
 Uric acid is more energetically expensive to produce than
urea



The amount of nitrogenous waste is coupled to the
animal’s energy budget
Type of waste depends on the evolutionary history and
habitat
Osmoregulation: Excretory System




Excretory systems regulate solute movement between
internal fluids and the external environment
Most excretory systems produce urine by refining a
filtrate derived from body fluids
Systems that perform basic excretory functions vary
widely among animal groups
They usually involve a complex network of tubules
Fig. 44-10
Filtration
Capillary
Excretory
tubule
Reabsorption
Secretion
Urine
Excretion
Mammalian Osmoregulation: Kidney



Kidneys, the excretory organs of vertebrates, function
in both excretion and osmoregulation
The mammalian excretory system centers on paired
kidneys, which are also the principal site of water
balance and salt regulation
The mammalian kidney conserves water by producing
urine that is much more concentrated than body fluids
Fig. 44-14a
Posterior
vena cava
Renal artery
and vein
Aorta
Ureter
Urinary
bladder
Urethra
(a) Excretory organs and major
associated blood vessels
Kidney
Fig. 44-14ab
Renal
medulla
Posterior
vena cava
Renal artery
and vein
Aorta
Renal
cortex
Kidney
Renal
pelvis
Ureter
Urinary
bladder
Urethra
(a) Excretory organs and major
associated blood vessels
Ureter
(b) Kidney structure
Section of kidney
from a rat
4 mm
Fig. 44-14b
Renal
medulla
Renal
cortex
Renal
pelvis
Ureter
(b) Kidney structure
Section of kidney
from a rat
4 mm
Fig. 44-14cd
Juxtamedullary
nephron
Cortical
nephron
10 µm
Afferent arteriole
from renal artery
SEM
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Renal
cortex
Efferent
arteriole from
glomerulus
Collecting
duct
Renal
medulla
To
renal
pelvis
(c) Nephron types
Branch of
renal vein
Loop of
Henle
Distal
tubule
Collecting
duct
Descending
limb
Ascending
limb
(d) Filtrate and blood flow
Vasa
recta
Fig. 44-14e
10 µm
SEM
Nephrons


Each kidney composed of many tubular nephrons
Each nephron composed of several parts







Glomerular capsule
Glomerulus
Proximal convoluted tubule
Loop of the nephron
Distal convoluted tube
Collecting duct
Urine production requires three distinct processes:

Glomerular filtration in glomerular capsule

Tubular reabsorption at the proximal convoluted tubule

Tubular secretion at the distal convoluted tubule
Stepwise Processing of the Blood
STEP 1: Ultrafiltration in the glomerulus
 Filtration occurs as blood pressure forces fluid from
the blood in the glomerulus into the lumen of
Bowman’s capsule
 Filtration of small molecules is nonselective
 The filtrate contains salts, glucose, amino acids,
vitamins, nitrogenous wastes, and other small
molecules
Fig. 44-14d
10 µm
Afferent arteriole
from renal artery
SEM
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Efferent
arteriole from
glomerulus
Branch of
renal vein
Loop of
Henle
(d) Filtrate and blood flow
Distal
tubule
Collecting
duct
Descending
limb
Ascending
limb
Vasa
recta
Fig. 44-15
Proximal tubule
NaCl
HCO3
–
Nutrients
H2O
K+
H+
NH3
Distal tubule
H2O
NaCl
K+
HCO3–
H+
Filtrate
CORTEX
Loop of
Henle
NaCl
OUTER
MEDULLA
H2O
NaCl
Collecting
duct
Key
Active
transport
Passive
transport
Urea
NaCl
INNER
MEDULLA
H2O
Stepwise Processing of the Blood
STEP 2: 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 secreted into the filtrate

The filtrate volume decreases
Fig. 44-15
Proximal tubule
NaCl
HCO3
–
Nutrients
H2O
K+
H+
NH3
Distal tubule
H2O
NaCl
K+
HCO3–
H+
Filtrate
CORTEX
Loop of
Henle
NaCl
OUTER
MEDULLA
H2O
NaCl
Collecting
duct
Key
Active
transport
Passive
transport
Urea
NaCl
INNER
MEDULLA
H2O
Stepwise Processing of the Blood
STEP 3: 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
STEP 4: 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
Fig. 44-15
Proximal tubule
NaCl
HCO3
–
Nutrients
H2O
K+
H+
NH3
Distal tubule
H2O
NaCl
K+
HCO3–
H+
Filtrate
CORTEX
Loop of
Henle
NaCl
OUTER
MEDULLA
H2O
NaCl
Collecting
duct
Key
Active
transport
Passive
transport
Urea
NaCl
INNER
MEDULLA
H2O
Stepwise Processing of the Blood
STEP 5: Distal Tubule
 The distal tubule regulates the K+ and NaCl
concentrations of body fluids
 The controlled movement of ions contributes to pH
regulation
STEP 6: Collecting Duct
 The collecting duct carries filtrate through the medulla
to the renal pelvis
 Water is lost as well as some salt and urea, and the
filtrate becomes more concentrated
 Urine is hyperosmotic to body fluids
Solute Gradients and Water
Conservation



Urine is much more concentrated than blood
The cooperative action and precise arrangement of
the loops of Henle and collecting ducts are largely
responsible for the osmotic gradient that
concentrates the urine
NaCl and urea contribute to the osmolarity of the
interstitial fluid, which causes reabsorption of water
in the kidney and concentrates the urine
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
The Two-Solute Model



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
Fig. 44-16-1
Osmolarity of
interstitial
fluid
(mOsm/L)
300
300
300
300
CORTEX
H2O
H2O
400
400
H2O
OUTER
MEDULLA
H2O
600
600
900
900
H2O
H2O
Key
Active
transport
Passive
transport
INNER
MEDULLA
H2O
1,200
1,200
Fig. 44-16-2
Osmolarity of
interstitial
fluid
(mOsm/L)
300
300
100
300
100
CORTEX
H2O
H2O
NaCl
400
H2O
OUTER
MEDULLA
H2O
Key
Active
transport
Passive
transport
INNER
MEDULLA
H2O
NaCl
200
400
NaCl
NaCl
600
400
600
700
900
NaCl
H2O
H2O
300
900
NaCl
NaCl
1,200
1,200
Fig. 44-16-3
Osmolarity of
interstitial
fluid
(mOsm/L)
300
300
100
300
100
CORTEX
H2O
H2O
NaCl
300
400
400
H2O
NaCl
400
300
200
H2O
NaCl
H2O
H2O
NaCl
NaCl
OUTER
MEDULLA
H2O
NaCl
600
400
600
600
H2O
NaCl
H2O
H2O
Urea
H2O
Key
Active
transport
Passive
transport
INNER
MEDULLA
H2O
900
NaCl
NaCl
700
H2O
900
Urea
H2O
Urea
1,200
1,200
1,200
Urine Formation and Homeostasis

Excretion of hypertonic urine
 Dependent
upon the reabsorption of water
 Absorbed from
 Loop
of the nephron, and
 The collecting duct
 Osmotic
gradient within the renal medulla causes
water to leave the descending limb along its entire
length
Adaptations of the Mammalian 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
The juxtamedullary nephron contributes 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
Osmoregulation and Homeostasis



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
Fig. 44-18
Maintenance of pH and Osmolality



More than 99% of sodium filtered at glomerulus is
returned to blood at the distal convoluted tubule
Reabsorption of sodium regulated by hormones

Aldosterone

Renin

Atrial Natriuretic Hormone (ANH)
pH adjusted by either

The reabsorption of the bicarbonate ions, or

The secretion of hydrogen ions
69
Hormonal Regulation: Antidiuretic Hormone



The osmolarity of the urine is regulated by nervous
and hormonal control of water and salt reabsorption
in the kidneys
Antidiuretic hormone (ADH) increases water
reabsorption in the distal tubules and collecting ducts
of the kidney
An increase in osmolarity triggers the release of
ADH, which helps to conserve water
Fig. 44-19a-1
Thirst
Osmoreceptors in
hypothalamus trigger
release of ADH.
Hypothalamus
ADH
Pituitary
gland
STIMULUS:
Increase in blood
osmolarity
Homeostasis:
Blood osmolarity
(300 mOsm/L)
(a)
Fig. 44-19a-2
Osmoreceptors in
hypothalamus trigger
release of ADH.
Thirst
Hypothalamus
Drinking reduces
blood osmolarity
to set point.
ADH
Increased
permeability
Pituitary
gland
Distal
tubule
H2O reabsorption helps
prevent further
osmolarity
increase.
STIMULUS:
Increase in blood
osmolarity
Collecting duct
Homeostasis:
Blood osmolarity
(300 mOsm/L)
(a)
Fig. 44-19b
COLLECTING
DUCT
LUMEN
INTERSTITIAL
FLUID
COLLECTING
DUCT CELL
ADH
cAMP
Second messenger
signaling molecule
Storage
vesicle
Exocytosis
Aquaporin
water
channels
H2O
H2O
(b)
ADH
receptor
Fig. 44-19
Osmoreceptors in
hypothalamus trigger
release of ADH.
Thirst
INTERSTITIAL
FLUID
COLLECTING
DUCT
LUMEN
Hypothalamus
COLLECTING
DUCT CELL
ADH
cAMP
Drinking reduces
blood osmolarity
to set point.
ADH
Increased
permeability
Second messenger
signaling molecule
Pituitary
gland
Storage
vesicle
Distal
tubule
Exocytosis
Aquaporin
water
channels
H2O
H2O reabsorption helps
prevent further
osmolarity
increase.
Collecting duct
Homeostasis:
Blood osmolarity
(300 mOsm/L)
(a)
H2O
STIMULUS:
Increase in blood
osmolarity
(b)
ADH
receptor


Mutation in ADH production causes severe
dehydration and results in diabetes insipidus
Alcohol is a diuretic as it inhibits the release of ADH
The Renin-Angiotensin-Aldosterone
System

The renin-angiotensin-aldosterone system (RAAS)
is part of a complex feedback circuit that functions in
homeostasis
Fig. 44-21-1
Distal
tubule
Renin
Juxtaglomerular
apparatus (JGA)
STIMULUS:
Low blood volume
or blood pressure
Homeostasis:
Blood pressure,
volume
Fig. 44-21-2
Liver
Angiotensinogen
Distal
tubule
Renin
Angiotensin I
ACE
Juxtaglomerular
apparatus (JGA)
Angiotensin II
STIMULUS:
Low blood volume
or blood pressure
Homeostasis:
Blood pressure,
volume
Fig. 44-21-3
Liver
Distal
tubule
Angiotensinogen
Renin
Angiotensin I
ACE
Juxtaglomerular
apparatus (JGA)
Angiotensin II
STIMULUS:
Low blood volume
or blood pressure
Adrenal gland
Aldosterone
Increased Na+
and H2O reabsorption in
distal tubules
Arteriole
constriction
Homeostasis:
Blood pressure,
volume
You should now be able to:
1.
2.
3.
4.
5.
Define homeostasis and distinguish between
positive and negative feedback loops
Define bioenergetic
Define thermoregulation and explain how
endotherms and ectotherms manage their heat
budgets
Distinguish between the following terms: isoosmotic,
hyperosmotic, and hypoosmotic; osmoregulators
and osmoconformers; stenohaline and euryhaline
animals
Define osmoregulation, excretion
5.
6.
7.
8.
9.
Compare the osmoregulatory challenges of
freshwater and marine animals
Describe some of the factors that affect the
energetic cost of osmoregulation
Using a diagram, identify and describe the function
of each region of the nephron
Explain how the loop of Henle enhances water
conservation
Describe the nervous and hormonal controls
involved in the regulation of kidney function
The organism in which these measurements
were made is an osmo___ and a thermal___.
a.
b.
c.
d.
conformer; regulator
regulator; conformer
conformer; conformer
regulator; regulator
Which is the best interpretation of the data
in this graph?
a.
b.
c.
Maia, the spider crab, is an
osmoconformer in saltwater but
is capable of osmoregulation
in freshwater.
Nereis, the clam worm, is an
osmoconformer in freshwater
and is capable of
osmoregulation in brackish
water.
Carcinus, the shore crab, is
capable of osmoregulation in
brackish water and freshwater.
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which of the following is an example
of a negative feedback response?
a.
b.
c.
d.
As the uterus contracts, more oxytocin is released to
intensify uterine contractions.
Meerkats bask in the sun at the beginning of the day
but avoid it during the heat of the day.
Sexual stimulation leads to arousal and climax.
A nursing baby stimulates the release of oxytocin,
which causes letdown of milk.
You are a biologist studying desert animals
on a day when the temperature is 110°F.
You take the following body temperature
measurements: snake found under a rock,
87°F; mouse in a burrow, 100°F; lizard on
a rock ledge, 105°F; beetle in the leaves
of a bush, 102°F. Which is most likely
endothermic?
a.
b.
c.
d.
Snake
Mouse
Lizard
beetle
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
The sea star Porcellanaster ceruleus
is found exclusively in the deep sea
where the water temperature is
around 4°C year round. How would
you classify this organism?
a.
b.
c.
d.
endothermic homeotherm
endothermic poikilotherm
ectothermic homeotherm
ectothermic poikilotherm
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
The naked mole rat, Heterocephalus glaber, is a
mammal that inhabits burrows with a stable
temperature of 28 to 32°C and has the following
characteristics: no fur, a poorly developed
subcutaneous fat layer, no sweat glands, and skin that
is highly permeable to water. Its body temperature
stays only slightly above ambient (0.5°C) over a range
of 12 to 37°C. How would you classify this mammal?
a.
b.
c.
d.
endothermic homeotherm
ectothermic poikilotherm
ectothermic homeotherm
endothermic poikilotherm
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which of these describes urea
molecules, the primary nitrogenous
waste of mammals?
a.
b.
c.
d.
less toxic than ammonia
more soluble in water than ammonia
produced mainly in cells of the kidney
require less energy to produce than ammonia
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Education, Inc., publishing as
Pearson Benjamin Cummings.
Kidney function requires a great
deal of ATP. Transport epithelium in
the nephron contains pumps for
active transport of all of the
following substances except
a.
b.
c.
d.
e.
urea.
sodium ions Na+.
potassium ions K+.
bicarbonate ions HCO3-.
hydrogen ions H+.
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which of the following is part of
the two-solute model explaining
urine production in the nephron?
a.
b.
c.
d.
e.
NaCl moves out of the nephron into interstitial fluid in the
descending loop of Henle.
Fluid entering the distal convoluted tubule is more concentrated
than fluid entering the proximal convoluted tubule.
Transport epithelium in the ascending loop of Henle is impermeable
to water.
All transport of urea is in the direction of interstitial fluid into tubule
fluid.
The ratio of NaCl to urea in interstitial fluid is about the same all
along the length of the nephron.
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which one of the following shortterm physiological phenomena (not
structural adaptations) tends to
lead to a decrease in the volume of
urine produced?
a.
b.
c.
d.
e.
increase in blood pressure
increase in filtration rate into the Bowman’s capsule
increase in density of aquaporin channels in collecting
duct
decrease in blood osmolarity
decrease in sodium ion reabsorption in collecting duct
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.