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
Exchange
0.15 mm
(a) Single cell
1.5 mm
(b) Two layers of cells
Exchange
Exchange
Mouth
Gastrovascularcavity
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
0.5 cmNutrients
Digestivesystem
Lining of small intestine
MouthFood
External environment
Animalbody
CO2 O2
Circulatorysystem
Heart
Respiratorysystem
Cells
Interstitialfluid
Excretorysystem
Anus
Unabsorbedmatter (feces)
Metabolic waste products(nitrogenous waste)
Kidney tubules
10 µm
50
µm
Lung tissue
Fig. 40-4a
Nutrients
Mouth
Digestivesystem
Anus
Unabsorbedmatter (feces)
Metabolic waste products(nitrogenous waste)
Excretorysystem
Circulatorysystem
Interstitialfluid
Cells
Respiratorysystem
Heart
Animalbody
CO2 O2Food
External environment
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
Hierarchical Organization of Body Plans
Table 40-1
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
Feedback control loops maintain the internal environment in many animals
Fig. 40-7
River otter (temperature regulator)
Largemouth bass(temperature conformer)
Bod
y t
em
pera
ture
(°C
)
0 10
10
20
20
30
30
40
40
Ambient (environmental) temperature (ºC)
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.
Homeostasis: Organ Systems The organ systems of the human body
contribute to homeostasis The digestive system
Takes in and digests food Provides nutrient molecules that replace used nutrients
The respiratory system Adds oxygen to the blood Removes carbon dioxide
The liver and the kidneys 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 FeedbackCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
uterus
pituitary gland
2. Signals cause pituitary gland to release the hormone oxytocin. As the level of oxytocin increases, so do uterine contractions until birth occurs.
1. Due to uterine contractions, baby’s head presses on cervix, and signals are sent to brain.
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
Epidermis
Dermis
Hypodermis
Adipose tissue
Blood vessels
Hair
Sweatpore
Muscle
Nerve
Sweatgland
Oil glandHair follicle
Homeostasis: Mammalian Thermoregulation
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 permeablemembrane
Net water flow
Hyperosmotic side
Hypoosmotic side
Water
Solutes
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 must expend energy to
maintain osmotic gradients
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
Many reptiles(including birds),insects, land snails
Ammonia Uric acidUrea
Most aquaticanimals, includingmost bony fishes
Mammals, mostamphibians, sharks,some bony fishes
Nitrogenous
bases
Amino acids
Proteins
Nucleic acids
Amino groups
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
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
Nitrogenous Waste Products
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
Capillary
Excretion
Secretion
Reabsorption
Excretorytubule
Filtration
Filtra
te
Urin
e
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
Posteriorvena cava
Renal arteryand vein
Urinarybladder
Ureter
Aorta
Urethra
(a) Excretory organs and major
associated blood vessels
Kidney
Fig. 44-14ab
Posteriorvena cavaRenal arteryand vein
Urinarybladder
Ureter
Aorta
Urethra
(a) Excretory organs and major
associated blood vessels
(b) Kidney structure
Section of kidneyfrom a rat
4 mm
Kidney
Ureter
RenalmedullaRenalcortex
Renalpelvis
Fig. 44-14b
(b) Kidney structure
Section of kidneyfrom a rat
4 mm
Renalcortex
Renalmedulla
Renalpelvis
Ureter
Fig. 44-14cd
Cortical
nephron
Juxtamedullary
nephron
Collecting
duct
(c) Nephron types
Torenalpelvi
s
Renalmedull
a
Renalcorte
x
10 µm
Afferent arteriole
from renal artery
Efferentarteriole
fromglomerulus
SEM
Branch ofrenal
vein
Descending
limb
Ascending
limb
Loop ofHenle
(d) Filtrate and blood flow
Vasarecta
Collectingduct
Distaltubule
Peritubular capillaries
Proximal tubuleBowman’s
capsule
Glomerulus
Fig. 44-14e
SEM
10 µm
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. 44-14dAfferent
arteriolefrom renal
artery
Efferentarteriole
fromglomerulus
SEM
Branch of
renal vein
Descending
limb
Ascending
limb
Loop of
Henle
(d) Filtrate and blood flow
Vasarecta
Collecting
duct
Distal
tubule
Peritubular capillaries
Proximal tubule
Bowman’s capsuleGlomerulus
10 µm
Fig. 44-15
Key
Activetranspor
tPassivetranspor
t
INNERMEDULL
A
OUTERMEDULL
A
H2O
CORTEX
Filtrate
Loop of
Henle
H2O K+HCO3–
H+NH
3
Proximal tubuleNaC
lNutrient
s
Distal tubule
K+ H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting
duct
NaCl
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
Key
Activetranspor
tPassivetranspor
t
INNERMEDULL
A
OUTERMEDULL
A
H2O
CORTEX
Filtrate
Loop of
Henle
H2O K+HCO3–
H+NH
3
Proximal tubuleNaC
lNutrient
s
Distal tubule
K+ H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting
duct
NaCl
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
Stepwise Processing of the Blood
Fig. 44-15
Key
Activetranspor
tPassivetranspor
t
INNERMEDULL
A
OUTERMEDULL
A
H2O
CORTEX
Filtrate
Loop of
Henle
H2O K+HCO3–
H+NH
3
Proximal tubuleNaC
lNutrient
s
Distal tubule
K+ H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting
duct
NaCl
Stepwise Processing of the BloodSTEP 5: Distal Tubule The distal tubule regulates the K+ and
NaCl concentrations of body fluids The controlled movement of ions
contributes to pH regulationSTEP 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 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
The Two-Solute Model
Fig. 44-16-1
Key
Activetranspo
rtPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 30
0
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of
interstitialfluid
(mOsm/L)
400
600
900
1,200
Fig. 44-16-2
Key
Activetranspo
rtPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 30
0
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of
interstitialfluid
(mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
Fig. 44-16-3
Key
Activetranspo
rtPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 30
0
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity of
interstitialfluid
(mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
1,200
300
400
600
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
Urea
Urea
Urea
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
64
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
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 inhypothalamus
triggerrelease of ADH.
Pituitary
gland
ADH
Hypothalamus
STIMULUS:Increase in
bloodosmolarity
Homeostasis:Blood osmolarit
y(300 mOsm/L)(a
)
Fig. 44-19a-2
Thirst
Drinking reduces
blood osmolarit
yto set point. Increased
permeability
Pituitary
gland
ADH
Hypothalamus
Distal
tubule
H2O reab-sorption
helpsprevent
furtherosmolarityincrease.
STIMULUS:Increase in
bloodosmolarity
Collecting duct
Homeostasis:Blood osmolarit
y(300 mOsm/L)(a
)
Osmoreceptors inhypothalamus
triggerrelease of ADH.
Fig. 44-19b
Exocytosis
(b)
Aquaporin
waterchannels
H2O
H2O
Storagevesicle
Second messenger
signaling molecule
cAMP
INTERSTITIALFLUID
ADHrecepto
r
ADH
COLLECTINGDUCTLUMEN
COLLECTINGDUCT CELL
Fig. 44-19
Thirst
Drinking reduces
blood osmolarit
yto set point.
Osmoreceptors in hypothalamus
triggerrelease of ADH.
Increasedpermeabili
ty
Pituitary
gland
ADH
Hypothalamus
Distal
tubule
H2O reab-sorption
helpsprevent
furtherosmolarityincrease.
STIMULUS:Increase in
bloodosmolarity
Collecting duct
Homeostasis:Blood osmolarit
y(300 mOsm/L)(a
)
Exocytosis
(b)
Aquaporin
waterchannels
H2O
H2O
Storage
vesicle
Second messenger
signaling molecule
cAMP
INTERSTITIALFLUID
ADHrecepto
r
ADH
COLLECTINGDUCTLUMEN
COLLECTING
DUCT CELL
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
Renin
Distaltubul
e
Juxtaglomerular
apparatus (JGA)
STIMULUS:Low blood
volumeor blood
pressure
Homeostasis:Blood pressure,
volume
Fig. 44-21-2
Renin
Distaltubul
e
Juxtaglomerular
apparatus (JGA)
STIMULUS:Low blood
volumeor blood
pressure
Homeostasis:Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Fig. 44-21-3
Renin
Distaltubul
e
Juxtaglomerular
apparatus (JGA)
STIMULUS:Low blood
volumeor blood
pressure
Homeostasis:Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
Arterioleconstrictio
n
Increased Na+
and H2O reab-
sorption indistal
tubules
You should now be able to:
1. Define homeostasis and distinguish between positive and negative feedback loops
2. Define bioenergetic
3. Define thermoregulation and explain how endotherms and ectotherms manage their heat budgets
4. Distinguish between the following terms: isoosmotic, hyperosmotic, and hypoosmotic; osmoregulators and osmoconformers; stenohaline and euryhaline animals
5. Define osmoregulation, excretion
5. Compare the osmoregulatory challenges of freshwater and marine animals
6. Describe some of the factors that affect the energetic cost of osmoregulation
7. Using a diagram, identify and describe the function of each region of the nephron
8. Explain how the loop of Henle enhances water conservation
9. 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. conformer; regulatorb. regulator; conformerc. conformer; conformerd. regulator; regulator
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
Which is the best interpretation of the data in this graph?
a. Maia, the spider crab, is an osmoconformer in saltwater but is capable of osmoregulation in freshwater.
b. Nereis, the clam worm, is an osmoconformer in freshwater and is capable of osmoregulation in brackish water.
c. Carcinus, the shore crab, is capable of osmoregulation in brackish water and freshwater.
Which of the following is an example of a negative feedback response?
a. As the uterus contracts, more oxytocin is released to intensify uterine contractions.
b. Meerkats bask in the sun at the beginning of the day but avoid it during the heat of the day.
c. Sexual stimulation leads to arousal and climax.
d. A nursing baby stimulates the release of oxytocin, which causes letdown of milk.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
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. Snake
b. Mousec. Lizardd. 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. endothermic homeotherm
b. endothermic poikilothermc. ectothermic homeothermd. 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. endothermic homeothermb. ectothermic poikilothermc. ectothermic homeothermd. 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. less toxic than ammoniab. more soluble in water than ammoniac. produced mainly in cells of the kidneyd. require less energy to produce than
ammonia
Copyright © 2008 Pearson 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. urea.b. sodium ions Na+.c. potassium ions K+.d. bicarbonate ions HCO3
-.
e. 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. NaCl moves out of the nephron into interstitial fluid
in the descending loop of Henle.b. Fluid entering the distal convoluted tubule is more
concentrated than fluid entering the proximal convoluted tubule.
c. Transport epithelium in the ascending loop of Henle is impermeable to water.
d. All transport of urea is in the direction of interstitial fluid into tubule fluid.
e. 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 short-term physiological phenomena (not structural adaptations) tends to lead to a decrease in the volume of urine produced?a. increase in blood pressureb. increase in filtration rate into the Bowman’s
capsulec. increase in density of aquaporin channels in
collecting ductd. decrease in blood osmolaritye. decrease in sodium ion reabsorption in
collecting duct