HOMEOSTASIS: THERMOREGULATION & OSMOREGULATION CHAPTER 2.1.

HOMEOSTASIS: THERMOREGULATION & OSMOREGULATION

CHAPTER 2.1

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.

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

Mechanisms of Homeostasis

Fig. 40-8Response:Heater turnedoff

Stimulus:Control center(thermostat)reads too hot

Roomtemperature

decreases

Setpoint:20ºC

Roomtemperature

increases

Stimulus:Control center(thermostat)

reads too cold

Response:Heater turnedon

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

Radiation Evaporation

Convection Conduction

Homeostasis: Thermoregulation

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

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


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


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


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


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

69

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.


bloodosmolarity

Collecting duct


y(300 mOsm/L)(a

)

Osmoreceptors inhypothalamus


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


Increasedpermeabili

ty

Pituitary

gland

ADH

Hypothalamus

Distal

tubule

H2O reab-sorption

helpsprevent

furtherosmolarityincrease.


bloodosmolarity

Collecting duct


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


volume

Liver

Angiotensinogen

Angiotensin I

ACE

Angiotensin II

Fig. 44-21-3

Renin

Distaltubul

e

Juxtaglomerular

apparatus (JGA)

STIMULUS:Low blood

volumeor 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.


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


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


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


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


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+.


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.


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

HOMEOSTASIS: THERMOREGULATION & OSMOREGULATION CHAPTER 2.1.

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Transcript of HOMEOSTASIS: THERMOREGULATION & OSMOREGULATION CHAPTER 2.1.