osmoregulation and excretion - universitas...

Chapter 44Chapter 44

Osmoregulation andExcretion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

• Overview: A balancing act

• The physiological systems of animals

– Operate in a fluid environment

• The relative concentrations of water andsolutes in this environment

– Must be maintained within fairly narrow limits


• Overview: A balancing act

• The physiological systems of animals

– Operate in a fluid environment

• The relative concentrations of water andsolutes in this environment

– Must be maintained within fairly narrow limits

• Freshwater animals– Show adaptations that reduce water uptake and

conserve solutes

• Desert and marine animals face desiccatingenvironments– With the potential to quickly deplete the body water


• Freshwater animals– Show adaptations that reduce water uptake and

conserve solutes

• Desert and marine animals face desiccatingenvironments– With the potential to quickly deplete the body water

Figure 44.1

• Osmoregulation

– Regulates solute concentrations and balancesthe gain and loss of water

• Excretion

– Gets rid of metabolic wastes


• Osmoregulation

– Regulates solute concentrations and balancesthe gain and loss of water

• Excretion

– Gets rid of metabolic wastes

• Concept 44.1: Osmoregulation balances theuptake and loss of water and solutes

• Osmoregulation is based largely on controlledmovement of solutes

– Between internal fluids and the externalenvironment


• Concept 44.1: Osmoregulation balances theuptake and loss of water and solutes

• Osmoregulation is based largely on controlledmovement of solutes

– Between internal fluids and the externalenvironment

Osmosis

• Cells require a balance

– Between osmotic gain and loss of water

• Water uptake and loss

– Are balanced by various mechanisms ofosmoregulation in different environments


• Cells require a balance

– Between osmotic gain and loss of water

• Water uptake and loss

– Are balanced by various mechanisms ofosmoregulation in different environments

Osmotic Challenges

• Osmoconformers, which are only marineanimals

– Are isoosmotic with their surroundings and donot regulate their osmolarity

• Osmoregulators expend energy to controlwater uptake and loss

– In a hyperosmotic or hypoosmotic environment


• Osmoconformers, which are only marineanimals

– Are isoosmotic with their surroundings and donot regulate their osmolarity

• Osmoregulators expend energy to controlwater uptake and loss

– In a hyperosmotic or hypoosmotic environment

• Most animals are said to be stenohaline

– And cannot tolerate substantial changes inexternal osmolarity

• Euryhaline animals

– Can survive large fluctuations in externalosmolarity


• Most animals are said to be stenohaline

– And cannot tolerate substantial changes inexternal osmolarity

• Euryhaline animals

– Can survive large fluctuations in externalosmolarity

Figure 44.2

Marine Animals

• Most marine invertebrates are osmoconformers

• Most marine vertebrates and someinvertebrates are osmoregulators


• Marine bony fishes are hypoosmotic to sea water

– And lose water by osmosis and gain salt by bothdiffusion and from food they eat

• These fishes balance water loss

– By drinking seawater


• Marine bony fishes are hypoosmotic to sea water

– And lose water by osmosis and gain salt by bothdiffusion and from food they eat

• These fishes balance water loss

– By drinking seawater

Figure 44.3a

Gain of water andsalt ions from foodand by drinkingseawater

Osmotic water lossthrough gills and other partsof body surface

Excretion ofsalt ionsfrom gills

Excretion of salt ionsand small amountsof water in scantyurine from kidneys

(a) Osmoregulation in a saltwater fish

Freshwater Animals

• Freshwater animals

– Constantly take in water from theirhypoosmotic environment

– Lose salts by diffusion


• Freshwater animals maintain water balance

– By excreting large amounts of dilute urine

• Salts lost by diffusion

– Are replaced by foods and uptake across the gills


Figure 44.3b

Uptake ofwater and someions in food

Osmotic water gainthrough gills and other partsof body surface

Uptake ofsalt ionsby gills

Excretion oflarge amounts ofwater in diluteurine from kidneys

(b) Osmoregulation in a freshwater fish

Animals That Live in Temporary Waters

• Some aquatic invertebrates living in temporaryponds

– Can lose almost all their body water andsurvive in a dormant state

• This adaptation is called anhydrobiosis100 µm


• Some aquatic invertebrates living in temporaryponds

– Can lose almost all their body water andsurvive in a dormant state

• This adaptation is called anhydrobiosis

Figure 44.4a, b (a) Hydrated tardigrade (b) Dehydrated tardigrade

100 µm

100 µm

Land Animals

• Land animals manage their water budgets

– By drinking and eating moist foods and byusing metabolic water Water

balance ina human

(2,500 mL/day= 100%)

Waterbalance in akangaroo rat

(2 mL/day= 100%)

Ingestedin food (0.2)

Ingestedin food (750)


Figure 44.5

Ingestedin liquid(1,500)

Derived frommetabolism (250)

Derived frommetabolism (1.8)

Watergain

Feces (0.9)

Urine(0.45)

Evaporation (1.46)

Feces (100)

Urine(1,500)

Evaporation (900)

Waterloss

• Desert animals

– Get major water savings from simple anatomicalfeatures

4

Wat

er lo

st p

er d

ay(L

/100

kg

body

mas

s)

Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that thefur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while theanimals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skinby fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, theycompared the water loss rates of unclipped and clipped camels.

EXPERIMENT

RESULTS Removing the fur of a camel increased the rateof water loss through sweating by up to 50%.


Figure 44.6

Control group(Unclipped fur)

Experimental group(Clipped fur)

4

3

2

1

0

Wat

er lo

st p

er d

ay(L

/100

kg

body

mas

s)

Removing the fur of a camel increased the rateof water loss through sweating by up to 50%.

The fur of camels plays a critical role intheir conserving water in the hot desertenvironments where they live.

CONCLUSION

Transport Epithelia

• Transport epithelia

– Are specialized cells that regulate solutemovement

– Are essential components of osmoticregulation and metabolic waste disposal

– Are arranged into complex tubular networks


• Transport epithelia

– Are specialized cells that regulate solutemovement

– Are essential components of osmoticregulation and metabolic waste disposal

– Are arranged into complex tubular networks

• An example of transport epithelia is found in thesalt glands of marine birds

– Which remove excess sodium chloride from theblood Nasal salt gland

Nostrilwith saltsecretions

(a) An albatross’s salt glandsempty via a duct into thenostrils, and the salty solutioneither drips off the tip of thebeak or is exhaled in a fine mist.


Figure 44.7a, b

Lumen ofsecretory tubule

NaCl

Bloodflow

Secretory cellof transportepithelium

Centralduct

Directionof saltmovement

Transportepithelium

Secretorytubule

Capillary

Vein

Artery

(a) An albatross’s salt glandsempty via a duct into thenostrils, and the salty solutioneither drips off the tip of thebeak or is exhaled in a fine mist.

(b) One of several thousandsecretory tubules in a salt-excreting gland. Each tubuleis lined by a transportepithelium surrounded bycapillaries, and drains intoa central duct.

(c) The secretory cells activelytransport salt from theblood into the tubules.Blood flows counter to theflow of salt secretion. Bymaintaining a concentrationgradient of salt in the tubule(aqua), this countercurrentsystem enhances salttransfer from the blood tothe lumen of the tubule.

• Concept 44.2: An animal’s nitrogenous wastesreflect its phylogeny and habitat

• The type and quantity of an animal’s wasteproducts

– May have a large impact on its water balance


• Concept 44.2: An animal’s nitrogenous wastesreflect its phylogeny and habitat

• The type and quantity of an animal’s wasteproducts

– May have a large impact on its water balance

Proteins Nucleic acids

Amino acids Nitrogenous bases

–NH2Amino groups

• Among the most important wastes

– Are the nitrogenous breakdown products ofproteins and nucleic acids


–NH2Amino groups

Most aquaticanimals, includingmost bony fishes

Mammals, mostamphibians, sharks,some bony fishes

Many reptiles(includingbirds), insects,land snails

Ammonia Urea Uric acid

NH3 NH2

NH2O C

C

CN

CO N

H H

C ONC

HN

OH

Figure 44.8

Forms of Nitrogenous Wastes

• Different animals

– Excrete nitrogenous wastes in different forms


Ammonia

• Animals that excrete nitrogenous wastes asammonia

– Need access to lots of water

– Release it across the whole body surface orthrough the gills


• Animals that excrete nitrogenous wastes asammonia

– Need access to lots of water

– Release it across the whole body surface orthrough the gills

Urea

• The liver of mammals and most adultamphibians

– Converts ammonia to less toxic urea

• Urea is carried to the kidneys, concentrated

– And excreted with a minimal loss of water


• The liver of mammals and most adultamphibians

– Converts ammonia to less toxic urea

• Urea is carried to the kidneys, concentrated

– And excreted with a minimal loss of water

Uric Acid

• Insects, land snails, and many reptiles,including birds

– Excrete uric acid as their major nitrogenouswaste

• Uric acid is largely insoluble in water

– And can be secreted as a paste with littlewater loss


• Insects, land snails, and many reptiles,including birds

– Excrete uric acid as their major nitrogenouswaste

• Uric acid is largely insoluble in water

– And can be secreted as a paste with littlewater loss

The Influence of Evolution and Environment onNitrogenous Wastes

• The kinds of nitrogenous wastes excreted

– Depend on an animal’s evolutionary historyand habitat

• The amount of nitrogenous waste produced

– Is coupled to the animal’s energy budget


• The kinds of nitrogenous wastes excreted

– Depend on an animal’s evolutionary historyand habitat

• The amount of nitrogenous waste produced

– Is coupled to the animal’s energy budget

• Concept 44.3: Diverse excretory systems arevariations on a tubular theme

• Excretory systems

– Regulate solute movement between internalfluids and the external environment


• Concept 44.3: Diverse excretory systems arevariations on a tubular theme

• Excretory systems

– Regulate solute movement between internalfluids and the external environment

Excretory Processes

• Most excretory systems

– Produce urine by refining a filtrate derived frombody fluids

Filtration. The excretory tubule collects a filtrate from the blood.Water and solutes are forced by blood pressure across theselectively permeable membranes of a cluster of capillaries andinto the excretory tubule.

Capillary

Excretorytubule

Filtrate

1


Figure 44.9

Reabsorption. The transport epithelium reclaims valuable substancesfrom the filtrate and returns them to the body fluids.

Secretion. Other substances, such as toxins and excess ions, areextracted from body fluids and added to the contents of the excretorytubule.

Excretion. The filtrate leaves the system and the body.Filtrate

Urine

2

3

4

• Key functions of most excretory systems are

– Filtration, pressure-filtering of body fluidsproducing a filtrate

– Reabsorption, reclaiming valuable solutes fromthe filtrate

– Secretion, addition of toxins and other solutesfrom the body fluids to the filtrate

– Excretion, the filtrate leaves the system


• Key functions of most excretory systems are

– Filtration, pressure-filtering of body fluidsproducing a filtrate

– Reabsorption, reclaiming valuable solutes fromthe filtrate

– Secretion, addition of toxins and other solutesfrom the body fluids to the filtrate

– Excretion, the filtrate leaves the system

Survey of Excretory Systems

• The systems that perform basic excretoryfunctions

– Vary widely among animal groups

– Are generally built on a complex network oftubules


• The systems that perform basic excretoryfunctions

– Vary widely among animal groups

– Are generally built on a complex network oftubules

Nucleusof cap cell

Cilia

Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)

Protonephridia: Flame-Bulb Systems

• A protonephridium

– Is a network of dead-end tubules lackinginternal openings


Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)

Tubule cell

Flamebulb

Nephridioporein body wall

TubuleProtonephridia(tubules)

Figure 44.10

• The tubules branch throughout the body

– And the smallest branches are capped by acellular unit called a flame bulb

• These tubules excrete a dilute fluid

– And function in osmoregulation


• The tubules branch throughout the body

– And the smallest branches are capped by acellular unit called a flame bulb

• These tubules excrete a dilute fluid

– And function in osmoregulation

Metanephridia

• Each segment of an earthworm

– Has a pair of open-ended metanephridia


Figure 44.11 Nephrostome Metanephridia

Nephridio-pore

Collectingtubule

Bladder

Capillarynetwork

Coelom

• Metanephridia consist of tubules

– That collect coelomic fluid and produce diluteurine for excretion


Digestive tract

Malpighian Tubules

• In insects and other terrestrial arthropods,malpighian tubules

– Remove nitrogenous wastes from hemolymphand function in osmoregulation


Midgut(stomach)

Malpighiantubules

RectumIntestine Hindgut

Salt, water, andnitrogenous

wastes

Feces and urine Anus

Malpighiantubule

Rectum

Reabsorption of H2O,ions, and valuableorganic molecules

HEMOLYMPHFigure 44.12

• Insects produce a relatively dry waste matter

– An important adaptation to terrestrial life


Vertebrate Kidneys

• Kidneys, the excretory organs of vertebrates

– Function in both excretion and osmoregulation


• Concept 44.4: Nephrons and associated bloodvessels are the functional unit of themammalian kidney

• The mammalian excretory system centers onpaired kidneys

– Which are also the principal site of waterbalance and salt regulation


• Concept 44.4: Nephrons and associated bloodvessels are the functional unit of themammalian kidney

• The mammalian excretory system centers onpaired kidneys

– Which are also the principal site of waterbalance and salt regulation

• Each kidney

– Is supplied with blood by a renal artery anddrained by a renal vein

Posterior vena cava


Figure 44.13a

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

(a) Excretory organs and majorassociated blood vessels

Kidney

• Urine exits each kidney

– Through a duct called the ureter

• Both ureters

– Drain into a common urinary bladder


Renalmedulla

Structure and Function of the Nephron and AssociatedStructures

• The mammalian kidney has two distinct regions

– An outer renal cortex and an inner renalmedulla


(b) Kidney structure

UreterSection of kidney from a rat

Renalmedulla

Renalcortex

Renalpelvis

Figure 44.13b

• The nephron, the functional unit of the vertebratekidney

– Consists of a single long tubule and a ball ofcapillaries called the glomerulus

Juxta-medullarynephron

Corticalnephron

Afferentarteriolefrom renalartery

Glomerulus

Bowman’s capsule


Figure 44.13c, d

Collectingduct

Torenalpelvis

Renalcortex

Renalmedulla

20 µm

Afferentarteriolefrom renalartery

Bowman’s capsuleProximal tubule

Peritubularcapillaries

SEM

Efferentarteriole fromglomerulus

Branch ofrenal vein

DescendinglimbAscendinglimb

Loopof

Henle

Distaltubule

Collectingduct

(c) Nephron

Vasarecta(d) Filtrate and

blood flow

Filtration of the Blood

• Filtration occurs as blood pressure

– Forces fluid from the blood in the glomerulusinto the lumen of Bowman’s capsule


• Filtration of small molecules is nonselective

– And the filtrate in Bowman’s capsule is amixture that mirrors the concentration ofvarious solutes in the blood plasma


Pathway of the Filtrate

• From Bowman’s capsule, the filtrate passesthrough three regions of the nephron

– The proximal tubule, the loop of Henle, and thedistal tubule

• Fluid from several nephrons

– Flows into a collecting duct


• From Bowman’s capsule, the filtrate passesthrough three regions of the nephron

– The proximal tubule, the loop of Henle, and thedistal tubule

• Fluid from several nephrons

– Flows into a collecting duct

Blood Vessels Associated with the Nephrons

• Each nephron is supplied with blood by an afferentarteriole

– A branch of the renal artery that subdivides into thecapillaries

• The capillaries converge as they leave the glomerulus

– Forming an efferent arteriole

• The vessels subdivide again

– Forming the peritubular capillaries, which surround theproximal and distal tubules


• Each nephron is supplied with blood by an afferentarteriole

– A branch of the renal artery that subdivides into thecapillaries

• The capillaries converge as they leave the glomerulus

– Forming an efferent arteriole

• The vessels subdivide again

– Forming the peritubular capillaries, which surround theproximal and distal tubules

Proximal tubule Distal tubule

NaCl NutrientsNaCl

H2OH2OHCO3

K+

H+ NH3

HCO3

K+ H+

1 4

From Blood Filtrate to Urine: A Closer Look

• Filtrate becomes urine

– As it flows through the mammalian nephronand collecting duct


FiltrateH2OSalts (NaCl and others)HCO3

–

H+

UreaGlucose; amino acidsSome drugs

Key

Active transportPassive transport

CORTEX

OUTERMEDULLA

INNERMEDULLA

Descending limbof loop ofHenle

Thick segmentof ascendinglimb

Thin segmentof ascendinglimb

Collectingduct

NaCl

NaCl

NaCl

Urea

H2O

H2O

32

3 5

Figure 44.14

• Secretion and reabsorption in the proximaltubule

– Substantially alter the volume and compositionof filtrate

• Reabsorption of water continues

– As the filtrate moves into the descending limbof the loop of Henle


• Secretion and reabsorption in the proximaltubule

– Substantially alter the volume and compositionof filtrate

• Reabsorption of water continues

– As the filtrate moves into the descending limbof the loop of Henle

• As filtrate travels through the ascending limb of theloop of Henle

– Salt diffuses out of the permeable tubule into theinterstitial fluid

• The distal tubule

– Plays a key role in regulating the K+ and NaClconcentration of body fluids

• The collecting duct

– Carries the filtrate through the medulla to the renalpelvis and reabsorbs NaCl


• As filtrate travels through the ascending limb of theloop of Henle

– Salt diffuses out of the permeable tubule into theinterstitial fluid

• The distal tubule

– Plays a key role in regulating the K+ and NaClconcentration of body fluids

• The collecting duct

– Carries the filtrate through the medulla to the renalpelvis and reabsorbs NaCl

• Concept 44.5: The mammalian kidney’s abilityto conserve water is a key terrestrial adaptation

• The mammalian kidney

– Can produce urine much more concentratedthan body fluids, thus conserving water


• Concept 44.5: The mammalian kidney’s abilityto conserve water is a key terrestrial adaptation

• The mammalian kidney

– Can produce urine much more concentratedthan body fluids, thus conserving water

Solute Gradients and Water Conservation

• In a mammalian kidney, the cooperative actionand precise arrangement of the loops of Henleand the collecting ducts

– Are largely responsible for the osmoticgradient that concentrates the urine


• Two solutes, NaCl and urea, contribute to theosmolarity of the interstitial fluid

– Which causes the reabsorption of water in thekidney and concentrates the urine

300100

Osmolarity ofinterstitial

fluid(mosm/L)

300


Figure 44.15

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

300 100

400

600

900

1200

700

400

200

100

ActivetransportPassivetransport

OUTERMEDULLA

INNERMEDULLA

CORTEX

H2OUrea

H2OUrea

H2OUrea

H2O

H2O

H2O

H2O

12001200

900

600

400

300

600

400

300

Osmolarity ofinterstitial

fluid(mosm/L)

300

• The countercurrent multiplier system involvingthe loop of Henle

– Maintains a high salt concentration in theinterior of the kidney, which enables the kidneyto form concentrated urine


• The collecting duct, permeable to water but notsalt

– Conducts the filtrate through the kidney’sosmolarity gradient, and more water exits thefiltrate by osmosis


• Urea diffuses out of the collecting duct

– As it traverses the inner medulla

• Urea and NaCl

– Form the osmotic gradient that enables thekidney to produce urine that is hyperosmotic tothe blood


• Urea diffuses out of the collecting duct

– As it traverses the inner medulla

• Urea and NaCl

– Form the osmotic gradient that enables thekidney to produce urine that is hyperosmotic tothe blood

Regulation of Kidney Function

• The osmolarity of the urine

– Is regulated by nervous and hormonal controlof water and salt reabsorption in the kidneys


• Antidiuretic hormone (ADH)

– Increases water reabsorption in the distaltubules and collecting ducts of the kidney

Osmoreceptorsin hypothalamus

Drinking reducesblood osmolarity

to set point

Hypothalamus

ADHIncreasedpermeability

Thirst


Figure 44.16a

H2O reab-sorption helpsprevent further

osmolarityincrease

STIMULUS:The release of ADH istriggered when osmo-receptor cells in the

hypothalamus detect anincrease in the osmolarity

of the blood

Homeostasis:Blood osmolarity

Pituitarygland

Increasedpermeability

Collecting duct

Distaltubule

(a) Antidiuretic hormone (ADH) enhances fluid retention by makingthe kidneys reclaim more water.

• The renin-angiotensin-aldosterone system (RAAS)

– Is part of a complex feedback circuit that functionsin homeostasis

Increased Na+

and H2O reab-sorption in

distal tubules

Homeostasis:Blood pressure,

volume

STIMULUS:The juxtaglomerular

apparatus (JGA) respondsto low blood volume or

blood pressure (such as dueto dehydration or loss of

blood)


Figure 44.16b

STIMULUS:The juxtaglomerular

apparatus (JGA) respondsto low blood volume or

blood pressure (such as dueto dehydration or loss of

blood)

Aldosterone

Adrenal gland

Angiotensin II

Angiotensinogen

Reninproduction

Renin

Arterioleconstriction

Distaltubule

JGA

(b) The renin-angiotensin-aldosterone system (RAAS) leads to an increasein blood volume and pressure.

• Another hormone, atrial natriuretic factor (ANF)

– Opposes the RAAS


• The South American vampire bat, which feedson blood

– Has a unique excretory system in which itskidneys offload much of the water absorbed froma meal by excreting large amounts of dilute urine


Figure 44.17

• Concept 44.6: Diverse adaptations of thevertebrate kidney have evolved in differentenvironments

• The form and function of nephrons in variousvertebrate classes

– Are related primarily to the requirements forosmoregulation in the animal’s habitat


• Concept 44.6: Diverse adaptations of thevertebrate kidney have evolved in differentenvironments

• The form and function of nephrons in variousvertebrate classes

– Are related primarily to the requirements forosmoregulation in the animal’s habitat

• Exploring environmental adaptations of thevertebrate kidney

MAMMALS

Bannertail Kangaroo rat(Dipodomys spectabilis)

BIRDS AND OTHER REPTILES

Roadrunner(Geococcyx californianus)


Figure 44.18

Beaver (Castor canadensis)

FRESHWATER FISHES AND AMPHIBIANS

Rainbow trout(Oncorrhynchus mykiss)

Frog (Rana temporaria)

Desert iguana(Dipsosaurus dorsalis)

MARINE BONY FISHES

Northern bluefin tuna (Thunnus thynnus)

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