44 Excretory System

7/22/2019 44 Excretory System

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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBio logy, Seventh Edit io n

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 44

Osmoregulation and

Excretion


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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


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Freshwater animals

Show adaptations that reduce water uptake andconserve solutes

Desert and marine animals face desiccating

environments

With the potential to quickly deplete the body water

Figure 44.1


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Osmoregulation

Regulates solute concentrations and balancesthe gain and loss of water

Excretion

Gets rid of metabolic wastes


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Concept 44.1: Osmoregulation balances the

uptake and loss of water and solutes Osmoregulation is based largely on controlled

movement of solutes

Between internal fluids and the external

environment


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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


7/60Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Osmotic Challenges

Osmoconformers, which are only marine

animals Are isoosmotic with their surroundings and do

not 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 external

osmolarity

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

Figure 44.3a

Gain of water and

salt ions from food

and by drinking

seawater

Osmotic water loss

through gills and other parts

of body surface

Excretion of

salt ions

from gills

Excretion of salt ions

and small amounts

of water in scanty

urine 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 of

water and some

ions in food

Osmotic water gain

through gills and other parts

of body surface

Uptake of

salt ions

by gills

Excretion of

large amounts of

water in dilute

urine from kidneys

(b) Osmoregulation in a freshwater fish



Animals That L ive in Temporary Waters Some aquatic invertebrates living in temporary

ponds Can lose almost all their body water and

survive in a dormant state

This adaptation is called anhydrobiosis

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

100 m

100 m


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Land Animals Land animals manage their water budgets

By drinking and eating moist foods and byusing metabolic water

Figure 44.5

Water

balance in

a human

(2,500 mL/day

= 100%)

Water

balance in a

kangaroo rat

(2 mL/day

= 100%)

Ingested

in food (0.2)

Ingested

in food (750)

Ingested

in liquid

(1,500)

Derived from

metabolism (250)Derived from

metabolism (1.8)

Water

gain

Feces (0.9)

Urine

(0.45)

Evaporation (1.46)

Feces (100)

Urine

(1,500)

Evaporation (900)

Water

loss


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Desert animals

Get major water savings from simple anatomicalfeatures

Figure 44.6

Control group

(Unclipped fur)Experimental group

(Clipped fur)

4

3

2

1

0Wat

erlostperday

(L/100kgbodymass)

Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the

fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70C, while the

animals skin remained more than 30C cooler. The Schmidt-Nielsens reasoned that insulation of the skin

by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they

compared the water loss rates of unclipped and clipped camels.

EXPERIMENT

RESULTS Removing the fur of a camel increased the rate

of water loss through sweating by up to 50%.

The fur of camels plays a critical role in

their conserving water in the hot desert

environments where they live.

CONCLUSION


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Transport Epithelia

Transport epithelia

Are specialized cells that regulate solutemovement

Are essential components of osmotic

regulation and metabolic waste disposal

Are arranged into complex tubular networks


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An example of transport epithelia is found in the

salt glands of marine birds

Which remove excess sodium chloride from theblood

Figure 44.7a, b

Nasal salt gland

Nostril

with salt

secretions

Lumen of

secretory tubule

NaCl

Blood

flowSecretory cell

of transport

epithelium

Central

duct

Direction

of salt

movement

Transportepithelium

Secretory

tubule

Capillary

Vein

Artery

(a)An albatrosss salt glands

empty via a duct into the

nostrils, and the salty solution

either drips off the tip of the

beak or is exhaled in a fine mist.

(b) One of several thousand

secretory tubules in a salt-

excreting gland. Each tubule

is lined by a transport

epithelium surrounded by

capillaries, and drains into

a central duct.

(c) The secretory cells actively

transport salt from the

blood into the tubules.

Blood flows counter to theflow of salt secretion. By

maintaining a concentration

gradient of salt in the tubule

(aqua), this countercurrent

system enhances salt

transfer from the blood to

the lumen of the tubule.


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Concept 44.2: An animals nitrogenous wastes

reflect its phylogeny and habitat The type and quantity of an animals waste

products

May have a large impact on its water balance


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Proteins Nucleic acids

Amino acids Nitrogenous bases

NH2

Amino groups

Most aquaticanimals, including

most 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 O

NC

HN

OH

Among the most important wastes

Are the nitrogenous breakdown products ofproteins and nucleic acids

Figure 44.8


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Forms of Nitrogenous Wastes

Different animals

Excrete nitrogenous wastes in different forms


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Ammonia Animals that excrete nitrogenous wastes as

ammonia

Need access to lots of water

Release it across the whole body surface or

through the gills


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Urea The liver of mammals and most adult

amphibians

Converts ammonia to less toxic urea

Urea is carried to the kidneys, concentrated

And excreted with a minimal loss of water


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Ur ic Acid Insects, land snails, and many reptiles,

including birds

Excrete uric acid as their major nitrogenous

waste

Uric acid is largely insoluble in water

And can be secreted as a paste with little

water loss


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The Influence of Evolution and Environment onNitrogenous Wastes

The kinds of nitrogenous wastes excreted Depend on an animals evolutionary history

and habitat

The amount of nitrogenous waste produced

Is coupled to the animals energy budget


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Concept 44.3: Diverse excretory systems are

variations on a tubular theme

Excretory systems

Regulate solute movement between internal

fluids and the external environment

E P


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Excretory Processes

Most excretory systems

Produce urine by refining a filtrate derived frombody fluids

Figure 44.9

Filtration.The excretory tubule collects a filtrate from the blood.

Water and solutes are forced by blood pressure across the

selectively permeable membranes of a cluster of capillaries and

into the excretory tubule.

Reabsorption.The transport epithelium reclaims valuable substances

from the filtrate and returns them to the body fluids.

Secretion.Other substances, such as toxins and excess ions, are

extracted from body fluids and added to the contents of the excretorytubule.

Excretion.The filtrate leaves the system and the body.

Capillary

Excretory

tubule

Filt

rate

Urine

1

2

3

4


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Key functions of most excretory systems are

Filtration, pressure-filtering of body fluidsproducing a filtrate

Reabsorption, reclaiming valuable solutes from

the filtrate

Secretion, addition of toxins and other solutes

from the body fluids to the filtrate

Excretion, the filtrate leaves the system

S f E t S t


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Survey of Excretory Systems

The systems that perform basic excretory

functions

Vary widely among animal groups

Are generally built on a complex network of

tubules

P t h idi F l B lb S t


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Nucleus

of cap cell

Cilia

Interstitial fluid

filters through

membrane where

cap cell and tubule

cell interdigitate

(interlock)

Tubule cell

Flame

bulb

Nephridiopore

in body wall

Tubule

Protonephridia

(tubules)

Protonephr idia: F lame-Bulb Systems A protonephridium

Is a network of dead-end tubules lackinginternal openings

Figure 44.10


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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

M t h idi


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Metanephr idia Each segment of an earthworm

Has a pair of open-ended metanephridia

Figure 44.11 Nephrostome Metanephridia

Nephridio-

pore

Collecting

tubule

Bladder

Capillary

network

Coelom


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Metanephridia consist of tubules

That collect coelomic fluid and produce diluteurine for excretion

M l i hi T b l


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Digestive tract

Midgut

(stomach)

Malpighian

tubules

Rectum

IntestineHindgut

Salt, water, and

nitrogenous

wastes

Feces and urineAnus

Malpighian

tubule

Rectum

Reabsorption of H2O,

ions, and valuable

organic moleculesHEMOLYMPH

Malpighian Tubules In insects and other terrestrial arthropods,

malpighian tubules

Remove nitrogenous wastes from hemolymph

and function in osmoregulation

Figure 44.12


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Insects produce a relatively dry waste matter

An important adaptation to terrestrial life

Vertebrate Kidneys


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Vertebrate Kidneys Kidneys, the excretory organs of vertebrates

Function in both excretion and osmoregulation


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Concept 44.4: Nephrons and associated blood

vessels are the functional unit of the

mammalian kidney

The mammalian excretory system centers on

paired kidneys Which are also the principal site of water

balance and salt regulation


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Each kidney

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

Figure 44.13a

Posterior vena cava

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

(a) Excretory organs and major

associated blood vessels

Kidney


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Urine exits each kidney

Through a duct called the ureter

Both ureters

Drain into a common urinary bladder

Structure and Function of the Nephron and Associated


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(b) Kidney structure

UreterSection of kidney from a rat

Renal

medulla

Renal

cortex

Renal

pelvis

Figure 44.13b

Structure and Function of the Nephron and AssociatedStructures

The mammalian kidney has two distinct regions An outer renal cortex and an inner renal

medulla


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The nephron, the functional unit of the vertebrate

kidney

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

Figure 44.13c, d

Juxta-

medullary

nephron

Cortical

nephron

Collecting

duct

Torenal

pelvis

Renal

cortex

Renal

medulla

20 m

Afferent

arteriole

from renalartery

Glomerulus

Bowmans capsule

Proximal tubule

Peritubular

capillaries

SEM

Efferent

arteriole from

glomerulus

Branch of

renal vein

Descending

limb

Ascending

limb

Loop

of

Henle

Distal

tubule

Collecting

duct

(c) Nephron

Vasa

recta(d) Filtrate and

blood flow

F iltration of the Blood


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F iltration of the Blood Filtration occurs as blood pressure

Forces fluid from the blood in the glomerulusinto the lumen of Bowmans capsule


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Filtration of small molecules is nonselective

And the filtrate in Bowmans capsule is amixture that mirrors the concentration of

various solutes in the blood plasma

Pathway of the F iltrate


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Pathway of the F iltrate From Bowmans capsule, the filtrate passes

through three regions of the nephron

The proximal tubule, the loop of Henle, and the

distal tubule

Fluid from several nephrons

Flows into a collecting duct

Blood Vessels Associated with the Nephrons


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Blood Vessels Associated with the Nephrons Each nephron is supplied with blood by an afferent

arteriole

A branch of the renal artery that subdivides into the

capillaries

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

From Blood Filtrate to Urine: A Closer Look


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Proximal tubule

Filtrate

H2O

Salts (NaCl and others)

HCO3

H+

Urea

Glucose; amino acids

Some drugs

Key

Active transport

Passive transport

CORTEX

OUTER

MEDULLA

INNER

MEDULLA

Descending limb

of loop of

Henle

Thick segment

of ascending

limb

Thin segmentof ascending

limb

Collecting

duct

NaCl

NaCl

NaCl

Distal tubule

NaCl Nutrients

Urea

H2O

NaCl

H2OH2OHCO3

K+

H+ NH3

HCO3

K+ H+

H2O

1 4

32

3 5

From Blood Filtrate to Urine: A Closer Look

Filtrate becomes urine

As it flows through the mammalian nephronand collecting duct

Figure 44.14


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Secretion and reabsorption in the proximal

tubule

Substantially alter the volume and composition

of filtrate

Reabsorption of water continues

As the filtrate moves into the descending limb

of the loop of Henle


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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


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Concept 44.5: The mammalian kidneys ability

to conserve water is a key terrestrial adaptation

The mammalian kidney

Can produce urine much more concentrated

than body fluids, thus conserving water

Solute Gradients and Water Conservation


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Solute Gradients and Water Conservation

In a mammalian kidney, the cooperative action

and precise arrangement of the loops of Henle

and the collecting ducts

Are largely responsible for the osmotic

gradient that concentrates the urine


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Two solutes, NaCl and urea, contribute to the

osmolarity of the interstitial fluid

Which causes the reabsorption of water in the

kidney and concentrates the urine

Figure 44.15

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

300

300 100

400

600

900

1200

700

400

200

100

Active

transport

Passive

transport

OUTERMEDULLA

INNER

MEDULLA

CORTEX

H2O

Urea

H2O

Urea

H2O

Urea

H2O

H2O

H2O

H2O

1200

1200

900

600

400

300

600

400

300

Osmolarity of

interstitial

fluid(mosm/L)300


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The countercurrent multiplier system involving

the loop of Henle

Maintains a high salt concentration in the

interior of the kidney, which enables the kidney

to form concentrated urine


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The collecting duct, permeable to water but not

salt

Conducts the filtrate through the kidneys

osmolarity gradient, and more water exits the

filtrate by osmosis


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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 to

the blood

Regulation of Kidney Function


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egu at o o d ey u ct o

The osmolarity of the urine

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


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Antidiuretic hormone (ADH)

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

Figure 44.16a

Osmoreceptors

in hypothalamus

Drinking reduces

blood osmolarity

to set point

H2O reab-

sorption helps

prevent further

osmolarity

increase

STIMULUS:

The release of ADH istriggered when osmo-

receptor cells in the

hypothalamus detect an

increase in the osmolarity

of the blood

Homeostasis:

Blood osmolarity

Hypothalamus

ADH

Pituitary

gland

Increased

permeability

Thirst

Collecting duct

Distal

tubule

(a)Antidiuretic hormone (ADH) enhances fluid retention by making

the kidneys reclaim more water.


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The renin-angiotensin-aldosterone system (RAAS)

Is part of a complex feedback circuit that functionsin homeostasis

Figure 44.16b

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 due

to dehydration or loss of

blood)

Aldosterone

Adrenal gland

Angiotensin II

Angiotensinogen

Renin

production

Renin

Arteriole

constriction

Distaltubule

JGA

(b) The renin-angiotensin-aldosterone system (RAAS) leads to an increase

in blood volume and pressure.


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Another hormone, atrial natriuretic factor (ANF)

Opposes the RAAS


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The South American vampire bat, which feeds

on 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


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Concept 44.6: Diverse adaptations of the

vertebrate kidney have evolved in different

environments

The form and function of nephrons in various

vertebrate classes

Are related primarily to the requirements for

osmoregulation in the animals habitat


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Exploring environmental adaptations of the

vertebrate kidney

Fi 44 18

MAMMALS

Bannertail Kangaroo rat

(Dipodomys spectabi l is)

Beaver (Castor canadensis)

FRESHWATER FISHES AND AMPHIBIANS

Rainbow trout

(Oncorrhynchus mykiss)

BIRDS AND OTHER REPTILES

Roadrunner

(Geococcyx cal i fornianus)

Desert iguana

(Dipsosaurus dorsal is)

MARINE BONY FISHES

Northern bluefin tuna (Thunnus thynnus)

44 Excretory System

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