Chapter 42

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 42Chapter 42

Circulation and Gas Exchange

Fig. 42-1


Concept 42.1: Circulatory systems link exchange surfaces with cells throughout the body

• In small and/or thin animals, cells can exchange materials directly with the surrounding medium

• In most animals, transport systems connect the organs of exchange with the body cells

• Most complex animals have internal transport systems that circulate fluid


Gastrovascular Cavities

• Simple animals, such as cnidarians, have a body wall that is only two cells thick and that encloses a gastrovascular cavity

• This cavity functions in both digestion and distribution of substances throughout the body

• Some cnidarians, such as jellies, have elaborate gastrovascular cavities

• Flatworms have a gastrovascular cavity and a large surface area to volume ratio

Fig. 42-2

Circularcanal

Radial canalMouth

(a) The moon jelly Aurelia, a cnidarian The planarian Dugesia, aflatworm

(b)

MouthPharynx

2 mm5 cm

Fig. 42-3

Heart

Hemolymph in sinusessurrounding organs

Heart

Interstitialfluid

Small branch vesselsIn each organ

Blood

Dorsal vessel(main heart)

Auxiliary hearts Ventral vessels

(b) A closed circulatory system(a) An open circulatory system

Tubular heart

Pores


Organization of Vertebrate Circulatory Systems

• Humans and other vertebrates have a closed circulatory system, often called the cardiovascular system

• The three main types of blood vessels are arteries, veins, and capillaries


• Arteries branch into arterioles and carry blood to capillaries

• Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid

• Venules converge into veins and return blood from capillaries to the heart

Fig. 42-4

Artery

Ventricle

AtriumHeart

Vein

Systemic capillaries

Systemiccirculation

Gillcirculation

Gill capillaries

single circulation

Fig. 42-5

Amphibians

Lung and skin capillaries

Pulmocutaneouscircuit

Atrium (A)

Ventricle (V)

Atrium (A)

Systemiccircuit

Right Left


Reptiles (Except Birds)

Lung capillaries

Pulmonarycircuit

Rightsystemicaorta

Right LeftLeftsystemicaorta


A A

VV


Pulmonarycircuit

Systemiccircuit

Right Left

A A

VV

Lung capillaries

Mammals and Birds

double circulation


Amphibians

• Frogs and other amphibians have a three-chambered heart: two atria and one ventricle

• The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit

• Underwater, blood flow to the lungs is nearly shut off


Reptiles (Except Birds)

• Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle

• In alligators, caimans, and other crocodilians a septum divides the ventricle

• Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit


Mammals and Birds

• Mammals and birds have a four-chambered heart with two atria and two ventricles

• The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood

• Mammals and birds are endotherms and require more O2 than ectotherms


Concept 42.2: Coordinated cycles of heart contraction drive double circulation in mammals

• The mammalian cardiovascular system meets the body’s continuous demand for O2


Mammalian Circulation

• Blood begins its flow with the right ventricle pumping blood to the lungs

• In the lungs, the blood loads O2 and unloads CO2

• Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle

• The aorta provides blood to the heart through the coronary arteries


• Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)

• The superior vena cava and inferior vena cava flow into the right atrium

Animation: Path of Blood Flow in Mammals

Fig. 42-6

Superiorvena cava

Pulmonaryartery

Capillariesof right lung

3

7

3

8

9

24

11

51

10

Aorta

Pulmonaryvein

Right atrium

Right ventricle

Inferiorvena cava

Capillaries ofabdominal organsand hind limbs

Pulmonaryvein

Left atrium

Left ventricle

Aorta

Capillariesof left lung

Pulmonaryartery

Capillaries ofhead andforelimbs

Fig. 42-7

Pulmonary artery

Rightatrium

Semilunarvalve

Atrioventricularvalve

Rightventricle

Leftventricle

Atrioventricularvalve

Leftatrium

Semilunarvalve

Pulmonaryartery

Aorta

The Mammalian Heart: A Closer Look

Fig. 42-8

Semilunarvalvesclosed

0.4 secAVvalvesopen

Atrial andventriculardiastole

1

2

0.1 sec

Atrial systole;ventriculardiastole

3

0.3 sec

Semilunarvalvesopen

AV valvesclosed

Ventricular systole;atrial diastole

Fig. 42-9-5

Signals spreadthroughoutventricles.

4

Purkinjefibers

Pacemakergenerates wave ofsignals to contract.

1

SA node(pacemaker)

ECG

Signals aredelayed atAV node.

2

AVnode

Signals passto heart apex.

3

Bundlebranches Heart

apex


Concept 42.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels

• The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems

Fig. 42-10Artery Vein

SEM100 µm

Endothelium

Artery

SmoothmuscleConnectivetissue Capillary

Basal lamina

Endothelium

Smoothmuscle

Connectivetissue

Valve

Vein

Arteriole Venule

Red blood cell

Capillary

15 µ

mL

M

Fig. 42-11

5,0004,0003,000

2,0001,000

0

0

5040302010

120

80100

604020

0

Are

a (

cm

2)

Ve

loc

ity

(cm

/se

c)

Pre

ss

ure

(mm

Hg

)

Ao

rta

Art

eri

es

Art

eri

ole

s

Ca

pil

lari

es

Ve

nu

les

Ve

ins

Ve

na

e c

av

ae

Diastolicpressure

Systolicpressure


Changes in Blood Pressure During the Cardiac Cycle

• Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries

• Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure

• A pulse is the rhythmic bulging of artery walls with each heartbeat


Regulation of Blood Pressure

• Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

• Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure

• Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall


• Vasoconstriction and vasodilation help maintain adequate blood flow as the body’s demands change

• The peptide endothelin is an important inducer of vasoconstriction

Fig. 42-12

Ser

RESULTS

Ser

Ser CysCys —NH3+

Leu

Met

Asp

LysGlu Cys Val Tyr Phe Cys His Leu Asp Ile Ile Trp —COO–

Endothelin

Parent polypeptide

TrpCys

Endothelin

53 731

203

Fig. 42-13-3

Pressure in cuffgreater than120 mm Hg

Rubbercuffinflatedwith air

Arteryclosed

120 120

Pressure in cuffdrops below120 mm Hg

Soundsaudible instethoscope

Pressure in cuff below70 mm Hg

70

Blood pressure reading: 120/70

Soundsstop


Fig. 42-14

Direction of blood flowin vein (toward heart) Valve (open)

Skeletal muscle

Valve (closed)

Fig. 42-15

Precapillary sphincters Thoroughfarechannel

Arteriole

Capillaries

Venule

(a) Sphincters relaxed

(b) Sphincters contracted

Arteriole Venule

Fig. 42-16

Body tissue

CapillaryINTERSTITIAL FLUID

Net fluidmovement out

Direction ofblood flow

Net fluidmovement in

Blood pressure

Inward flow

Outward flowOsmotic pressure

Arterial end of capillary Venous end

Pre

ss

ure


Fluid Return by the Lymphatic System

• The lymphatic system returns fluid that leaks out in the capillary beds

• This system aids in body defense

• Fluid, called lymph, reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system

• The lymphatic system drains into veins in the neck


• Lymph nodes are organs that filter lymph and play an important role in the body’s defense

• Edema is swelling caused by disruptions in the flow of lymph


Concept 42.4: Blood components function in exchange, transport, and defense

• In invertebrates with open circulation, blood (hemolymph) is not different from interstitial fluid

• Blood in the circulatory systems of vertebrates is a specialized connective tissue


Blood Composition and Function

• Blood consists of several kinds of cells suspended in a liquid matrix called plasma

• The cellular elements occupy about 45% of the volume of blood

Fig. 42-17

Plasma 55%

Constituent Major functions

Water Solvent forcarrying othersubstances

Ions (blood electrolytes)

Osmotic balance,pH buffering, andregulation ofmembranepermeability

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balancepH buffering

Clotting

Defense

Plasma proteins

Albumin

Fibrinogen

Immunoglobulins(antibodies)

Substances transported by blood

Nutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones

Separatedbloodelements

Cellular elements 45%

Cell type FunctionsNumberper µL (mm3) of blood

Erythrocytes(red blood cells)

5–6 million Transport oxygenand help transportcarbon dioxide

Leukocytes(white blood cells)

5,000–10,000 Defense andimmunity

Basophil

Neutrophil

Eosinophil

Lymphocyte

Monocyte

Platelets Blood clotting250,000–400,000


Blood Clotting

• When the endothelium of a blood vessel is damaged, the clotting mechanism begins

• A cascade of complex reactions converts fibrinogen to fibrin, forming a clot

• A blood clot formed within a blood vessel is called a thrombus and can block blood flow

Collagen fibersPlateletplug

Platelet releases chemicalsthat make nearby platelets sticky

Clotting factors from:

PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin5 µm

Fibrin clot

Red blood cell

Fig. 42-18-4


Stem Cells and the Replacement of Cellular Elements

• The cellular elements of blood wear out and are replaced constantly throughout a person’s life

• Erythrocytes, leukocytes, and platelets all develop from a common source of stem cells in the red marrow of bones

• The hormone erythropoietin (EPO) stimulates erythrocyte production when oxygen delivery is low

Fig. 42-19

Stem cells(in bone marrow)

Myeloidstem cells

Lymphoidstem cells

LymphocytesB cells T cells

Erythrocytes

Platelets

Neutrophils

BasophilsEosinophils

Monocytes


Cardiovascular Disease

• Cardiovascular diseases are disorders of the heart and the blood vessels

• They account for more than half the deaths in the United States


Atherosclerosis

• One type of cardiovascular disease, atherosclerosis, is caused by the buildup of plaque deposits within arteries

Fig. 42-20

Connectivetissue

Smoothmuscle Endothelium Plaque

(a) Normal artery (b) Partly clogged artery50 µm 250 µm


Heart Attacks and Stroke

• A heart attack is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

• A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head


Treatment and Diagnosis of Cardiovascular Disease

• Cholesterol is a major contributor to atherosclerosis

• Low-density lipoproteins (LDLs) are associated with plaque formation; these are “bad cholesterol”

• High-density lipoproteins (HDLs) reduce the deposition of cholesterol; these are “good cholesterol”

• The proportion of LDL relative to HDL can be decreased by exercise, not smoking, and avoiding foods with trans fats


• Hypertension, or high blood pressure, promotes atherosclerosis and increases the risk of heart attack and stroke

• Hypertension can be reduced by dietary changes, exercise, and/or medication


Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

• Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide


Partial Pressure Gradients in Gas Exchange

• Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure

• Partial pressure is the pressure exerted by a particular gas in a mixture of gases


• A gas diffuses from a region of higher partial pressure to a region of lower partial pressure

• In the lungs and tissues, O2 and CO2 diffuse from where their partial pressures are higher to where they are lower


Respiratory Media

• Animals can use air or water as a source of O2, or respiratory medium

• In a given volume, there is less O2 available in water than in air

• Obtaining O2 from water requires greater efficiency than air breathing


Respiratory Surfaces

• Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water

• Gas exchange across respiratory surfaces takes place by diffusion

• Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs


Gills in Aquatic Animals

• Gills are outfoldings of the body that create a large surface area for gas exchange

Fig. 42-21

Parapodium (functions as gill)

(a) Marine worm

Gills

(b) Crayfish (c) Sea star

Tube foot

Coelom

Gills


• Ventilation moves the respiratory medium over the respiratory surface

• Aquatic animals move through water or move water over their gills for ventilation

• Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills; blood is always less saturated with O2 than the water it meets

Fig. 42-22

Anatomy of gills

Gillarch

Waterflow Operculum

Gillarch

Gill filamentorganization

Bloodvessels

Oxygen-poor blood

Oxygen-rich blood

Fluid flowthrough

gill filament

Lamella

Blood flow throughcapillaries in lamella

Water flowbetweenlamellae

Countercurrent exchange

PO2 (mm Hg) in water

PO2 (mm Hg) in blood

Net diffu-sion of O2

from waterto blood

150 120 90 60 30

110 80 20Gill filaments

50140


Tracheal Systems in Insects

• The tracheal system of insects consists of tiny branching tubes that penetrate the body

• The tracheal tubes supply O2 directly to body cells

• The respiratory and circulatory systems are separate

• Larger insects must ventilate their tracheal system to meet O2 demands

Fig. 42-23

Air sacs

Tracheae

Externalopening

Bodycell

AirsacTracheole

Tracheoles Mitochondria Muscle fiber

2.5 µmBody wall

Trachea

Air


Lungs

• Lungs are an infolding of the body surface

• The circulatory system (open or closed) transports gases between the lungs and the rest of the body

• The size and complexity of lungs correlate with an animal’s metabolic rate


Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts conveys air to the lungs

• Air inhaled through the nostrils passes through the pharynx via the larynx, trachea, bronchi, bronchioles, and alveoli, where gas exchange occurs

• Exhaled air passes over the vocal cords to create sounds

• Secretions called surfactants coat the surface of the alveoli

Fig. 42-24

Pharynx

Larynx

(Esophagus)

Trachea

Right lung

Bronchus

Bronchiole

DiaphragmHeart SEM

Leftlung

Nasalcavity

Terminalbronchiole

Branch ofpulmonaryvein(oxygen-richblood)

Branch ofpulmonaryartery(oxygen-poorblood)

Alveoli

ColorizedSEM50 µm 50 µm


Concept 42.6: Breathing ventilates the lungs

• The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air


How an Amphibian Breathes

• An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea


How a Mammal Breathes

• Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs

• Lung volume increases as the rib muscles and diaphragm contract

• The tidal volume is the volume of air inhaled with each breath


• The maximum tidal volume is the vital capacity

• After exhalation, a residual volume of air remains in the lungs

Fig. 42-25

Lung

Diaphragm

Airinhaled

Rib cageexpands asrib musclescontract

Rib cage getssmaller asrib musclesrelax

Airexhaled

EXHALATIONDiaphragm relaxes

(moves up)

INHALATIONDiaphragm contracts

(moves down)


How a Bird Breathes

• Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs

• Air passes through the lungs in one direction only

• Every exhalation completely renews the air in the lungs

Fig. 42-26

Anteriorair sacs

Posteriorair sacs Lungs

Air

Lungs

Air

1 mm

Trachea

Air tubes(parabronchi)in lung

EXHALATIONAir sacs empty; lungs fill

INHALATIONAir sacs fill


Control of Breathing in Humans

• In humans, the main breathing control centers are in two regions of the brain, the medulla oblongata and the pons

• The medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid

• The medulla adjusts breathing rate and depth to match metabolic demands

• The pons regulates the tempo

Fig. 42-27

Breathingcontrolcenters

Cerebrospinalfluid

Pons

Medullaoblongata

Carotidarteries

Aorta

Diaphragm

Rib muscles


Concept 42.7: Adaptations for gas exchange include pigments that bind and transport gases

• The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2

Fig. 42-28

Alveolus

PO2 = 100 mm Hg

PO2 = 40 PO2

= 100

PO2 = 100PO2

= 40

Circulatorysystem

Body tissue

PO2 ≤ 40 mm Hg PCO2

≥ 46 mm Hg

Body tissue

PCO2 = 46 PCO2

= 40

PCO2 = 40PCO2

= 46

Circulatorysystem

PCO2 = 40 mm Hg

Alveolus

(b) Carbon dioxide(a) Oxygen


Respiratory Pigments

• Respiratory pigments, proteins that transport oxygen, greatly increase the amount of oxygen that blood can carry

• Arthropods and many molluscs have hemocyanin with copper as the oxygen-binding component

• Most vertebrates and some invertebrates use hemoglobin contained within erythrocytes

Fig. 42-UN1

Chains

IronHeme

Chains

Hemoglobin


PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 43Chapter 43

The Immune System


Overview: Reconnaissance, Recognition, and Response

• Barriers help an animal to defend itself from the many dangerous pathogens it may encounter

• The immune system recognizes foreign bodies and responds with the production of immune cells and proteins

• Two major kinds of defense have evolved: innate immunity and acquired immunity


Fig. 43-1

1.5 µm


• Innate immunity is present before any exposure to pathogens and is effective from the time of birth

• It involves nonspecific responses to pathogens

• Innate immunity consists of external barriers plus internal cellular and chemical defenses


• Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances

• It involves a very specific response to pathogens


Fig. 43-2

INNATE IMMUNITY

Recognition of traitsshared by broad rangesof pathogens, using asmall set of receptors

•

•Rapid response

•Recognition of traitsspecific to particularpathogens, using a vastarray of receptors

•Slower response

ACQUIRED IMMUNITY

Pathogens(microorganisms

and viruses)

Barrier defenses:SkinMucous membranesSecretions

Internal defenses:Phagocytic cellsAntimicrobial proteinsInflammatory responseNatural killer cells

Humoral response:Antibodies defend againstinfection in body fluids.

Cell-mediated response:Cytotoxic lymphocytes defendagainst infection in body cells.


Concept 43.1: In innate immunity, recognition and response rely on shared traits of pathogens

• Both invertebrates and vertebrates depend on innate immunity to fight infection

• Vertebrates also develop acquired immune defenses


Innate Immunity of Invertebrates

• In insects, an exoskeleton made of chitin forms the first barrier to pathogens

• The digestive system is protected by low pH and lysozyme, an enzyme that digests microbial cell walls

• Hemocytes circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria


Fig. 43-3

Microbes

PHAGOCYTIC CELL

Vacuole

Lysosomecontaining enzymes


Fig. 43-5RESULTS

% s

urv

ival

Wild type

Fruit fly survival after infection by N. crassa fungi

100

75

50

25

00 24 7248 96 120

100

75

50

25

00 24 7248 96 120

Hours post-infection

Fruit fly survival after infection by M. luteus bacteria

Hours post-infection

% s

urv

ival

Mutant + drosomycin

Mutant + defensinMutant

Wild type

Mutant +drosomycin

Mutant +defensin

Mutant


Innate Defenses—Barrier Defenses

• Barrier defenses include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts

• Mucus traps and allows for the removal of microbes

• Many body fluids including saliva, mucus, and tears are hostile to microbes

• The low pH of skin and the digestive system prevents growth of microbes


Innate Defenses—Cellular Defenses

• White blood cells (leukocytes) engulf pathogens in the body

• Groups of pathogens are recognized by TLR, Toll-like receptors


Fig. 43-6

EXTRACELLULARFLUID Lipopolysaccharide

FlagellinTLR4

TLR5

Helperprotein

TLR9

TLR3

WHITEBLOODCELL

VESICLE

CpG DNA

ds RNA

Inflammatoryresponses


• A white blood cell engulfs a microbe, then fuses with a lysosome to destroy the microbe

• There are different types of phagocytic cells:

– Neutrophils engulf and destroy microbes

– Macrophages are part of the lymphatic system and are found throughout the body

– Eosinophils discharge destructive enzymes

– Dendritic cells stimulate development of acquired immunity


Fig. 43-7

Adenoid

Tonsil

Lymphnodes

Spleen

Peyer’s patches(small intestine)

Appendix

Lymphaticvessels Lymph

nodeMasses ofdefensive cells

Bloodcapillary

Lymphaticvessel

Tissuecells

Interstitial fluid


Antimicrobial Peptides and Proteins

• Peptides and proteins function in innate defense by attacking microbes directly or impeding their reproduction

• Interferon proteins provide innate defense against viruses and help activate macrophages

• About 30 proteins make up the complement system, which causes lysis of invading cells and helps trigger inflammation


Inflammatory Responses

• Following an injury, mast cells release histamine, which promotes changes in blood vessels; this is part of the inflammatory response

• These changes increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissues

• Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation


Fig. 43-8-3

Pathogen Splinter

Macrophage

Mast cell

Chemicalsignals

Capillary

Phagocytic cellRed blood cells

Fluid

Phagocytosis


Natural Killer Cells

• All cells in the body (except red blood cells) have a class 1 MHC protein on their surface

• Cancerous or infected cells no longer express this protein; natural killer (NK) cells attack these damaged cells


Innate Immune System Evasion by Pathogens

• Some pathogens avoid destruction by modifying their surface to prevent recognition or by resisting breakdown following phagocytosis

• Tuberculosis (TB) is one such disease and kills more than a million people a year


Concept 43.2: In acquired immunity, lymphocyte receptors provide pathogen-specific recognition

• White blood cells called lymphocytes recognize and respond to antigens, foreign molecules

• Lymphocytes that mature in the thymus above the heart are called T cells, and those that mature in bone marrow are called B cells


• Lymphocytes contribute to immunological memory, an enhanced response to a foreign molecule encountered previously

• Cytokines are secreted by macrophages and dendritic cells to recruit and activate lymphocytes


Acquired Immunity: An Overview

• B cells and T cells have receptor proteins that can bind to foreign molecules

• Each individual lymphocyte is specialized to recognize a specific type of molecule


Antigen Recognition by Lymphocytes

• An antigen is any foreign molecule to which a lymphocyte responds

• A single B cell or T cell has about 100,000 identical antigen receptors


Fig. 43-9

Antigen-bindingsite

Antigen-binding site

Antigen-bindingsite

Disulfidebridge

Variableregions

Constantregions

Transmembraneregion

Plasmamembrane

Lightchain

Heavy chains

T cell

chain chain

Disulfide bridge

Cytoplasm of T cell

(b) T cell receptor

Cytoplasm of B cell

(a) B cell receptor

B cell

V

V

C C

V

V

C C C C

VV


• All antigen receptors on a single lymphocyte recognize the same epitope, or antigenic determinant, on an antigen

• B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins


Fig. 43-10

Antigen-binding sites

Antigen-bindingsites

Epitopes(antigenicdeterminants)

Antigen

Antibody B

Antibody CAntibody A

CC

CV

V

V

V

C


Fig. 43-11

Antigen

Top view: binding surfaceexposed to antigen receptors

Plasmamembrane ofinfected cell

AntigenClass I MHCmolecule


Fig. 43-12

Infected cell

Antigenfragment

Class I MHCmolecule

T cellreceptor

(a)

Antigenassociateswith MHCmolecule

T cellrecognizescombination

Cytotoxic T cell (b) Helper T cell

T cellreceptor

Class II MHCmolecule

Antigenfragment

Antigen-presentingcell

Microbe

1

11

2

22


Fig. 43-13

DNA of undifferentiated B cell

1

DNA of differentiated B cell

pre-mRNA

mRNA

Light-chain polypeptide

Variableregion

Constantregion

Translation

B cell

B cell receptor

RNA processing

Transcription

DNA deleted between randomly selected V and Jsegments

Functional gene

V37 V38 V39 V40 J1 J2 J3 J4 CJ5 Intron

V37 V38 V39 CJ5 Intron

V39 CJ5 Intron

V39 CJ5 Poly-A tailCap

CV

VV

V

V

C C

C C

2

3

4


Origin of Self-Tolerance

• Antigen receptors are generated by random rearrangement of DNA

• As lymphocytes mature in bone marrow or the thymus, they are tested for self-reactivity

• Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional


Amplifying Lymphocytes by Clonal Selection

• In the body there are few lymphocytes with antigen receptors for any particular epitope

• The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly

• This proliferation of lymphocytes is called clonal selection

• Two types of clones are produced: short-lived activated effector cells and long-lived memory cells


Fig. 43-14

B cells thatdiffer inantigen specificity

Antibodymolecules

Antigenreceptor

Antigen molecules

Clone of memory cells Clone of plasma cells


• The first exposure to a specific antigen represents the primary immune response

• During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms

• In the secondary immune response, memory cells facilitate a faster, more efficient response

Animation: Role of B Cells


Fig. 43-15

Antibodiesto A

Antibodiesto B

Secondary immune response toantigen A produces antibodies to A;primary immune response to antigenB produces antibodies to B.

Primary immune responseto antigen A producesantibodies to A.

An

tib

od

y co

nce

ntr

atio

n(a

rbit

rary

un

its)

Exposureto antigen A

Exposure toantigens A and B

Time (days)

104

103

102

101

100

0 7 14 21 28 35 42 49 56


Concept 43.3: Acquired immunity defends against infection of body cells and fluids

• Acquired immunity has two branches: the humoral immune response and the cell-mediated immune response

• Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies

• Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells

• Helper T cells aid both responses


Fig. 43-16

Humoral (antibody-mediated) immune response

B cell

Plasma cells

Cell-mediated immune response

Key

Stimulates

Gives rise to

+

+

++

+

+

+Memory B cells

Antigen (1st exposure)

Engulfed by

Antigen-presenting cell

MemoryHelper T cells

Helper T cell Cytotoxic T cell

MemoryCytotoxic T cells

ActiveCytotoxic T cells

Antigen (2nd exposure)

Secretedantibodies

Defend against extracellular pathogens by binding to antigens,thereby neutralizing pathogens or making them better targetsfor phagocytes and complement proteins.

Defend against intracellular pathogensand cancer by binding to and lysing theinfected cells or cancer cells.

+

+ +


Helper T Cells: A Response to Nearly All Antigens

• A surface protein called CD4 binds the class II MHC molecule

• This binding keeps the helper T cell joined to the antigen-presenting cell while activation occurs

• Activated helper T cells secrete cytokines that stimulate other lymphocytes

Animation: Helper T Cells


Fig. 43-17

Antigen-presentingcell

Peptide antigen

Cell-mediatedimmunity (attack on

infected cells)

Class II MHC moleculeCD4

TCR (T cell receptor)

Helper T cell

Humoralimmunity

(secretion ofantibodies byplasma cells) Cytotoxic T cell

Cytokines

B cell

Bacterium

+

+ +

+


Cytotoxic T Cells: A Response to Infected Cells

• Cytotoxic T cells are the effector cells in cell-mediated immune response

• Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell

• Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer

• The activated cytotoxic T cell secretes proteins that destroy the infected target cell

Animation: Cytotoxic T Cells


Fig. 43-18-3

Cytotoxic T cell

Perforin

Granzymes

TCRCD8

Class I MHCmolecule

Targetcell

Peptideantigen

Pore

Released cytotoxic T cell

Dying target cell


B Cells: A Response to Extracellular Pathogens

• The humoral response is characterized by secretion of antibodies by B cells

• Activation of B cells is aided by cytokines and antigen binding to helper T cells

• Clonal selection of B cells generates antibody-secreting plasma cells, the effector cells of humoral immunity


Fig. 43-19

Antigen-presenting cell

Endoplasmicreticulum ofplasma cell

Secretedantibodymolecules

Bacterium

B cellPeptideantigen

Class II MHCmolecule

TCR CD4

Helper T cellActivatedhelper T cell

Cytokines

Clone of memoryB cells

Clone of plasma cells

2 µm

+


Fig. 43-20Class of Immuno-

globulin (Antibody)

IgG(monomer)

IgM(pentamer)

J chain

IgA(dimer)

IgE(monomer)

IgD(monomer)

Trans-membraneregion

J chain

Secretorycomponent

Distribution Function

First Ig classproduced afterinitial exposure toantigen; then itsconcentration inthe blood declines

Promotes neutraliza-tion and cross-linking of antigens;very effective incomplement systemactivation

Present insecretions suchas tears, saliva,mucus, andbreast milk

Only Ig class thatcrosses placenta,thus conferringpassive immunityon fetus

Triggers release frommast cells andbasophils of hista-mine and otherchemicals that causeallergic reactions

Present primarilyon surface ofB cells that havenot been exposedto antigens

Acts as antigenreceptor in theantigen-stimulatedproliferation anddifferentiation ofB cells (clonalselection)

Most abundant Igclass in blood;also present intissue fluids

Promotes opsoniza-tion, neutralization,and cross-linking ofantigens; less effec-tive in activation ofcomplement systemthan IgM

Provides localizeddefense of mucousmembranes bycross-linking andneutralization of antigens

Presence in breastmilk conferspassive immunityon nursing infant

Present in bloodat low concen-trations


Fig. 43-21

Viral neutralization

Virus

Opsonization

Bacterium

Macrophage

Activation of complement system and pore formation

Complement proteins

Formation ofmembraneattack complex

Flow of waterand ions

Pore

Foreigncell


Active and Passive Immunization

• Active immunity develops naturally in response to an infection

• It can also develop following immunization, also called vaccination

• In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory


• Passive immunity provides immediate, short-term protection

• It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk

• It can be conferred artificially by injecting antibodies into a nonimmune person


Fig. 43-22


Immune Rejection

• Cells transferred from one person to another can be attacked by immune defenses

• This complicates blood transfusions or the transplant of tissues or organs


Blood Groups

• Antigens on red blood cells determine whether a person has blood type A (A antigen), B (B antigen), AB (both A and B antigens), or O (neither antigen)

• Antibodies to nonself blood types exist in the body

• Transfusion with incompatible blood leads to destruction of the transfused cells

• Recipient-donor combinations can be fatal or safe


Tissue and Organ Transplants

• MHC molecules are different among genetically nonidentical individuals

• Differences in MHC molecules stimulate rejection of tissue grafts and organ transplants


• Chances of successful transplantation increase if donor and recipient MHC tissue types are well matched

• Immunosuppressive drugs facilitate transplantation

• Lymphocytes in bone marrow transplants may cause the donor tissue to reject the recipient


Concept 43.4: Disruption in immune system function can elicit or exacerbate disease

• Some pathogens have evolved to diminish the effectiveness of host immune responses


Exaggerated, Self-Directed, and Diminished Immune Responses

• If the delicate balance of the immune system is disrupted, effects range from minor to often fatal


Allergies

• Allergies are exaggerated (hypersensitive) responses to antigens called allergens

• In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells


Fig. 43-23

Allergen

IgE

Granule

Mast cell

Histamine


• The next time the allergen enters the body, it binds to mast cell–associated IgE molecules

• Mast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptoms

• An acute allergic response can lead to anaphylactic shock, a life-threatening reaction that can occur within seconds of allergen exposure


Autoimmune Diseases

• In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body

• Autoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis


Fig. 43-24


Exertion, Stress, and the Immune System

• Moderate exercise improves immune system function

• Psychological stress has been shown to disrupt hormonal, nervous, and immune systems


Immunodeficiency Diseases

• Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses

• Acquired immunodeficiency results from exposure to chemical and biological agents

• Acquired immunodeficiency syndrome (AIDS) is caused by a virus


Acquired Immune System Evasion by Pathogens

• Pathogens have evolved mechanisms to attack immune responses


Antigenic Variation

• Through antigenic variation, some pathogens are able to change epitope expression and prevent recognition

• The human influenza virus mutates rapidly, and new flu vaccines must be made each year

• Human viruses occasionally exchange genes with the viruses of domesticated animals

• This poses a danger as human immune systems are unable to recognize the new viral strain


Fig. 43-25

Weeks after infection

Mill

ion

s o

f p

aras

ites

per

mL

of

blo

od

Antibodies tovariant 1appear



Variant 3Variant 2Variant 1

25 26 27 280

0.5

1.0

1.5


Latency

• Some viruses may remain in a host in an inactive state called latency

• Herpes simplex viruses can be present in a human host without causing symptoms


Attack on the Immune System: HIV

• Human immunodeficiency virus (HIV) infects helper T cells

• The loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS

• HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA

Animation: HIV Reproductive Cycle


Fig. 43-26

Latency

Relative antibodyconcentration

AIDSH

elp

er T

cel

l co

nce

ntr

atio

nin

blo

od

(ce

lls/m

m3 )

Helper T cellconcentration

Relative HIVconcentration

Years after untreated infection0 1 2 3 4 5 6 7 8 9 10

0

200

400

600

800


• People with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse

• The spread of HIV is a worldwide problem

• The best approach for slowing this spread is education about practices that transmit the virus


Cancer and Immunity

• The frequency of certain cancers increases when the immune response is impaired

• Two suggested explanations are

– Immune system normally suppresses cancerous cells

– Increased inflammation increases the risk of cancer


Fig. 43-UN1Stem cell

Cell division and gene rearrangement

Antigen

Clonal selection

Elimination ofself-reactiveB cells

Formation of activated cell populationsAntibody

Microbe

Memory cells Effector B cells

Receptors bind to antigens

Documents

Chapter 42