Gas Exchange

Gas ExchangeGas Exchange

Chapter 45Chapter 45

Learning Objective 1Learning Objective 1

• Compare the advantages and Compare the advantages and disadvantages of air and water as disadvantages of air and water as mediums for gas exchange mediums for gas exchange

• Describe adaptations for gas exchange Describe adaptations for gas exchange in airin air

Gas Exchange in Air and WaterGas Exchange in Air and Water

• Air has a higher concentration of Air has a higher concentration of molecular oxygen than does watermolecular oxygen than does water

• Oxygen diffuses faster through air than Oxygen diffuses faster through air than through water through water

• Air is less dense and less viscous than Air is less dense and less viscous than water (less energy needed to move air water (less energy needed to move air over gas exchange surface)over gas exchange surface)

Terrestrial AnimalsTerrestrial Animals

• Have adaptations that protect their Have adaptations that protect their respiratory surfaces from dryingrespiratory surfaces from drying

KEY CONCEPTSKEY CONCEPTS

• Air has a higher concentration of Air has a higher concentration of molecular oxygen than water does, and molecular oxygen than water does, and animals require less energy to move air animals require less energy to move air than to move water over a gas exchange than to move water over a gas exchange surface surface

• Adaptations in terrestrial animals protect Adaptations in terrestrial animals protect their respiratory surfaces from dryingtheir respiratory surfaces from drying


• Describe the following adaptations for gas Describe the following adaptations for gas exchange: exchange: body surfacebody surface, , tracheal tubestracheal tubes, , gillsgills, and , and lungslungs

Adaptations for Gas Exchange 1Adaptations for Gas Exchange 1

• Small aquatic animalsSmall aquatic animals• exchange gases by diffusionexchange gases by diffusion• no specialized respiratory structures no specialized respiratory structures

• Some invertebrates (most annelids) and Some invertebrates (most annelids) and some vertebrates (many amphibians)some vertebrates (many amphibians)• exchange gases across exchange gases across body surfacebody surface


• Insects and some other arthropodsInsects and some other arthropods• air enters network of air enters network of tracheal tubes tracheal tubes ((tracheaetracheae) )

through through spiraclesspiracles along body surface along body surface• tracheal tubestracheal tubes branch, extend to all body branch, extend to all body

regionsregions

Tracheal TubesTracheal Tubes

Fig. 45-2a, p. 973

Spiracle

Tracheal tube

(a) Location of spiral and tracheal tubes.

Fig. 45-2b, p. 973

Epithelial cell

O2

Tracheal tube

Tracheole Spiracle

CO2

Muscle

(b) Structure and function of a tracheal tube.

Fig. 45-2c, p. 973


• Aquatic animals have Aquatic animals have gillsgills• thin projections of body surfacethin projections of body surface

• ChordatesChordates• gillsgills usually internal, along edges of usually internal, along edges of gill slitsgill slits


• Bony fishesBony fishes• operculumoperculum protects protects gillsgills • countercurrent exchange systemcountercurrent exchange system maximizes maximizes

diffusion of Odiffusion of O22 into blood, CO into blood, CO22 out of blood out of blood

• Animals carry on Animals carry on ventilationventilation• actively move air or water over respiratory actively move air or water over respiratory

surfacessurfaces

Gills in Bony FishesGills in Bony Fishes

Fig. 45-3a, p. 974

Gill arch

CO2

O2

Opercular chamber

(a) Location of gills.

Fig. 45-3b, p. 974

Gill arch

Blood vessels

Gill filaments

(b) Structure of a gill.

Fig. 45-3c, p. 974

Afferent blood vessel (low O2 concentration)

Efferent blood vessel (rich in O2)

(c) Countercurrent flow.

Fig. 45-3d, p. 974

Fig. 45-3e, p. 974


• Terrestrial vertebrates have Terrestrial vertebrates have lungslungs• and some means of ventilating them and some means of ventilating them

• Amphibians and reptiles have Amphibians and reptiles have lungslungs • with some ridges or folds that increase with some ridges or folds that increase

surface areasurface area


• In birdsIn birds• lungs have extensions (lungs have extensions (air sacsair sacs) that draw air ) that draw air

into system into system • 2 cycles of inhalation and exhalation2 cycles of inhalation and exhalation

Gas Exchange in BirdsGas Exchange in Birds

• One-way flow of air through lungsOne-way flow of air through lungs• from outside into posterior air sacs, to lung, from outside into posterior air sacs, to lung,

through anterior air sacs, out of body through anterior air sacs, out of body

• Gas exchanged through walls of Gas exchanged through walls of parabronchiparabronchi • crosscurrent arrangement (blood flow at right crosscurrent arrangement (blood flow at right

angles to parabronchi) increases amount of Oangles to parabronchi) increases amount of O22

entering bloodentering blood

Gas Exchange in BirdsGas Exchange in Birds

Fig. 45-5, p. 975

Trachea

AirsacsAir

Lung Anterior air sacs

Posterior air sacs

(a) Structure of the bird respiratory system.

(b) First inhalation. As the bird inhales, fresh air flows into the posterior air sacs (blue) and partly into the lungs (not shown).

(c) First exhalation. As the bird exhales, air from the posterior air sacs is forced into the lungs.

(d) Second inhalation. Air from the first breath moves into the anterior air sacs and partly into the lungs (not shown). Air from the second inhalation flows into the posterior air sacs (pink).

(e) Second exhalation. Most of the air from the first inhalation leaves the body, and air from the second inhalation flows into the lungs.

Evolution Evolution of of

Vertebrate Vertebrate LungsLungs

Fig. 45-4, p. 975

Trachea

To other lung

Salamander's lungs Frog's lungs Toad's lung

Trachea

To other lung

Air sac

Air sac

Reptile's lung Bird's lungs

Adaptations for Adaptations for Gas ExchangeGas Exchange

Fig. 45-1a, p. 972

Earthworm

(a) Body surface.

Fig. 45-1b, p. 972

Grasshopper

(b) Tracheal tubes.

Fig. 45-1c, p. 972

Internal gillsExternal

gills

Gills

Fish Mud puppy

(c) Gills.

Fig. 45-1d, p. 972

Book lung

Lungfish

Spider

Mammal

(d) Lungs.

Learn more about adaptations Learn more about adaptations for gas exchange, including gills for gas exchange, including gills in bony fishes, vertebrate lungs, in bony fishes, vertebrate lungs, and the bird respiratory system, and the bird respiratory system,

by clicking on the figures in by clicking on the figures in ThomsonNOW.ThomsonNOW.


• Adaptations for gas exchange include a Adaptations for gas exchange include a thin, moist body surface; gills in aquatic thin, moist body surface; gills in aquatic animals; and tracheal tubes and lungs in animals; and tracheal tubes and lungs in terrestrial animalsterrestrial animals


• Trace the passage of oxygen through the Trace the passage of oxygen through the human respiratory system from human respiratory system from nostrilsnostrils to to alveolialveoli

The Human Respiratory SystemThe Human Respiratory System

• Includes lungs and system of airways Includes lungs and system of airways

• Each lung occupies a Each lung occupies a pleural cavitypleural cavity and is and is covered with a covered with a pleural membranepleural membrane

• Air passes through Air passes through nostrils, nasal cavities, nostrils, nasal cavities, pharynx, larynx, trachea, bronchi, pharynx, larynx, trachea, bronchi, bronchioles, alveolibronchioles, alveoli

The Human Respiratory SystemThe Human Respiratory System

Fig. 45-6, p. 976

SinusesRespiratory centers Nasal cavity

Tongue

Pharynx Epiglottis

LarynxEsophagus

Trachea

Space occupied by heart

Bronchioles

BronchusRight lung Left lung

Diaphragm

Structure of AlveoliStructure of Alveoli

Fig. 45-7a, p. 977

Bronchiole

Alveolus

Capillary

Macrophage

Red blood cells

Capillaries

Alveolus

Epithelial cell of the adjacent alveolus

Epithelial cell of the wall of the alveolus

Alveolus

(a)

Fig. 45-7b, p. 977

Fig. 45-7c, p. 977

1 µm

Wall of alveolus Wall of capillary Red blood cell

(c)

Insert “Human respiratory Insert “Human respiratory system”system”

human_respiratory_v2.swfhuman_respiratory_v2.swf

Learn more about the human Learn more about the human respiratory system by clicking respiratory system by clicking

on the figures in ThomsonNOW.on the figures in ThomsonNOW.


• Summarize the mechanics and the Summarize the mechanics and the regulation of breathing in humans regulation of breathing in humans

• Describe gas exchange in the lungs and Describe gas exchange in the lungs and tissuestissues

Mechanics of BreathingMechanics of Breathing

• DiaphragmDiaphragm contracts contracts• expanding chest cavity expanding chest cavity

• Membranous walls of lungs move outward Membranous walls of lungs move outward along with chest wallsalong with chest walls• lowering pressure within lungs lowering pressure within lungs

• Air rushes in through air passagewaysAir rushes in through air passageways• until pressure in lungs equals atmospheric pressureuntil pressure in lungs equals atmospheric pressure

Mechanics of Mechanics of BreathingBreathing

Fig. 45-8ab, p. 978

Trachea

Lung

Diaphragm

(a) Inhalation. (b) Exhalation.

Fig. 45-8cd, p. 978

Diaphragm

(c) Forced inhalation. (d) Forced exhalation.

Respiratory MeasurementsRespiratory Measurements

• Tidal volumeTidal volume • amount of air moved into and out of lungs with amount of air moved into and out of lungs with

each normal breath each normal breath

• Vital capacityVital capacity• maximum volume exhaled after lungs fill to maximum volume exhaled after lungs fill to

maximum extent maximum extent

• Residual capacityResidual capacity • air volume remaining in lungs at end of air volume remaining in lungs at end of

normal expirationnormal expiration

Regulation of BreathingRegulation of Breathing

• Respiratory centersRespiratory centers in medulla and pons in medulla and pons• regulate respiration regulate respiration

• ChemoreceptorsChemoreceptors • sensitive to increase in COsensitive to increase in CO22 concentration concentration • stimulate stimulate respiratoryrespiratory centerscenters • respond to increase in Hrespond to increase in H++ or very low O or very low O22

concentrationconcentration

Gas ExchangeGas Exchange

• OO22 and CO and CO22 exchange between alveoli and exchange between alveoli and

blood by diffusionblood by diffusion

• Pressure of a particular gas determines its Pressure of a particular gas determines its direction and rate of diffusiondirection and rate of diffusion

Partial PressurePartial Pressure

• Dalton’s law of partial pressuresDalton’s law of partial pressures • in a mixture of gases, total pressure is the in a mixture of gases, total pressure is the

sum of the pressures of the individual gases sum of the pressures of the individual gases

• Each gas exerts a Each gas exerts a partial pressurepartial pressure• same pressure as if it were present alone same pressure as if it were present alone

• Partial pressure of atmospheric oxygen Partial pressure of atmospheric oxygen (Po(Po22) is 160 mm Hg at sea level) is 160 mm Hg at sea level

Fick’s Law of DiffusionFick’s Law of Diffusion

• The greater the difference in pressure on The greater the difference in pressure on two sides of a membrane, and the larger two sides of a membrane, and the larger the surface area, the faster the gas the surface area, the faster the gas diffuses across the membranediffuses across the membrane

Gas Exchange in Gas Exchange in Lungs and TissuesLungs and Tissues

Fig. 45-9, p. 979

PO2 = 100 mm Hg PCO2 = 40 mm Hg Alveoli in lung

O2

Capillary in tissue

Capillary in lung

Cells in body

CO2

PO2 = 40 mm Hg PCO2 = 46 mm Hg

Insert “Respiratory cycle”Insert “Respiratory cycle”

breathing_m.swfbreathing_m.swf

See the breathing mechanisms See the breathing mechanisms in action by clicking on the in action by clicking on the figures in ThomsonNOW.figures in ThomsonNOW.


• In mammals, oxygen and carbon dioxide In mammals, oxygen and carbon dioxide are exchanged between alveoli and blood are exchanged between alveoli and blood by diffusion; the pressure of a particular by diffusion; the pressure of a particular gas determines its direction and rate of gas determines its direction and rate of diffusiondiffusion


• What is the role of hemoglobin in oxygen What is the role of hemoglobin in oxygen transport?transport?

• Identify factors that determine and Identify factors that determine and influence the oxygen-hemoglobin influence the oxygen-hemoglobin dissociation curvedissociation curve

HemoglobinHemoglobin

• Respiratory pigment in vertebrate bloodRespiratory pigment in vertebrate blood

• Almost 99% of oxygen in human blood is Almost 99% of oxygen in human blood is transported as transported as oxyhemoglobin (HbOoxyhemoglobin (HbO22))

Oxygen MeasurementOxygen Measurement

• Oxygen-carrying capacityOxygen-carrying capacity • maximum amount of oxygen that can be transported maximum amount of oxygen that can be transported

by hemoglobin by hemoglobin

• Oxygen contentOxygen content • actual amount of oxygen bound to hemoglobinactual amount of oxygen bound to hemoglobin

• Percent OPercent O22 saturation saturation• ratio of oxygen content to oxygen-carrying capacityratio of oxygen content to oxygen-carrying capacity• highest in pulmonary capillarieshighest in pulmonary capillaries

Oxygen-Hemoglobin Oxygen-Hemoglobin DissociationDissociation Curve 1Curve 1

• As oxygen concentration increases, the As oxygen concentration increases, the amount of hemoglobin that combines with amount of hemoglobin that combines with oxygen progressively increases oxygen progressively increases

• Affected by pH, temperature, COAffected by pH, temperature, CO22

concentrationconcentration

Oxygen-Hemoglobin Oxygen-Hemoglobin DissociationDissociation Curve 2Curve 2

• Oxyhemoglobin dissociates more readily Oxyhemoglobin dissociates more readily as COas CO22 concentration increases concentration increases• COCO22 combines with water and produces combines with water and produces

carbonic acid, which lowers pH carbonic acid, which lowers pH

• Bohr effectBohr effect • displacement of oxygen-hemoglobin displacement of oxygen-hemoglobin

dissociation curve by change in pH dissociation curve by change in pH

Oxygen-Hemoglobin Oxygen-Hemoglobin DissociationDissociation CurvesCurves

Fig. 45-10a, p. 980

Oxygen-rich blood leaving the lungs

Oxygen-poor blood returning from tissuesP

erce

nt

O2

satu

rati

on

Partial pressure of oxygen (mm Hg)

Fig. 45-10b, p. 980

7.6 7.4 7.2

Per

cen

t O

2 sa

tura

tio

n

Partial pressure of oxygen (mm Hg)


• Summarize the mechanisms by which Summarize the mechanisms by which carbon dioxide is transported in the bloodcarbon dioxide is transported in the blood

COCO22 Transport Transport

• About 60% of COAbout 60% of CO22 in blood is transported in blood is transported

as bicarbonate ions as bicarbonate ions

• About 30% combines with hemoglobinAbout 30% combines with hemoglobin

• About 10% is dissolved in plasmaAbout 10% is dissolved in plasma

Buffer System 1Buffer System 1

• Carbon dioxide combines with water to Carbon dioxide combines with water to form carbonic acidform carbonic acid• catalyzed by catalyzed by carbonic anhydrasecarbonic anhydrase

• Carbonic acid dissociates, formingCarbonic acid dissociates, forming• bicarbonate ions (HCObicarbonate ions (HCO33

--) ) • hydrogen ions (Hhydrogen ions (H++) )

Buffer System 2Buffer System 2

• Hemoglobin combines with HHemoglobin combines with H++

• buffering the blood buffering the blood

• Chloride shiftChloride shift • many bicarbonate ions diffuse into the plasma many bicarbonate ions diffuse into the plasma

and are replaced by Cland are replaced by Cl--

COCO22

TransportTransport

Fig. 45-11a, p. 981

Tissue cell

CO2

PlasmaCO2

Tissue capillary wallRed blood cell

CO2 H2O

CO2 + H2OCarbonic anhydrase

Hemoglobin

CO2

H2CO3 Carbonic acid H +

Cl–

HCO3– + H+

Chloride shift

Cl– HCO3–

Bicarbonate

Bicarbonate

Fig. 45-11b, p. 981

Fig. 45-11b, p. 981

Cl– HCO3–

Bicarbonate

Plasma

Chloride shift HCO3

– + H+ BicarbonateCl–

H2CO3 Carbonic acid

Hemoglobin

H +

H2OCO2

CO2

Pulmonary capillary

wall

CO2 + H2OCO2

CO2

Alveoli

Plasma Tissue capillary wall

Tissue cell

CO2

CO2

Fig. 45-11a, p. 981

Stepped Art

Cl–

Chloride shift

Cl–HCO3

– Bicarbonate

Red blood cellCO2 H2O

CO2 + H2OCarbonic anhydrase H2CO3

Carbonic acid

CO2

HCO3– + H+

Bicarbonate

HemoglobinH +


• Respiratory pigments combine with Respiratory pigments combine with oxygen and transport it oxygen and transport it

• Almost all of the oxygen in vertebrate Almost all of the oxygen in vertebrate blood is transported as oxyhemoglobin; blood is transported as oxyhemoglobin; carbon dioxide is transported mainly as carbon dioxide is transported mainly as bicarbonate ionsbicarbonate ions


• Describe the physiological effects of Describe the physiological effects of hyperventilationhyperventilation and of and of sudden sudden decompressiondecompression when a diver surfaces too when a diver surfaces too quickly from deep waterquickly from deep water

HyperventilationHyperventilation

• Reduces COReduces CO22 concentration in alveolar air concentration in alveolar air

and blood and blood

• A certain COA certain CO22 concentration in blood is concentration in blood is

needed to maintain normal blood pressureneeded to maintain normal blood pressure

Effects of Barometric PressureEffects of Barometric Pressure

• As altitude increases, barometric pressure As altitude increases, barometric pressure falls, less oxygen enters the blood falls, less oxygen enters the blood • hypoxiahypoxia, loss of consciousness, death, loss of consciousness, death

• Rapid decrease in barometric pressure Rapid decrease in barometric pressure can cause can cause decompression sicknessdecompression sickness• among divers who ascend too rapidlyamong divers who ascend too rapidly

Diving MammalsDiving Mammals

• Have high concentrations of Have high concentrations of myoglobinmyoglobin• pigment that stores oxygen in muscles pigment that stores oxygen in muscles

• Diving reflexDiving reflex • group of physiological mechanismsgroup of physiological mechanisms• including decrease in metabolic rate including decrease in metabolic rate • activated when a mammal dives to its limitactivated when a mammal dives to its limit

Diving MammalsDiving Mammals


• Describe the defense mechanisms that Describe the defense mechanisms that protect the lungsprotect the lungs

• Describe the effects of polluted air on the Describe the effects of polluted air on the respiratory systemrespiratory system

Defense MechanismsDefense Mechanisms

• Ciliated mucous lining traps inhaled Ciliated mucous lining traps inhaled particles inparticles in• nose nose • pharynxpharynx• trachea trachea • bronchi bronchi

Inhaling Polluted Air or Inhaling Polluted Air or Cigarette SmokeCigarette Smoke

• Results inResults in• bronchial constrictionbronchial constriction, increased mucus , increased mucus

secretion, damage to ciliated cells, coughing secretion, damage to ciliated cells, coughing

• Can causeCan cause• chronic bronchitis, pulmonary emphysema, chronic bronchitis, pulmonary emphysema,

lung cancerlung cancer

Effects of Cigarette SmokeEffects of Cigarette Smoke

Gas Exchange

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