Gas Exchange
Chapter 45
Learning Objective 1
•
Compare the advantages and
disadvantages of air and water as
mediums for gas exchange
•
Describe adaptations for gas exchange
in air
Gas Exchange in Air and Water
•
Air has a higher concentration of
molecular oxygen than does water
•
Oxygen diffuses faster through air than
through water
•
Air is less dense and less viscous than
water (less energy needed to move air
over gas exchange surface)
Terrestrial Animals
•
Have adaptations that protect their
respiratory surfaces from drying
KEY CONCEPTS
•
Air has a higher concentration of
molecular oxygen than water does, and
animals require less energy to move air
than to move water over a gas exchange
surface
•
Adaptations in terrestrial animals protect
their respiratory surfaces from drying
Learning Objective 2
•
Describe the following adaptations for gas
exchange: body surface, tracheal tubes,
gills, and lungs
Adaptations for Gas Exchange 1
•
Small aquatic animals
•
•
•
exchange gases by diffusion
no specialized respiratory structures
Some invertebrates (most annelids) and
some vertebrates (many amphibians)
•
exchange gases across body surface
Adaptations for Gas Exchange 2
•
Insects and some other arthropods
•
•
air enters network of tracheal tubes (tracheae)
through spiracles along body surface
tracheal tubes branch, extend to all body
regions
Tracheal Tubes
Spiracle
Tracheal tube
(a) Location of spiral and tracheal tubes.
Fig. 45-2a, p. 973
Epithelial cell
O2
Tracheal tube
Tracheole
Spiracle
CO2
Muscle
(b) Structure and function of a tracheal tube.
Fig. 45-2b, p. 973
Fig. 45-2c, p. 973
Adaptations for Gas Exchange 3
•
Aquatic animals have gills
•
•
thin projections of body surface
Chordates
•
gills usually internal, along edges of gill slits
Adaptations for Gas Exchange 4
•
Bony fishes
•
•
•
operculum protects gills
countercurrent exchange system maximizes
diffusion of O2 into blood, CO2 out of blood
Animals carry on ventilation
•
actively move air or water over respiratory
surfaces
Gills in Bony Fishes
Gill arch
CO2
O2
Opercular chamber
(a) Location of gills.
Fig. 45-3a, p. 974
Gill arch
Blood vessels
Gill filaments
(b) Structure of a gill.
Fig. 45-3b, p. 974
Afferent blood vessel
(low O2 concentration)
Efferent blood vessel
(rich in O2)
(c) Countercurrent flow.
Fig. 45-3c, p. 974
Fig. 45-3d, p. 974
Fig. 45-3e, p. 974
Adaptations for Gas Exchange 5
•
Terrestrial vertebrates have lungs
•
•
and some means of ventilating them
Amphibians and reptiles have lungs
•
with some ridges or folds that increase
surface area
Adaptations for Gas Exchange 6
•
In birds
•
•
lungs have extensions (air sacs) that draw air
into system
2 cycles of inhalation and exhalation
Gas Exchange in Birds
•
One-way flow of air through lungs
•
•
from outside into posterior air sacs, to lung,
through anterior air sacs, out of body
Gas exchanged through walls of parabronchi
•
crosscurrent arrangement (blood flow at right
angles to parabronchi) increases amount of O2
entering blood
Gas Exchange in Birds
Trachea
Airsacs
Lung
Anterior
air sacs
Air
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.
Fig. 45-5, p. 975
Evolution
of
Vertebrate
Lungs
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
Fig. 45-4, p. 975
Adaptations for
Gas Exchange
Earthworm
(a) Body surface.
Fig. 45-1a, p. 972
Grasshopper
(b) Tracheal tubes.
Fig. 45-1b, p. 972
External
gills
Internal gills
Gills
Fish
Mud puppy
(c) Gills.
Fig. 45-1c, p. 972
Book
lung
Lungfish
Spider
Mammal
(d) Lungs.
Fig. 45-1d, p. 972
Learn more about adaptations
for gas exchange, including gills
in bony fishes, vertebrate lungs,
and the bird respiratory system,
by clicking on the figures in
ThomsonNOW.
KEY CONCEPTS
•
Adaptations for gas exchange include a
thin, moist body surface; gills in aquatic
animals; and tracheal tubes and lungs in
terrestrial animals
Learning Objective 3
•
Trace the passage of oxygen through the
human respiratory system from nostrils to
alveoli
The Human Respiratory System
•
Includes lungs and system of airways
•
Each lung occupies a pleural cavity and is
covered with a pleural membrane
•
Air passes through nostrils, nasal cavities,
pharynx, larynx, trachea, bronchi,
bronchioles, alveoli
The Human Respiratory System
Respiratory centers
Pharynx
Sinuses
Nasal cavity
Tongue
Epiglottis
Larynx
Esophagus
Space
occupied
by heart
Trachea
Bronchioles
Bronchus
Right lung
Left lung
Diaphragm
Fig. 45-6, p. 976
Structure of Alveoli
Capillary
Red
blood
cells
Bronchiole
Macrophage
Capillaries
Alveolus
Alveolus
Alveolus
Epithelial cell of the
wall of the alveolus
Epithelial cell of the
adjacent alveolus
(a)
Fig. 45-7a, p. 977
Fig. 45-7b, p. 977
Wall of alveolus
Wall of capillary
Red blood cell
1 µm
(c)
Fig. 45-7c, p. 977
Insert “Human respiratory
system”
human_respiratory_v2.swf
Learn more about the human
respiratory system by clicking
on the figures in ThomsonNOW.
Learning Objective 4
•
Summarize the mechanics and the
regulation of breathing in humans
•
Describe gas exchange in the lungs and
tissues
Mechanics of Breathing
•
Diaphragm contracts
•
•
Membranous walls of lungs move outward
along with chest walls
•
•
expanding chest cavity
lowering pressure within lungs
Air rushes in through air passageways
•
until pressure in lungs equals atmospheric pressure
Mechanics of
Breathing
Trachea
Lung
Diaphragm
(a) Inhalation.
(b) Exhalation.
Fig. 45-8ab, p. 978
Diaphragm
(c) Forced inhalation.
(d) Forced exhalation.
Fig. 45-8cd, p. 978
Respiratory Measurements
•
Tidal volume
•
•
Vital capacity
•
•
amount of air moved into and out of lungs with
each normal breath
maximum volume exhaled after lungs fill to
maximum extent
Residual capacity
•
air volume remaining in lungs at end of
normal expiration
Regulation of Breathing
•
Respiratory centers in medulla and pons
•
•
regulate respiration
Chemoreceptors
•
•
•
sensitive to increase in CO2 concentration
stimulate respiratory centers
respond to increase in H+ or very low O2
concentration
Gas Exchange
•
O2 and CO2 exchange between alveoli and
blood by diffusion
•
Pressure of a particular gas determines its
direction and rate of diffusion
Partial Pressure
•
Dalton’s law of partial pressures
•
•
Each gas exerts a partial pressure
•
•
in a mixture of gases, total pressure is the
sum of the pressures of the individual gases
same pressure as if it were present alone
Partial pressure of atmospheric oxygen
(Po2) is 160 mm Hg at sea level
Fick’s Law of Diffusion
•
The greater the difference in pressure on
two sides of a membrane, and the larger
the surface area, the faster the gas
diffuses across the membrane
Gas Exchange in
Lungs and Tissues
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
Alveoli in lung
O2
CO2
Capillary
in tissue
Capillary
in lung
Cells in body
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
Fig. 45-9, p. 979
Insert “Respiratory cycle”
breathing_m.swf
See the breathing mechanisms
in action by clicking on the
figures in ThomsonNOW.
KEY CONCEPTS
•
In mammals, oxygen and carbon dioxide
are exchanged between alveoli and blood
by diffusion; the pressure of a particular
gas determines its direction and rate of
diffusion
Learning Objective 5
•
What is the role of hemoglobin in oxygen
transport?
•
Identify factors that determine and
influence the oxygen-hemoglobin
dissociation curve
Hemoglobin
•
Respiratory pigment in vertebrate blood
•
Almost 99% of oxygen in human blood is
transported as oxyhemoglobin (HbO2)
Oxygen Measurement
•
Oxygen-carrying capacity
•
•
Oxygen content
•
•
maximum amount of oxygen that can be transported
by hemoglobin
actual amount of oxygen bound to hemoglobin
Percent O2 saturation
•
•
ratio of oxygen content to oxygen-carrying capacity
highest in pulmonary capillaries
Oxygen-Hemoglobin
Dissociation Curve 1
•
As oxygen concentration increases, the
amount of hemoglobin that combines with
oxygen progressively increases
•
Affected by pH, temperature, CO2
concentration
Oxygen-Hemoglobin
Dissociation Curve 2
•
Oxyhemoglobin dissociates more readily
as CO2 concentration increases
•
•
CO2 combines with water and produces
carbonic acid, which lowers pH
Bohr effect
•
displacement of oxygen-hemoglobin
dissociation curve by change in pH
Oxygen-Hemoglobin
Dissociation Curves
Percent O2 saturation
Oxygen-rich blood
leaving the lungs
Oxygen-poor blood
returning from
tissues
Partial pressure of oxygen (mm Hg)
Fig. 45-10a, p. 980
Percent O2 saturation
7.6
7.4
7.2
Partial pressure of oxygen (mm Hg)
Fig. 45-10b, p. 980
Learning Objective 6
•
Summarize the mechanisms by which
carbon dioxide is transported in the blood
CO2 Transport
•
About 60% of CO2 in blood is transported
as bicarbonate ions
•
About 30% combines with hemoglobin
•
About 10% is dissolved in plasma
Buffer System 1
•
Carbon dioxide combines with water to
form carbonic acid
•
•
catalyzed by carbonic anhydrase
Carbonic acid dissociates, forming
•
•
bicarbonate ions (HCO3-)
hydrogen ions (H+)
Buffer System 2
•
Hemoglobin combines with H+
•
•
buffering the blood
Chloride shift
•
many bicarbonate ions diffuse into the plasma
and are replaced by Cl-
CO2
Transport
Tissue cell
CO2
Plasma
CO2
Red blood cell
H2O
CO2
CO2 + H2O
CO2
Carbonic
anhydrase
H2CO3
Carbonic acid H +
HCO3– + H+
Cl–
Chloride
shift
Cl–
Tissue
capillary
wall
Hemoglobin
Bicarbonate
HCO3–
Bicarbonate
Fig. 45-11a, p. 981
Fig. 45-11b, p. 981
Plasma
Cl–
Chloride
shift
Cl–
HCO3–
Bicarbonate
HCO3– + H+
Bicarbonate
H2CO3
H+
Carbonic acid
Hemoglobin
CO2 + H2O
H2O
CO2
CO2
CO2
Pulmonary
capillary
wall
Alveoli
CO2
Fig. 45-11b, p. 981
Tissue cell
CO2
Plasma
CO2
Red blood cell
H2O
Tissue
capillary
wall
CO2
CO2 + H2O
CO2
Carbonic
anhydrase H CO
2
3
Carbonic acid H +
Hemoglobin
Cl– HCO – + H+
3
Bicarbonate
Chloride
shift
Cl–
HCO3–
Bicarbonate
Stepped Art
Fig. 45-11a, p. 981
KEY CONCEPTS
•
Respiratory pigments combine with
oxygen and transport it
•
Almost all of the oxygen in vertebrate
blood is transported as oxyhemoglobin;
carbon dioxide is transported mainly as
bicarbonate ions
Learning Objective 7
•
Describe the physiological effects of
hyperventilation and of sudden
decompression when a diver surfaces too
quickly from deep water
Hyperventilation
•
Reduces CO2 concentration in alveolar air
and blood
•
A certain CO2 concentration in blood is
needed to maintain normal blood pressure
Effects of Barometric Pressure
•
As altitude increases, barometric pressure
falls, less oxygen enters the blood
•
•
hypoxia, loss of consciousness, death
Rapid decrease in barometric pressure
can cause decompression sickness
•
among divers who ascend too rapidly
Diving Mammals
•
Have high concentrations of myoglobin
•
•
pigment that stores oxygen in muscles
Diving reflex
•
•
•
group of physiological mechanisms
including decrease in metabolic rate
activated when a mammal dives to its limit
Diving Mammals
Learning Objective 8
•
Describe the defense mechanisms that
protect the lungs
•
Describe the effects of polluted air on the
respiratory system
Defense Mechanisms
•
Ciliated mucous lining traps inhaled
particles in
•
•
•
•
nose
pharynx
trachea
bronchi
Inhaling Polluted Air or
Cigarette Smoke
•
Results in
•
•
bronchial constriction, increased mucus
secretion, damage to ciliated cells, coughing
Can cause
•
chronic bronchitis, pulmonary emphysema,
lung cancer
Effects of Cigarette Smoke