Download BIO3420.2010.9 Respiratory Systems

Respiratory
Systems
Chapter 9; 29.10.-01.11.2010
Overview
 Respiration
 Sequence of events that result in the exchange of
oxygen and carbon dioxide between the external
environment and the mitochondria
 Mitochondrial respiration
 Production of ATP by oxidation of carbohydrates,
amino acids, or fatty acids; oxygen is consumed and
carbon dioxide is produced
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Overview
 External respiration
 Gas exchange at the respiratory surface
 Internal respiration
 Gas exchange at the tissue
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Overview
 Unicellular and small multicellular organisms rely
on diffusion for gas exchange
 Larger organisms must rely on a combination of
bulk flow and diffusion for gas exchange
 Bulk flow
 Ventilation
 Moving medium (air or water) over respiratory
surface (lung or gill)
 Circulation
 Transport of gases in the circulatory system
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Overview
Respiratory strategies of animals:
Diffusion alone is too slow to maintain the rates
of gas exchange needed to support the
metabolism of larger animals. Larger organisms
rely on a combination of bulk flow and diffusion
for gas exchange.
Figure 9.1
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The Physics of Respiratory Systems
 Diffusion of gases
 Fick equation
 dQ/dt = D  A  (dC/dx)




dQ/dt = Rate of diffusion
D = diffusion coefficient (D)
A = area of the membrane (A)
dC/dx = gradient
 Difference in pressure (not concentration)
 To maximize diffusion respiratory surfaces are
typically thin, with a large surface area
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Dalton’s Law of Partial Pressure
 The pressure exerted by a gas is related to the
number of moles of the gas and the volume of the
chamber
 Ideal gas law
 pV = nRT
The ideal gas law is the equation of state of a hypothetical ideal gas.
where p is the absolute pressure of the gas; V is the volume; n is the amoun
of substance; R is the universal gas constant; and T is the absolute
temperature.
In SI units, p is measured in pascals; V in cubic metres; n in moles; and T in
kelvin. R has the value 8.314472 J·K−1·mol−1 in SI units.
 Air is a mixture of gases
 Nitrogen (78%), oxygen (21%), argon (0.9%), and
carbon dioxide (0.03%)
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Dalton’s Law of Partial Pressure
 In a gas mixture each gas exerts its own partial
pressure
 The sum of all partial pressures is equal to the total
pressure of the mixture
PressureTotal = Pressure1 + Pressure2 ... Pressuren
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Henry’s Law
 Gas molecules in the air must first dissolve in
liquid in order to diffuse into a cell
 The concentration of gas in a liquid is proportional
to its partial pressure
 Henry’s law
 [G] = Pgas  Sgas
 [G] = concentration of the gas
 Pgas = partial pressure of the gas
 Sgas = solubility of the gas
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Henry’s Law
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Figure 9.2b
Diffusion Rates
 Graham’s law
 Diffusion rate is proportional to solubility/MW
 Combining the Fick equation with Henry’s law and
Graham’s law
 Diffusion rate of a gas molecule is proportional to
 D  A  DPgas  Sgas / X  MW
D - diffusion coefficient
A - cross-sectional area
DPgas - partial pressure gradient
Sgas - solubility of the gas in the fluid
X - diffusion distance
MW - molecular weight of the gas
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CO2 vs O2
O2 diffuses almost
300,000 times more
slowly in water than
in air
Gases in Air and Water
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Table 9.1
Bulk Flow of Gases
 Fluids flow from areas of high pressure to areas of
low pressure
 Boyle’s law
 P1V1 = P2V2
 P1V1 = initial pressure and volume of the gas
 P2V2 = final pressure and volume of the gas
 For example, if you increase the volume of a chamber
of gas, the pressure of the gas will decrease
 The rate of flow (Q) determined by the difference
in pressure (DP) and the resistance to flow (R)
 Q = DP/R
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Bulk Flow of Gases
Liquids are incompressible
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Figure 9.3
Surface Area to Volume Ratio
 As radius increases, volume increases faster than
surface area
 As organisms grow larger, the ratio of surface area
to volume decreases
 Larger size limits the surface area available for
diffusion and increases the diffusion distance
 Only very small organisms can rely solely on the
diffusion oxygen to support metabolism
 Larger animals must transport oxygen by bulk flow
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Surface Area to Volume Ratio
As radius increases, volume increases faster
than surface area
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Figure 9.4
Respiratory Strategies
Animals more than a few millimeters thick use one of three
respiratory strategies
 Circulating the external medium through the body
 Sponges, cnidarians, and insects
 Diffusion of gases across the body surface accompanied by
circulatory transport
 Cutaneous respiration
 Skin must be thin and moist
 Most aquatic invertebrates, some amphibians, eggs of birds
 Diffusion of gases across a specialized respiratory surface
accompanied by circulatory transport
 Gills (evaginations) or lungs (invaginations)
 Vertebrates
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Ventilation
 Ventilation of respiratory surfaces reduces the
formation of static boundary layers (oxygen
depletion in the immediate area)
 Types of ventilation
 Nondirectional
 Medium flows past the respiratory surface in an
unpredictable pattern
 Tidal
 Medium moves in and out of the chamber
 Unidirectional
 Medium enters the chamber at one point and exits at
another
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Ventilation
 The pattern, but not the direction, of ventilation can
change with environmental or metabolic conditions
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Patterns of Ventilation
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Table 9.2
Orientation of Medium and Blood Flow
 Gases enter the blood at the respiratory surface
 Movement of blood through the respiratory surface
can affect efficiency of gas exchange
 Both the mode of ventilation and the orientation of
the flow of the respiratory medium and the blood
affect the efficiency of gas exchange
 Comparison of Po2 in medium and blood as they enter
and leave the respiratory surface
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Orientation of Medium and Blood Flow
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Figure 9.6a–c
Orientation of Medium and Blood Flow
With unidirectional ventilation, the blood can flow
in three ways relative to the flow of the medium
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Figure 9.6d–f
Ventilation of Water and Air
 Because of the different physical properties of air
and water, animals use different strategies
depending on the medium in which they live
 Differences
 [Oair] is 30 times greater than [Owater]
 30 times more water than air must be ventilated to get the
same amount of oxygen
 Water is more dense and viscous than air
 It is more difficult to ventilate water
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Ventilation of Water vs. Air
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Table 9.1
Ventilation of Water vs. Air
Ventilation strategies
 Unidirectional
 Most water breathers
 Allows for countercurrent exchange
 Tidal
 Air-breathers
 Air flows easily; it would require too much work for tidal
ventilation of water
 Air-filled tubes
 Insects
 High diffusion rates of gases in air
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Sponges and Cnidarians
 Circulate external
medium through an
internal cavity
 Sponges
 Flagella move water in
through ostia and out
through the osculum
 Cnidarians
 Muscle contractions
move water in and out
through the mouth
 Gases diffuse directly in
and out of cells
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Figure 9.7
Molluscs
 Two strategies for ventilating gills (ctenidia)
 Snails and clams
 Cilia on gills move water across the gills unidirectionally
 Flow is countercurrent
 Cephalopods
 Muscular contractions of mantle propel water
unidirectionally past the gills in the mantle cavity
 Flow is countercurrent
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Molluscs
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Figure 9.8
Crustaceans
 Filter feeding (barnacles) or small species
(copepods) lack gills and rely on diffusion
 Shrimp, crabs, and lobsters have gills derived
from modified appendages within a branchial
cavity
 Movements of gill bailer propels water out of
branchial chamber; negative pressure sucks water
across gills
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Figure 9.9
Echinoderms
 Most sea stars and sea
urchins use their tube
feet for gas exchange
 Water is sucked in,
and exits through, the
madreporite
 External gill-like
structures (respiratory
papulae) can absorb
oxygen from water
 Cilia move water over
the surface
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Figure 9.10a
Echinoderms
 Brittle stars and sea
cucumbers have
internal invaginations
 Brittle stars use cilia to
move water into
saclike cavity (bursae)
 Sea cucumbers use
muscular contractions
of the cloaca and the
respiratory tree to
pump water tidally via
the anus
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Figure 9.10b
Jawless Fishes
Lamprey and hagfish have multiple pairs of gill sacs
 Hagfish
 Muscular pump (velum)
propels water through
respiratory cavity
 Water enters the mouth
and leaves through the
gill opening
 Flow is unidirectional
 Blood flow is
countercurrent
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Figure 9.11a
Jawless Fishes
 Lamprey
 When not feeding,
ventilation is similar
to hagfish
 When feeding, the
mouth is attached to a
prey
 Ventilation is tidal
through gill openings
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Figure 9.11b
Elasmobranchs
 Steps in ventilation
 Expand buccal cavity
 Increased volume sucks
water into buccal cavity
via mouth and spiracles
 Mouth and spiracles close
 Muscles around the buccal
cavity contract, forcing
water past gills and out the
gill slits
 Blood flow is
countercurrent
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Figure 9.12
Teleost Fishes
 Gills are located in the opercular cavity protected
by the flaplike operculum
 Steps in ventilation
 With the mouth open and the opercular valve closed,
the buccal and opercular cavities expand
 Pressure decreases and sucks water in through mouth
 Mouth closes
 Floor of buccal cavity raises and operculum expands
 Pressure pushes water into opercular cavity
 Opercular valve opens and water leaves through the
opercular slit
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Teleost Fishes
 Active fish can also use ram ventilation
 Swimming with mouth and opercular valve open
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Teleost Fishes
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Figure 9.13
Countercurrent Flow in Fish Gills
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Figure 9.14
Ventilation and Gas Exchange in Air
 Two major animal lineages have colonized
terrestrial habitats
 Vertebrates




Amphibians
Reptiles
Birds
Mammals
 Arthropods
 Crustaceans
 Chelicerates
 Insects
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Crustaceans
 Terrestrial crabs
 Respiratory structures and ventilation are similar to
marine relatives, but
 Gills are stiff so they do not collapse in air
 Branchial cavity itself is highly vascularized and acts as
the primary site of gas exchange
 Terrestrial isopods (woodlice and sowbugs)
 Have a thick layer of chitin on one side of the gill for
support
 Anterior gills contain air-filled tubules
(pseudotrachea)
 Gases diffuse from pseudotrachea into blood
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Chelicerates (Spiders and Scorpions)
 Have four book lungs
 10–100 lamellae
project into air-filled
cavity
 Cavity opens to
outside via spiracle
 Gases diffuse in and
out
 Some spiders also
have a tracheal system
 Series of air-filled
tubes
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Figure 9.15
Insects
 Have an extensive tracheal system
 Air-filled tubes called tracheae
 Open to outside via spiracle
 Tracheae branch to form tracheoles
 Ends of tracheoles are filled with hemolymph
 Gases diffuse in and out
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Figure 9.16
Insect Ventilation
Mechanisms
 Contraction of abdominal muscles or movements of
the thorax
 Tidal
 Air flows in and out of the same spiracles
 Unidirectional
 Air enters anterior spiracles, flows through tracheae, and
exits abdominal spiracles
 Ram ventilation (draft ventilation) in some flying
insects
 Expansion and contraction of tracheae
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Discontinuous Gas Exchange in Insects
 Phase 1 (closed phase)
 Spiracles are closed; no gas exchange with
environment
 O2 used and CO2 converted to HCO3–
 Decrease in total pressure in tracheae
 Phase 2 (flutter phase)
 Spiracles open and close in rapid succession (“flutter”)
 Air enters tracheae
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Discontinuous Gas Exchange in Insects
 Phase 3
 Excess CO2 can no longer be stored as HCO3–
 Total pressure in tracheae increases
 Spiracles open and CO2 is released
 Adaptive value of discontinuous gas exchange is
unknown
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Air Breathing in Fish
 Air breathing has evolved multiple times in fishes
 Types of respiratory structures
 Reinforced gills that do not collapse in air
 Highly vascularized mouth or pharyngeal cavity
 Highly vascularized stomach
 Specialized pockets of the gut
 Lungs
 Ventilation is tidal using buccal force similar to
other fish
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Air Breathing in Fish
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Figure 9.19
Amphibians
 Types of respiratory structures
 Cutaneous respiration
 External gills
 Simple bilobed lungs
 More complex lungs in terrestrial frogs and toads
 Ventilation is tidal using a buccal force pump
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Amphibians
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Figure 9.20
Reptiles
 Most have two lungs
 In snakes, one lung is reduced or absent
 Can be simple sacs with honeycombed walls or highly
divided chambers in more active species
 More divisions create more surface area
 Tidal ventilation
 Generally rely on suction pumps
 May supplement this with buccal pump
 Separation of feeding and respiratory muscles
 Two phases
 Inspiration and expiration
 Several mechanisms change volume of the chest
cavity
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Reptiles
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Figure 9.21
Birds
 Lungs are stiff and change
little in volume
 Lungs are between a
series of air sacs that act
as bellows
 Posterior and anterior air
sacs
 Gas exchange occurs as
air flows through
parabronchi in lungs
 Air flow through
parabronchi is
unidirectional
 Blood flow is crosscurrent
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Figure 9.22a
Bird Ventilation
Requires two cycles of inhalation and exhalation
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Figure 9.23
Mammals
 Two main parts to respiratory system
 Upper respiratory tract
 Mouth, nasal cavity, pharynx, trachea
 Lower respiratory tract
 Bronchi and gas exchange surfaces (alveoli)
 Alveoli are the site of gas exchange
 Thin wall of type I alveolar cells
 Type II surfactant cells secrete fluid
 Outer surface of alveoli are covered in capillaries
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Mammals
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Figure 9.24
Pleural Sac
 Each lung is surrounded
by a pleural sac
 Two layers of cells with
small space between
them
 Pleural cavity
 Pleural cavity contains a
small volume of pleural
fluid
 Intrapleural pressure is
subatmospheric
 Keeps lung expanded
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Figure 9.25
Mammalian Tidal Ventilation: Inspiration
 Inhalation
 Motor neuron stimulates inspiratory muscles
 Contraction of the external intercostals and diaphragm
 Ribs move outwards and the diaphragm moves
downward
 Volume of thorax ; intrathoracic pressure 
 Transpulmonary pressure gradient 
 Lungs expand and air is pulled in
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Mammalian Tidal Ventilation: Exhalation
 Exhalation
 Nerve stimulation of inspiratory muscles stops
 Muscles relax
 Ribs and diaphragm return to their original positions
 Volume of thorax ; intrathoracic pressure 
 Passive recoil of the lungs pushes air out
 During rapid, heavy breathing, forced exhalation is by
contraction of the internal intercostal muscles
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Mammalian Ventilation
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Figure 9.26
Lung Compliance and Surfactants
 Lung compliance
 How easily the lungs stretch during inhalation
 Surface tension in alveolar fluid lowers compliance
 Surfactants
 Reduces surface tension by disrupting the cohesive
forces between water molecules
 In humans, surfactant synthesis does not begin until
late gestation
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Airway Resistance
 Airway diameter affects resistance to air flow
 As diameter , resistance 
 Higher resistance requires a large transpulmonary
pressure gradient
 Parasympathetic nerve stimulation causes
bronchoconstriction
 Sympathetic nerve stimulation causes bronchodilation
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Dead Space
 Tidal volume (VT)
 Volume of air moved in one ventilatory cycle
 Dead space (VD)
 Air that does not participate in gas exchange
 Two components
 Anatomical dead space
 Volume of trachea and bronchi
 Alveolar dead space
 Volume of alveoli that are not perfused
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Dead Space
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Figure 9.27
Alveolar Ventilation
 Alveolar ventilation volume (VA)
 Volume of fresh air that enters alveoli with each
respiratory cycle
 VA = VT – VD
 Alveolar minute ventilation
 Volume of fresh air that enters alveoli each minute
 VA = f(VT – VD)
 f = breathing rate in breaths per minute
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Lung Volumes and Capacities
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Figure 9.28
Ventilation–Perfusion Matching
 Efficient gas exchange at respiratory surface
requires matching of ventilation and blood flow
 Arterioles dilate or constrict to distribute blood to
well-ventilated alveoli
 For example, low Po2 in alveolus causes constriction
of arteriole
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Gas Transport
 Sponges, cnidarians, and insects circulate external
medium (water or air) past almost every body cell
and can rely on diffusion
 Larger animals use circulatory systems
 Transport of gases in blood
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Oxygen Transport in the Blood
 Solubility of oxygen in aqueous fluids is low
 Metalloproteins (respiratory pigments)
 Proteins containing metal ions which reversibly bind
to oxygen and
 Increase oxygen carrying capacity by 50-fold
 Three major types of respiratory pigments
 Hemoglobins
 Hemocyanins
 Hemerythrins
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Hemoglobins
 Vertebrates, nematodes,
some annelids,
crustaceans, and insects
 Globin protein bound to a
heme molecule containing
iron
 Usually within blood cells
 Appears red when
oxygenated
 Myoglobin is a type of
hemoglobin found in
muscles
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Figure 9.29
Fetal hemoglobin (human)
Fetal Hemoglobin
2 a chains
2 g chains
37 a.a. different
High hematocrit in fetus
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Adult Hemoglobin
2 a chains
2 b chains
Hemocyanins and Hemerythrins
 Hemocyanins




Arthropods and molluscs
Contain copper
Usually dissolved in the hemolymph
Appears blue when oxygenated
 Hemerythrins




Sipunculids, priapulids, brachiopods, some annelids
Contains iron directly bound to protein
Usually found inside coelomic cells
Appears violet-pink when oxygenated
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Oxygen Equilibrium Curves
 Relationship between Po2
in plasma and the percent
of oxygenated respiratory
pigment in blood
 As Po2 increases more
pigment molecules will
bind oxygen, until 100%
saturation
 P50
 Po2 at which pigment is
50% saturated
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Figure 9.30
Shapes of Oxygen Equilibrium Curves
 Can be hyperbolic or sigmoidal
 Myoglobin has a hyperbolic curve because each
oxygen binds independently
 Hemoglobin has a sigmoidal curve because of
cooperativity
 Hemoglobin has a higher affinity for oxygen as more of
its heme groups bind to oxygen
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Shapes of Oxygen Equilibrium Curves
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Figure 9.31
Conditions That Affect Oxygen Affinity
 pH and PCO2
 Bohr effect or shift
 Decrease in pH or increase in PCO2 reduces oxygen
affinity; “right shift”
 P50 is increased
 Facilitates oxygen transport to active tissues and
facilitates oxygen binding at the respiratory surfaces
 Root effect
 A Bohr effect with a reduction in the oxygen carrying
capacity
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Bohr Affect and Root Affect
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Figure 9.32 and Figure 9.33
Conditions That Affect Oxygen Affinity
 Temperature
 Increases in temperature decrease oxygen affinity;
“right shift”
 P50 is increased
 Promotes oxygen delivery to warm muscles during
exercise
 Organic modulators (e.g., DPG)
 Increases in these modulators decrease oxygen
affinity; “right shift”
 Helps oxygen unloading at tissues
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Temperature and Organic Modulators
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Figure 9.34 and Figure 9.35
•Carbon monoxide (carboxyhemoglobin HbCO)
- colorless, tasteless, odourless, non-irritant
(not detectable in inhaled air)
- CO binds to Fe2+ in heme, competes with O2
CO 200x greater affinity for Hb than O2
(in mixture 0.1% CO & 21% O2, half Hb will carry CO)
- reduces HbO2 capacity
- air breathers more sensitive to  CO2 than  O2
decreased HbO2 due to increased HbCO does not activate a
physiological warning response
 homeostasis fails
 hypoxia
Carbon Dioxide Transport in the Blood
 CO2 is transported in three ways
 Small amounts of CO2 gas are transported in the
plasma
 CO2 is more soluble in body fluids than O2
 Some CO2 binds to proteins
 For example, carbaminohemoglobin
 Most CO2 is transported as bicarbonate (HCO3–)

carbonic acid
bicarbonate
 Carbonic anhydrase catalyzes the formation of HCO3–
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Transport of CO2 and H+ by Hb
•Carbamino hemoglobin
CO2 binds to amine-terminal end of each of the 4 globin chains
•Protonated hemoglobin
H+ binds to a.a residue in b chain and in a chain
HbO2 + H+ ↔ O2 + HbH+
Deoxyhemoglobin acts as a proton acceptor and minimizes
changes in pH
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Carbon Dioxide Transport in the Blood
 At respiratory surface, CO2 diffuses out of blood
 Carbaminohemoglobin releases CO2
 Bicarbonate reaction goes “to the left”
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Carbon Dioxide Equilibrium Curve
 Relationship between
PCO2 and total CO2
content of the blood
 Shape of the curve
depends on the
kinetics of HCO3–
formation
 Deoxygenated blood
can carry more CO2
than oxygenated blood
(Haldane effect)
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Figure 9.36
Vertebrate Red Blood Cells (RBC) and CO2
Transport
 Carbonic anhydrase is located within RBCs
 Reactions to synthesize HCO3– occur in the RBCs
 HCO3– is exchanged for Cl– in the plasma
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Figure 9.37
Dissolved CO2
in plasma 5%
in RBC 3%
Carbamino Pr
in plasma
<1%
Carbamino Hb
in RBC 12%
HCO3-
in RBC 23%
in plasma
57%
Fig. 10.37
Carbonic anhydrase (CA)
H2O + CO2 
H2CO3
Reversible reaction
CO2 Excretion and Body Fluid pH
 Pco2 affects the [HCO3–] and pH of body fluids

 As Pco2 , [HCO3–]  and pH  (i.e., [H+] )
 Reaction goes “to the right”
 As Pco2 , [HCO3–]  and pH  (i.e., [H+] )
 Reaction goes “to the left”
 Changes in ventilation affect body fluid pH
 Hyperventilation causes Pco2 
 Hypoventilation causes Pco2 
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Fate of H+ in the body
•production through metabolism of ingested foods
(production of CO2)
•shifts of H+ between compartments
alkaline/acid tide following ingestion of heavy meal
(stomach acid/alkaline pancreatic juices)
muscle storage vs protection of the brain
•buffering capacity of Hb, plasma proteins
•excretion through lungs (CO2)/gills and kidneys (H+, HCO3- )
Respiratory acidosis (if lung ventilation is reduced and body CO2 )
Respiratory alkalosis (lung ventilation increased and body CO2  )
Metabolic acidosis (e.g. anaerobic metabolism)
Metabolic alkalosis (e.g. vomiting)
CO2 Excretion and Body Fluid pH
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Figure 9.38
summary
LIGANDS OF HEMOGLOBIN
•OXYGEN (oxyhemoglobin), attaches to Fe2+ in heme units (4O2/Hb)
Hb + O2 ↔ HbO2
when 1 or 2 of the heme subunits bind O2, small conformational changes occur and
quaternary structure of entire molecule changes
increased affinity for O2 and reduced affinity for H+ and for CO2
•CARBON DIOXIDE (carbamino hemoglobin)
attaches to NH2-terminal end of globin chains (4CO2/Hb)
Hb + CO2 ↔ HbCO2
Decreases Hb affinity for O2
•HYDROGEN ION (protonated hemoglobin)
attaches to a.a. residue in globin chains (4H+/Hb)
HHb+ + O2 ↔ HbO2 + H+
Decreases Hb affinity for O2
•2-3-DIPHOSPHOGLYCERATE
attaches as bridge between b chains (1DPG/Hb)
HbO2 + DPG ↔ HbDPG + O2
Decreases Hb affinity for O2
Regulation of Respiratory Systems
 Vertebrate respiratory and circulatory systems work
together to regulate gas delivery by
 Regulating ventilation depth and rate
 Altering oxygen carrying capacity and affinity
 Altering perfusion
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Regulation of Ventilation
 Rhythmic firing of
central pattern
generators in the
medulla initiate
ventilatory movements
via nerve signal
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Figure 9.39
Regulation of Ventilation
 Chemoreceptors detect
changes in CO2, H+, and
O2
 O2 is the primary
regulator in waterbreathers
 CO2 is the primary
regulator in air-breathers
 Chemosensory input
modulates output of
central pattern generators
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 9.40
REGULATION OF BREATHING - Medullary Respiratory Centre
Inspiratory neurons  respiratory muscles
phasic (active ~2 sec, inactive ~3 sec)
generate rhythmic breathing
impose rhythm
inhibit E neurons
Expiratory neurons - not active during normal quiet breathing
function during forced expiration
continuously active if no I activity (i.e. not phasic)
Rhythm influenced by neuronal inputs from:
pulmonary stretch receptors
pulmonary irritant receptors
peripheral chemoreceptors
central chemoreceptors
Environmental Hypoxia
 Hypoxia
 Lower than normal Po2 in environment or blood
 Causes
 Environmental hypoxia
 For example, high altitude
 Inadequate ventilation (hypoventilation)
 Reduced blood hemoglobin content (anemia)
 Hypercapnia
 Higher than normal Po2 in environment or blood
 Hypocapnia
 Lower than normal Po2 in environment or blood
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Diving by air-breathing vertebrates
Females
Time underwater (%)
91%
Avg dive duration (min)
22 min
Max dive duration (min)
80 min
Avge dive depth (m)
522 m
Max dive depth (m)
1567 m
e.g. Northern Elephant Seals
Males
90%
22 min
89 min
366 m
1581 m
Source: Stewart & DeLong, 1995, J. Mammalogy
Problems:
infrequent opportunities to air breath
CNS must receive O2
fetus must receive O2
submerge to great depths
lung compression  “bends”
lung re-inflation
Solutions?
Oxygen stores
large blood volume
high hematocrit
high myoglobin
large spleen
14% of body mass
60%
(vs. 7%)
(vs. 45%)
Diving responses in seals
•Exhale before diving
lungs collapse (at 40 m depth)
non-respiratory air ducts do not collapse (cartilage rings)
residual volume forced into non-respiratory ducts
•Inhibition of breathing
receptors detect water on face
inhibit inspiratory neurons
•Selective perfusion of tissues
blood flow to CNS, eye, heart, placenta
increase RBC count by release of RBC from spleen
stop blood flow to most other tissues
O2 unloads from myoglobin
anaerobic metabolism & lactic acid storage
reduced metabolism on prolonged dives, pH stable
BREATHING AT HIGH ALTITUDE
Problems:
Po2 declines with altitude
Sea level
3000 m
6000 m
Po2 kPa
21.2
14.5
9.7
PAo2 kPa
13.8
8.9
5.3
9000 m
6.3
2.8
hypoxia = insufficient O2 to tissues
breathlessness, dizziness, nausea, headache
Solutions ?:
 PAo2 
(systemic vasodilation &
New problems?
hyperventilation  ??
pulmonary vasoconstriction)
hypocapnia  hypoventilation
uneven breathing, conflict between peripheral & central chemoreceptors
reduced blood flow to alveoli
Acclimation to Altitude
Polycythemia - increased RBC production by bone marrow
- increased Hb content
- increased blood volume
Vascular responses
- increased heart rate & cardiac output
- capillary proliferation
Regular hyperventilation
-central chemoreceptors not stimulated by low PACO2
-peripheral chemoreceptors adjust respiration to PAO2
Renal compensation (1-2 weeks)
-increased HCO3- excretion, stabilize pH at 7.5
Increased 2,3-DPG
decreased O2 affinity of Hb
enhances unloading of O2 at tissues
High-Altitude Hypoxia
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Figure 9.41