Transcript Gas Exchange - De Anza College

Gas
Exchange
Part I
Respiration –
taking up O2 giving up CO2
Photosynthesis –
taking up CO2, giving up O2.
Respiratory
medium
(air or water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
fuel molecules
from food
Cellular respiration
ATP

What is diffusion?
epswww.unm.edu/.../eps462/graphics/diffusion.gif

Depends on


partial pressure,
surface area

A gas always diffuses from an area of high
partial pressure to low partial pressure.

What is equilibrium?
Partial pressure of gases: pressure exerted
by a particular gas in a mixture of gases.
We need to know:




Pressure that is exerted by mixture
Fraction of mixture represented by the particular
gas
Atmosphere is 21% by volume O2. At sea level
atmospheric pressure is 760mm Hg.
PO2 is 760mm Hg X 0.21 = 160mm Hg

What happens in water?

Amount of gas dissolved in water is
proportional to


partial pressure in air
solubility in water.

At equilibrium partial pressure of a gas in air
(PO2 of 160mm Hg) = partial pressure of that
gas in solution (PO2 of 160mm Hg)

Concentration of a gas depends on the
solubility of the gas.


Solubility decreases with increase of temperature
and dissolved solids.
Concentration of O2 [O2] is about 40 times more in
air than water.

Comparison of the two respiratory media:
Air
Water
density
less
more
viscosity
less
more
[O2]
higher
lower

Aquatic animals have had to evolve very
effective and efficient gas exchange
strategies.


Respiratory surfaces are plasma membranes
which must be moist. Gas exchange takes
place by diffusion.
Rate of diffusion is



directly proportional to the surface area across
which it occurs
inversely proportional to the square of the
distance the molecules have to travel.
To speed up the rate of diffusion, respiratory
surfaces have to be LARGE and THIN.

In unicellular and simple animals diffusion
occurs between all cells and environment.

If body surface is enough then skin
can be a respiratory organ.

Earthworm – surface is moist, supplied
richly by capillaries
Dorsal vessel
(main heart)
Auxiliary hearts
A closed circulatory system.
Ventral vessels

If body surface area is insufficient – need for
specialized respiratory organs

Larger animals have respiratory organs
consisting of respiratory surfaces and other
structures.

Size of respiratory surface depends on


Size of organism
Metabolic demands

To accommodate large respiratory surfaces
inside the body –


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Folded
Branced
Examples: gills, trachea, lungs

Gills: outfoldings of
the body that are
suspended in water;
surface area much
larger than the rest of
the body.

There are a large
variety of gills
Parapodia
Gill
Marine
Worm
Marine
worm
LE 42-20d
Gills
Crayfish
Crayfish
LE 42-20a
Gills
Coelom
Tube foot
Sea Star
Sea star
Oxygen-poor
blood
Oxygen-rich
blood
Gill
arch
Gill
arch
Water
flow
Lamella
Blood
vessel
Operculum
Gill
filaments
Water flow
O2
over lamellae
showing % O2 Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange

Ventilation: movement of respiratory
medium over respiratory surface.

Promoted by



moving the gills
moving water over the gills
swimming

Countercurrent exchange: exchange of
substance between two fluids (blood and
water) flowing in opposite directions and
thereby maximizing gas exchange
efficiency (about 80%)

Gills are unsuitable for land:


water supports the filaments and keep them
separate
gills would dry up

Tracheal systems: Most common respiratory structure.
Consists of:
 Large tubes (trachea – supported by chitin rings) branch into…
 Smaller tubes, tracheoles (fluid at terminal end); bring enough O2
to the tissues and removes enough CO2 from the tissues.
 Air sacs: supply air to organs with higher O2 needs.
Tracheae
Air sacs
Spiracle
Body
cell
Air
sac
Tracheole
Trachea
Air
Body wall
Tracheoles Mitochondria Myofibrils
2.5 µm

O2 demand can go up during flight by up to
200X.

The demand is met by:

Contraction and relaxation of the flight muscles
pumps air through the tracheal system

Flight muscles rich in mitochondria.

Withdrawal of fluid from tracheole into body
increases surface area.

Lungs:
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

localized respiratory organs;
inflodings of the body surface separated
consisting of numerous small pockets.
Circulatory system transports O2 to the body
from the lungs and CO2 from the body to the
lungs

Most reptiles, all birds and mammals use
lungs for gas exchange

Amphibians and some reptiles (turtles)
supplement lungs with parts of their skin.

Some aquatic animals (lungfishes) use lungs
for gas exchange
Gills
Trachea
Lungs
habitat of organisms
water
land
land
involves circulatory
system
yes
no
yes
location in body
hangs outside
in localized
areas
through out
the body
localized
organs
inside the
body
For animals with gills or lungs –
endotherms have greater surface area than
ectotherms.
Gas
Exchange
Part II

Pathway of air to the gas
exchange surface in
mammals:
Nasal cavity
Pharynx
Nasal
cavity
Pharynx
Larynx
Glottis (covered by epiglottis
during swallowing)
Larynx
Esophagus
Left
lung
Trachea
Trachea
Right
lung
Bronchi
Bronchus
Bronchiole
Diaphragm
Bronchioles
Heart
Alveoli

Mucus traps dust, beating cilia move the
mucus to esophagus

Millions of alveoli in lungs, total area about
100 m2.

Alveoli are
surrounded by
capillaries.
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Branch
from
pulmonary
artery
(oxygen-poor
blood)
Terminal
bronchiole


Surface is coated
by moist fluid that
helps in gas
exchange.
Alveoli
Surfactants keep
alveoli from
collapsing.
SEM
Colorized SEM

Breathing: process to ventilate lungs.

Amphibian breathing: positive airflow.

Mammalian breathing: negative pressure
breathing.

Mammalian breathing

During inhalation - expand thoracic cavity, causes
lower air pressure in thoracic chamber, air rushes
in; opposite process for exhalation.

Rib muscles, diaphragm, double layered
membrane between lungs and thoracic cavity
participate.

During exercise muscles of neck, back and chest
are also involved.
LE 42-24
Rib cage
expands as
rib muscles
contract
Air
inhaled
Rib cage gets
smaller as
rib muscles
relax
Air
exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
EXHALATION
Diaphragm relaxes
(moves up)

Tidal volume: volume of air inhaled and exhaled at
each breath (~ 500ml)

Vital capacity:




maximum volume of air that a person can exhale after
maximum inhalation, OR
maximum volume of air that a person can inhale after
maximum exhalation. 3.4L in college age women, 4.8L in
college age men.
decreases with age.
Residual volume: Air that remains after forced
exhalation.

Avian breathing:

Ventilation is more efficient and more complex.

Maximum PO2 is higher than that of mammals.

Birds are better adapted to higher altitudes than
humans.

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Airflow over gas exchange surface is in one
direction only
No mixing of fresh and used air.
8 – 9 pairs of air sacs that act as bellows.
Parabronchi in the lungs, no alveoli
2 sets of inhalation and exhalation are needed to
completely pass air through the system.
LE 42-25
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Lungs
Air tubes
(parabronchi)
in lung
INHALATION
Air sacs fill
EXHALATION
Air sacs empty; lungs fill
1 mm

Breathing is controlled (involuntarily) to
ensure

Gas exchange coordinates with circulation

Metabolic needs are met
Cerebrospinal
fluid
Pons
Breathing
control
centers

Medulla
oblongata
Breathing is controlled by two regions at the
base of the brain – pons and medulla
oblongata

During respiration cells produce CO2.

CO2 concentration in blood goes up.

CO2 diffuses from blood to cerebrospinal fluid
(CSF).

In CSF
CO2 + H2O
H2CO3
HCO3- + H+

Increased metabolic activity (exercise) –
[CO2] increases

Results in increase in [H+]

Results in decrease in pH.




pH in CSF is an indicator of blood [CO2].
Decrease in pH is an indicator of increased
[CO2]
Decreased pH in cerebropspinal fluid results
in control centers of the brain increasing the
rate and depth of breathing.
When CO2 is exhaled, pH increases and
breathing is returned to normal.
Cerebrospinal
fluid
Pons
Breathing
control
centers
Medulla
oblongata
Carotid
arteries
Aorta
Diaphragm
Rib muscles

CO2 concentration is primarily used to control
breathing

O2 concentration influences breathing only
when it is very low.


Aorta and carotid arteries have O2 sensors which
signal the brain ti increases breathing
Increased breathing is always coupled with
increased cardiac output.

Coordination of circulation and gas
exchange.
LE 42-5



Heart is a dual
pump.
Circulatory
system is
divided into
pulmonary
circuit and
systemic circuit.
Blood with
higher PCO2
and lower PO2
comes from the
heart to the
lungs.
Capillaries of
head and
forelimbs
Anterior
vena cava
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Pulmonary
vein
Right atrium
Right ventricle
Posterior
vena cava
Aorta
Capillaries
of left lung
Pulmonary
vein
Left atrium
Left ventricle
Aorta
Capillaries of
abdominal organs
and hind limbs



Air in the alveoli has
higher PO2 and lower
PCO2 than blood in the
capillaries.
O2 in the alveoli
dissolves in the fluid
coating the alveolar
epithelium and
diffuses into the blood.
CO2 dissolves from
blood to the air in the
alveoli.
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
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Blood leaving the lungs
and going to the heart
has higher PO2 and
lower PCO2 than the
blood entering the lungs.
From the heart the blood
goes into the systemic
circulation.
In the tissues cellular
respiration removes the
O2 from the cells and
adds CO2.
PO2 is higher and PCO2
is lower in the blood in
the tissue capillaries
than in the tissues.
O2 diffuses out of the
blood and enters the
cells and CO2 diffuses
out of the cells and
enters the blood.
This blood is returned to
heart and sent to lungs.
Exhaled air
Inhaled air
160 0.2
O2 CO2
Alveolar spaces
120 27
O2 CO2
104 40
Alveolar
epithelial
cells
Blood
entering
alveolar
capillaries
40
45
O2 CO2
O2 CO2
CO2
O2
Alveolar
capillaries
of lung
Pulmonary
arteries
Systemic
veins
Blood
leaving
alveolar
capillaries
104 40
O2 CO2
Pulmonary
veins
Heart
Systemic
arteries
Tissue
capillaries
Blood
entering
tissue
capillaries
Blood
leaving
tissue
capillaries
40
45
O2 CO2
CO2
O2
Tissue
cells
< 40 > 45
O2 CO2
100 40
O2 CO2


Diffusion of O2 in the blood alone is
inadequate for meeting metabolic needs.
O2 transport is done to a large degree by
respiratory pigments.

During exercise cardiac output is

12.5L of blood per minute with respiratory
pigment

555L without the pigment

Respiratory pigments: protein bound to
metal, have distinctive color

Hemoglobin: protein and iron (vertebrates)

Hemocyanin: protein and copper (some
arthropods and molluscs)


Hemoglobin (Hb): 4 polypeptide subunits
each with an iron atom cofactor.
Found in red blood cells.
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Polypeptide chain

Functions of hemoglobin:



carries O2,
carries C O2,
acts as a buffer in blood

Binds to
oxygen
reversibly.
Subunits
show cooperativity in
binding and
release.
O2 saturation of hemoglobin (%)

100
O2 unloaded from
hemoglobin
during normal
metabolism
80
60
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
metabolism
40
20
0
0
20
40
60
Tissues during Tissues
exercise
at rest
PO2 (mm Hg)
PO2 and hemoglobin dissociation at 37°C and pH 7.4
80
100
Lungs


Cellular
respiration
increases
CO2
production.
CO2
production
lowers pH
Lower pH
decreases Hb
affinity for
oxygen.
(Bhor shift)
O2 saturation of hemoglobin (%)

100
pH 7.4
80
Bohr shift:
additional O2
released from
hemoglobin at
lower pH
(higher CO2
concentration)
60
pH 7.2
40
20
0
0
20
40
60
80
PO (mm Hg)
2
pH and hemoglobin dissociation
100

When cellular respiration is higher Hb
releases more O2.

CO2 transport.



In solution (7%)
Bound to Hb (23%)
Bicarbonate (HCO3-) 70%
Tissue cell
CO2 transport
from tissues
CO2 produced

CO2
transport
from tissues
to alveolar
space
Interstitial
fluid
CO2
Blood plasma
within capillary
CO2
Capillary
wall
CO2
H2 O
Red
H2CO3
Hb
blood
cell Carbonic acid
HCO3– +
Bicarbonate
Hemoglobin
picks up
CO2 and H+
H+
HCO3–
To lungs
CO2 transport
to lungs
HCO3–
HCO3– +
H2CO3
H+
Hb
Hemoglobin
releases
CO2 and H+
H2 O
CO2
CO2
CO2
CO2
Alveolar space in lung
Tissue cell
CO2 produced






From tissue and interstitial
fluid to plasma
Large part (~90%) diffuses
into the red blood cells
Some picked up by Hb
CO2 and water in red blood
cells react forming carbonic
acid
Carbonic acid dissociates
into bicarbonate and
hydrogen ions.
Hb binds most of the H+; this
helps maintain pH,
preventing Bhor sift.
Interstitial
fluid
CO2
Blood plasma
within capillary
CO2
CO2 transport
from tissues
Capillary
wall
CO2
H2O
Red
H2CO3
Hb
blood
Carbonic acid
cell
HCO3– +
Bicarbonate
H+
HCO3–
To lungs
Hemoglobin
picks up
CO2 and H+
To lungs
CO2 transport
to lungs
HCO3–






HCO3- diffuses into the
plasma.
At the lungs HCO3diffuses back into the red
blood cells.
Combines with H+ to form
CO2 and water
CO2 is unloaded from Hb.
Diffuses from plasma into
interstitial fluid.
CO2 diffuses into alveolar
space, exhaled out.
HCO3– +
H2CO3
H+
Hb
Hemoglobin
releases
CO2 and H+
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung

Animals like cheetah, pronghorned antelope
have been selected enhancement normal
physiological mechanisms at every stage of
O2 metabolism.

Diving mammals have myoglobin that have
higher affinity for O2 than human myoglobin.