Transcript Chapter 11

Why oxygen is import
Most animals satisfy their energy requirement by oxidation of
food, in the processes forming carbon dioxide and water
Oxygen is most abundant element in the earth’s crust (49.2%)
In atmosphere
O2
CO2
N2
Argon
Total
Per liter water (150C, 1 atm)
20.95%
7.22 ml
0.03%
1019.0 ml
78.09%
16.9 ml
0.93%
100%
760 mm
Vacuum
Pressure exerted by
atmospheric air above
Earth’s surface
Pressure at
sea level
Mercury (Hg)
Oxygen and carbon dioxide in physical environment
Oxygen is added to atmosphere:
Photosynthesis (dominant)
Photodissociation of water vapor
Oxygen is removed from atmosphere:
Living organism respiration
Oxidizing of organic matter, rocks, gases and fossil fuels
"Global warming" is a real phenomenon: Earth's
temperature is increasing.
True
False
Fig. 11-2, p.464
Oxygen and carbon dioxide in physical environment
Solubility of oxygen decreases with increasing water temperature
and salinity
Temperature
Fresh water
Sea water
ml O2/L water
ml O2/L water
0
10.29
7.97
10
8.02
6.35
15
7.22
5.79
20
6.57
5.31
30
5.57
4.46
Normoxic water: 100% saturated with oxygen
Hypoxic water contains less oxygen than normoxic water
Anoxic water contains no dissolved oxygen
Transport O2 and CO2 in living systems
Diffusion is common mechanism for transport both O2 and
CO2 across the body surface
To maximize the rate of gas transfer
•Large respiratory surface area
•Small diffusion distance
bronchial tree
The lungs contain many branching
airways which collectively are known
as the bronchial tree
• The trachea and all the bronchi have
supporting cartilage which keeps the
airways open.
• Bronchioles lack cartilage and contain
more smooth muscle in their walls than the
bronchi, for airflow regulation
• The airways from the nasal cavity
through the terminal bronchioles are called
the conducting zone.
•The air is moistened, warmed, and filtered
as it flows through these passageways.
•The pulmonary arteries carry blood which is low
in oxygen from the heart to the lungs.
• These blood vessels branch repeatedly,
eventually forming dense networks of capillaries
that completely surround each alveolus.
• oxygen and carbon dioxide are exchanged
between the air in the alveoli and the blood in the
pulmonary capillaries.
• Blood leaves the capillaries via the pulmonary
veins, which transports the oxygenated blood out
of the lungs and back to the heart.
Alveoli
• ~ 300 million air sacs.
– Large surface area (60 – 80
m2).
• Each alveolus is 1 cell layer
thick.
• Total air barrier is 2 cells across
(0.5 mm).
• 3 types of cells:
• Alveolar type I:
– Structural cells.
• Alveolar type II:
– Secrete surfactant.
Ventilation
• Mechanical process to move air
in and out of the lungs.
• O2 of air is higher in the lungs
than in the blood, O2 diffuses
from air to the blood.
• C02 moves from the blood to
the air by diffusing down its
concentration gradient.
• Gas exchange occurs entirely
by diffusion.
• Diffusion is rapid because of
the large surface area and the
small diffusion distance.
Three types of cells:
1. simple epithelium cells
2. alveolar macrophages
3. surfactant-secreting cells
• The wall of an alveolus is primarily
composed of simple epithelium, or
Type I cells. Gas exchange occurs
easily across this very thin
epithelium.
• The alveolar macrophages, or dust
cells, creep along the inner surface
of the alveoli, removing debris and
microbes.
• The alveolus also contains scattered
surfactant-secreting, or Type II,
cells.
• Water in the fluid creates a surface tension.
•Surface tension is due to the strong attraction
between water molecules at the surface of a
liquid, which draws the water molecules closer
together.
• Surfactant, which is a mixture of
phospholipids and lipoproteins, lowers the
surface tension of the fluid by interfering with
the attraction between the water molecules,
preventing alveolar collapse.
• Without surfactant, alveoli would have to be
completely reinflated between breaths, which
would take an enormous amount of energy.
• The wall of an alveolus and
the wall of a capillary form
the respiratory membrane,
where gas exchange occurs.
Summary
• The lungs contain the bronchial tree,
the branching airways from the
primary bronchi through the terminal
bronchioles.
• The respiratory zone of the lungs is
the region containing alveoli, tiny
thin-walled sacs where gas exchange
occurs.
• Oxygen and carbon dioxide diffuse
between the alveoli and the pulmonary
capillaries across the very thin
respiratory membrane.
Three main factors:
1.The surface area and
structure of the respiratory
membrane.
2. Partial pressure gradients
3. Matching alveolar airflow to
pulmonary capillary blood
flow
Atmosphere
760 mm Hg
Atmospheric pressure (the pressure
exerted by the weight of the gas in the
atmosphere on objects on the Earth’s
surface—760 mm Hg at sea level)
Airways (represents all airways collectively)
Thoracic wall
(represents entire thoracic cage)
Intra-alveolar pressure (the
pressure within
the alveoli—760 mm Hg
when equilibrated
with atmospheric pressure)
760 mm Hg
756 mm Hg
Pleural sac
(space represents pleural cavity)
Lungs (represents all alveoli collectively)
Intrapleural pressure (the pressure within
the pleural sac—the pressure exerted
outside the lungs within the thoracic
cavity, usually less than atmospheric
pressure at 756 mm Hg)
Fig. 11-17, p.480
760
Airways
Pleural cavity
(greatly exaggerated)
Lung wall
Lungs (alveoli)
Thoracic wall
756
760
760
756
760
756
Transmural pressure gradient
across lung wall =
intra-alveolar pressure minus
intrapleural pressure
Numbers are mm Hg pressure.
Transmural pressure gradient
across thoracic wall =
atmospheric pressure minus
intrapleural pressure
Fig. 11-18, p.481
Accessory
muscles of
inspiration
(contract only
during forceful
inspiration)
Sternocleidomastoid
Scalenus
Internal
intercostal
muscles
Sternum
Ribs
Muscles
of active
expiration
(contract only
during active
expiration)
External
intercostal
muscles
Diaphragm
Major
muscles of
inspiration
(contract every
inspiration;
relaxation
causes passive
expiration)
Abdominal
muscles
Fig. 11-20, p.482
External
intercostal
muscles
(relaxed)
Elevated
rib cage
Elevation of ribs
causes sternum
to move upward and
outward, which
increases front-to-back
dimension
of thoracic cavity
Contraction
of external
intercostal
muscles
Sternum
Contraction of
diaphragm
Diaphragm
(relaxed)
Before inspiration
Inspiration
Lowering of diaphragm on
contraction increases vertical
dimension of thoracic cavity
Contraction of external intercostal
muscles causes elevation of ribs,
which increases side-to-side
dimension of thoracic cavity
(a)
Fig. 11-21a, p.483
Contraction of internal intercostal muscles
flattens ribs and sternum, further reducing
side-to-side and front-to-back dimensions
of thoracic cavity
Relaxation
of external
intercostal
muscles
Contraction
of internal
intercostal
muscles
Relaxation of
diaphragm
Contraction of
abdominal
muscles
Position of
relaxed
abdominal
muscles
Passive expiration
Return of diaphragm, ribs, and sternum
to resting position on relaxation of
inspiratory muscles restores thoracic
cavity to preinspiratory size
(b)
Active expiration
Contraction of abdominal muscles
causes diaphragm to be pushed
upward, further reducing vertical
dimension of thoracic cavity
(c)
Fig. 11-21bc, p.483
H2O molecules
An alveolus
Fig. 11-23, p.486
Fig. 11-26, p.489
Fig. 11-27, p.490
Factors affecting the exchange of oxygen and carbon dioxide during
internal respiration:
1.The available surface area
2. Partial pressure gradients.
3. The rate of blood flow in a specific tissue.
Oxygen and Carbon Dioxide Transportation
• The blood transports oxygen and carbon dioxide
between the lungs and other tissues throughout
the body.
• These gases are carried in several different
forms:
1. dissolved in the plasma
2. chemically combined with hemoglobin
3. converted into a different molecule
Hemoglobin and 02 Transport
• 280 million
hemoglobin/ RBC.
• Each hemoglobin has
4 polypeptide chains
and 4 hemes.
• Each heme has 1 atom
iron that can combine
with 1 molecule O2
• Each hemoglobin can
combine with 4
molecule O2
• Combine reversibly
with O2 depend on PO2
Hemoglobin's affinity for
oxygen increases as its
saturation increases
the affinity of hemoglobin for
oxygen decreases as its
saturation decreases
Hemoglobin
• Oxyhemoglobin:
– Normal heme contains iron in the reduced
form. Reduced form of iron can share
electrons and bond with oxygen.
• Deoxyhemoglobin:
– When oxyhemoglobin dissociates to release
oxygen, the heme iron is still in the reduced
form.
Hemoglobin
• Hemoglobin production controlled by
erythropoietin.
• Production stimulated by P02 delivery to kidneys.
• Loading/unloading depends:
– P02 of environment.
– Affinity between hemoglobin and 02.
Oxyhemoglobin Dissociation Curve
•Oxygen
dissociation curve
describes the relation
between percent of
saturation and the
partial pressure of
oxygen (S-shape,
sigmoid)
•At high PO2, a large
amount of O2 is
bound
•At low PO2, only
small amount of O2
is bound
Hemoglobin saturation is
determined by the partial
pressure of oxygen
S-shaped curve
Oxyhemoglobin Dissociation Curve
• Loading and unloading of 02.
• Steep portion of the curve, small
changes in P02 produce large
differences in % saturation (unload
more 02).
• Decreased pH, increased temp.,
and increased 2,3 DPG, increase
CO2 affinity of Hb for 02
decreases.
• Shift to the right greater
unloading.
Bohr effect
Muscle Myoglobin
• Slow-twitch skeletal fibers
and cardiac muscle cells are
rich in myoglobin.
– Has a higher affinity for 02
than hemoglobin.
• Acts as a “go-between” in
the transfer of 02 from
blood to the mitochondria
within muscle cells.
• May also have an 02 storage
function in cardiac muscles.
Human fetal hemoglobin
contains g chains, which has
a high O2 affinity than adult
b hemoglobin
In humans, the oxygen
affinity of blood decrease
for about 3 months after
the birth
This reaction is catalyzed by the enzyme carbonic anhydrase.
C02 Transport
• C02 transported in the blood:
–
–
–
–
–
HC03- (70%).
Dissolved C02 (7%).
Carbaminohemoglobin (23%).
HCO3- is high in plasma than in erythrocytes
CO2 enters and leaves the blood as molecular CO2
rather than HCO3-
Chloride Shift at Systemic Capillaries
• H20 + C02
H2C03
H+
+ HC03• At the tissues, C02 diffuses
into the RBC, reaction shifts
to the right.
• Increased [HC03-] in RBC,
HC03- diffuses into the
plasma with assistance of
band III protein.
• RBC becomes more +.
• Cl- diffuses in (Cl- shift).
• HbC02 formed, give off 02.
At Pulmonary Capillaries
• H20 + C02
H2C03
H+
+ HC03• At the alveoli, C02 diffuses
into the alveoli, reaction shifts
to the left.
• Decreased [HC03-] in RBC,
HC03- diffuses into the RBC.
• RBC becomes more -.
• Cl- diffuses out (Cl- shift).
• Hb02 formed, give off HbC02.
Summary
• O2 is transported in two ways:
• dissolved in plasma, and
• bound to hemoglobin as oxyhemoglobin
• The O2 saturation of hemoglobin is affected by:
• PO2, pH , temperature, PCO2, and DPG
CO2 is transported in three ways:
• dissolved in plasma, bound to hemoglobin as
carbaminohemoglobin, and converted to bicarbonate ions
Oxygen loading facilitates carbon dioxide unloading from
hemoglobin. This is known as the Haldane effect.
• When the pH decreases, carbon dioxide loading facilitates oxygen
unloading. The interaction between hemoglobin's affinity for oxygen
and its affinity for hydrogen ions is called the Bohr effect.
Pons
Pons
respiratory
centers
Respiratory
control
centers in
brain stem
Medullary
respiratory
center
Pneumotaxic center
Apneustic center
Pre-Bötzinger
complex
Dorsal respiratory
group
Ventral respiratory
group
Medulla
Fig. 11-40, p.513
Input from other areas––
some excitatory, some inhibitory
Inspiratory neurons
in DRG
(rhythmically firing)
Medulla
+
Spinal cord
Phrenic nerve
Not shown are intercostal nerves to external intercostal muscles.
+
Diaphragm
Fig. 11-41, p.513
Sensory
nerve fiber
Sensory
nerve fiber
Carotid sinus
Carotid bodies
Carotid artery
Aortic bodies
Aortic arch
Heart
Fig. 11-42, p.514
Emergency
life-saving
mechanism
_
+
Peripheral
chemoreceptors
Relieves
Arterial PO2 < 60 mm Hg
+
Medullary
respiratory
center
No
effect
on
_
Central
chemoreceptors
Ventilation
Arterial PO2
Fig. 11-43, p.515
Fig. 11-44, p.516