Download Respiratory System and Gas Exchange

David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.blu
C – Il corpo umano
Respiratory System and
Gas Exchange
Respiratory System and Gas Exchange
• What physical factors govern respiratory
gas exchange?
• What adaptations maximize respiratory
gas exchange?
• How do human lungs work?
• How is breathing regulated?
• How does blood transport respiratory
gases?
Respiratory System and Gas Exchange - What physical factors govern respiratory gas exchange?
O2 and CO2 are respiratory gases
exchanged by diffusion along their
concentration gradients.
Partial pressure is the concentration of
a gas in a mixture.
Barometric pressure: atmospheric
pressure at sea level is 760 mmHg.
Partial pressure of O2 (PO2) is 159
mmHg.
Respiratory System and Gas Exchange - What physical factors govern respiratory gas exchange?
The vital capacity is the sum of the
tidal volume, the inspiratory reserve
volume, and the expiratory reserve
volume.
The residual volume is the air that
cannot be expelled from the lungs.
The total lung capacity is the sum of
the vital capacity and the residual
volume.
Respiratory System and Gas Exchange - What adaptation maximize respiratory gas exchange?
Tidal breathing reduces PO2 and does
not permit countercurrent gas
exchange.
Two features offset the inefficiency of
tidal breathing in mammals:
• an enormous surface area;
• a very short path length for diffusion.
Respiratory System and Gas Exchange - How do human lungs work?
Air enters the human lung through the
oral cavity or nasal passage via the
trachea.
The trachea branches into two
bronchi, then into bronchioles, and
then into alveoli—the sites of gas
exchange.
Respiratory System and Gas Exchange - How do human lungs work?
The human respiratory system (part 1)
Respiratory System and Gas Exchange - How do human lungs work?
The human respiratory system (part 2)
Respiratory System and Gas Exchange - How do human lungs work?
The human respiratory system (part 3)
Respiratory System and Gas Exchange - How do human lungs work?
Human lungs are inside a right and left
thoracic cavity.
The diaphragm is a sheet of muscle
at the bottom of the cavities.
The pleural membrane lines each
cavity and covers each lung, and
encloses the pleural space.
Respiratory System and Gas Exchange - How do human lungs work?
The pleural space contains fluid to
help the membranes slide past each
other during breathing.
A negative pressure is created in the
pleural space when the volume
increases in the thoracic cavity.
The slight negative pressure present in
between breaths keeps the alveoli
inflated.
Respiratory System and Gas Exchange - How do human lungs work?
Inhalation begins when the diaphragm contracts.
The diaphragm pulls down on the thoracic cavity
and on the pleural membranes.
The pleural membranes pull on the lungs, air enters
through the trachea, and the lungs expand.
Exhalation begins when the diaphragm stops
contracting and relaxes.
The elastic lung tissues pull the diaphragm back up
and push air out of the airways.
Respiratory System and Gas Exchange - How do human lungs work?
The intercostal muscles, located
between the ribs, can also change
the volume of the thoracic cavity.
The external intercostal muscles lift the
ribs up and outward, expanding the
cavity.
The internal intercostal muscles
decrease the volume by pulling the
ribs down and inward.
Respiratory System and Gas Exchange - How do human lungs work?
Into the lungs and out again
Respiratory System and Gas Exchange - How is breathing regulated?
Breathing is controlled in the medulla,
in the brain stem.
In humans and mammals, the
breathing rate is more sensitive to
changes in PCO2 than to PO2.
The PCO2 of blood is the primary
metabolic feedback for breathing.
Respiratory System and Gas Exchange - How is breathing regulated?
Breathing is generated in the brain stem
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
Respiratory gases are transported in
the blood.
Blood contains molecules that bind
reversibly to O2, depending on its
partial pressure.
O2 is picked up where its partial
pressure is high and is released
where the partial pressure is lower.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
Hemoglobin is a protein with four
polypeptide subunits.
Each polypeptide surrounds a heme
group that can bind a molecule of O2.
One molecule of hemoglobin can bind
up to four molecules of O2.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
Hemoglobin will pick up or release O2
depending on the PO2 of the
environment.
If PO2 of the plasma is high, as in the
lungs, hemoglobin will pick up its
maximum of four O2 molecules.
As blood circulates through tissues
with lower PO2, hemoglobin will
release some O2.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
The relationship between PO2 and the
O2 that binds is S-shaped.
Low PO2: one subunit binds O2.
Positive cooperativity: one subunit
binds and changes shape, making it
easier for the next one to bind—the
affinity for O2 is increased.
When three subunits are bound, a
larger increase in PO2 is needed.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
Myoglobin is a single polypeptide
molecule in muscles and can bind
one molecule of O2.
• It has a higher affinity for O2, binds it
at low PO2 values when hemoglobin
molecules would release their O2.
• It provides a reserve for high
metabolic demand for O2.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
Oxygen-binding adaptation
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
The affinity of hemoglobin for O2
varies. Three factors are:
• hemoglobin composition;
• pH - blood circulating through active
tissues has a lower pH and H+ ions
bind to the hemoglobin molecule in
place of O2;
• 2,3-bisphosphoglyceric acid - also
lowers the affinity for O2.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
CO2 is transported away from the
tissues after diffusing into the blood.
In the blood plasma, CO2 is slowly
converted into bicarbonate ions
(HCO3–).
In endothelial cells and red blood cells
carbonic anhydrase speeds up the
conversion.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
The conversion keeps PCO2 low and
facilitates diffusion away from the
tissues.
Some CO2 binds to hemoglobin
molecules.
In the lungs the conversion reaction is
reversed: CO2 diffuses from the blood
into the alveoli and is exhaled.
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
CO2 is transported as HCO3- ions (part 1)
Respiratory System and Gas Exchange - How does blood transport respiratory gases?
CO2 is transported as HCO3- ions (part 2)