Respiratory System
Gas Transport
Gas Transport
• Oxygen and carbon dioxide are carried
between the lungs and body cells by the blood
• These gases can be:
1. Dissolved into blood plasma
2. Or, chemically combined with other atoms or
molecules present in the blood
Oxygen Transport
• Oxygen can be carried in the blood by:
1. Loosely binding to the iron present in the protein
hemoglobin in the red blood cells (creating a
new compound called oxyhemoglobin).
2. Or, dissolving in the plasma.
Oxygen Transport
• Transport via hemoglobin:
– Accounts for over 98% of oxygen transport
– The amount of oxygen that hemoglobin binds is
determined by the partial pressure of the oxygen
Oxygen Transport
• Transport via hemoglobin:
– Greater partial pressure leads to an increase in the
number of oxygen molecules bound to
hemoglobin
– Oxygen atoms continue to be bound to
hemoglobin until the hemoglobin is saturated
• Each molecule of hemoglobin can bind up to four
oxygen molecules
Oxygen Transport
• Transport via hemoglobin:
– Oxygen is released from the oxyhemoglobin molecule
as the partial pressure of oxygen decreases
– The number of oxygen molecules released increases
when:
•
•
•
•
Oxygen is used for respiration in nearby tissues
Partial pressure of carbon dioxide in the blood increases
Acidity increases
Temperature increases
Carbon Dioxide Transport
• Carbon dioxide is transported:
– Dissolved in plasma (about 7%)
– Bound to hemoglobin (15% to 25%)
– As part of a bicarbonate ion (about 70%)
Carbon Dioxide Transport
• Transport via plasma:
– Amount of carbon dioxide dissolved in plasma is
determined by the partial pressure of carbon
dioxide
• The higher the partial pressure of carbon dioxide in
nearby tissues the higher the amount dissolved into
solution
Carbon Dioxide Transport
• Transport via hemoglobin:
– Carbon dioxide loosely binds to the amino groups
(-NH2) of hemoglobin to form the compound
carbaminohemoglobin (very slow process)
– Carbon dioxide is released from
carbaminohemoglobin when the partial pressure
of carbon dioxide is low
Carbon Dioxide Transport
• Transport via bicarbonate ions:
1. Carbon dioxide enters the red blood cells and
combines with water to form carbonic acid
– This process is normally very slow but is very quick in the red
blood cells where the enzyme carbonic anhydrase is present
Carbon Dioxide Transport
• Transport via bicarbonate ions:
2. After carbonic acid forms in the red blood cells it
immediately dissociates releasing hydrogen ions
and bicarbonate ions
a. The hydrogen ions bind to deoxyhemoglobin in the
red blood cells
b. The bicarbonate ions diffuse back into the blood
plasma and are replaced in the red blood cells by
chloride ions from the plasma (called the chloride
shift)
Carbon Dioxide Transport
• Transport via bicarbonate ions:
3. As blood passes into the capillaries of the lungs,
dissolved CO2 diffuses into the alveoli, dropping
the partial pressure of carbon dioxide in the
plasma
• As this happens, hydrogen ions and bicarbonate ions in
the red blood cells recombine to form carbonic acid,
which then quickly forms carbon dioxide and water