15.3 Gas Exchanges in the Body
1. Overview
a. Diffusion is the underlying reason why O2 or CO2 enters or leaves the
blood in the lungs and in the tissues.
2. External Respiration
a. The exchange of gases between the air in the alveoli and blood in the
pulmonary capillaries
b. Partial pressure: the pressure each gas exerts
i. PO2 = partial pressure of oxygen
ii. PCO2 = partial pressure of carbon dioxide
c. In the blood of the pulmonary capillaries, PCO2 > PO2 , therefore CO2
diffuses out of the plasma into the lungs and O2 diffuses out of the
lungs and into the plasma of the blood.
d. CO2
i. Most CO2 is carried by the blood as the bicarbonate ion (HCO3-)
ii. As CO2 diffuses out, more HCO3- becomes CO2 through the
following reaction:
H+ + HCO3-  H2CO3  H20 + CO2
Hydrogen ion + bicarbonate ion  carbonic acid  water and carbon dioxide
Carbonic anhydrase (an enzyme) speeds up the breakdown of
H2CO3
e. Hyperventilation
i. Breathing at a high rate
ii. Reaction is pushed too far to the right
iii. Blood has fewer hydrogen ions, so pH becomes too high
(alkaline) = alkalosis
iv. Symptoms: dizziness, uncontrolled muscle contractions
v. Buffers bring down pH or coma and/or death may result
f. O2
i. blood in the pulmonary capillaries is low in oxygen and alveolar
sacs contain a higher partial pressure of oxygen
ii. O2 diffuses into the plasma and then into the red blood cells in
the lungs
iii. Hemoglobin (Hb) carries the oxygen and becomes
oxyhemoglobin (HbO2)
Hb + O2  HbO2
g. Actual gas use in external respiration
i. Inhaled air has about 21% O2, exhaled air still contains 16-17%
O2
ii. Explains why artificial respiration can work
3. Internal Respiration
a. Refers to the exchange of gases between the blood in systemic
capillaries and the tissue fluid
b. Brings O2 to cells and removes CO2 from cells
c. Needed for ATP production
d. Oxygen diffuses out of the blood into the tissues b/c PO2 is higher
outside the cells than inside the cells. This is because O2 is
continually being used in cellular respiration.
e. Carbon dioxide diffuses into the blood from the tissues b/c PCO2 is
higher inside the cells than outside the cells. This is because CO2 is
being continually produced by cellular respiration.
f. The reverse reactions with hemoglobin and carbonic anhydrase occur
compared to external respiration
Answer p.291 #1-2
15.3 Gas Exchanges in the Body
1. Overview
a. ____________________ is the underlying reason why O2 or CO2
enters or _________________ the blood in the _________________
and in the tissues.
2. External Respiration (blood and lungs)
a. The ________________ of gases between the air in the
_________________ and blood in the _________________
capillaries
b. _________________ pressure: the pressure each gas exerts
i. PO2 = partial pressure of _________________
ii. PCO2 = partial pressure of _______________ _______________
c. In the blood of the _________________ capillaries, PCO2 > PO2 ,
therefore _________________ diffuses _________________ of the
plasma into the _________________ and O2 diffuses out of the lungs
and into the plasma of the blood.
d. CO2
i. Most CO2 is carried by the _________________ as the
_________________ ion (HCO3-)
ii. As CO2 _________________ out, more HCO3- becomes CO2
through the following reaction:
+
H + HCO3-  H2CO3  H20 + CO2
Hydrogen ion + bicarbonate ion  carbonic acid  water and carbon dioxide
Carbonic _________________ (an enzyme) speeds up the
breakdown of H2CO3
e. Hyperventilation
i. Breathing at a _________________ rate
ii. Reaction is pushed too far to the right
iii. Blood has _________________ hydrogen ions, so pH becomes
too _________________ (alkaline) = _________________
iv. Symptoms: dizziness, uncontrolled muscle
_________________
v. Buffers bring _________________ pH or coma and/or death
may result
f. O2
i. blood in the _________________ capillaries is
_________________ in oxygen and alveolar sacs contain a
_________________ partial pressure of oxygen
ii. O2 _________________ into the plasma and then into the red
blood cells in the lungs
iii. Hemoglobin (Hb) carries the oxygen and becomes
_________________ (HbO2)
Hb + O2  HbO2
g. Actual gas use in external respiration
i. Inhaled air has about ________% O2, exhaled air still contains
_____-_____ O2
ii. Explains why artificial respiration can work
3. Internal Repiration (blood and cells)
a. Refers to the exchange of gases between the blood in
_________________ capillaries and the _________________ fluid
b. Brings O2 to _________________ and _________________ CO2 from
cells
c. Needed for _________ production
d. Oxygen diffuses _________ of the blood into the tissues b/c PO2 is
_________________ outside the cells than _________________ the
cells. This is because O2 is continually being used in
_________________ respiration.
e. Carbon dioxide diffuses into the blood from the tissues b/c PCO2 is
_________________ inside the cells than _________________ the
cells. This is because CO2 is being continually _________________ by
cellular respiration.
f. The reverse reactions with hemoglobin and carbonic anyhydrase
occur compared to external respiration
Helpful review: http://quizlet.com/13901560/gas-exchange-flash-cards/
Answer p.291 #1-2