BPK 105 Study Guide - Final Guide: Bronchiole, Pulmonary Vein, Extracellular Fluid
27 Apr 2018
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Module 10 - Review Questions - Part 3
6. Describe gas exchange in the pulmonary and systemic circulatory systems for oxygen
and carbon dioxide. Include the changes in partial pressures for both of these dissolved
gases and the driving force for exchange at each location. What impact would pulmonary
edema, an increase in interstitial fluid in the lungs, have on gas exchange? List the other
factors could influence the rate of gas exchange at the respiratory membrane. [8 marks]
In pulmonary gas exchange, CO2 enters the alveoli that have low CO2 pressure. O2 enters the
bloodstream which has low O2 pressure. In systemic gas exchange O2 moves from hemoglobin
to tissue because of high CO2 pressure, low O2 pressure, low pH and high
Diffusion of Gases in the Lungs [Tissues ---> Lungs ----> Alveoli/Capillaries]
- The cells of the body use O2 and produce CO2.
- Thus, blood returning from tissues and entering the lungs has a decreased Po2 and an
increased Pco2 compared to alveolar air (figure 15.13).
- Oxygen diffuses from the alveoli into the pulmonary capillaries because the Po2 in the
alveoli is greater than that in the pulmonary capillaries. In contrast, CO2 diffuses from
the pulmonary capillaries into the alveoli because the Pco2 is greater in the pulmonary
capillaries than in the alveoli (figure 15.13, step 1).
- When blood enters a pulmonary capillary, the Po2 and Pco2 in the capillary are different
from the Po2 and Pco2 in the alveolus. By the time blood flows through the first third of
the pulmonary capillary, an equilibrium is achieved, and the Po2 and Pco2 in the
capillary are the same as in the alveolus. Thus, in the lungs, the blood gains O2 and
loses CO2 (figure 15.13, step 2).
- There is a slight decrease in Po2 in the pulmonary veins due to mixing with
deoxygenated blood from veins draining the bronchi and bronchioles; however, the Po2
in the blood is still higher than that in the tissues (figure 15.13, step 3).
Diffusion of Gases in the Tissues
- Blood flows from the lungs through the left side of the heart to the tissue capillaries.
- Figure 15.13 illustrates the partial pressure differences for O2 and CO2 across the wall
of a tissue capillary.
- Oxygen diffuses from the capillary into the interstitial fluid because the Po2 is lower in
the interstitial fluid than in the capillary.
- Oxygen diffuses from the interstitial fluid into cells, in which the Po2 is less than in the
interstitial fluid (figure 15.13, step 4).
- Within the cells, O2 is used in cellular respiration. There is a constant difference in Po2
between the tissue capillaries and the cells because the cells continuously use O2.
There is also a constant diffusion gradient for CO2 from the cells. Carbon dioxide
therefore diffuses from cells into the interstitial fluid and from the interstitial fluid into the
Document Summary
Module 10 - review questions - part 3: describe gas exchange in the pulmonary and systemic circulatory systems for oxygen and carbon dioxide. Include the changes in partial pressures for both of these dissolved gases and the driving force for exchange at each location. List the other factors could influence the rate of gas exchange at the respiratory membrane. In pulmonary gas exchange , co2 enters the alveoli that have low co2 pressure . O2 enters the bloodstream which has low o2 pressure . In systemic gas exchange o2 moves from hemoglobin to tissue because of high co2 pressure , low o2 pressure , low ph and high. Diffusion of gases in the lungs [tissues ---> lungs ----> alveoli/capillaries] The cells of the body use o2 and produce co2. Thus, blood returning from tissues and entering the lungs has a decreased po2 and an increased pco2 compared to alveolar air (figure 15. 13).
