Respiratory CD Worksheet #3

Gas Exchange

Graphics are used with permission of A.D.A.M.® Software, Inc. and Benjamin/Cummings Publishing Co.

Introduction

• Oxygen and carbon dioxide diffuse between the alveoli and pulmonary capillaries in the lungs, and between the systemic capillaries and cells throughout the body.

• The diffusion of these gases, moving in opposite directions, is called gas exchange.

Goals

• To apply gas law relationships - between partial pressure, solubility, and concentration - to gas exchange.

• To explore the factors which affect external and internal respiration.

 

Study Questions:

  1. What four gases are found in the atmosphere? Oxygen, O2, carbon dioxide, CO2, nitrogen, N2, and water, H2O
  2. Each of these gases exerts a pressure, what is the total pressure of all the gases in the atmosphere called? The atmospheric pressure
  3. What is a typical atmospheric pressure at sea level in millimeters of Hg? 760 mm Hg
  4. What is Dalton's Law of Partial Pressures? In a mixture of gases, the total pressure equals the sum of the partial pressures exerted by each gas
  5. As altitude increases, what happens to the atmospheric pressure? Atmospheric pressure decreases
  6. Oxygen gas makes up 20.9% of the atmosphere at sea level where the atmospheric pressure is 760 mm Hg.

a. What percentage of oxygen gas is there at a high altitude, where the atmospheric pressure is 440 mm Hg? 20.9%

b. Explain what happens to the partial pressure of oxygen gas at the high altitude. Partial pressure of oxygen decreases because the total pressure of gases decreases

 
  1. Henry's Law states that the amount of gas which dissolves in a liquid is proportional to what two factors? (1) the partial pressure of the gas (2) the solubility of the gas in the liquid
  2. In a container containing water and oxygen gas, some of the oxygen dissolves in the water. When equilibrium is reached, the pressure of the oxygen gas above the water ____________ the pressure of oxygen in the liquid.

a. is greater than b. is less than c. is equal to answer = c
  1. In a container containing water and oxygen gas, some of the oxygen dissolves in the water. When equilibrium is reached, the rate of oxygen gas diffusing into the water ____________ the rate of oxygen gas diffusing out of the water.

    2. a. is greater than b. is less than c. is equal to answer = c

  2. In a container containing water and oxygen gas, if you increase the pressure in the container ______ oxygen molecules dissolves in the liquid, moving from a region of _________ pressure. answer = c

    3. a. more, low to high b. less, low to high

    c. more, high to low d. less high to low

  3. If you have two closed containers of water and gas at the same pressure and one container contains oxygen gas and the other contains carbon dioxide gas, which of these statements is true? answer = b

    4. a. Both gases dissolve equally in the water.

    b. The carbon dioxide gas dissolves in the water to a greater extent than the oxygen gas.

    c. The oxygen gas dissolves in the water to a greater extent than the carbon dioxide gas.

  4. Which is more soluble in water, carbon dioxide or oxygen? carbon dioxide
  5. a. Where do both internal and external respiration occur? Internal respiration occurs at the systemic capillaries within the tissues of the body. External respiration occurs at the pulmonary capillaries within the lungs

b. What happens to oxygen and carbon dioxide during both internal and external respiration? In internal respiration oxygen diffuses from the systemic capillaries into the cells, and carbon dioxide diffuses from the cells into the systemic capillaries. In external respiration carbon dioxide diffuses from the pulmonary capillaries into the alveoli and oxygen diffuses from the alveoli into the pulmonary capillaries

 

 

 

 

 

 

 

 
  1. Efficient external respiration depends on what three main factors? (1) The surface area and structure of the respiratory membrane. (2) The partial pressure gradients between the alveoli and capillaries. (3) Efficient gas exchange requires matching alveolar airflow to pulmonary capillary blood flow.

    2.  

     

     

     

  2. What two factors account for the surface area and structure of the respiratory membrane allowing for efficient external respiration? (1) The 300 million alveoli, covered with a dense network of pulmonary capillaries, provide an enormous surface area for efficient gas exchange. (2) The thinness of the respiratory membrane increases efficiency

    3.  

     

     

  3. What three factors account for the differences in the partial pressures in the alveoli from those in the atmosphere? 1) Humidification of inhaled air. (2) Gas exchange between the alveoli and pulmonary capillaries. (3) Mixing of new and old air.
  4. As air travels through the respiratory passageways to the alveoli it is humidified, picking up water molecules. What effect does this have on the partial pressure of water? The partial pressure of water in inhaled gases increases as it passes through the respiratory passageways

    5.  

  5. As gases are exchanged between the alveoli and pulmonary capillaries, what happens to the partial pressures of both gases? The partial pressures of both gases are changed as oxygen diffuses out of the alveoli into the pulmonary capillaries and carbon dioxide diffuses from the pulmonary capillaries into the alveoli

    6.  

  6. Do the alveoli completely empty between breaths? No, the air in the alveoli is a mixture of new air and air remaining from previous breaths

    7.  

  7. The PO2 of the alveolar air is 104 mm Hg. At rest, the oxygen-poor blood entering the pulmonary capillaries has a PO2 of 40 mm Hg. As blood flows past the alveolus, the PO2 ___________.

a. increases b. decreases answer = a

 
  1. The PO2 of the alveolar air is 104 mm Hg. At rest, the oxygen-poor blood entering the pulmonary capillaries has a PO2 of 40 mm Hg. During external respiration there is a net diffusion of oxygen along its partial pressure gradient, from the alveolus into the blood, until equilibrium is reached. As this occurs, the PO2 of the blood ______________.

    2. a. increases to 104 mm Hg b. decreases to 40 mm Hg answer = a

  2. During external respiration, oxygen equilibrium is reached _______________ of the pulmonary capillary.

    3. a. at the end b. within the first half c. within the first third answer = c

     

  3. The PCO2 of the alveolar air is 40 millimeters of mercury. At rest, the PCO2 of the blood entering the pulmonary capillaries is 45 millimeters of mercury. As blood flows past the alveolus, the PCO2 _____________.

    4. a. increases b. decreases answer = b

  4. The PCO2 of the alveolar air is 40 millimeters of mercury. At rest, the PCO2 of the blood entering the pulmonary capillaries is 45 millimeters of mercury. During external respiration carbon dioxide diffuses along its partial pressure gradient, from the blood into the alveolus, until equilibrium is reached. As blood flows past the alveolus, the PCO2 _____________.

    5. a. increases to 45 mm Hg b. decreases to 40 mm Hg answer = b

     

  5. During external respiration, carbon dioxide equilibrium is reached _______________ of the pulmonary capillary.

    6. a. at the end b. within the last half c. within the first four-tenths answer = c

     

  6. Why does carbon dioxide have a smaller partial pressure gradient than oxygen? Carbon dioxide is very soluble in blood therefore a large number of molecules diffuse along this small partial pressure gradient. Oxygen gas is less soluble in blood therefore requiring a much larger concentration gradient to provide adequate oxygen to the body

    7.  

     

     

  7. Explain how ventilation-perfusion coupling facilitates efficient gas exchange. Pulmonary arterioles associated with bronchioles which have a restricted airflow, vasoconstrict. Pulmonary arterioles associated with bronchioles which have a high airflow, vasodilate. In this way blood supply is maximized to the alveoli that contain the most oxygen

    8.  

     

     

  8. What factor causes vasoconstriction and vasodilation associated with ventilation-perfusion coupling? Low PO2 causes the local arterioles to vasoconstrict. High PO2 causes the local arterioles to vasodilate

    9.  

  9. How do bronchioles respond to levels of blood gases? Bronchioles dilate when PCO2 rises. Bronchioles constrict when PCO2 drops

    10.  

  10. What would cause the PCO2 in the bronchioles to rise? When the airflow through a bronchiole is lower than normal, carbon dioxide can't be blown off as well so the levels remain high in the bronchiole

    11.  

     

  11. During ventilation-perfusion coupling, the arterioles respond to changes in _________ and the bronchioles respond to changes in _____________ .

    12. a. PO2 b. PCO2 answer = a

  12. Match the following: a. Low PO2 b. High PO2 c. Low PCO2 d. High PCO2
    13.

    a. Arterioles constrict

    b. Arterioles dilate

    c. Bronchioles constrict

    d. Bronchioles dilate

    Low PCO2

    Low PO2

    High PCO2

    High PO2

     

  13. What three factors affect the exchange of oxygen and carbon dioxide during internal respiration? (1) The available surface area. (2) Gases diffuse along their partial pressure gradients. (3) The rate of blood flow in a specific tissue

    14.  

  14. Why would the rate of blood flow vary within a tissue? Precapillary sphincters open or close depending on various factors including metabolic factors. For example, when muscles are active, they need more oxygen and nutrients so more blood would flow to that tissue

    15.  

  15. As gases are exchanged between the tissues and systemic capillaries, what happens to the partial pressures of both gases? The partial pressures of both gases are changed as oxygen diffuses out of the systemic capillaries into the tissues and carbon dioxide diffuses from the tissues into the systemic capillaries

    16.  

  16. The PO2 of the blood entering the systemic capillaries is 100 mm Hg. As blood flows through the systemic capillaries, the PO2 ___________.

    17. a. increases b. decreases answer b

  17. The PCO2 of the blood entering the systemic capillaries is 40 mm Hg. As blood flows through the systemic capillaries, the PCO2 ___________.

    18. a. increases b. decreases answer = a

     

  18. The PO2 of the blood entering the systemic capillaries is 100 mm Hg. During internal respiration there is a net diffusion of oxygen along its partial pressure gradient, from the blood into the tissues, until equilibrium is reached. As this occurs, the PO2 of the blood ______________.

    19. a. increases to 104 mm Hg b. decreases to about 40 mm Hg answer = b

  19. The PCO2 of the blood entering the systemic capillaries is about 40 millimeters of mercury. At rest, the PCO2 of the blood leaving the systemic capillaries is about 45 millimeters of mercury. As blood flow through the systemic capillaries, the PCO2 _____________.

    20. a. increases b. decreases answer = a

  20. During internal respiration carbon dioxide diffuses along its partial pressure gradient until equilibrium is reached. As blood flows through the systemic capillaries, the PCO2 _____________.
    21.

    a. increases to about 45 mm Hg b. decreases to about 40 mm Hg answer = a

    Summary

    • Gas laws show the relationship between partial pressure, solubility, and concentration of gases.

    • Gases diffuse along their partial pressure gradients, from regions of high partial pressure to regions of low partial pressure.

    • During external respiration, oxygen loads from alveoli into pulmonary capillaries and carbon dioxide unloads from pulmonary capillaries into alveoli.

    • During internal respiration, oxygen unloads from systemic capillaries into cells and carbon dioxide loads from cells into systemic capillaries.

    • Efficient gas exchange depends on several factors including surface area, partial pressure gradients, blood flow and airflow.

    • During external respiration, ventilation-perfusion coupling maintains airflow and blood flow in proper proportions for efficient gas exchange.