1. Chapter Two

2.  Key Point – Gas exchange is continuously occurring between air, blood, and tissue. Gases move by a passive process called diffusion along a gradient from high pressure to low pressure. The challenge during exercise is to ensure that the gradient is maintained, requiring changes in ventilation and in the cardiovascular system.

3.  Gas exchange in the lungs as well as in other body tissues, takes place according to a passive process known as diffusion.  Gas will move along a gradient from an area of higher partial pressure to lower partial pressure.  Partial pressure is similar to concentration, but reprents the pressure exerted by a single gas (ex.O2) within a mixture (ex. Air, blood, tissue fluid)

4.  In the lungs, the air breathed in is high in O2 and low in carbon dioxide.  The blood being pumped to the lungs from the active tissue via the heart is lower in O2 and higher in carbon dioxide.  Meaning…oxygen will diffuse from the alveolus into the blood and carbon dioxide will diffuse form the blood into the alveolus.

5.  Therefore, the blood leaving the lungs, now high in oxygen and low in carbon dioxide will be pumped to the tissues via the heart.  At the tissues where oxygen is being used up and carbon dioxide produced the pressure gradient will drive oxygen from blood into tissues and carbon dioxide from tissues into the blood.

6.  During exercise, the pressure gradient at the tissues and lungs becomes greater as more oxygen is being used up and more carbon dioxide is being produced (refer to figure 2.3).

7.  The challenge for the lungs is to maintain resting partial pressures in the alveoli.  This is achieved by breathing out the air with less oxygen and more carbon dioxide and then breathing in fresh air to maintain the pressure gradients for diffusion to occur.  Otherwise exercise could not be sustained for long.

8. How would you use a flow map to illustrate the following: 1. Ventilatory system 2. Gas exhange in the lungs In your groups discuss each of these in a separate flow map. This will count as a quiz grade! You may use your notes. Group assignments are on the board.

9.  Ve = minute ventilation and describes the volume of air being exhaled per minute (and inhaled since we do not store air)  Ve is determined as the product of the size of each breath (Vt = tidal volume) multiplied by the number of breaths per minute (Bf = breath frequency).