Chapter Two

 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.

 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)

 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.

 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.

 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).

 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.

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.

 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).