Breathing.  We all do it but rarely think about it.  Breathing, or known by its more medical term, respiration, happens automatically as the diaphragm (muscle across the bottom of the rib cage) contracts and expands the lungs downward.  This is like stretching a rubber band and it creates a negative pressure (vacuum) within the lungs, causing outside air to rush in and fill the spaces called alveoli (small air sacs).  This is the first part of respiration, called inspiration or inhalation, and it occurs actively through muscle contraction.  The alveoli are covered with tiny little blood vessels called capillaries and this is where the ‘exchange’ takes place. 

When the blood travels throughout the body, it picks up carbon dioxide as it drops off fresh oxygen to all of the cells.  When the blood gets back to the lungs, the carbon dioxide is released into the alveoli as the oxygen is pulled from the alveoli into the capillary where it binds to the red blood cells.  Once this exchange takes place, the diaphragm relaxes and the little alveoli sacs contract like a stretched rubber band returning to its original size, passively pushing the carbon dioxide back out.  This is the second part of respiration, called expiration or exhalation, and it occurs passively from the elastic rebound of the alveoli. 

There is more to it than what I describe here but essentially this gives you the idea of what happens.  Two main components of respiration can improve with training: 1) efficiency of gas exchange and 2) muscular action that expands the rib cage and diaphragm which expanding the lungs to create a negative pressure and rapidly fill the alveoli with fresh air.

Your body has a specialized type of cell, called epithelial cells, that cover the surface of the airways (bronchioles), leading to the alveoli.  These cells secrete mucus (a thick, sticky fluid) which traps particles in the air.  These cells have finger-like projections called cilia, which moves the mucus up the ‘pipe’ where it will be forcefully ‘coughed-up’ and swallowed.   

As a side note, many factors can affect the epithelial cells.  Pollen or even the common cold can irritate the epithelial cells, creating a histamine response which produces excessive mucus.  Many people will counter this by taking an anti-histamine and using guaifenesin (brand name Mucinex) to help loosen and ease the ‘coughing-up’ of mucus.  This ‘coughing-up’ is called expectorating and can be somewhat controlled by taking an expectorant, commonly found in many cold medicines.  In many cases, you WANT to expectorate the mucus, so taking an expectorant is counter-productive.

Many factors can affect this respiratory process.  For instance, smoking can cause damage to the alveolar walls (Emphysema) which affects their ability to exchange oxygen and carbon dioxide.  Smoking also produces carbon monoxide which has a much stronger bond to red blood cells than carbon dioxide (which is also why it can lead to death.)  When the ‘exchange’ is supposed to take place, the carbon monoxide doesn’t let go so there is no room for the oxygen to attach to the red blood cells.  When the blood gets pumped back out through the body, it has little or no oxygen to deliver to the cells, leading to a whole series of problems, most of which are obvious (but listing them is beyond the scope of this article!)

Other diseases can also have an impact on either the lung tissue or the muscles that attach to the lung tissue and work to expand the lungs.  When the disease affects the tissue directly, it can become hardened, or fibrotic, so that it doesn’t expand as much and fill with air.  Less air coming in means a decrease in the ability to ‘exchange’ oxygen and carbon dioxide.  It also means that there is less ‘elastic’ rebound or ability to expectorate.  This can cause a build up or mucus which can further diminish the lungs ability for exchange.  Diseases that affect the muscles responsible for breathing can leave you with similar results of decreased lung capacity.

Hopefully this article has given you a better understanding of how the circulatory (heart/blood) and respiratory (lungs/air/oxygen) systems work together to supply the body with what it needs to function.  In addition, understanding how these functions fit into your everyday life and how they are affected with allergies, medications and diseases should help you make better choices to lead a healthier and more productive life.