Two of the most notable organs behind the left side of the rib cage are the left lung and the spleen. The lungs are responsible for processing oxygen through the body, while the spleen filters the blood and protects against some bacteria.
The lungs are two separate but connected organs located in the upper chest, covered by the rib cage. The purpose of the lungs is to take in oxygen from the environment and filter out any impurities or harmful pollutants. Air reaches the lungs through the trachea, located beneath the throat. The actual filtering of air happens in small branched areas of the lungs called bronchi, which contain small sacs that process the inhaled air. Oxygen is pulled out of the inhaled air and passed into the blood for use by the body. The unused elements in the air, as well as the waste product carbon dioxide, is pushed back through the bronchi and up the trachea to be exhaled by the body.
The spleen is the largest filtering organ in the body and is broken up into two components: the red pulp and the white pulp. When blood passes through the spleen, the red pulp scans the blood for dead blood cells and removes them. The white pulp creates new blood cells and places them back into the blood.