The equine respiratory tract is responsible for many different functions and is, on a basic level, quite similar to the human respiratory tract. One of its primary functions is the exchange of oxygen between the lungs and the red blood cells, which allows oxygen to be delivered to tissues throughout the body and becomes especially important during exercise when the oxygen consumption of the tissues increases. Another important function is the clearance of irritants such as dust, ammonia, and bacteria, from the respiratory tract. This is done by filtering large dust particles in the nose, coughing, sneezing, and trapping irritants in the airway mucus. However, excess nasal discharge, coughing, sneezing, and mucus secretion are all signs that a horse may be suffering from respiratory problems.