Which buffer system is found in the human body?

The correct answer is the bicarbonate buffer system.  

The bicarbonate buffer system refers to an acid-base homeostatic mechanism taking part in the balance of bicarbonate ion, carbonic acid, and carbon dioxide in order to sustain the pH in the duodenum and blood, among other tissues, to support the entire metabolic activities.  

The bicarbonate buffer system plays a vital role in the human body systems. In the duodenum and the stomach, the bicarbonate buffer system functions to both neutralize gastric acid and steady the intracellular pH of epithelial cells through the secretion of bicarbonate ion into the gastric mucosa.