Shauna is a healthy, fit 28-year-old who decided to go on a 2-week tour of Mexico for young singles. One hot afternoon in a small market community, she grabbed some fruit juice from a street vendor. Several hours later, she developed abdominal cramping and diarrhea. The diarrhea became so severe that she missed 3 days of the tour and stayed in her hotel room. By the end of her illness, she felt weak and tired. Her head ached, but the mild fever had disappeared, and she was able to join her new friends for the rest of the tour.

What is the acid–base imbalance Shauna might have experienced and its etiology?
What are the functions and importance of the bicarbonate buffer system in the body?