<qa>  What is the pathophysiology of nausea and vomiting?Although the pathophysiology of nausea and vomiting is not well understood, we know that chemotherapy causes damage to the gastrointestinal GI mucosa. The pathobiology of the mucosal damage has been reviewed by Blijlevens and can be divided into four phases: the inflammatory phase, the epithelial phase, the ulcerativebacteriological phase and the healing phase. This mucosal injury is usually self-limiting with a complete cycle of injury to healing lasting approximately 2-3 weeks. The mucosal damage can be increased in patients receiving chemotherapy and corticosteroids which breast cancer patients require as pre-medications. Since cytotoxic chemotherapy damages the mucosal lining, it leaves the GI mucosa exposed to the normal acid-producing gastric parietal cells. The resultant damage has been seen endoscopically in patients receiving chemotherapy with cytosine arabinoside. Hence, suppression of acid secretion from the gastric parietal cells should reduce mucosal injury and related symptoms. 