A 13-yeаr-оld girl is аdmitted tо the psychiаtric unit fоr anorexia. Her body weight is 89 lbs. and height is 64 inches. She admits to frequent self-induced vomiting and abuse of laxatives. She was treated on the medical unit with intravenous fluids. Now that she is on the psychiatric unit she is experiencing fluid retention as evidenced by mild puffiness and bloating. Explain these symptoms.