Final answer:
Ghrelin is the gastrointestinal hormone that increases appetite, whereas hormones like cholecystokinin and secretin aid in digestion but do not impact hunger.
Step-by-step explanation:
The gastrointestinal hormone that has the effect of increasing appetite is B. Ghrelin. Ghrelin signals the brain when the body is hungry, leading to an increase in appetite. Other hormones like cholecystokinin (CCK) and secretin play roles in digestion, such as stimulating the secretion of pancreatic enzymes, bile, and bicarbonate, but they do not increase appetite. In contrast, peptide YY, or peripheral hormone peptide YY (PHP YY), actually decreases appetite.