Final answer:
Option E) Gastrin is the regulatory chemical that stimulates gastric gland activity and motility. It causes the secretion of gastric acid and aids motility, distinct from secretin and CCK which function in the pancreas and duodenum.
Step-by-step explanation:
The chemical that stimulates gastric gland activity and motility is gastrin. Gastrin is secreted by the stomach in response to the presence of food. It is the main digestive hormone responsible for stimulating the secretion of gastric acid by the parietal cells of the stomach’s mucosa. In addition to its acid-stimulating action, gastrin contributes to gastrointestinal motility.
Gastrin plays a crucial role in the gastric phase of digestion, beginning when food reaches the stomach. This hormone is distinct from other hormones such as secretin and cholecystokinin (CCK), which have different roles primarily in the duodenum and pancreas. While secretin promotes a bicarbonate-rich pancreatic juice secretion, CCK stimulates the secretion of pancreatic enzymes and bile.