Q.Select odd one out on the basis of digestive functions of tongue.

Of the parts listed, only the oesophagus is purely a conduction/transport tube -- mouth, stomach, and duodenum all secrete digestive enzymes/juices, while the oesophagus's muscular wall simply propels the bolus onward by peristalsis.

Each part of the alimentary canal contributes to digestion except the oesophagus: the mouth secretes salivary amylase (ptyalin) via the salivary glands; the stomach secretes gastric juice containing pepsin (protease) and other enzymes; the duodenum receives pancreatic enzymes (trypsin, amylase, lipase) and also has its own intestinal (succus entericus) enzymes. The oesophagus, by contrast, has mucus-secreting glands for lubrication but no digestive enzyme of its own -- its sole role is mechanical transport of the bolus to the stomach.

(Note: this is core content of 'Digestion and Absorption', a chapter dropped from the current CBSE-rationalised Class-11 syllabus; mapped above to the closest retained Human Physiology chapter for surfacing purposes.)

The Sphincter of Oddi is a ring of smooth muscle that controls the opening of the hepatopancreatic duct (the combined duct formed by the bile duct and pancreatic duct) into the duodenum.

Bile from the liver/gallbladder travels via the common bile duct, and pancreatic juice from the pancreas travels via the pancreatic duct. These two ducts join just before entering the small intestine, forming a short common channel called the hepatopancreatic duct (or hepatopancreatic ampulla, also known as the ampulla of Vater), which opens into the duodenum. The Sphincter of Oddi is the muscular valve surrounding this combined duct's opening; it relaxes to allow bile and pancreatic juice to flow into the duodenum (especially after a meal, under hormonal control) and contracts to prevent backflow and to allow bile to be stored/concentrated in the gallbladder between meals.

The other named ducts (pancreatic duct alone, cystic duct which connects the gallbladder to the common bile duct, and common bile duct alone) each have their own separate role, but the sphincter specifically named 'of Oddi' guards the shared hepatopancreatic duct's exit into the gut.