Q.Explain the structure of tooth. Explain why human dentition is considered as thecodont, diphyodont and heterodont.

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 sol …

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 gallbladd …