Sphincter of oddi is present at :

The correct option is: Junction of hepato-pancreatic duct and duodenum.

Detailed Explanation:
The Sphincter of Oddi (also known as the hepatopancreatic sphincter) is a specialized muscular valve located at the junction where the hepato-pancreatic duct opens into the duodenum (the first part of the small intestine).
Its primary physiological roles are to regulate the flow of digestive juices (bile from the liver/gallbladder and pancreatic juice from the pancreas) into the duodenum, and to prevent the reflux of duodenal contents back into the biliary and pancreatic duct systems.

Let us examine the locations described in all the options to understand why the other choices are incorrect:
1. Junction of hepato-pancreatic duct and duodenum: This is the precise location of the Sphincter of Oddi. The common bile duct and the main pancreatic duct merge to form the hepato-pancreatic duct (ampulla of Vater), which enters the duodenum. The muscle fibers surrounding this junction form the sphincter.
2. Ileo-caecal junction: This is the boundary between the ileum (the last portion of the small intestine) and the caecum (the beginning of the large intestine). It is regulated by the ileocaecal valve, which controls the passage of materials into the large intestine and prevents backflow.
3. Gastro-oesophageal junction: This lies at the boundary between the oesophagus and the stomach. It is regulated by the gastro-oesophageal sphincter (also called the cardiac sphincter), which prevents stomach acid from refluxing into the oesophagus.
4. Junction of jejunum and duodenum: This is the transition zone within the small intestine where the duodenum ends and the jejunum begins. It is supported by the suspensory muscle of the duodenum (ligament of Treitz) rather than a muscular sphincter.