The common bile duct is a small tube that carries bile from the liver and gallbladder to the small intestine. It plays a crucial role in the digestion and absorption of fats in our body. The opening of the common bile duct is located in the duodenum, which is the first part of the small intestine.

The duodenum is a short, C-shaped section of the small intestine that connects the stomach to the jejunum. It receives various digestive secretions from different organs, including the pancreas and the liver. The common bile duct opens into the duodenum through a small opening called the major duodenal papilla.

Here is a detailed explanation of the process:

1. Bile production: The liver produces bile, which is a yellowish-green fluid that helps in the digestion and absorption of fats. Bile is continuously produced by the liver and stored in the gallbladder.

2. Release of bile: When we eat a meal that contains fats, the gallbladder contracts and releases the stored bile into the common bile duct. The bile then flows through the duct and enters the duodenum.

3. Role of bile: Bile contains bile salts, which help in the breakdown and emulsification of fats. Emulsification is the process of breaking down large fat globules into smaller droplets, increasing their surface area for better digestion by enzymes.

4. Mixing with other digestive juices: The common bile duct joins with the pancreatic duct just before entering the duodenum. The pancreatic duct carries pancreatic juices, which contain digestive enzymes, into the duodenum. The mixture of bile and pancreatic juices further aids in the digestion of fats, carbohydrates, and proteins.

5. Function in digestion: Once in the duodenum, bile helps in the digestion and absorption of fats. The bile salts break down fats into smaller molecules called fatty acids and glycerol, which can be easily absorbed by the small intestine.

In conclusion, the common bile duct opens into the duodenum, which is the first part of the small intestine. It is responsible for carrying bile from the liver and gallbladder to the small intestine, where it aids in the digestion and absorption of fats.