The organ that secretes bile juice is the liver. The bile is produced by the liver mainly in the hepatocytes and via bile ducts, it reaches the gallbladder.

The correct answer is option 'D', the liver.

The liver is an essential organ in the human body that performs several important functions. One of its major functions is the production and secretion of bile.

- The Liver:
The liver is the largest glandular organ in the human body and is located on the right side of the abdomen, just below the diaphragm. It plays a crucial role in various metabolic processes and performs over 500 vital functions. Some of its functions include detoxification, protein synthesis, nutrient storage, and production of bile.

- The Bile:
Bile is a yellowish-green fluid that is produced by the liver cells, known as hepatocytes. It is then stored and concentrated in the gallbladder before being released into the small intestine. Bile is composed of water, bile salts, cholesterol, bilirubin, and other substances.

- Bile Production and Secretion:
The liver continuously produces bile, which is essential for the digestion and absorption of fats. Bile is synthesized in the liver by the hepatocytes and then secreted into small bile ducts within the liver. These ducts merge together to form larger bile ducts, which eventually join the common hepatic duct.

- The Gallbladder:
While the liver produces bile, it is not directly responsible for its storage and release. The bile produced by the liver is transported through the bile ducts to the gallbladder for storage. The gallbladder is a small pear-shaped organ located beneath the liver. It acts as a reservoir for bile, allowing it to be concentrated and stored.

- Bile Release:
When we consume a meal, especially one high in fat content, the gallbladder contracts and releases bile into the small intestine through the common bile duct. Bile helps in the emulsification and breakdown of fats, allowing for their proper digestion and absorption.

In conclusion, the liver is the organ responsible for the production and secretion of bile. Bile is then stored in the gallbladder before being released into the small intestine to aid in the digestion and absorption of fats.