The digestive system is a complex organ system located throughout most of the body, mainly within the trunk. The organs of the digestive system are positioned in the head, neck, thoracic and abdominal cavities and pelvis. Therefore, it is one of the largest organ systems of the human body. 

The digestive system includes a series of hollow organs connected to each other, extending from the mouth to the anus. The organs of the digestive system provide functions that facilitate digestion, such as mechanical and chemical food processing, absorption of nutrients and excretion of undigested remains.

Overall, the digestive system is composed of two main parts - the gastrointestinal tract (also known as the alimentary tract or digestive tract) and the accessory organs. 

Accessory organs of digestive tract

The accessory organs of the digestive tract have a role in digestion, and they mostly include various glandular organs that secrete substances needed for chemical food processing. It is important to mention that the food does not pass through the accessory organs. Instead, the accessory organs of the digestive system are connected to the gastrointestinal tract via various ducts.

The minor and major (parotid, submandibular, and sublingual) salivary glands are classified as the accessory organs of the digestive tract. They are a group of exocrine glands that are located within the soft tissue of the head and neck near or within the oral cavity. They produce and excrete a substance called saliva, which is a mixture of water, electrolytes and enzymes. Saliva contributes to digestion by moistening and lubricating food in the oral cavity and beginning the digestion process. All salivary glands excrete saliva in the oral cavity via their ducts.

Besides the salivary glands, the liver (Read more!) is also classified as an accessory organ of the digestive system. It is the largest gland, and it produces and secretes a greenish-yellow fluid called bile. The main functions of the bile include aiding in digestion and absorption of lipids and neutralization of gastric acid. 

The bile is stored and concentrated in a pear-shaped sac-like organ called the gallbladder (Read more!) and further released into the first part of the small intestine via the biliary tree. The biliary tree (biliary tract) is a system of ducts that collect and transport bile from the liver to the duodenum. These structures are adjacent and related to the liver, so they are also classified as accessory organs of the digestive system. 

The pancreas (Read more!) is another accessory organ of the digestive system. It produces pancreatic juice containing enzymes that break down fats (lipases), proteins (proteases) and carbohydrates (amylases). Like the bile, the pancreatic juice is also released into the duodenum. 

Note: The tongue and teeth are also considered accessory organs of the digestive tract. The teeth provide mechanical food processing by chewing, while the tongue assists teeth and also provides sensory analysis.