The accessory organs are not part of the digestive system but help in digestion. The salivary glands, pancreas, liver, and gallbladder produce different secretions that contain digestive enzymes.
Saliva is a secretion released in the oral cavity. Three main salivary glands produce saliva. These include the parotid glands on the inside of each cheek, the sublingual glands under the tongue, and the submandibular glands on the bottom of the lower jaw. Saliva contains amylase to break down starch, bicarbonate to help neutralize acids, mucus to lubricate food and the mouth, and lysozyme that kills bacteria. Secretion of saliva is regulated by the parasympathetic nervous system.
The pancreas has several functions, one being to release certain enzymes into the lumen of the small intestine as a way to aid in digestion. The pancreas is found in the abdomen behind and beneath the stomach. This organ has two parts: the exocrine pancreas and endocrine pancreas. The exocrine pancreas is composed of specialized cells, each called an acinar cell that produces and releases pancreatic juices into the small intestine. The endocrine pancreas is made of several cells, each called an islet cell, that secretes hormones directly into the bloodstream. Pancreatic juice contains salts, bicarbonate, and digestive enzymes including carboxypeptidase, chymotrypsinogen, amylase, lipase, and nuclease. The pancreas is regulated by neurons and local chemical effects.
The liver is a large organ (weighing approximately three pounds), which has two sections, or lobes. The liver supports digestion by producing bile, a fluid mixture that emulsifies lipids in the small intestine. Bile is stored and concentrated in the gallbladder before being released into the first part of the small intestine, or duodenum. Bile contains bicarbonate, phospholipids, and bile salts that are derived from cholesterol. These components in bile break down fats into small droplets, increasing the surface area that is exposed to enzymatic digestion. The gallbladder is located under the liver. The gallbladder contracts to secrete bile into the common bile duct, sending it to the duodenum. The common bile duct and the pancreatic duct meet at the ampulla of Vater. The sphincter of Oddi is a sphincter that allows pancreatic juices and bile to flow from the pancreas and liver into the small intestine.