18 - Digestive System: Glands

Abstract

The extramural glands of the digestive system produce materials that aid the digestive process and deliver them to the oral cavity and duodenum. The extramural glands are the major salivary glands (parotid, submandibular, and sublingual glands), whose ducts lead into the oral cavity and the pancreas and liver (and its associated gallbladder), whose common bile duct enters the duodenum. The salivary glands manufacture saliva that not only moistens the masticated food but also produces enzymes that begin the digestive process. The pancreas is an exocrine gland that produces enzymes that digest fats, proteins, and carbohydrates and a bicarbonate-rich fluid that neutralizes the acidic chyme. The pancreas is also an endocrine gland that manufactures a series of hormones, including insulin, gastrin, and glucagon. The exocrine secretion of the liver, known as bile, is stored and concentrated in the gallbladder until it is needed by the duodenum, where bile emulsifies lipids so that they can be digested. The endocrine secretions of the liver enter the vascular system and are necessary to maintain the life of the individual. The liver also functions in detoxifying blood-borne toxins, manufacturing factors required for coagulation, and producing protein components of blood as well as vitamins necessary for life.