Salivary Glands
The salivary glands are located in the mouth (fig. 1-53). Within the salivary glands are two types of secretory cells, serous cells and mucous cells. The serous cells produce a watery fluid that contains a digestive juice called amylase. Amylase splits starch and glycerol into complex sugars. The mucous cells secrete a thick, sticky liquid called mucus. Mucus binds food particles together and acts to lubricate during swallowing. The fluids produced by the serous and mucous cells combine to form saliva. Approximately 1 liter of saliva is secreted daily.

Pancreas
The pancreas is a large, elongated gland lying posteriorly to the stomach (fig. 1-53). As discussed earlier in "The Endocrine System," the pancreas has two functions: It serves both the endocrine system and the digestive system. The digestive portion of the pancreas produces digestive juices (amylase, proteinase, and lipase) that are secreted through the pancreatic duct to the duodenum. These digestive juices break down carbohydrates (amylase), proteins (proteinase), and fats (lipase) into simpler compounds.

Liver
The liver is the largest gland in the body. It is located in the upper abdomen on the right side, just under the diaphragm and superior to the duodenum and pylorus (fig. 1-53).

Of the liver's many functions, the following are important to remember:

It metabolizes carbohydrates, fats, and proteins preparatory to their use or excretion.

It forms and excretes bile salts and pigment from bilirubin, a waste product of red blood cell destruction.
It stores blood; glycogen; vitamins A, D, and B12; and iron.

It detoxifies the end products of protein digestion and drugs.
It produces antibodies and essential elements of the blood-clotting mechanism.

Gallbladder
The gallbladder is a pear-shaped sac, usually stained dark green by the bile it contains. It is located in the hollow underside of the liver (fig. 1-53). Its duct, the cystic duct, joins the hepatic duct from the liver to form the common bile duct, which enters the duodenum. The gallbladder receives bile from the liver and then concentrates and stores it. It secretes bile when the small intestine is stimulated by the entrance of fats.