ACCESSORY ORGANS OF DIGESTION
The accessory organs of digestion include the
salivary glands, pancreas, liver, and gallbladder. As
stated earlier, during the digestive
process, the accessory organs produce
secretions that assist the organs of
the alimentary canal.
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
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.
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
· 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
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