Anatomy of the Accessory Organs
Learning Objective: Examine the anatomy of the accessory organs.
   Accessory organs have a role in digestive activities, though they are not part of the gastrointestinal tract. Accessory organs include the salivary glands, liver, gallbladder, and pancreas. These structures secrete fluids into the GI tract, aiding in digestion. Each of these accessory organs will be discussed in the following sections.
Salivary Glands
Learning Objective: Describe the anatomy of the large intestine.
   Three pairs of salivary glands are found in the mouth. The parotid glands are near the ear in the cheeks. The submandibular glands are on the floor of the mouth, and the sublingual glands are under the tongue. These glands produce and secrete saliva, which mixes with the food eaten. Saliva not only moistens the food but also aids in the breakdown and swallowing of food. Saliva contains salivary amylase, an enzyme that will be discussed later in the chapter.
Liver
Learning Objective: Describe the anatomy of the large intestine.
   The liver is one of the largest organs in the body and is located just below the diaphragm, in the right hypochondriac and epigastric regions (see FIGURE 19.2). The liver is divided into two major lobes and two smaller lobes.
The hepatic artery brings oxygenated blood to the liver. The hepatic portal vein brings blood from the digestive tract, which can contain nutrients, medications, alcohol, and toxic substances. These substances are filtered from the blood and are processed, stored, changed, detoxified, and returned to the blood or eliminated in the stool. Besides these roles, the liver has additional important functions:
        • Producing plasma proteins (e.g., albumin and blood clotting factors).
• Breaking down old or damaged blood cells.
        • Breaking down proteins and fats and producing energy.
        • Producing up to a liter of bile a day. Bile contains bilirubin (a breakdown product of red blood cells), bile acids or salts, cholesterol, water, salts (e.g., sodium, potassium), and metals (e.g., copper). Bile is stored in the gallbladder until it is secreted into the duodenum. Bile breaks down fats into fatty acids.
        • Removing extra minerals (e.g., iron and copper), vitamins (B12, A, D, and K), and glucose from the blood and storing them in the liver. The liver releases them into the blood when needed. (For instance, the liver stores extra glucose as glycogen. When the blood glucose level decreases, the liver breaks down the glycogen and releases the glucose into the blood.)
        • Manufacturing triglycerides and cholesterol.
19.4 Critical Thinking Application
Keith is amazed at all of the activities that occur in the liver. List at least four roles of the liver.
Gallbladder
Learning Objective: Describe the anatomy of the large intestine.
   The gallbladder (GB) is found in a small area on the underside of the liver (see FIGURE 19.2). The gallbladder stores and concentrates bile. The bile is made by the liver and then flows through the common bile duct to smaller ducts before going into the gallbladder, where it is stored. When a person eats, the gallbladder contracts and squeezes the bile through the bile duct and into the common bile duct before emptying into the duodenum. If gallbladder emptying is delayed (as in pregnancy), gallstone formation can occur.
Pancreas
Learning Objective: Describe the anatomy of the large intestine.
   The pancreas is a gland found behind the stomach and in front of the spine (see FIGURE 19.2). It is about 6 to 10 inches long. The pancreas has two main roles:
        • Exocrine function: About 95% of the pancreas is made up of exocrine tissue that produces digestive enzymes. These enzymes are released into the duodenum.
        • Endocrine function: About 5% of the pancreas is made up of endocrine cells, called islets of Langerhans, which make hormones (e.g., insulin) that regulate blood sugar and pancreatic secretions. (See Chapter 24 for additional details.)
   The pancreatic enzymes created in the exocrine tissue include trypsin, chymotrypsin, amylase, and lipase. When food enters the stomach, pancreatic enzymes and sodium bicarbonate are released into the main pancreatic duct. This duct joins the common bile duct to form the ampulla of Vater (also called the hepatopancreatic duct or ampulla), which is located at the duodenum.