Learning Objectives

To understand the anatomy and functions of the accessory digestive organs. For more on the digestive system see Digestive System 1.

Notes, Pictures & Videos

Teeth and Supporting Structures

Teeth Types and Uses and X-rays:
Teeth are designed for eating: the incisors (the four front teeth) for biting, the canines (the eye teeth) for tearing, and the molars and premolars (back teeth) for chewing. The furthest back teeth (the third molars) are commonly known as the wisdom teeth and these do not usually appear in the mouth until the age of 17 to 21 years. These different teeth have evolved functions from both meat eaters such as tigers and lions, and grinders such as horses and cattle because we, and our teeth, are designed to eat both meat and vegetables. In other words, we are omnivorous. The adult mouth has the possibility of Thirty-Two teeth. Four of these are "wisdom teeth". Some people are missing adult teeth which is a congenital birth defect. Other people have extra adult teeth that cause problems and need to be removed. The best diagnostic tool is a panoramic x-ray to show all of the teeth and the jaws and the position of the joint. This can also diagnose cysts, tumors and trauma to the bones. Occlusal x-rays show just the upper jaw or lower jaw and teeth. This shows placement and amount of teeth. Especially used in children. Can also diagnose cysts, tumors and trauma. Individual tooth diagnosis is best when a PA or Periapical x-ray film is used.

Tooth Structure:
Each tooth has a pulp in the core which consists of nerves and blood vessels and this is surrounded by dentin, a hard bone-like substance which is itself covered with enamel over the crown. Enamel is the hardest tissue in the body and has no feeling in it. It is made of calcium crystals (hydroxyapatite), whereas the underlying dentin, which is in contact with the central nerves, is sensitive, and can be painful if exposed to hot or cold or to some foodstuffs like sugar. Variations in enamel is more than just the color. Some people are born with thin or no enamel on their teeth. Some people have pourous marks on their teeth.

Ligaments, Gingiva and TMJ joint:
The teeth are held in the bones of the jaws by ligaments called the periodontium and the bones and the necks of the teeth are covered by gum tissue (the gingiva). When they are healthy the ligaments are constantly tightening to keep the teeth together and to let you know how hard you need to bite when you’re chewing food. The jaw bones are called the maxilla (the top jaw) and the mandible (the bottom jaw). The mandible is a horseshoe shape and joins on to the base of the skull at the temporomandibular joints (TM joints), which lie directly in front of the ears. The TM joints have a cartilage like the knee joint and can occasionally click when you open and close your mouth but, although this may be annoying, it is often harmless. Harmful clicking is when your bite between maxillay and mandible does not fit together correctly creating pain. An orthodontist with a degree, rather than a certificate, is who should help with bite diagnosis. Braces, appliances or surgery may be necessary to correct bite and joint problems.

Teeth and Jaw Bone Growth:
Teeth and biting is what stimulates your jaw bones to grow. Without teeth, such as dentures only or just some missing teeth, the jaw bone is not stimulated to grow and people with dentures may say they do not fit anymore. They need a reline of the surface due to bone shrinkage. Most people think that there is something wrong with the denture. The denture and the dentist is not to blame! It is best to take care of your own teeth. If there is trauma or permanent teeth were not formed, the next best thing is to get a tooth implant. This will continue to stimulate bone and will generally last for 10 or more years with correct care.

Try out your skills with "The Tongue Twister Database!"

Tongue

The tongue consists of four types of taste buds--salty, sweet, sour, and bitter--and is a very maneuverable and pliable arrangement of muscle. It helps to remove, and dislocate food particles in the teeth and shifts food around in the mouth in order to assist with the all important act of swallowing.

The act of swallowing food, which at this place in the system is called a bolus, brings many organs into action. As the top of your tongue presses up against the hard palate , the roof of your mouth, food is shoved to the back of the mouth. This action in turn brings the soft palate and uvula (the place at the very back of the mouth where there is a teardrop shape located) into action. They keep the food from being misguided toward the nose. Once past the soft palate, the food is in the pharynx, a train station with two tracks, one leading to the trachea (windpipe), the other to the esophagus (food tube). The epiglottis projects out from the trachea side and helps to admit free movement of air as it is swallowed and at the same time restricts entrance to the esophagus.

The larynx, provides the epiglottis with most of its muscle for movement. It applies an upward force that helps to relax some tension on the esophagus, so that food enters where it is meant to go, down the esophagus and not down the windpipe. Many people have experienced at some time or another when the swallowing action did not go as it was supposed to. Cough. Cough. Choke. The larynx is for sound production and commonly known as our voice box or vocal cords. It is surrounded by cartilage called thyroid cartilage that forms our "adam's apple".

Salivary Glands

Three pairs of major salivary glands (parotid, submandibular, and sublingual glands) and numerous smaller ones secrete saliva into the oral cavity, where it is mixed with food during mastication (chewing). Saliva contains water, mucus, and enzyme amylase. Functions of saliva include the following:

• It has a cleansing action on the teeth.
• It moistens and lubricates food during mastication and swallowing.
• It dissolves certain molecules so that food can be tasted.
• It begins the chemical digestion of starches through the action of amylase, which breaks down polysaccharides into disaccharides.

Anatomy of the pancreas:

The pancreas is an elongated, tapered organ located across the back of the abdomen, behind the stomach and retroperitoneal. The right side of the organ (called the head) is the widest part of the organ and lies in the curve of the duodenum (the first section of the small intestine). The tapered left side extends slightly upward (called the body of the pancreas) and ends near the spleen (called the tail).
The pancreas is made up of two types of tissue:

• exocrine tissue
  The exocrine tissue secretes digestive enzymes. These enzymes are secreted into a network of ducts that join the main pancreatic duct, which runs the length of the pancreas.

• endocrine tissue
  The endocrine tissue, which consists of the islets of Langerhans, secretes hormones into the bloodstream.

Functions of the pancreas:

The pancreas has digestive and hormonal functions:

• The enzymes secreted by the exocrine tissue in the pancreas help break down carbohydrates, fats, proteins, and acids in the duodenum. These enzymes travel down the pancreatic duct into the bile duct in an inactive form. When they enter the duodenum, they are activated. The exocrine tissue also secretes a bicarbonate to neutralize stomach acid in the duodenum.

• The hormones secreted by the endocrine tissue in the pancreas are insulin and glucagon (which regulate the level of glucose in the blood), and somatostatin (which prevents the release of the other two hormones).
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Anatomy of the liver:

The liver is located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm and on top of the stomach, right kidney, and intestines. Shaped like a triangle, the liver is a dark reddish-brown organ that weighs about three pounds. It is also the largest internal organ of the body.
There are two distinct sources that supply blood to the liver:

• oxygenated blood flows in from the hepatic artery
• nutrient-rich blood flows in from the portal vein

The liver holds about one pint (13 percent) of the body's blood supply at any given moment.
The liver consists of two main lobes, both of which are made up of thousands of lobules divided by the falciform ligament. These lobules are the structural and functional units of the liver and are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct. The hepatic duct transports the bile produced by the liver cells to the gallbladder and duodenum (the first part of the small intestine).

Functions of the liver:

The liver regulates most chemical levels in the blood and excretes a product called "bile," which helps carry away waste products from the liver. All the blood leaving the stomach and intestines passes through the liver. The liver processes this blood and breaks down the nutrients and drugs into forms that are easier to use for the rest of the body. More than 500 vital functions have been identified with the liver. Some of the more well-known functions include:

• Production of bile, which helps carry away waste and break down fats in the small intestine during digestion.
• Production of certain proteins for blood plasma.
• Production of cholesterol and special proteins to help carry fats through the body.
• Conversion of excess glucose into glycogen for storage. (This glycogen can later be converted back to glucose for energy.)
• Regulation of blood levels of amino acids, which form the building blocks of proteins.
• Processing of hemoglobin for use of its iron content. (The liver stores iron.)
• Conversion of poisonous ammonia to urea. (Urea is one of the end products of protein metabolism that is excreted in the urine.)
• Filtering the blood of drugs and other poisonous substances.
• Regulating blood clotting.
• Resisting infections by producing immune factors and removing bacteria from the blood stream.

When the liver has broken down harmful substances, its by-products are excreted into the bile or blood. Bile by-products enter the intestine and ultimately leave the body in the feces. Blood by-products are filtered out by the kidneys, and leave the body in the form of urine.

Gallbladder

The gallbladder is a pear-shaped sac that is attached to the visceral surface of the liver by the cystic duct. The principal function of the gallbladder is to serve as a storage reservoir for bile. Bile is a yellowish-green fluid produced by liver cells. The main components of bile are water, bile salts, bile pigments, and cholesterol. The bile can then leave the gallbladder via the cystic duct which connects the the gallbladder to the common bile duct.