Introduction: Digestive System

The digestive organs are many and varied, ranging from those of the digestive tube, to accessory glands, to those of the oral cavity. Major functions of the digestive system include transport of ingested water and food, secretion of fluids, electrolytes, and digestive enzymes; digestion and absorption of digested products; and excretion of indigestible remains. The digestive system can be broken down into three sections: oral cavity and associated structures, esophagus and gastrointestinal tract, and liver, gallbladder, and pancreas.

Beginning with the oral cavity and associated structures, the tongue is covered by papillae in the dorsal surface. There are four types of papillae and they are: filiform, fungiform, circumvallate, and foliate. There are three major salivary glands that are paired glands with ducts that empty into the oral cavity. They consistsof the parotid, submandibular, and sublingual glands.

Moving along to the esophagus and the gastrointestinal tract, we find the portion of the alimentary canal that extends from the proximal part of the esophagus to the distal part of anal canal which is a hollow tube of varying diameter. Its wall is formed by four distinctive layers. The layers are: the mucosa, submucosa, muscularis externa, and the serosa or adventitia. The esophagus is a fixed muscular tube that delivers food and liquid from the pharynx to the stomach. The stomach receives the bolus of macerated food from the esophagus and is divided into three regions. The small intestine is the principle site for the digestion of food and absorption of the products of digestion. It is divided anatomically into three portions. The large intestine comprises the cecum, vermiform appendix, colon, rectum, and anal canal. The colon can be divided anatomically into four portions.

Now we come to the glandular tissue of the digestive tract. This consists of the liver and pancreas and then there is the gallbladder.