Anatomy
The alimentary canal, also known as the digestive tract, is the pathway by which food enters and is expelled from the body. It begins at the mouth, then follows to the pharynx, esophagus, stomach, small intestine, large intestine, and ends at the anus.
The main structures of the mouth, or oral cavity, are the teeth, tongue, and palate. The teeth tear and grind food down so that it is small enough to proceed through digestion, this is called bolus. The tongue is a large and powerful muscle that helps mix food, and houses sensory receptors for taste. The lingual frenulum is a fold of mucosa that secures the tongue to the floor of the mouth. Lastly, the palate separates the oral cavity from the nasal cavity, allowing separate passages for air and food. The mouths moist environment, provided by mucous membranes and salivary glands, aid in softening food and facilitate swallowing.
The pharynx, commonly called the throat, has three main sections. The first section is the nasopharynx, which makes up the back of the nasal cavity. It connects to the second region, the oropharynx, by a passage called the isthmus. The oropharynx begins at the back of the mouth and continues down to the epiglottis, a flap of tissue that covers the air passage to the lungs and directs food to the esophagus. The third region, the laryngopharynx, which begins at the epiglottis and leads to the esophagus, regulates the passage of air and food.
The next stop is the esophagus, which can expand or contract to allow the passage of food. Each end of the esophagus is closed off by muscular constrictions, called sphincters. At the anterior end is the upper esophageal sphincter. At the distal end of the esophagus is the lower esophageal sphincter. The mouth, pharynx, and esophagus are lined with nonkeratinized type stratified squamous epithelium, which protects from abrasion and have