The components that are essential for the successful integration of food into the body; such as, the mouth, esophagus, stomach, small intestines, large intestines, liver, and pancreas; all of which digest ingested (eaten) food or nutritional elements so they can be absorbed into the bloodstream and then these organs also eliminate body wastes.

The various digestive or gastrointestinal-tract systems include the following:

The oral cavity or mouth area:

• The lips form the opening to the mouth.
• When a person eats, the lips hold the food in the mouth and aid the tongue and cheeks to guide food between the teeth for chewing.

The palate that forms the roof of the mouth:


• The hard palate is the bony back part of the palate which is covered with specialized mucous membrane.
• The soft palate is the flexible back part which functions as closing the nasal passage during swallowing to prevent food and liquid from moving up into the nasal cavity.
• The uvula hangs from the free edge of the soft palate and during the swallowing process, it moves up with the soft palate.

The tongue which helps in speech and moves food during chewing and swallowing:


• The top of the tongue is the dorsum which has a tough protective covering and, in some areas, small bumps known as papillae which contain taste buds, which are the sensory receptors for the sense of taste.
• The sublingual part of the tongue has tissues under the tongue that are covered with delicate tissues that are very vascular or containing many blood vessels.
• The presence of the rich blood supply under the tongue makes it good for administering certain medications where they are quickly absorbed into the blood system.
• The lingual frenum attaches the tongue to the bottom of the mouth and limits it movements.

Soft tissues of the mouth:


• The periodontium that consists of the bone and soft tissues that surround and support the teeth.
• The gingiva which is commonly known as the gums are the specialized mucous membrane that surrounds the teeth, covers the bone of the dental arches, and lines the cheeks.

The dental arches:


• The boney parts of the mouth cavity include the maxillary and mandibular arches.
• These formations are commonly referred to as the upper and lower jaws that hold the teeth in position for chewing and speaking.
• At the back of the mouth where the maxillary and mandibular arches come together is call the temporomandibular joint.
• The maxillary arch does not move because it is part of the skull.
• The mandibular arch is a separate bone and it is a moveable part of the joint.

The teeth:


• The natural teeth that are arranged in the upper and lower jaws are called dentition.
• Human dentition includes four types of teeth:
1. Incisors and canines, or cuspids, that make it possible to bite and to tear food apart.
2. Premolars, or bicuspids, and molars that are used for the chewing and the grinding of food.
• Primary dentition, or deciduous dentition, or "baby teeth", contain twenty teeth which are usually lost during childhood which consist of eight incisors, four canines, eight molars, and no premolars; all of which are replaced with the "permanent" teeth.
• Permanent dentition normally has thirty-two teeth which include eight incisors, four canines, eight premolars, and twelve molars.
• After the natural "permanent teeth" have been lost, the condition is called edentulous or "without teeth".
• Occlusion of the teeth refers to the contacts that are made between the chewing surfaces of the lower and upper teeth.
• Any situation that is not a "normal positioning" of the upper teeth against the lower teeth is called "malocclusion".

Salivary glands and saliva:


• Saliva provides liquids for the mouth, begins the process of digestion, and lubricates food during the chewing and swallowing process all of which are provided by three pairs of salivary glands that secrete saliva which is carried by ducts into the mouth.
1. The parotid glands that are located on the face in front of and slightly below each ear, have ducts on the inside of the cheek near the upper molars.
2. The sublingual glands and their ducts are located on the bottom of the mouth are under the tongue.
3. The submandibular glands are located on the bottom of the mouth with their ducts near the mandible.

The pharynx, commonly known as the throat, controls the transportation of air, food, and liquids:


• During swallowing, the soft palate, which is the muscular back part of the roof of the mouth moves up and backward to close off the nasopharynx which prevents food or liquids from going up into the nose.
• There is also the epiglottis that is like a lid located at the base of the tongue and which swings downward and closes off the laryngopharynx so food doesn't go into the trachea (windpipe) and the lungs.

The stomach which is an organ like a sac that is shaped similar to a small bag:


• The stomach is composed of the fundus (upper, rounded part), the body (main section), and antrum (lower portion).
• Rugae are the folds in the mucosa that line the inside of the stomach and the glands that are located inside these folds produce gastric juices, which help to digest food and liquids, and mucus that functions to create a protective coating for the lining of the stomach.
• In addition, there is the pyorus which is the narrow passage that connects the stomach with the small intestine.
• Another section that exists before going into the duodenum is a kind of muscle that controls the flow of digested elements from the stomach.

The small intestine is a coiled organ that is up to twenty feet in length which goes from the pyloric sphincter to the first part of the large intestine and has three sections where food is digested and the nutrients are absorbed into the bloodstream:


1. The duodenum is the first part of the small intestine that extends from the pylorus to the jejunum.
2. The jejunum consists of the middle section of the small intestine and goes from the duodenum to the ileum.
3. Then the last and longest part of the small intestine goes from the jejunum to the cecum of the large intestine.