It begins with mastication, where the ingested food is broken down mechanically into smaller pieces through chewing and the use of teeth. Saliva lubricates and loosen the foodstuff into a bolus. Once this bolus is swallowed it is propelled through the GI tract via peristalsis. In the stomach, the the bolus is churned and liquefied through muscular stomach contractions, hydrolyzing enzymes and acids. This partially digested volume is called chyme. Once the chyme hits the small intestine digestive secretions from the accessory organs are mixed in through segmentation the back and forth muscular contractions which mix and push through the volume through the small intestine to the large intestine. In the large intestine the volume is dehydrated and compacted, and turned into feces. The feces are defecated, eliminated from the GI tract, through the anus.
Oral cavity
The oral cavity is the is where digestion begins. The teeth and tongue mechanically digest the food into smaller bits, while the salivary glands moisten and lubricate the ingested food. The saliva contains digestive enzymes, lysozyme, antibodies (IgA) and other proteins / ions. Amylase is often cited as the start of chemical digestion. Ptyalin (salivary amylase), converts starch a oligosaccharide into a smaller disaccharide maltose.
Before the bolus can enter the esophagus it must traverse the pharynx. The pharynx can be broken down into 3 sections, the: nasopharynx, oropharynx, and laryngopharynx. Unless food is inhaled through the nose, the bolus never sees the nasopharynx. (**remeber F-arynx is First, before larynx)
The esophagus is a long muscular tube that connects the larygopharnyx (pharynx) to the to the stomach. The esophagus passed through the diaphragm, the opening is called the esophageal hiatus. Rhythmic smooth muscle contractions, called peristalsis propel the bolus downward. Two sphincters, the upper esophageal sphincter and lower esophageal sphincter (Cardiac sphincter), circular muscles that surround the esophagus, further control entry of the bolus into the stomach.