The mouth starts the digestion process by breaking food down into a more easily digestible form. It does this through a combination of mechanical and chemical digestion.

After people take food in through the mouth, it moves down the throat, also known as the pharynx. It then passes through the esophagus and into the stomach.

Read on to learn more about the biology of the mouth and its role in digestion. This article also explains the functions of other parts of the digestive system.

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The mouth is the beginning of the gastrointestinal (GI) tract. A person’s GI tract comprises hollow organs that connect. The tract is around 8–9 meters long and stretches from the mouth to the anus.

The mouth is made up of several parts that help with digestion. These parts have various functions.

The first stage of digestion is ingestion, where a person puts food into their mouth with their hands or another utensil.

Chewing, which doctors may call mastication, is the start of mechanical digestion. This is the process through which the mouth breaks large pieces of food down into smaller ones.


A person’s jaws consist of an upper jaw, the maxilla, and a lower jaw, the mandible. When eating, people separate their jaws to allow food into the mouth.

The lips contain sensory receptors that help assess food texture and temperature. The lips and cheeks help keep food in place inside the mouth. Muscles attached to the jaws allow them to move up and down to chew.

The jaws contain teeth people use to cut, tear, crush, and grind food. A primary set of teeth, or milk teeth, contains 20. An adult set contains 32 teeth. The cheeks help move food between the teeth for chewing.

The tongue is a large muscle that has various roles in digestion, such as:

  • sucking food
  • moving food between the teeth
  • aiding with swallowing by pushing chewed food to the back of the throat
  • encouraging the production of saliva, also known as spit
  • nutrient absorption via its underside

The tongue also contains many small bumps on its surface called papillae, which have two different functions.

Mechanical papillae allow a person to feel food texture and form. Taste papillae contain taste buds, which allow a person to taste their food. Certain tastes encourage the production of saliva and stomach acid, aiding digestion.

During chewing, saliva mixes with food and helps soften and break it down. Saliva also lubricates food particles and makes them easier to swallow.

When food and saliva mix, they form a bolus. This is what a person swallows after chewing.


Salivary glands produce saliva, which is made up of the following substances that help with the chemical digestion of food:

  • water
  • mucus
  • the enzymes amylase and lingual lipase, which help break down starch and fats
  • sodium
  • potassium
  • calcium
  • bicarbonate

A person has three pairs of large salivary glands in the following locations in their mouth:

  • parotid glands in front of and underneath the ears
  • submandibular glands under the mandible
  • sublingual glands under the tongue

The mouth also contains hundreds of smaller salivary glands.

When chewing, a person’s tongue compresses food against the mouth’s two palates. This helps form the bolus, which they can then swallow.


The hard palate is the roof of the mouth. The soft palate is behind this, leading into the throat. It helps prevent food from entering the nasal cavity.

Once a person has finished chewing their food, the tongue pushes the bolus into the throat. From there, it travels down the esophagus and into the stomach.

The following table shows the roles that other organs play in digestion:

StomachFurther breaks down food using acid and enzymes.
PancreasMakes digestive juice to break down carbohydrates, fats, and proteins that the body secretes into the small intestine.
LiverProduces bile, a digestive juice that breaks down fats and certain vitamins.
GallbladderStores bile and secretes it into the small intestine when required.
Small intestineForms a digestive juice to mix with the bile and pancreatic juice to finalize the breakdown of fats, carbohydrates, and proteins. Absorbs water and certain nutrients.
Large intestineAbsorbs more water from the GI tract into the bloodstream. Breaks down remaining nutrients to make vitamin K. Any remaining waste products become stool.
RectumStores stool until it the body excretes it via the anus.

Below are answers to some commonly asked questions about the role of the mouth in digestion.

What digestive processes is the mouth involved in?

The mouth is involved in the following four processes:

  • ingestion
  • mechanical digestion
  • chemical digestion
  • nutrient absorption

Which digestive enzymes are in the mouth?

A person’s mouth contains the enzymes amylase and lingual lipase, which help break down starch and fats.

The mouth is an important part of the digestive process. Digestion begins in a person’s mouth, which breaks down food into smaller particles.

Once a person has finished chewing, their food can pass into the esophagus and the stomach. The gastrointestinal tract processes food further before the anus excretes any waste.