The mouth is where food first enters the digestive system. The parts of the mouth are the lips and cheeks, gums and teeth, tongue and salivary glands. Together they take food and turn it into a liquid so that it can be swallowed and sent to the stomach.
Lips and Cheeks
The lips form the entry to the mouth and join the gums and cheek muscles. The outer surface of the lips is skin and the inside is a mucus membrane. Lips get their red colour from the network of blood vessels which are visible under the surface. The cheeks are similar to the lips but have a large area of fat under the surface of the skin. At the back of the mouth on the cheeks are glands which release the mucous found in the mouth.
Teeth and Gums
Gums are mucous tissue which hold the teeth in place. The gums have blood vessels at the base of the teeth, which give the teeth nutrients. Teeth are used to hold, tear and chew food so that it can be swallowed. Not all teeth are the same as they do different jobs. Incisors are the front teeth and are used for biting and cutting while our back teeth or molars are used for grinding down our food.
Tongue
When food first enters the mouth the tongue moves it towards the molars so that it can be ground down. The tongue is a muscle and has glands that secrete some of the saliva found in the mouth. It is also covered in taste buds which can sense sweet, sour, salty and bitter flavours in the food. The tongue then sends signals to the brain and it is the combination of these four flavours that give every piece of food its unique flavour. An interesting function of the tongue is that its movement creates a negative pressure in the mouth which lets mammals suckle milk from their mothers.
Salivary Glands
As you eat teeth break food down into smaller pieces which are then mixed with saliva. There are many small salivary glands found on the tongue and cheek but there are also three main pairs. The largest pair are 20-30 grams (0.7-1.0 ounce) while the smallest are 2-3 grams (0.07-0.11 ounces). When your body becomes dehydrated and there is not enough water in the bloodstream it is taken from the salivary glands.
You become thirsty because the mouth is dry from lack of saliva.
Saliva
Saliva is slightly acidic with a pH of 6.7 and dissolves foods so that they can be easily tasted and digested. Saliva is 99% water and contains enzymes which chemically break down the food into its different nutrients. The food then becomes a tasteless watered down mixture so it can pass easily into the stomach. The sight or smell of food can stimulate the nerves that control the flow of saliva, with most people producing two to three pints (0.9-1.4 litres) every day. Saliva can be watery and flow very easily or thicker and flow slowly, depending on the type of food being eaten. Sour foods need more saliva as they are harder to break down, while foods that are already moist and in smaller sections need less saliva.
The substance in saliva that chemically breaks down the food is called ptyalin. When the saliva first comes in contact with the food it breaks down the complex starches into simpler ones. Even when the food reaches the stomach the ptyalin is still acting on the food and making it more digestible.
