Breaking Down Food
Food is digested during a journey through a canal some 10 meters long, starting at the mouth and ending at the anus. This gastrointestinal tract, or alimentary canal, bulges in places such as the stomach and colon but is uninterrupted.
Even before food reaches the mouth the body prepares to break it down into its basic components, mainly carbohydrates (sugars and starches), fats, and protein. The sight or smell of food or the sounds of a meal being prepared will stimulate the parotid and other glands to secrete saliva into the mouth in anticipation of what is to come. Saliva contains an enzyme, or organic catalyst, which assists chemical changes. Called salivary amylase, it starts the breakdown of starches. Saliva also lubricates. Food during chewing so that it can be swallowed more easily. The salivary glands produce from a liter to a liter and a half of fluid every day for digestion and to moisten the mucous membrane of the mouth and lubricate the tongue and lips during a speech. Excess production is swallowed and reabsorbed.
Chewing merely prepares food for swallowing. It serves no digestive purpose. When the teeth have broken food into small lumps., the tongue rolls them into a bolus or soft mass that can be swallowed. Any conscious influence on digestion ceases once the food is swallowed. We are blissfully unaware of most of the following events as the bolus slips into the throat and the unconscious centers of the brain take over.
