How does the gastrointestinal system work?

GASTROINTESTINAL TRACT - Consists of the tract that the swallowed food travels through:

• Mouth - Breaks down food into smaller pieces for easier digestion and nutrient absorption (the food that is swallowed is known as a bolus). The mouth also digests starch chemically.

• Esophagus - Pushes food down to stomach using peristalsis (waves of muscle that push the bolus down)

• Stomach - Contains acid (has a high pH) to digest the food. The food turns into chyme (a liquidy substance). The stomach absorbs very few substances.

• Small intestine - The majority of nutrients are absorbed here, such as proteins and carbohydrates. There are three parts of this intestine; the duodenum, jejunum, and ileum. The difference between these parts is at the cellular level.

• Large intestine - Water and vitamins are absorbed here. This is the final stage of absorption.

• Rectum - A storage place for the feces after they have been through the large intestine.

There are also many sphincters (contractile muscle rings - almost like valves) along the tract that control when and where the food goes.

ACCESSORY ORGANS - Organs that secrete chemicals or helps with digestion in some way:

• Liver - The liver creates bile and secretes many substances to aid with chemical digestion. Most substances from the liver travel to the
  stomach.

• Gallbladder - The gallbladder stores bile that has been produced by the liver.

• Pancreas - The pancreas produces important enzymes and chemicals for digestion. These usually go to the small intestine.