What Are the Characteristics of the Digestive System?

When you smell food that makes your mouth water, the digestive process has begun. Salivating is the first signal your brain sends to your stomach to prepare for digestion, a process that can take up to 20 hours or more after you have eaten your favorite meal. Digestion is one of the most essential of the body's functions, helping to break down the food you eat into nutrients that power your body.

Mouth

• Your mouth acts as the gatekeeper to your digestive system. If you don't eat or you spit out food that is not palatable, digestion cannot begin. When you think of food, smell food or see food, salivary glands beneath your tongue produce saliva, which also helps to moisten the food you eat to make it easier to enter your esophagus. Saliva also begins the process of extracting nutrients from food through the secretion of amylase, an enzyme that breaks down carbohydrates.

Esophagus

• From your mouth, food passes into your esophagus, which is a tube of muscle that extends from your throat down into your stomach. The esophagus acts as a kind of "conductor" for the food and includes a safety valve known as an esophageal sphincter that prevents you from regurgitating food into the esophagus. Food is passed through your esophagus into your stomach through a series of muscle contractions known as peristalsis.

Stomach and Small Intestine

• Your stomach is a powerful mixer and grinder that reduces food into a gelatinous liquid referred to as chyme, which then passes into your small intestine. Three sections make up the small intestine: the duodenum, jejunum and ileum. An adult's small intestine is between 20 and 23 feet long, and is lined with tiny, hairlike projections known as villi, that help absorb nutrients from food. The duodenum performs the bulk of digestion, aided by the pancreas, which secretes enzymes; the liver, which creates bile to clean blood and help absorb fat; and the gallbladder, which stores the bile the liver produces. The jejunum and ileum are primarily responsible absorbing nutrients.

Large Intestine

• The remnants of food that is not digested passes from your small intestine into your large intestine through a valve that blocks food from going back into the small intestine. The large intestine has three sections: the cecum, colon and rectum. The cecum is a sac that joins the small and large intestine. The colon absorbs any remaining water from the food that is not digested, creating solid waste known as stool or feces. Once the colon is filled with stool, it expels this waste into your rectum, then your anus.