The Digestive System

What is it? The digestive or gastrointestinal tract is about 30 feet long. It extends from the mouth to the anus. It contains many parts that work together both mechanically and chemically to help the body use food.

The Digestion Process Two phases: Mechanical Phase Chemical Phase

Mechanical Phase Begins in the mouth. The teeth chew the food and break it down into smaller pieces. These contractions mix food particles and break them into smaller pieces. Then with waves of contractions called peristalsis muscles also push food through the digestive tract.

Interesting Facts Emotions such as sadness, depression, and fear can slow down the peristalsis Anger and aggression can speed up peristalsis.

The Chemical Phase Also begins in the mouth. As you chew food is mixed with saliva, which is a mucus and enzyme containing liquid secreted by the mouth. It moistens food particles helping them move down the esophagus into the stomach. It also begins to break down starches.

The Chemical Phase In the stomach gastric juices containing hydrochloric acid and several enzymes are secreted. These juices break down the food further. An ordinary meal leaves the stomach in about 2 to 3 hours. Carbohydrates first Proteins second Fats third

The Chemical Phase As digestion continues the semiliquid food mass leaves the stomach and enters the small intestine. Here intestinal juices, pancreatic juices, and bile act on the food. They contain enzymes that help break down carbohydrates, proteins, and fats into simple substances the body can absorb and use. Once digestion is complete absorption can take place.

Leftovers Indigestible residue, bile pigments, other waste, and water travel from the small intestine to the large intestine. The large intestine acts as a reservoir. Eventually the body will excrete these materials in the feces.

Absorption The body can absorb water, ethyl alcohol, and simple sugars directly from the stomach. They pass through the stomach walls into the bloodstream. Most absorption takes place in the small intestine. Millions of hair like fingers called villi line the small intestine. They increase the absorptive surface by 600 percent.

Metabolism Is the chemical processes that take place in the cells after the body absorbs nutrients.