How Digestion Works Step by Step

The order in which food progresses through the digestive system is as follows: the mouth, esophagus, lower esophageal sphincter, stomach, small intestine, large intestine (colon), and rectum.

Digestion is the process by which your body breaks down the foods you eat into the nutrients such as proteins, fats, carbohydrates, vitamins, minerals, and water that the body needs for survival. 

The digestive system breaks down these nutrients into smaller components that the body can use for energy, growth, and cell repair.

• Proteins break down into amino acids
• Fats break down into fatty acids and glycerol
• Carbohydrates break down into simple sugars

Foods move through the gastrointestinal (GI) tract, which runs from the mouth through the anus. Food progresses through the digestive system as follows: 

• Mouth
  • The first part of the digestive system
  • Foods you eat are chewed and saliva produced by the salivary glands helps moisten food and enzymes break down starches
  • The tongue helps push food into the throat
  • The epiglottis, a small flap of tissue, folds over the airway to prevent choking as the food passes into the esophagus
• Esophagus
  • This is the tube that runs from the mouth to the stomach
  • Foods are swallowed and a process called peristalsis moves the food and liquid through the gastrointestinal tract 
• Lower esophageal sphincter
  • At the end of the esophagus is a ring-like muscle that allows food to pass into the stomach
  • This sphincter usually remains closed to prevent the contents of the stomach from flowing back up into the esophagus 
• Stomach
  • The upper muscle in the stomach relaxes to let food enter, and the lower muscle mixes food with digestive juice
  • Stomach acid and enzymes help break down proteins
  • Stomach muscles mix food with these digestive juices 
  • The contents of the stomach, called chyme, are emptied into the small intestine
• Small intestine
  • Peristalsis moves food and liquid through the small intestine
  • Digestive fluids and enzymes in the small intestine further break down carbohydrates, proteins, and carbohydrates
  • The walls of the small intestine absorb water with other nutrients from the bloodstream to help break down food
  • While in the small intestine, digestive juices from the pancreas, liver, and gallbladder mix in to aid in digestion
    • The pancreas secretes pancreatic enzymes delivered to the small intestine through ducts to break down carbohydrates, fats, and proteins
    • The liver secretes bile acids via bile ducts that help break down fats and some vitamins
    • The gallbladder stores bile between meals, and after you eat the gallbladder pushes bile through the bile ducts into the small intestine
• Large intestine (colon)
  • More water moves from the GI tract into the bloodstream
  • Bacteria help break down leftover nutrients and produce vitamin K
  • Waste products from the digestive process such as undigested food, fluids, and older cells lining the digestive tract are changed from liquid into the stool
  • Peristalsis helps move stool into the rectum
• Rectum
  • The end of the large intestine
  • The stool is stored until it is pushed out of the anus during a bowel movement