Photograph by SPL/Photo Researchers, Inc.
Cone-shaped tongue papillae, seen here in a colored scanning electron micrograph, contain nerve endings that receive and transmit touch sensations to the brain. As we begin chewing, the tongue shapes food in a ball-shaped bolus for swallowing.
Inside the Human Mouth
Photograph by Lennart Nilsson
Inside the mouth, shown magnified here, teeth, tongue, and saliva work together to physically and chemically break down food. Humans produce up to 3 pints (1.4 liters) of saliva daily, and chemical enzymes in the saliva play a major role in disintegrating starchy foods.
Man Eating a Burger
Photograph by Steve Niedorf Photography
A man prepares to eat his lunch, a hamburger. The digestive system helps break down complex meals into the constituent parts the body can use: carbohydrates, proteins, fats, vitamins, and minerals.
Small Intestine Blood Vessels
Photograph by Susumu Nishinaga
This colored scanning micrograph shows a cast of blood vessels from the external wall of the small intestine. Measuring about 22 feet (6.7 meters) in length, the small intestine performs most of the major digestion and absorption of nutrients. The walls of the small intestine are lined with millions of projections called villi, which absorb and transmit nutrients into the bloodstream.
Illustration by PureStock
Once food is swallowed, it passes through the esophagus into the stomach, the pink organ shown here above the yellow pancreas. A large, muscular chamber, the stomach produces digestive juices like pepsin, lipase, and hydrochloric acid, which digest and dissolve stomach contents.
Lower Digestive Organs
Image by Anatomical Travelogue/Science Photo Library
This image shows the lower digestive organs, including liver and stomach (enclosed by the rib cage) and the small and large intestines. After the small intestine absorbs food nutrients, leftover waste passes into the large intestine, where it's worked on by billions of harmless bacteria and mixed with dead cells to form solid feces. The feces are moved into the rectum to await expulsion.
Photograph by Barry Slaven
For the amounts of food it is constantly processing, the digestive system is an incredibly efficient machine, but problems can arise. Here, a surgeon performs a cyst gastrostomy, the removal of non-cancerous growths from the pancreas. The growths can form after a bout of pancreatitis.
Explore More From Nat Geo
Meet these visionary, young trailblazers from around the world.
Follow mountaineer Conrad Anker, photographer Cory Richards, and their team as they attempt the West Ridge route in the alpine style, carrying all their own food, shelter, and equipment.
National Geographic Magazine
The space-weather forecast for the next few years: solar storms, with a chance of catastrophic blackouts on Earth. Are we prepared?
Archaeologists and artists, armed with the latest tools and techniques, are bringing the life-size army of painted clay soldiers back to life.
Each month, National Geographic magazine features breathtaking photographs in Visions of Earth. Browse through visions of the world as seen through a photographer's eye.
Shop Our Space Collection
The updated companion book to Carl Sagan's Cosmos, featuring a new forward by Neil deGrasse Tyson is now available. Proceeds support our mission programs, which protect species, habitats, and cultures.