This is Bob. He has a digestive system just like you! One of his favorite foods to eat is pizza, but what happens to the pizza when he eats it? Let's find out.

The pizza will travel through the digestive system. The digestive system consists of multiple organs that work together to digest food, absorb nutrients, and eliminate waste. Most organs make up the gastrointestinal tract, but the ones that don't are called accessory organs.

So where does it all begin? It actually starts at your mouth. Bob uses his teeth, which start mechanical digestion by grinding down the pizza into small pieces. His tongue helps to push the pizza back into his pharynx, or throat. Saliva also breaks the pizza down chemically.

The pizza then goes through the esophagus, which is a long, muscular tube lined with mucus, that connects the mouth with the stomach. Peristalsis occurs in the esophagus, as it pushes the food down through involuntary muscle movements.

Once pushed through the esophagus, the pizza will make its way to the stomach. The stomach is a muscular pouch that can hold one to three liters of food. The walls of the stomach are lined with mucus to protect them from acid. The stomach churns to break down food mechanically and acid in the stomach breaks the food down chemically.

What once was a piece of pizza, makes its way from the stomach to the small intestine. There are three parts of the small intestine. They are called the duodenum, jejunum, and ileum. The duodenum is a muscular tube that is lined with villi. Each villus looks like a tiny finger and allows water and nutrients to pass through the walls of the duodenum. The jejunum and ileum make up most of the small intestine and can be as long as 22 feet. Villi along the walls of the jejunum and ileum also absorb nutrients and water. In fact, 90% of absorption happens in the small intestine.

The large intestine absorbs water and Vitamin K from the pizza. Bacteria in the large intestine helps break down fiber and other materials. 

The pizza will never travel through the pancreas, but it still has an important role. The pancreas produces digestive enzymes that help to break down the pizza.

In our body, there are different enzymes. Enzymes help to break down food. Amylase breaks down carbohydrates into monosaccharides,  trypsin breaks down proteins into amino acids, and lipase breaks down lipids into fatty acids and glycerol. These enzymes are located in the pancreas.

The liver and gallbladder work together to help digest the pizza as well. The liver secretes bile into small canals that lead to the common bile duct. From there the bile goes through the gallbladder, then to the small intestine. Bile helps break down food.