pizza: . Think about a slice of cheese pizza. Starting at the mouth, trace the path that the pizza will take through the digestive system. Explain what is happening to the pizza at each step, matching the key digestive processes with the 3 main components of pizza: crust, cheese and sauce. Describe when, where and how each component is digested.|||Sorry... This is kinda long, because it's very detailed. This is the general idea of the complete digestion in the body. In this case, just subsitute 'pizza' in it. The Mouth: ----------------------------------- The process of mechanical digestion begins as you take your first bite of food. Your teeth carry out the first stage of mechanical digestion. Your centre teeth/incisors, cut the food into bit-sized pieces. On either side of the incisors are sharp and pointy teeth called canines. These teeth tear and slash the food in your mouth into smaller pieces. Behind the canines are the premolars and molars, which crush and grind the food. As the teeth do their work, saliva mixes with the pieces of food, moistening them into one slippery mass. When you eat a candy, it tastes sweet. It does because a chemical in the saliva has broken down the starch in the candy into sugar molecules. The breakdown of complex molecules into simpler ones-has taken place. This is called chemical digestion, and it is accomplished by enzymes.[A protein that speeds up chemical reactions in the body] ----------------------------------- The Esophagus: ----------------------------------- As you swallow, muscles in your throat move the food downward. While this happens, a flap of tissue called the epiglottis seals off your windpipe, preventing the food from entering. After that, food goes into the esophagus, a muscular tube that connects the mouth to the stomach. The esophagus is lined with mucus. Mucus is a thick, slippery substance produced by the body. Food only remains in the esophagus for about 10seconds. After food enters the esophagus, contractions of smooth muscles push the food toward the stomach. These involuntary waves of muscle contraction are called peristalsis. --------------------------------------… The Stomach: --------------------------------------… Food enters the stomach after it leaves the esophagus. Stomach is a J-shaped, muscular pouch located in the abdomen. As you eat, your stomach ach expands to hold all of the food that you swallow. An average adult's stomach holds about 2-2.5 litres of food. Three strong layers of muscle contract to produce a churning motion. This action squeezes the food, mixing it with fluids. The churning of the stomach mixes food with digestive juice, a fluid produced by cells in the lining of the stomach. Digestive juice contains the enzyme pepsin that breaks down proteins in your food into amino acids. Hydrochloric acid keeps the stomach functioning properly: keeping the stomach an acidic environment→1. Pepsin works best in an acidic environment. 2.→ This very strong acid kills many bacteria that you swallow along with your food. Food remains in the stomach until all of the solid material has been broken down into liquid form. Proteins will be chemically digested into chains of amino acids. The food, now a thick liquid, is released into the next part of the liquid, is released into the next part of the digestive system→ That is where final chemical digestion and absorption will take place. --------------------------------------… The Small Intestine: --------------------------------------… After the thick liquid leaves the stomach, it enters the small intestine. It is at about 6metres. It makes up 2/3 of the digestive system. It is called 'The SMALL Intestine' because it has a small diameter→It is only about 2-3 centimetres wide. As the liquid moves into the small intestine, it mixes with enzymes and secretions. They are produced by 3 different organs→The small intestine, the liver, and the pancreas. The liver and the pancreas deliver their substances to the small intestine through small tubes. The liver produces bile→which breaks up the fat particles. Bile flows into the gallbladder, storing bile until the small intestine needs it.[Bile is not an enzyme, because it doesn't chemically digest foods. It breaks up large fat particles into smaller droplets]→The droplets will be digested by enzymes produced by the pancreas. The small nutrient molecules are ready to be absorbed by the body. Millions of tiny finger-shaped structures absorb nutrient molecules. Nutrients pass from cells on the surface of a villus into blood vessels. --------------------------------------… The Large Intestine: --------------------------------------… By the time material reaches the end of the small intestine, most nutrients have been absorbed. The remaining material moves from the S.I. into the L.I.. The large intestine is the last section of the digestive system. It is about 1&1/2metres long. The L.I. contains bacteria feeding on the material passing through. The bacteria normally do not cause disease. They are actually helpful because they make certain vitamins, including vitamin K. The material entering the L.I. contains water and undigested food such as fibre. As the material moves through the L.I., water is absorbed into the bloodstream. The remaining material is readied for elimination from the body. ------------------------------- The large intestine ends in a short tube called the rectum. Here waste material is compressed into a solid form. This material is eliminated from the body through the anus, a muscular opening at the end of the rectum. ------------------------------ :)