Digestion Unit 11 Nutrition Kevin Browne Stages of Digestion Four Stages of Digestion • • • • Ingesting Digesting Absorbing Eliminating Stage 1:Ingesting • The starting point of the digestion process. Stage 2: Digesting • Mouth: Mechanical and Chemical digestion begins. • Mechanical digestion is the chewing and breaking food down into smaller pieces • Each small piece of food is a bolus • Saliva lubricates the food, and contains an enzyme, called amylase. • Chemical digestion occurs when amylase begins to break down complex carbohydrates. • Esophagus: as food passes through the pharynx, the epiglottis covers the airway tube. • The food moves on to the esophagus. • The esophagus is a tube that connects the pharynx and the stomach. • The esophagus is long and muscular • The bolus is pushed through the esophagus in a process called peristalsis. Absorbing: Stomach • Your stomach is like a stretchable muscular bag. • Inside the stomach is gastric juice, which is very acidic. • The stomach walls are lined with mucus, that protects the tissue. • Pepsin is an enzyme which breaks down protein, and needs an acidic environment. • The bolus breaks down into a liquid called chyme. Small Intestine • Once the chyme leaves the stomach, it empties into the small intestine. • The first metre is called the duodenum. Digestion is complete after foods leaves. • Within the first 30 cm are ducts that connect to other organs. • Pancreas: produces enzymes • Liver: produces bile. The Large Intestine or Colon • The large intestine is the final part of the digestive tract and is about 1.5 metres long. Any food not already digested makes it here. However, there is normally not much in the way • of nutrients left at this point in the system. Soluble fibre is partly absorbed here, and any water left over from the whole process is re-absorbed here as well. Once water is removed, the waste product becomes harder and forms faeces. Eliminating: The Rectum • Anything reaching the rectum should be purely waste, because the digestive system is very efficient at removing nutrients. • From here, faeces are passed into the anus for expulsion from the body.