1. How it works!

2. Enzymes are necessary Biological catalysts – globular proteins which will increase reaction rates due to the lowering of activation energy – now the reaction does not require as much energy nor as high temperatures so proteins will not be denatured and cells not damaged Biological catalysts are released from GLANDS along the digestive tract and some from organs outside the tract as well Since they break down larger molecules they are called Catabolic reactions http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/ animation__how_enzymes_work.htmlhttp://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/ animation__how_enzymes_work.html

3. Mouth And Esophagus The Mouth is the site of Mechanical Digestion. The process of chewing breaks down the large chunks of food The salivary glands release enzymes like salivary amylase that break down large carbohydrate molecules (starch) into smaller units A bolus is created and by the use of the tongue and muscles – it is swallowed The epiglottis closes over so the bolus passes to the esophagus and not the trachea and lungs Peristalic muscle contractions push the bolus toward the stomach through the cardiac sphincter

4. The Stomach Mechanical digestion occurs when muscular contractions churn the contents. There is a high content of HCl – hydrochloric acid that breaks down food and kills bacteria The enzyme pepsin begins the breakdown of proteins in the low pH environment (pH = 2 or 3) As the wall of the stomach is stretched signals are sent to release the enzymes – pepsinogen is the precursor to pepsin The gastric pits also release mucous and the gastric acids. The mucous is for protection for the wall lining of the stomach There are both circular muscles and longitudinal muscles present

5. The Small Intestine – The duodenum Bile is made in the liver and released from the bile duct and is used to emulsify fats and increase the pH of the contents Pancreatic amylase is released from the pancreas to continue the breakdown of the smaller carbohydrate chains Trypsin is released to further breakdown the proteins to amino acids Digestion is completed here The jejunum also will release digestive enzymes and absorption takes place in the ileum The ileum has massive amounts of finger- like projections called villi Peristalsis keeps the mixture of both digested and undigested food moving through the small intestine toward the large intestine where the ileum spills into

6. The Villi Absorption occurs through the villi of the small intestine There is a single layer of surface cells so absorption is easier due to a short diffusion path The molecules pass from the lumen of the small intestine and are carried to blood vessels or the lacteal The capillary carries blood too (oxygenated) and from (deoxygenated with nutrients) and maintains the concentration gradient The lacteal will transport the fats (lipoproteins to the circulatory system (lymph vessels) There is a high amount of mitochondria in the lining cells as they are needed for active transport of particles across the cell membranes The microvilli serve to enhance the surface area as well

7. Large Intestine and Rectum http://youtu.be/jsVgi8hoFFc Now all the food nutrients have been absorbed, you are left with a liquid waste of indigestible matter Most of the water must be recalimed back to the blood before egestion Mucous is excreted so movement of the harder stool will continue with the peristalsis The surface area is maxed by foldings Fibre rich diets keep the ‘flow’ going and reduce the risks of diseases like colon cancer and diverticulitis The RECTUM serves as a holding area until egestion The faeces is composed of: Lignin and Cellulose, Dead intestinal cells, Bacteria and bile pigments (friom liver breaking down old blood cells