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Food’s journey through the . . . DIGESTIVE SYSTEM Digestion ▪ Digestion breaks food molecules down into smaller molecules ▪ It is necessary to make smaller molecules because these nutrients need to be used by CELLS. ▪ Only small molecules can pass through the cell membrane and into the cell so it can be used. ▪ EX: We break starch ( a large molecules) down into glucose (a small molecule that can cross cell membranes) so our cells can do respiration and make energy! Digestion What are each of the following broken down into??? ▪Proteins → Amino Acids ▪Starch → Glucose ▪Lipids → Fatty Acids ▪Carbohydrates → Simple Sugars Steps of Digestion: Ingestion → Digestions → Absorption → Excretion Types of Digestion ▪ Mechanical – physically breaking food down into smaller pieces ▫ This creates more surface area, so enzymes can get to more molecules ▪ Chemical – use of chemicals and enzymes to break food into substances that can be absorbed Mouth ▪ Teeth are used for mechanical digestion to break the food into smaller pieces, so it can be easily swallowed. ▪ Saliva contains an enzyme (amylase) used in chemical digestion, which breaks down starches into simple sugars ▪ The tongue is your strongest muscle used to manipulate food during mastication Esophagus ▪ The tube the food travels down to get to the stomach ▪ Peristalsis is the motion that pushes the food down the tube. The tube pinches off above the food pushing it toward the stomach ▪ You have an epiglottis that covers your esophagus while you are breathing and covers your trachea while you are swallowing ▪ This prevents food from “going down the wrong tube” Stomach ▪ The stomach performs mechanical and chemical digestion of food. ▪ The stomach secretes a powerful acid (pepsin) that breaks food down ▪ It also churns mixing the food with the acid and breaking it down mechanically ▪ Chyme is the mixture of stomach acid (pepsin), broken down food, and saliva that flows from the stomach into the small intestine Duodenum ▪ This is the first section of the small instestine, where most of the chemical digestion of carbohydrates, lipids, and proteins occurs ▪ Chyme is joined with enzymes from the liver and pancreas that reduce acidity of the chyme and chemically digest the food Small Intestine ▪ The small intestine are covered in little finger like projections called villi ▪ Villi increase the surface area of the small intestine to increase absorption of nutrients ▪ The usable nutrients are removed from the chyme and travel across the villi into the blood vessels that are inside it Large Intestine ▪ When the food arrives in the large intestine it is nutrient free ▪ The large intestine pulls any excess water out of the remaining indigestible material creating feces ▪ The large intestine is filled with bacteria that help our digestion process ▪ When the large intestine is not removing enough water, diarrhea will result ▪ When the large intestine removes too much water, constipation will occur Rectum ▪ The rectum will store the feces until there is enough to pass out of the body ▪ When the rectum is full, you feel the urge to go to the bathroom ▪ There is a sphincter muscle at the bottom of the rectum called the anus ▪ This squeezes shut to keep feces in the rectum and expands to allow it out when passing a stool Liver, Pancreas, & ▪Gallbladder The liver and pancreas secrete enzymes and digestive fluids that mix with the chyme in the duodenum ▪ The pancreas secretes a fluid to neutralize the acidity of the stomach acid ▪ The liver secretes bile, which is used to break down fatty acids (lipids) ▪ Bile is stored in the gallbladder Appendix ▪ Is located near the junction of the small and large intestine ▪ The appendix is a vestigial organ, which means it was once used but shrunk in size as it became less useful ▪ Some organisms use the appendix to help break down cellulose in very fibrous substances (leaves) Common Diseases What diseases or problems do you think of when you think of the digestive system? ▫ Diarrhea ▫ Diverticulitis ▫ Constipation ▫ Ulcerative Colitis ▫ Appendicitis ▫ Hemorrhoids ▫ GERD ▫ Celiac’s ▫ IBS ▫ Lactose ▫ Ulcers Intolerance ▫ Stomach Ache ▫ Cirrhosis Diarrhea and Constipation ▪ Diarrhea – too much fluid in the bowel movements ▪ Constipation – too much water being removed from the ▫ Caused by the large bowel movements intestine not removing enough water ▫ Can be caused by viruses, bacteria, etc. ▫ Can lead to dehydration and eventually death ▫ Can be caused by poor diet or not taking in enough water ▫ Symptoms can be alleviated by taking laxatives http://nature.ca/discover/ex m/blddgstvsystm/index_e.cfm ▪ http://kitses.com/anim ation/swfs/digestion.s wf