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Objective: You will be able to identify the structures of the digestive system. Do Now: • Read all of page 978 • Give the function of the digestive system Figure 41.12 The four stages of food processing Small molecules Pieces of food Mechanical digestion Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Undigested material Food 1 INGESTION 2 DIGESTION 3 ABSORPTION 4 ELIMINATION Figure 41.13 The human digestive system Oral Cavity • Mechanical digestion breaks food into smaller pieces – Increases surface area for chemical digestion • Chemical digestion of starch occurs here – Done by salivary amylase Esophagus • No digestion occurs here • It moves food from oral cavity to stomach by using muscles – Called peristalsis Figure 41.16 From mouth to stomach: the swallowing reflex and esophageal peristalsis (layer 1) Bolus of food Tongue Epiglottis up Pharynx Glottis Larynx Trachea To lungs Esophageal sphincter contracted Esophagus To stomach Figure 41.16 From mouth to stomach: the swallowing reflex and esophageal peristalsis (layer 2) Bolus of food Tongue Epiglottis up Pharynx Glottis Larynx Trachea To lungs Esophageal Epiglottis sphincter down contracted Esophagus To stomach Glottis up and closed Esophageal sphincter relaxed Figure 41.16 From mouth to stomach: the swallowing reflex and esophageal peristalsis (layer 3) Epiglottis up Bolus of food Tongue Glottis down and open Epiglottis up Pharynx Glottis Larynx Trachea To lungs Esophageal Epiglottis sphincter down contracted Esophageal sphincter relaxed Esophageal sphincter contracted Esophagus To stomach Glottis up and closed Relaxed muscles Contracted muscles Relaxed muscles Esophagus Cardiac orifice Stomach 5 µm Pyloric sphincter Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pit leading into tubular gastric glands. Small intestine Folds of epithelial tissue Epithelium 3 Pepsinogen Pepsin (active enzyme) 2 HCl Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells. 1 2 HCl converts pepsinogen to pepsin. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. 3 Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Chief cells secrete pepsinogen, an inactive form of the digestive enzyme pepsin. Parietal cell Parietal cells secrete hydrochloric acid (HCl). 1 Pepsinogen and HCI are secreted into the lumen of the stomach. Chief cell Stomach • Mechanical digestion occurs by the grinding of the stomach’s muscles • Chemical digestion of proteins begins here – Gastric glands in stomach release a HCl and protease – The HCl provides a highly acidic environment – The protease actually breaks down the protein Figure 41.19 The duodenum Liver Bile Gallbladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine Small Intestine • Lipid digestion starts here • Most of the chemical digestion occurs here – Intestinal glands and the accessory organs help to digest food • Liver, gall bladder and pancreas • All of the absorption of food into the body occurs here • No food is digested AFTER it leaves the small intestine Figure 41.19 The duodenum Liver Bile Gallbladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine Accessory organs • The liver makes the bile but it stores it in the gall bladder • It’s the gall bladder that actually secretes bile into the small intestine – Bile emulsifies fats (breaks them down) • The pancreas secretes amylase, protease and lipase Figure 41.19 The duodenum Liver Bile Gallbladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine Large Intestine • This organs main function is to absorb water • It does NOT absorb food nor does it digest food!!!! End of the line • Strong peristaltic action from the rectum pushes waste out of the anus Group Roles • Leader – keeps the group focused and on task • Recorder – Writes down the work for the group • Reporter – Informs the class/teacher about the work done by the group • Noise monitor – Makes sure that the group works quietly Activity • Create story about the digestive canal of horrors where a group of teenage worm friends enter a tunnel but end up being digested by enzymes • Remember that only some of the carbohydrate and protein digestion happens outside intestines • Be sure to include each structure and describe in full detail what they do. Objective: You will be able list and describe the disorders that affect the digestive system. Do Now: • Read “Absorption in the small intestine” on p. 982-983 • Describe the structure of the villi Figure 41.23 The structure of the small intestine Microvilli (brush border) Vein carrying blood to hepatic portal vessel Blood capillaries Epithelial cells Muscle layers Villi Epithelial cells Large circular folds Lacteal Key Nutrient absorption Intestinal wall Villi Lymph vessel Figure 41.18 Ulcer-causing bacteria Bacteria 1 µm Mucus layer of stomach Disorders of the Digestive System • Ulcers are erosions of the digestive tract • Appendicitis is the infection and inflammation of the appendix • Gallstones is the accumulation of hardened cholesterol deposits on the gall bladder Disorders continued • Constipation occurs when the large intestine absorbs too much water • Diarrhea occurs when the large intestine does NOT absorb enough water Objective: You will be able to answer review questions on the digestive system. Do Now: • Read all of page 971 • Besides energy, what are the other uses of food?