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Chapter 12 – Digestive System Digestion: changing food into forms that can be absorbed through cell membranes Layers of alimentary canal: 1. Mucosa: innermost, protects tissues beneath it; carries on absorption and secretion 2. Submucosa: nourishes surrounding tissue and carries away absorbed material 3. Muscular layer: two layers of smooth muscle; circular (diameter)and longitudinal (short) 4. Serosa: moistens and lubricates outer tube so organs will slide freely over it Alimentary canal – 9 meters long; openings at each end Organ Mouth Components Teeth Deciduous – primary teeth, 10 per jaw Permanent – secondary teeth, 16 each jaw Incisors – front bite, used on large pieces of food Cuspids – canine, grasping or tearing Bicuspids – premolars; grinding Molars - grinding Tongue Function Receives food and reduces it Breaks food into smaller pieces to increase surface area for digestive enzymes Crown – above gingiva Root – below gingiva Gingiva – gum Composed of dentin Disease / Disorder Dental caries (decay): decalcification of enamel and destruction of dentin; causes a cavity – caused by bacteria on dirty teeth and a diet high in sugar; causes bacteria to produce acids that decay the teeth Skeletal muscle connected to floor by frenulum; mixes food particles; anchored to hyoid and lingunal tonsil 1 Palate Cheeks Lips Salivary glands Pharynx Roof of oral cavity (hard and soft); during swallowing uvula covers entrance to nasal cavity; contains palatine tonsils Chewing Sensory receptors for temperature and texture Moistens food and binds it together Secretions – serous, moistens, submandibular s.g. (floor of mouth); amylase, begins starch digestion, - parotid s.g. (below ear); mucus, binds food, – sublingual s.g. (under tongue) Connects nasal and oral cavities with larynx and esophagus; swallowing 1. food chewed and mixed with saliva, mixture turns into a bolus, forced into pharynx by tongue 2. bolus reaches pharynx and stimulates sensory receptors to trigger swallowing reflex > soft palate, uvula raised preventing food from entering nasal cavity>hyoid bone and larynx elevated so food won’t enter trachea, epiglottis covers opening to trachea (glottis)> muscles in lower part of pharynx relax opening of esophagus > peristaltic waves begins and forces food into esophagus 3. food transported to stomach by esophagus Tonsillitis – infection most commonly of the palatine tonsils 2 Esophagus Passageway for food from mouth to stomach straight collapsible tube 25 cm long Hiatal hernia – weak place in diaphragm, abdominal organs may protrude through the esophagus cause the person to feel a choking sensation. Heartburn – gastric juice refluxes into esophagus 3 Stomach Capacity of 1 liter; receives food; initiates protein digestion; mixes food with gastric juice; carries on limited absorption (water, glucose, certain salts, alcohol, lipid soluble drugs) moves food into the small intestine;regions: cardiac, fundic, body, pyloric Gastric secretions Mucous cells – mucus and alkaline substance Parietal cells – HCl + intrinsic factor=gastric juice Chief cells – digestive enzymes, pepsinogen + HCl = pepsin, protein splitting enzyme, intrinsic factor aids in absorption of vitamin B12, controlled by hormonal and neuronal mechanisms – ACh stimulates gastric glands to secrete gastric juices, gastrin also secreted by some stomach cells > stimulates gastric glands even more; gastrin also stimulates cell growth in mucosa to repair tissue; Ulcer – open sore in mucosa; commonly caused by bacterial infection Vomiting – triggered by irritation or distention of alimentary canal; emetic center in medulla oblongata; response cause the stomach to squeeze from all sides Chyme – paste of food particles + gastric juice Chyme is pumped into the small intestine a little at a time; liquids pass through rapidly, fatty foods remain 3-6 hours, proteins and carbohydrates pass through quickly 4 Pancreas Gallbladder Closely associated with the small intestine; Pancreatic juice Pancreatic amylase: splits starch or glucagen into disaccharides Lipase ; breaks triglycerides into fatty acids and glycoxol Proteinase: (trypsin, chymotrypsin, carboxypeptidase) splits bonds b/w different combinations, activated by other enzymes in sm. Int. Nucleases: breaks down nucleic acids into nucleotides Attached to ventral surface of liver by cystic duct which joins hepatic duct; stores bile b/w meals; common bile duct – union of hepatic and cystic ducts Pancreatitis – blocked duct, cuases back up in portions of pancrease, may become digested Gallstone: crystal of cholesterol; blocks the flow of bile into the sm. int; remove stones or gallbladder 5 Liver 2 lobes: right (larger), left (smaller); bile secreted by hepatic cells Metabolic activities; carbohydratesmonitors level of glucose, protein metabolism used in blood filtering; most vital is deamination; stores glycogen, iron, vit. A,D,B12 detoxification Jaundice: excretion on bile is prevented causing a yellowish tinge Hepatitis: inflammation of liver, caused by a virus Type A – children or young adults; spread by touching contaminated 0virus containing feces) objects; nausea, jaundice, abdominal pain, complete recovery no liver damage Type B – symptoms similar to type A, effects last longer; spread by body fluids (STD) most recover, but some become carriers Non A and non B – blood transfusions, drugs, alcohol, chronic (6 months or longer) may have liver damage 6 Small intestine Large intestine Receives pancreatic secretions, completes digestion of nutrients in chyme; regions – duodenum, jejumum, ileum; suspended from posterior abdominal cavity wall by mesentery; contains many intestinal villi, mostly in duodemum and jejumum; most important absorbing organ, mixing and peristalsis Enzymes: stilumalted by direct contact with chyme 1. peptidases: split peptides into amino acids 2. sucrase, maltase, lactase: split disacchrides into monosaccharides sucrose > glucose, maltose > fructose, lactose > galactose 3. intestinal lipase: fats > fatty acids and glycerol Absorption of water and salts; concentrates chyme into feces Lactose intolerance: insufficient quantities of lactase to break down milk sugar; remains undigested causes an increase in osmotic pressure; water drawn into intestine; intestinal bacteria produce organic acids and gases bloating, diarrhea, cramps Blocked colon, 7