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The Digestion System An 8m tube, from mouth to anus. Why Digest? Most nutrients are too large and insoluble Physical breakdown increases s.a Chemical breakdown increases solubility Digestive System Alimentary canal- mouth to anus Functions Movement Secretion Digestion Absorption Assimilation Egestion Nutrient production (by bacteria) II. Digestion Products: Proteins Carbo- hydrates Lipids Amino acids subunits Muscle,enzymes,Hb Last use for food Simple sugar (glucose) Quick energy food 1st used Fatty acids & glycerol Long term food, insulation,protection 2nd used for food Be able to draw the gut: GI Tract Food Bolus Chyme “Waste” Mouth Esophagus Stomach Duodenum Ileum Jejunum Cecum Ascending colon Transverse colon Descending colon Sigmoid colon What do you think actually happens? Complete the cartoon strip on the board using diagrams I 1) Mouth: Mechanically breaks up food Chemically digests Carbohydrates Basic pH Enzyme amylase from salivary glands Wets & forms “bolus” Digestion and the Mouth Cooking Mastication Saliva Enzymes to help breakdown simple sugars Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria Tongue Taste receptors (Flavor is enhanced with the olfactory cells) Enzymes to help breakdown fatty acids Epiglottis Movement http://www.lionden.com/peristalsis.htm 2. Stomach Mechanically churns Stores food Chemically digests Proteins Acid pH Enzyme Pepsinsinogen and rennin Stretch receptors initiate gastric hormone Mucus Lining prevents digestion of itself ! What stimulates acid production? Stimulated by Animation of acid production Gastrin- activates HCl, pancreas, and small intestine Stomach distention Histamine Thoughts of food (nerve input) Food itself Prevents autodigestion Stop secretion when pH is ~2 Thick mucus layer Gastrin Originated from the pyloric region of the stomach and upper duodenum Stimulated by food, thoughts of food Stimulates flow of stomach enzymes and HCl Stimulates contraction of cardiac sphincter Slows gastric emptying The Liver and bile Liver involved in storage of vitamins & minerals, glycogen. Detoxifies chemicals like alcohol. Controls protein levels (deamination) to make uric acid Controls salt levels Bile is a mixture of unwanted cholestrols (emulsifiers), bicarbonate ions, excess salts and pygments like haem. The Pancreas Bicarbonate ions: HCO3- neutralises acids Amylase: starch to maltose Trypsin: proteins to polypeptides Phospholipase: phospholipids to P.lipids, f.a Lipase: lipids to glycerol & f.a. Pancreatic Juice pH 8 Secretin Originated from the duodenum, jejunum Stimulated by the presence of acidic chyme and the presence of peptones in the duodenum Stimulates the secretion of bicarbonate Slows gastric emptying Explain the structural features of exocrine gland cells. Exocrine glands – secrete into a duct. Endocrine….? (ductless) Describe the common structures H.3.1Draw and label a diagram showing a transverse section of the ileum as seen under a light microscope. 3. Small Intestine Absorption of food Digestion of Lipids (fats) Carbos Trypsinogen activated by HCl Lipase & Amylase from the pancreas Immobilised enzymes on epithelium Digestion in Small Intestines Absorption Folds, villi, microvilli expand absorptive surface Most nutrients absorbed here Fat-soluble nutrients go into lymph Other nutrients into blood Explain the structural features of villi including microvilli, mitochondria, pinocytotic vesicles and tight junctions. H.2.5 Outline the role of membrane-bound enzymes on the surface of epithelial cells in the small intestine in digestion Immobilised enzymes in the plasma membrane They are……. Overview of Absorption Absorptive mechanisms Passive diffusion • Facilitated diffusion • Active transport Absorption from Large Intestines Large intestine = 1.5m long (caecum, colon, rectum). No digestion Site of water, salt, vitamin absorption (leaving a mass in a semi-solid state). Vitamin K by bacteria. Almost everything of nutritional value has been utilized by time it reaches the large intestines -leaving only waste (cellulose, pectins, pentosans, other) Feces contains some water, dead mucosal cells, bacteria, non-absorbed remains of digestion (inorganic matter and lipid) 9. Appendix: vestigial organ Cows and their bacteria… Without intestinal symbiotic bacteria, humans wouldn’t be able to digest many fibrous foods or get many essential vitamins. H.2.6 Outline the reasons for cellulose not being digested in the alimentary canal Major component of the plant cell wall Do not possess cellulase enzymes No not have bacteria/protozoan in the gut which produces cellulase (herbivores do) Good consequence?? Fibre! To maintain peristalsis The Gastrointestinal Tract-Recap Objective 6.1.3 Enzyme Amylase Protease Lipase Example of enzyme Salivary amylase Pepsin Pancreatic lipase Source Saliva Stomach Pancreas Substrate Starch Protein Triglycerides (fats or oils) Products Maltose (needs to be further broken down) Small polypeptides (chain of amino acids) Fatty Acids and Glycerol Optimum pH pH7 (7.2) 2 7–8 Control of Digestion by the Nervous System Nutrition and GI Disorders Constipation Hard, dry, infrequent stools Reduced by high fiber, fluid intake, exercise Diarrhea Loose, watery, frequent stools Symptom of diseases/infections Can cause dehydration Diverticulosis Pouches along colon High fiber diet reduces formation Ulcers Helicobacter pylori Heavy use of aspirin Excessive acid production in the stomach Symptoms Pain 2 hours after eating Treatment Antibiotics Antacid Heartburn Gastroesophageal reflux disease Gnawing pain in the upper chest Acid from the stomach to the esophagus Treatment Smaller meals Less fatty meals Stop smoking Do not lie down after eating Avoid offending foods Constipation Slows movement of fecal matter Increases fluid reabsorption; hardening of the feces Causes: Results from ignoring normal urge Antacids, calcium and iron supplements Treatment Plenty of dietary fiber and fluids Laxatives Quiz 1. 2. 3. 4. 5. 6. 7. 8. True or false is stress the cause of stomach ulcers? What is the name of the organism that causes ulcers? Why does the HCl and pepsin have no effect on the organism? Why can it survive where it lives? How does the immune system respond and what are the consequences of this? What effect does the organism have on the gastric acid? What is the consequence of this? A very bad infection of the bacteria could lead to what? Quiz Answers 1. 2. 3. 4. 5. 6. 7. 8. 9. Stress does not cause stomach ulcers Helicobacter Pylori The bacteria lives in the mucus on the surface of the epithelial cells. pH is higher and no enzyme can get to it The immune system responds by white blood cells Accumulation of WBCs can damage tissue and cause and ulcer The bacteria decreases the amount of gastric acid More chance of ulcers with less acidity Very bad infection of the bacteria could lead to cancer