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Key Concepts • Why eat? Eat what? • Design of digestive systems • Processing steps and their hormonal control • Challenge of herbivory Animal Nutrition Animals are heterotrophs, obtain nutrition from other organisms • herbivores • carnivores • omnivores • detritivores • frugivores What do animals get from food? 1. Energy from chemical bonds 2. C skeletons (ex. acetyl, some amino acids) 3. Minerals - macro- and micronutrients 4. Vitamins Extracting these substances is an engineering ‘problem’ Different diets need different processing machinery • Carnivores large canines, slashing premolars • Herbivores sharp incisors and molar grinding surfaces • Omnivores relatively unspecialized teeth, to do a little of everything 1 • vegetarian mosquito larva has brushy mouthparts to produce currents • carnivorous mosquito larva has sorry brushes and large nasty jaws • vegetarian mosquito larva has brushy mouthparts to produce currents • carnivorous mosquito larva has weak brushes and large nasty jaws gut=long tube Specialized sections • continuous space with outside of organism • extracellular digestion • specialization of different regions Tissue layers are similar along its length AND in different animals From the inside out • mucosa • submucosa • muscle layers • • • • esophagus stomach small intestine large intestine Esophagus Storage? Humans In other animals, can be used for food storage. Honeypot ants – enormous storage capacity 2 Stomach Gastric glands contain 3 types of secretory cells • Extra muscle • Preliminary digestion of protein • Some absorption of small molecules • mucus • hydrochloric acid • pepsinogen • Mucus protects cell surfaces • Hydrochloric acid dissolves extracellular matrix, kills most bacteria, low pH (2) • Pepsinogen? Zymogen activation - they are activated when their catalytic action is appropriate trypsinogen zymogens Pepsinogen is an inactive form of a protein-digesting enzyme, pepsin Pepsinogen is an inactive form of a protein-digesting enzyme, pepsin trypsin How is pesinogen activated? • By low pH • Pepsin works well at low pH 3 The sequence of digestion along the long tube is coordinated by hormones food Gastric mucosal cells secrete a hormone, gastrin, in response to food in the stomach hormone secretion initiates digestion product inhibits food gastrin secretion into bloodstream stomach secretes gastric juices including HCl low pH (very acid) Each hormone can stimulate more than one response food gastrin secretion stomach secretes gastric juices increase stomach movement low pH (very acid) moves mix into small intestine Most digestion and absorption takes place small intestine 4 The duodenum is a receiving center. Structure of the intestine LIVER It receives material from the stomach, the liver, and the pancreas. • large circular folds • villi • muscle layers PANCREAS Villi Surface area of small intestine • • • • Tube 3 cm x 6 meters, SA Circular folds add Villi add Microvilli add ~0.6 m2 ~ 3x ~ 10x ~ 20x 600 x • microvilli • capillaries • lymph duct (lacteal) TOTAL SURFACE AREA = 360 m2 What is this S.A. for? agents of digestion Increased surface area for absorption general feature of animal digestive systems • Liver Æ bile which emulsifies fats • Pancreas Æ enzymes to digest carbos, proteins and fats 5 Protein Amino Acids Carbohydrate Monosaccharides This means The products of both protein and carbohydrate digestion are water soluble • they CANNOT passively cross cell membranes (lipid bilayer), • but they CAN dissolve in the blood Actively transported Fat and the products of fat digestion are NOT water soluble Once they reach the blood they are carried in solution. This means •they CANNOT dissolve in the intestine or in blood, but •they CAN passively cross cell membranes Transport of fat across wall Digestion of fats 1. bile salts stabilize small fat droplets 2. lipase cuts fats into fatty acids and monoglycerides 3. bile salts are recycled 1. 2. 3. Fatty acids are lipid soluble. They can pass through cell membrane In the intestinal cell, fatty acids are repackaged into chylomicrons Chylomicrons are transported out of cell into lymph system 6 Control of digestion in the SMALL INTESTINE by hormones food delivered from stomach hormone secretion initiates nutrientspecific digestion muscle movement muscle movement mix enters the small intestine fats and proteins low pH cholecystokinin (CKK) released by intestinal cells 1. gall bladder releases bile salts secretin released by intestinal cells pancreas secretes bicarbonate which neutralizes acid 2. pancreas secretes digestive enzymes Examples from the small intestine: 1. Cholecystokinin 2. Secretin chyme enters the small intestine fats and proteins cholecystokinin (CKK) released by intestinal cells 1. gall bladder contracts to release bile salts 2. pancreas secretes digestive enzymes low pH secretin released by intestinal cells pancreas secretes bicarbonate NEXT ... the large intestine, where water and ions are reabsorbed * vestigial cecum If evolution is so clever, why do we have appendices? 7 Remember that... Different diets require different processing machinery These requirements are ALSO reflected in the ‘design’ of the digestive system Plants have tough cell walls. Cellulose: most animals cannot digest (without help from other kingdoms) It isn’t easy being an herbivore What to do, gutwise? 1. Longer guts for longer processing time 2. Help from bacteria and protists that have CELLULASE or other useful enzymes 3. Chew well Carnivore Vegetarian Ruminant herbivores • • • • • • Cattle Sheep Goats Deer Giraffes Antelope and their relatives, the camels and llamas 8 Ruminant herbivores and their relatives, the camels and llamas, have • multiple stomach compartments • bacterial fermentation aiding digestion • cud-chewing Ruminants have 4 stomach compartments 1. rumen 2. reticulum 3. omasum 4. abomasum Other cellulose eaters with symbionts 9