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OLD NOTES – FOR REFERENCE ONLY! Chapter 41 – Animal Nutrition I. Nutritional Requirements a. Glucose regulation = form of homeostasis i. Pancreas secretes: 1. Insulin stimulates liver to store glucose; decreases blood glucose; secreted after eating a lot 2. Glucagon stimulates liver to break down glycogen; increases blood glucose b. Undernourishment vs. Overnourishment c. Feedback mechanism of appetite i. Leptin hormone produced by adipose cells 1. high leptin levels = depress appetite and increase energy consuming activities 2. low leptin levels = increase appetite d. Essential Nutrients must be obtained in food, body cannot make i. 4 classes: 1. amino acids animals can make about ½; others come from diet 2. fatty acids can make MOST from carbon skeletons, but some exceptions (ex. Linoleic acid) 3. vitamins 4. minerals inorganic; ex. Calcium and phosphorus II. Food Types and Feeding Mechanisms a. Opportunistic feeders; Heterotrophs = herbivores, carnivores, omnivores b. Four major mechanisms for food ingestion: i. Suspension Feeders sift small particles; ex. Clams, oysters, baleen whales ii. Substrate Feeders live in or on food source; ex. Maggots 1. Deposit feeders – type of substrate feeder, salvage partially decayed organic materials consumed with soil; ex. Earthworm iii. Fluid Feeder suck nutrient-rich fluids from living host; ex. Mosquito and leech iv. Bulk Feeder eat large amounts at a time; ex. Python III. Food Processing a. Four Main stages of food Processing i. Ingestion act of eating; organisms need to break down the macromolecules in order to use them ii. Digestion process of breaking down food iii. Absorption cells absorb molecules (such as amino acids) iv. Elimination undigested material passes out of digestive compartment IV. b. Digestion occurs in specialized compartments (contains enzymes, no selfdigestion) i. Intracellular Digestion (food vacuoles) vs. Extracellular Digestion ii. Gastrovascular Cavities 1. single opening compartment 2. simple animals (cnidarians, hydra) 3. function in both digestion and distribution of nutrients iii. Complete Digestive Tract (Alimentary Canal) 1. two openings – mouth and anus 2. most animals have this 3. set of tubes that can be divided into specialized regions a. Ex. Mouth Pharynx Esophagus Crop Gizzard Stomach Intestine Mammalian Digestive System a. Consists of alimentary canal and accessory glands (salivary glands, pancreas, liver, gallbladder) b. Peristalsis smooth muscle contractions that push food through digestive tract c. Beginning of Food Processing: i. Oral Cavity 1. grinds food; releases saliva 2. Salivary Amylase enzyme in saliva that breaks down carbohydrates ii. Pharynx 1. opens to both esophagus and trachea (windpipe) 2. Swallowing = epiglottis (flap) blocks trachea opening (glottis) 3. Fig 41.14 pg. 861 iii. Esophagus 1. moves food from pharynx down to stomach d. Food Storage and Preliminary Digestion i. Stomach = elastic ii. Stomach secretes gastric juice (a digestive fluid) 1. pH of 2 (acidic!) 2. contains Pepsin enzyme (hydrolysis of proteins) a. Pepsin secreted in inactive form – Pepsinogen b. Once food enters stomach, HCl is also secreted, binds with pepsinogen and activates the pepsin POSITIVE FEEDBACK c. Fig 41.15 pg. 862 iii. Stomach has mucus lining to protect against self-digestion iv. Pyloric Sphincter opening from stomach to small intestine e. Small Intestine i. Major Function = digestion and absorption ii. Longest part of alimentary canal iii. Three parts: 1. Duodenum first 25 cm, breaks down food a. The acid chyme from the stomach mixes with the digestive juices from the accessory glands here i. Pancreas makes bicarbonate to act as a buffer ii. Liver produces bile that can help digest fats iii. Gall Bladder stores the bile until its needed 2. Jejunum role in absorption of nutrients and water 3. Ileum role in absorption of nutrients and water iv. Carbohydrate Digestion 1. Polysaccharides Disaccharides Monosaccharides (glucose!) 2. Maltase enzyme that breaks disaccharides into glucose 3. Begins with salivary amylase in oral cavity; finishes with pancreatic amylase 4. Monomers absorbed into the blood v. Protein Digestion 1. Begins with Pepsin in stomach; eventually broken down into amino acids 2. Relevant enzymes: a. Trypsin and Chymotrypsin target peptide bonds and break large proteins b. Carboxypeptidase takes off one amino acid at a time starting at carboxyl group c. Aminopeptidase takes off one amino acid at a time beginning at the amino end d. All these enzymes are secreted by the pancreas in an inactive form; the enzyme enteropeptidase must be secreted to activate them vi. Nucleic Acid Digestion 1. Nucleases enzymes that break down DNA and RNA into nucleotides vii. Fat Digestion 1. Reach small intestine undigested 2. Emulsification process where bile salts keep fat from coalescing a. Therefore, the fat droplets stay small and the enzyme lipase can hydrolyze them ***** Fig 41.17 pg. 864 – All Enzymes Necessary in Human Digestion***** viii. Absorption of Nutrients 1. Small Intestine has a very large surface area 2. Fingerlike projections = Villi, which contain microvilli, which increase the rate of absorption 3. Lacteal small vessels of the lymph system (contain lymph) that go through the villi; nutrients diffuse into here 4. Capillaries and veins that drain nutrients away from villi empty into the hepatic portal vessel, which drains to the liver (first chance at nutrients!) a. Function of liver = helps regulate blood/glucose levels 5. HIGH energy cost to digest food f. Hormones help regulate digestion i. Make sure digestive juices are only present when needed ii. Gastrin hormone secreted by stomach wall when food arrives; stimulates production of gastric juices iii. Enterogastrones secreted by duodenum, stimulates secretion of hormone secretin (which signals the pancreas to release bicarbonate buffer) 1. Cholecystokinin (CCK) causes gallbladder to contract and release bile; triggers release of pancreatic enzymes g. Large Intestine (colon) i. Major Function = reclaiming water ii. Cecum one small part of large intestine, contains fingerlike extensions (appendix = dispensable) iii. Lined with bacteria iv. Rectum terminal portion of colon; stores feces until eliminated; sphincter muscles V. Adaptations of Vertebrate Digestive System a. Dentition structural differences in teeth based on diet b. Length of alimentary canal correlated with diet c. Digestive systems include symbiotic bacteria (help with cellulose digestion) d. Ruminant (deer, cattle, sheep) Digestion: i. Stomach = 4 chambers; digest these symbiotic organisms that are rapidly reproducing in the digestive tract