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Lecture #9 – Animal Nutrition and Digestion 1 Key Concepts: • Animals are heterotrophic! • Nutritional needs – what animals get from food • Food processing • The human digestive system 2 Critical Thinking • Is this animal approaching the fruit or the flower??? • Why??? 3 Critical Thinking • Is this animal approaching the fruit or the flower??? • Why??? 4 Animals are always consumers • Only photosynthesis can convert solar energy to usable chemical energy • Plants store chemical energy • Animals eat plants (or other animals) • ….of course this is somewhat simplified…. but NO animals are autotrophic 5 Critical Thinking • Why do we eat??? Specifically, what do we get from food??? 6 Critical Thinking • Why do we eat??? Specifically, what do we get from food??? 7 Why we eat – energy • Animals generate ATP by aerobic respiration • Main substrate is carbohydrates Fats are also used Proteins are used as a “last resort” • Digestion converts consumed polymers to the monomers used in respiration 8 Remember bioenergetics • Managing the energy budget is essential to maintaining animal function • ATP powers basal metabolism, other activities; maintains homeostasis; etc… • Animals must eat to make ATP Diagram – bioenergetics and the fate of food 9 Why we eat – carbon skeletons • Animals need organic carbon scaffolds to build our own organic molecules – such as??? 10 Why we eat – carbon skeletons • Animals need organic carbon scaffolds to build our own organic molecules – • These are the 4 main categories of macromolecules common to all forms of life • Animals can’t make organic molecules from CO2 11 Why we eat – essential nutrients • Molecules that animals cannot make at all Do not have the right biosynthetic pathways • Must be eaten in pre-assembled form • Some common to all animals; some specialized Essential amino acids Essential fatty acids Vitamins Minerals 12 Essential Amino Acids • Most animals use the same 20 amino acids to make what??? 13 Essential Amino Acids • Most animals use the same 20 amino acids to make • Most animals can only synthesize about half • Remaining amino acids must be consumed All animal proteins are complete – contain all the essential amino acids All plant proteins are incomplete – missing some of the essential amino acids 14 Human vegetarian diets must mix plant groups to obtain all essential amino acids Chart – essential amino acids; overlap between grains and legumes 15 Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies Essential Fatty Acids • Some unsaturated fatty acids cannot be synthesized • Most animals (especially humans!) get adequate essential fatty acids from their diet • We use fatty acids for???? 16 Essential Fatty Acids • Some unsaturated fatty acids cannot be synthesized • Most animals (especially humans!) get adequate essential fatty acids from their diet • We use fatty acids for 17 Vitamins • Organic molecules used in small quantities • Water soluble vitamins usually function as coenzymes • Fat soluble vitamins function in nutrient absorption, as antioxidants, etc.. • Deficiencies are rare with an adequate, balanced diet 18 Critical Thinking • Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why??? 19 Critical Thinking • Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why??? 20 Table – essential vitamins; sources and functions Study table in text for a general understanding 21 Minerals • Inorganic elements Some required in small amounts; some in larger Requirements vary by taxon • Many different functions Some metabolic; some structural • Know top 8 minerals and their main functions 22 Mineral Functions??? • • • • • • • • Calcium – Phosphorous – Sulfur – Potassium – Chlorine – Sodium – Magnesium – Iron – 23 Mineral Functions??? • • • • • • • • Calcium – Phosphorous – Sulfur – Potassium – Chlorine – Sodium – Magnesium – Iron – 24 Food Processing • Ingestion • Digestion • Absorption • Elimination Diagram – food procession in a small mammal 25 Evolution of Compartmentalization • Food digestion must be contained Why??? • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination 26 Evolution of Compartmentalization • Food digestion must be contained • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination 27 Evolution of Compartmentalization • Food digestion must be contained • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination 28 Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes Diagram – sponges and their choanocytes 29 Evolution of Compartmentalization • Food digestion must be contained Avoids digestion of body cells and tissues • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination 30 Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles Diagram – two cell layers in cnidarians Images – a jellyfish and a flatworm 31 Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles 32 Evolution of Compartmentalization • Food digestion must be contained Avoids digestion of body cells and tissues • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening – More complex animals have a digestive tube with an opening for ingestion and one for elimination 33 Evolution of Compartmentalization • Food digestion must be contained Avoids digestion of body cells and tissues • Earliest containment structures are food vacuoles Sponges digest entirely intra-cellularly • Most animals digest at least partly outside the cells Simplest body plans have a digestive sac with one opening More complex animals have a digestive tube with an opening for ingestion and one for elimination 34 Critical Thinking • The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste • Can you think of another advantage for the 2-hole tube plan??? 35 Critical Thinking • The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste • Can you think of another advantage for the 2-hole tube plan??? 36 Tubular system allows for specialization and efficiency • Specialization based on habitat and diet • Both divergent and convergent patterns have emerged Diagram – development of specialization in 2-hole tubular digestive tracts in earthworms, insects and birds All mammals have a cecum Both earthworms and birds have developed crops 37 The Human Digestive System • Relatively straightforward adaptations to an omnivorous diet • Tube running from mouth to anus with specialized regions for food processing, absorption, and elimination of wastes • Accessory glands supply lubrication, digestive enzymes and other secretions Schematic diagram – the human digestive system 38 Diagram – the human digestive tract 39 Oral cavity, pharynx and esophagus allow for chewing and swallowing food • Teeth cut and grind • Tongue mixes and pushes bolus to back • Saliva lubricates food, protects the mouth lining, buffers pH, kills bacteria, and begins the digestion of carbohydrates Diagram – the oral cavity, pharynx and esophagus; same diagram on next two slides 40 Oral cavity, pharynx and esophagus allow for chewing and swallowing food • Epiglottis tips down to direct food from pharynx to esophagus (so you don’t breathe your food) Diagram – specifically the function of the epiglottis 41 Oral cavity, pharynx and esophagus allow for chewing and swallowing food • Peristaltic contractions in esophagus push food to stomach • Food does not fall by gravity – remember our quadruped ancestors… • Sphincter (ring) muscles also control passage of food 42 Stomach continues the action… • Stores food (very folded and stretchy) • Muscle contractions mix food • Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor 43 • Controls passage of food into small intestine Stomach continues the action… • Stores food (very folded and stretchy) • Muscle contractions mix food • Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor 44 • Controls passage of food into small intestine Diagram – the somach lining and secreting cells 45 Ulcers….. • Stomach lining replaces itself by mitosis about every 3 days • Lesions still sometimes occur • Ulcer risk factors??? 46 Ulcers….. • Stomach lining replaces itself by mitosis about every 3 days • Lesions still sometimes occur • Ulcer risk factors Helicobacter pylori Tobacco Alcohol Caffeine Aspirin Chocolate! Ouch!! 47 Other animals can get ulcers, too • From a student’s extra credit • Causes include stress, diet, genetic abnormalities, microbial infections, very finely ground grains, heredity, bile reflux that destroys stomach lining 48 Stomach continues the action… • Stores food (very folded and stretchy) • Muscle contractions mix food • Lining secretes gastric juice Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria Pepsin begins protein hydrolysis Stomach lining protected from self-digestion by thick mucus and secretion of inactive pepsin precursor 49 • Controls passage of food into small intestine Diagram – the cells lining the stomach, secretion of digestive juices 50 The Small Intestine • Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI • • • • More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis • Most absorption occurs in the latter 5.75m of the small intestine 51 Diagram – the human small intestine 52 Four levels of folding function to increase surface area – tube, interior folds, villi, microvilli Diagram – levels of folding in the human small intestine 53 Increased surface area, especially of transport epithelia, is a hallmark of large, complex, multi-dimensional animals Factoids from humans: • Lungs have 100 m2 of surface area (almost 1/2 as big as room) • Small intestine has surface area of a tennis court • 80 km of tubules in a single kidney • 100,000 km of blood vessels = almost 3X circumference of earth 54 The Small Intestine • Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI • • • • More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis • Most absorption occurs in the latter 5.75m of the small intestine 55 Pancreas secretes enzymes and bicarbonate; liver secretes bile Diagram – the pancreas, liver and gall bladder; structure and function 56 Digestive enzymes and substrates Chart – digestive enzymes; point of secretion and substrate; same on next slide 57 Most digestion in duodenum (1st 25cm) 58 The Small Intestine • Completes digestion and absorbs monomers Some absorption occurs in other parts of the digestive tract, but most in the SI • • • • More than 6m long Multiple levels of folding increase SA Surface area about 600m2!! Most digestion occurs in the first 25cm of the small intestine Enzymatic hydrolysis • Most absorption occurs in the latter 5.75m of the small intestine 59 Monomers cross into epithelial cells, then into interstitial fluid, then into the lymph or bloodstream Diagram – close-up of villi and microvilli • Some transport is facilitated, some active • Each villus includes lymph and blood vessels 60 Fat Digestion Diagram – fat digestion process; same next slide • Fats are hydrophobic • Bile salts emulsify large fat droplets into smaller droplets more surface area • Lipase digestion produces fatty acids and monoglycerides • These monomers form into micelles 61 Fat Absorbtion • Micelles are tiny enough to diffuse into epithelial cells • Monomers are recombined into fats in the epithelial cells • Fats mix with cholesterol and are coated with proteins • Resulting globules are transported into the lymph, and eventually into the blood (at shoulder ducts) 62 Intestinal blood vessels drain directly into the hepatic portal vein • Nutrients get sent straight to the liver for metabolic processing Diagram – how blood vessels absorb nutrients; same next slide 63 Intestinal blood vessels drain directly into the hepatic portal vein • From the liver, the blood goes straight to the heart for distribution throughout the body 64 Critical Thinking • Where will the levels of blood sugar and other nutrients vary the most??? Diagram – circulation patterns in humans showing relationship between circulation and major organs 65 Critical Thinking • Where will the levels of blood sugar and other nutrients vary the most??? 66 The large intestine, AKA the colon • Connected to SI at T junction • Dead-end of T is the cecum • Appendix extends off cecum Cecum functions as fermentation chamber in many animals, especially herbivores Human cecum is small, relatively functionless Appendix contributes to immune function, but is dispensable Appendix may function to repopulate intestines with beneficial bacteria after intestinal infections 67 Diagrams – the cecum in omnivores (humans) vs. specialized herbivores (koalas) 68 The large intestine, AKA the colon • Remainder of LI is ~ 1.5m • Main function is to absorb water 7l of fluid is secreted into intestinal lumen Additional water is consumed in diet SI and LI together absorb ~ 90% Inflammation of LI reduces water absorption diarrhea • LI also houses both commensal and mutualistic bacteria Live on undigested or unabsorbed materials Produce important vitamins (K, B’s, folic acid, biotin) Some produce stinky gasses as a byproduct of metabolism 69 The large intestine, AKA the colon • Final section of LI is the rectum • Feces are produced as water is absorbed from waste organic materials Waste includes LOTS of bacteria; cellulose 40% of the dry weight of feces is bacteria • Feces are stored in the rectum • When the “time” comes, feces are eliminated through the anus Sphincter muscles control elimination One is voluntary, one involuntary Some, but not complete control over defecation 70 Diagram – the human digestive tract with the large intestine highlighted 71 Diet is a selection pressure • Dentition Different tooth shapes for ripping and grinding • Length of small intestine Herbivores typically have much longer SI • Other compartments and symbioses Fermentation chambers that house microorganisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants) 72 Critical Thinking • • • • How might diet affect tooth evolution? Carnivores – Herbivores – Omnivores – 73 Critical Thinking • • • • How might diet affect tooth evolution? Carnivores – Herbivores – Omnivores – 74 Ripping, crushing and shredding teeth Diagram – differences in tooth structure Biting and grinding teeth Combo of teeth for biting, tearing, grinding and crushing 75 Diet is a selection pressure • Dentition Different tooth shapes for ripping and grinding • Length of small intestine Herbivores typically have much longer SI • Other compartments and symbioses Fermentation chambers that house microorganisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants) 76 Most plant material is tough and fibrous – the longer digestive tract in herbivores allows more time and space for digestion and absorption of both nutrients and water Diagram – differences in the digestive tract of carnivore vs. herbivore 77 Diet is a selection pressure • Dentition Different tooth shapes for ripping and grinding • Length of small intestine Herbivores typically have much longer SI • Other compartments and symbioses Fermentation chambers that house microorganisms that can digest cellulose (animals lack cellulases) Enlarged ceca (first feces are re-eaten) Esophageal pouches (crops in some birds, the “stomachs” of ruminants) 78 Extra compartments house symbiotic micro-organisms – food is often regurgitated and / or re-consumed Diagram – the digestive system of a cow 79 Review – Key Concepts: • Animals are heterotrophic! • Nutritional needs Energy Carbon skeletons Essential nutrients • Food processing • The human digestive system • Diet as a selection pressure 80