Nutrition, Digestion, and Absorption51 Animals are heterotrophs derive nutrition by eating other organisms Autotrophs can synthesize their necessary nutrients heterotrophs depend on this synthesis and have adapted to take advantage of it Energy needs can be measured Measures of heat energy: calorie is amount of heat needed to raise 1 gram of water 1C Very small amount A kilocalorie (kcal) = 1,000 calories Kilocalories are used by nutritionists and scientists but refer to them as caloriesCalorimeter used to measure energy content Animals must store food between meals Carbohydrates stored in liver and muscle cells as glycogen enough for about one days energy needs Fat stores more energy per gram and with little water, making it more compactMuscle fibers with glycogen storage vacuolesAdipose tissue cells almost completely filled with fat vacuole Undernourished too little food taken in and metabolism of bodys own molecules begins Protein is lost rapidly to protein synthesis Glycogen and fat are broken down Decreased protein can lead to edema in abdomen Overnourished more food taken in than needed excess stored as increased body mass Glycogen reserves are built up Extra carbohydrates, fats, and proteins are converted to body fatFat cat Amino acids are building blocks of proteins Each species has essential amino acids that they cannot synthesize Complementary diets can supply all eight essential amino acids for adult humans Other amino acids are conditionally essential Macronutrients elements required in large amounts, like calcium Micronutrients elements required in tiny amounts, like iron Vitamins carbon compounds that cannot be synthesized Species-specific Water-soluble or fat-soluble How organisms acquire nutrition: Saprobes absorb nutrients from dead organic matter -- mushrooms Detritivores actively feed on dead organic matter pillbug Predators feed on living organisms Pillbug Predators can be: Herbivores consume plants Carnivores prey on animals Omnivores prey on bothBos bisonCanis lupesSus scrofa Filter feeders filter small organisms from an aquatic environment, including baleen whales, clams Fluid feeders include mosquitoes, vampire bats, nectivorous birdsSpirobranchus giganteusDiaemus youngi Mammalian teeth have similar structure Enamel composed of calcium phosphate covers crown Dentine is in crown and root Pulp cavity contains blood vessels, nerves and dentine- producing cells Mammalian teeth have shapes adapted to specific diets: Incisors: used for cutting, chopping, or gnawing Canines: for stabbing, gripping, or ripping Molars and premolars: shearing, crushing, or grindings/anatomical_images/rodent_jaws/zygoplate.jpg Digestion in animals is extracellular and usually begins in a body cavity Gastrovascular cavities connect to outside through single opening Tubular (complete) guts Opening at each end Mouth takes in food and wastes eliminated via anus Food is broken up mechanically in mouth cavity by teeth, radula (snails), or mandibles (arthropods) Birds grind food with small stones in gizzards Stomachs and crops are storage chambers that allow for gradual digestion Small food particles are delivered into midgut or intestines Nutrients are absorbed in midgut Hindgut recovers ions and water and stores feces Muscular rectum expels feces In bony fishes, and tetrapods, the gut wall has folds with projections called villi Surface cells of villi have smaller projections called microvilli Macromolecules are broken down by digestive enzymes, known by substances they hydrolyze Protease breaks bonds of amino acids Carbohydrase breaksdown carbohydrates Peptidase peptides Lipase fats Nuclease nucleic acidsDigestive_Net_Pages/Digestive_Graphics/Digetive_diagram.gif Digestive enzymes are produced in an inactive form a zymogen Cannot act on cells that produce it In gut, zymogen is activated by another enzyme Cells lining gut are protected from enzymes by mucus Vertebrate gut has layered plan Lumen gut cavity Mucosa Layer of epithelial cells (mucosal epithelium) that secretes mucus, digestive enzymes or hormones some absorb nutrients via microvilli Submucosa has blood and lymph vessels, and nerves Circular muscle layer innermost cells oriented around gut constricts gut Longitudinal muscle layer outermost cells oriented along gut shortens gut Mechanical activity in digestion: Tongue pushes food bolus to soft palate, and initiates swallowing Food passes into esophagus Food kept out of trachea by closed larynx and the epiglottis Peristalsis Waves of muscle contractions that move food toward stomach Parts of esophagus are either skeletal muscle or smooth muscle As food reaches smooth muscle, esophagus contracts and pushes food toward the stomach Chief cells Secrete pepsinogen inactive form of proteolytic enzyme, pepsin Low pH of stomach converts it to active form Newly active pepsin activates other pepsinogen molecules process called autocatalysis Stomach releases contents to the small intestine Chyme is mixture of gastric juice and partly digested food Stomach walls contract and move chyme to bottom of stomach Pyloric sphincter allows small amounts to enter small intestine Most chemical digestion occurs in the small intestine Small intestine has three sections Duodenum initial section and site of most digestion Jejunum and ileum carry out most of nutrient absorption Liver synthesizes bile salts and secretes them as bile flows through hepatic duct to duodenum through branch to gallbladder Fat entering duodenum signals gallbladder to contract Bile released and flows via common bile duct to duodenum Contents of small intestine pass into large intestine, or colon Absorbs water and ions, and produces feces Too much water absorption leads to constipation Too little leads to diarrhea Large populations of bacteria live in the colon includes Escherichia coli synthesizes vitamin K and biotin that are absorbed across colon wall Prolonged intake of antibiotics can kill normal intestinal bacteria and upset floral balance digestive problems vitamin deficiency Herbivores cannot produce cellulases enzymes that break down cellulose Rely on symbiotic microorganisms living within digestive tracts to digest celluloseThe protozoa Trichonympha lives in each termite's gut and breaks down cellulose so termite can obtain nutrition from its food./ Ruminants (cud chewers) Have four-chambered stomachs: rumen, reticulum, omasum and abomasum Rumen and reticulum contain microorganisms that metabolize cellulose into nutrients for hostDusty the llama Cecum Fermentation chamber in some species Nutrient absorption is incomplete from undigested food In humans, the appendix is just off the cecum Long thought to have no function (vestigial) May function as refuge for bacterial flora or in immunity Lipoproteins produced in liver are classified by density (more fat lower density) High-density lipoproteins (HDLs) remove cholesterol from tissue and carry it to liver good Low-density lipoproteins (LDLs) transport cholesterol in body bad Very-low-density lipoproteins (VLDLs) transport triglycerides to fat cells. Insulin released by pancreas during absorptive period, when blood glucose rises Insulin promotes uptake and utilization or storage of glucose Acts in skeletal muscle, adipose tissue, and liver