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General Biology “Maintenance of Life” Animal Nutrition Noppadon Kitana, Ph.D. Department of Biology Chulalongkorn University August 28, 2012 Animals = Heterotrophs • Organisms require energy for growth, biological processes, maintenance and repair, regulation, and reproduction. – Plants use light energy to build organic molecules from water and CO2, and then use those organic molecules for fuel. (=autotrophs) – Animals are heterotrophs and must obtain their chemical energy in food that contains organic molecules synthesized by other organisms. August 28, 2012 • Food is digested and absorbed by body cells. • Fuel molecules are used to generate ATP by cellular respiration and fermentation. • The remaining molecules can be used in biosynthesis. – body growth and repair – synthesis of storage materials – production of gametes • Requires both carbon skeletons for new structures and ATP to power their assembly Self study: essential nutrients andAugust carbon 28, 2012skeleton (pp. 849-852) Food Processing Small molecules Pieces of food Mechanical digestion Chemical digestion Nutrient (enzymatic hydrolysis) molecules enter body cells Food Undigested material • Ingestion: an act of eating • Digestion: a process of breaking food down into molecules small enough for the body to absorb • Absorption: a process that animal’s cells take up small molecules from the digestive compartment • August Elimination: a process that the undigested material passes 28, 2012 out of the digestive compartment Digestion • Food contains macromolecules including polymers (starch, protein) and large substances (fat) which are too large to pass through membranes and enter animal cells. • Digestion cleaves macromolecules into their component monomer. – – – – Polysaccharides → monosaccharide Fats → glycerol and fatty acids Proteins → amino acids Nucleic acids → nucleotides • Animal uses these monomer to make its own August 28, 2012 molecules or as fuel for ATP production. • Digestion reverses the process that a cell uses to link monomers to form macromolecules. – Digestion breaks bonds with the addition of water via enzymatic hydrolysis. • Chemical digestion is usually preceded by mechanical fragmentation of food (e.g. chewing). – Breaking food into smaller pieces increases the surface area exposed to hydrolytic enzymes. • Most organisms conduct digestion in specialized compartments to avoid digesting their own cells and tissues. August 28, 2012 Intra-cellular Digestion • The simplest digestive compartments are food vacuoles (=organelles in cell). • hydrolytic enzymes break down food without digesting the cell’s own cytoplasm • example: heterotrophic protists and sponges (the only animal that digest their food this way) August 28, 2012 Extra-cellular Digestion • The breakdown of food occurs outside cells. • Animals with simple body plans have digestive sacs with single openings, called gastrovascular cavities. • Example: cnidarians (hydra) and flatworms, – capture and pass prey into the gastrovascular cavity – Prey will be partially digested by enzymes in cavity. – absorb food particles and continue hydrolysis intracellularly August 28, 2012 • Most animals have complete digestive tracts or alimentary canals with 2 openings (mouth and anus). – Food is ingested through the mouth and moved in one direction. – This enables organisms to ingest additional food before earlier meals are completely digested August 28, 2012 Mammalian (human) Digestive System • alimentary canal = digestive tract • accessory glands = secrete digestive juice August 28, 2012 Oral cavity, Pharynx, and Esophagus • Both physical and chemical digestion of food begins in the mouth (oral cavity). • Salivary glands deliver saliva to the oral cavity. • Saliva contains: – a glycoprotein called mucin: protects the mouth from abrasion and lubricates the food – buffers: help neutralizing acid in the mouth – antibacterial agents: kill bacteria that enter the mouth – salivary amylase: an enzyme that hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose August 28, 2012 • The tongue tastes food and helps shape the food into a ball called a bolus. – During swallowing, the tongue pushes a bolus back into the oral cavity and into the pharynx. • The pharynx is a junction that opens to both the esophagus and the trachea (windpipe). • The esophagus conducts food from the pharynx down to the stomach by peristalsis. • After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach. August 28, 2012 • Peristalsis: rhythmic waves of contraction by smooth muscles in the walls of the alimentary canal. • Sphincters: muscular ringlike valves, regulate the passage of material between specialized chambers of the canal. August 28, 2012 Stomach • stores food and performs preliminary digestion • can stretch to accommodate ~ 2 L of food and fluid • The stomach secretes a digestive fluid called gastric juice. – pH of the gastric juice is about 2 (HCl), • can disrupts the matrix that binds cells together and kills most bacteria – also contains pepsin, an enzyme that begins the hydrolysis of proteins. • Pepsin works well in strongly acidic environments, and help breaks peptide bonds producing smaller polypeptides. August 28, 2012 • Pepsin is secreted as pepsinogen (=inactive form) by chief cells in gastric pits. • HCl (secreted by parietal cells in the pits) converts pepsinogen to the active pepsin when both reach the lumen of the stomach. • In a positive-feedback system, activated pepsin can activate more pepsinogen molecules. August 28, 2012 • every ~20 seconds, the stomach contents are mixed by the action of smooth muscles. – A recently swallowed meal becomes a nutrient-rich broth known as acid chyme. • Stomach is closed off at either end. – Cardiac orifice (at the esophagus side) dilates when a bolus arrives. – The occasional backflow of acid chyme from the stomach into the lower esophagus causes heartburn (acid reflux). – Pyloric sphincter (at the small intestine side) regulate the passage of chyme into the intestine. • It takes about 2 to 6 hours after a meal for the stomach to empty. August 28, 2012 Small Intestine • The longest section of the canal (~6 m in human). • Major organ of digestion and nutrient absorption (occur over a period of 5 to 6 hours) • Duodenum (the first portion of small intestine) receives acid chyme from stomach and mixes with digestive juices from the pancreas, liver, gall bladder, and gland cells of the intestinal wall. August 28, 2012 • Pancreas produces enzymes and an alkaline solution (bicarbonate) which buffers the acidity of the chyme. • Liver produces bile which is then stored in gall bladder until needed. – Bile contains bile salts which act as detergents that aid in the digestion and absorption of fats. – Bile also contains pigments that are by-products of red blood cell destruction in the liver. – These bile pigments are eliminated from the body with the feces. August 28, 2012 Carbohydrate Digestion • Begin by salivary amylase in the oral cavity, continues in the small intestine. • Pancreatic amylases hydrolyze starch, glycogen, and smaller polysaccharides into disaccharides. • Disaccharidases hydrolyze each disaccharide into monomers. – Maltase: maltose → two glucose molecules – Sucrase: sucrose → glucose and fructose – These enzymes are built into the membranes and extracellular matrix of the intestinal epithelium which is also the site of absorption. August 28, 2012 Protein Digestion • Start in stomach by pepsin. • Continue digestion in small intestine (duodenum): – Trypsin and chymotrypsin break larger polypeptides into shorter chains. – Dipeptidase, attached to the intestinal lining, split smaller chains. – Carboxypeptidases split off one amino acid from the carboxyl end of a peptide. – Aminopeptidase split off one amino acid from the amino end of a peptide. August 28, 2012 • Aminopeptidase are secreted by the intestinal epithelium. • Trypsin, chymotrypsin, and carboxypeptidase are secreted in inactive form by the pancreas. – Another intestinal enzyme, enteropeptidase, converts inactive trypsinogen into active trypsin. – Active trypsin then activates the other two. August 28, 2012 Nucleic Acid Digestion • Nucleases in small intestine hydrolyzes DNA and RNA into their component nucleotides. • Other enzymes break nucleotides down into nucleosides, nitrogenous bases, sugars, and phosphates. Fat Digestion • Fat is insoluble in water and tends to form large drop of fat. • Bile salts from gallbladder coat fats droplets and keep them from coalescing (=emulsification). • Lipase hydrolyzes fat into glycerol, fatty acids, August 28, glycerides. 2012 and Overview of Food Digestion August 28, 2012 • Most digestion occurs in the duodenum. • The other two sections of the small intestine, the jejunum and ileum, function mainly in the absorption of nutrients and water. • The small intestine has a large surface area (~300 m2) that help increases the rate of absorption. – Large circular folds in the lining bear fingerlike projections called villi. – Each epithelial cell of a villus has many microscopic appendages called microvilli that are exposed to the intestinal lumen. August 28, 2012 • Nutrients are absorbed across the intestinal epithelium and then across the epithelium of capillaries (blood vessels) or lacteals (lymph August 28, 2012 vessels) Large Intestine • Large intestine or colon functions to recover water that entered the alimentary canal. – About 7 L of fluid are secreted into the lumen of the digestive tract of a person each day. – Over 90% of the water is reabsorbed in small intestine and colon. • Digestive wastes, the feces, become more solid as they are moved along the colon by peristalsis. – Movement in the colon is sluggish, requiring 12 to 24 hours for material to travel the length of the organ. – Diarrhea results if insufficient water is absorbed and constipation if too much water is absorbed. August 28, 2012 • Living in the large intestine is a rich flora of mostly harmless bacteria. – One of the most common inhabitants of the human colon is Escherichia coli. – Many colon bacteria generate gases, including methane and hydrogen sulfide. – Some bacteria produce vitamins, including biotin, folic acid, vitamin K, and several B vitamins, which supplement our dietary intake of vitamins. August 28, 2012 Roles of Symbiotic Microorganisms • Many vertebrates have large populations of symbiotic bacteria and protists in special fermentation chambers. – These microorganisms have enzymes that can digest cellulose to simple sugars that the animal can absorb. • Herbivorous mammals (e.g. horses) house symbiotic microorganisms in a large cecum. • The symbiotic bacteria of rabbits and some rodents live in the large intestine and cecum. – Since nutrients are absorbed in small intestine, these organisms recover nutrients from fermentation in large intestine by eating some of their feces and passing food a second time. Augustthrough 28, 2012 Ruminants: deer, cattle, and sheep (1) When the cow chews and swallows grass, boluses enter the rumen and (2) the reticulum. – Symbiotic bacteria and protists digest this celluloserich meal, secreting fatty acids. – Periodically, the cow regurgitates and rechews the cud, which further breaks down the cellulose fibers. (3) The cow then reswallows the cud, which moves to the omasum, where water is removed. (4) The cud, with many microorganisms, passes to the abomasum for digestion by the cow’s enzymes. August 28, 2012 Microorganisms in human digestive tract • At birth, the digestive tract is sterile and cannot digest food. • Bacteria ingested during birth and subsequent food intake rapidly colonize the tract. • Microorganism inside human digestive tract = 1014 cells August 28, 2012 • Play roles in digestion process, vitamin production and body’s natural defense system Probiotics (= for life) • Ilya Ilyich Mechnikov (Russian Scientist; Nobel Laureate in Physiology or Medicine, 1908) observed the positive role of bacteria and suggested that it would be possible to modify the gut flora (symbiotic microorganisms in digestive tract), and to replace harmful microbes by useful microbes. • Probiotics (FAO/WHO) = live microorganisms which when administered in adequate amounts confer a health benefit on the host. • Probiotics – microorganisms isolated from digestive tract of animals – can grow in digestive tract conditions (high acid, low oxygen, etc.) – mainly lactic acid producing bacteria August 28, 2012 Probiotics products • cultured of microorganisms isolated from human digestive tract • Probiotics products are mainly yoghurt, but some yoghurt may not contain any probiotics! • Example of probiotics – Lactobacillus casei Shirota – Lactobacillus johnsonnii La1 – Bifidobacterium animalis August 28, 2012 Bifidobacterium animalis DN 173010 Trade name • Bifidus digestivum (UK) • Bifidus regularis (USA) • Bifidus actiregularis (Italy) • Bifidus activo (Spain) • Bifidus essensis (Germany) • Bifidobacterium lactis (Canada) • Acti regularis (Thailand) August 28, 2012