Biolove chapter 1 digestive system


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Biolove chapter 1 digestive system

  2. 2. BIOLOVE 2013 Ways of ingesting • Substrate feeders – caterpillar - Live in or on the food source - Ingest the food source and also eliminate on the food source. Photo 1 : caterpillar (substrate feeder) • Bulk feeders – humans, snake, tiger - Ingest large pieces of foods. • Fluid feeder – mosquito - Sucking nutrient from a living host • Suspension feeder – tube worm, whale, oyster, clam Photo 2 : Aphid sucking nutrient from phloem - Extract food particles suspended in the surrounding water. Food processing Baleen • Ingestion – the act of eating • Digestion – the break down food into smaller molecules • Absorption – cells lining in the digestive tract take Photo 3 : whale (suspension feeder) up the products of digestion • Elimination/defecation – undigested material passes out of the digestive tract Digestion mechanical chemical breakdown of food into hydrolysis pieces digestive using teeth enzyme Figure 1: Digestion DivisionIKMAL_nik/2013 Page 2
  3. 3. BIOLOVE 2013 Nutrient travel to body cells Absorption process occurred Excess nutrients Combine mainly in the small intestine together become stored as fats macromolecules Macromolecules will break to supply energy Figure 2: AbsorptionQUESTIONQuestion 1 (OCT 2010)a) Describe in detail four (4) types of feeding mechanisms used by animals. (8marks)ANSWER: -ADAPTATION! - Organisms have special compartment where the food is digested without digesting their own cellsIntracellular digestion  Hydrolysis of food inside vacuoles.  After cells engulf food by phagocytosis or liquid food by pinocytosis.  Newly formed food vacuoles fuses with lysosome, an organelle containing hydrolytic enzymes.  Example : spongesIKMAL_nik/2013 Page 3
  4. 4. BIOLOVE 2013 Intracellular digestion in Paramecium sp.Extracellular digestion - Breakdown of food in compartments that are continuous with the outside of the animal’s body - Advantage of having more extracellular compartments – enables an animal to devour much larger sources of food than can be ingested by phagocytosis.Example : HydraGastrovascular cavity • Animals with simple body plans • A digestive compartment with single opening. • Functions : Digestion & distribution of nutrientExample: flatwormAlimentary canal  Digestive tube extending between two openings – mouth and anus  A complete digestive tract.  Advantage: can ingest food while earlier meals are being digested. Question [Part A] 1. Which of these animals has a gastrovascular cavity? A. Bird B. Hydra C. Mammal D. Insect E. AnnelidIKMAL_nik/2013 Page 4
  5. 5. BIOLOVE 2013Question:Difference between gastrovascular cavity and alimentary canalAnswer: Gastro vascular cavity Alimentary canalSingle opening for both ingestion and Separate part for ingestion and elimination – haselimination opposite ends Structure Functions Pharynx Sucks food in through mouth Crop Store and moisten food Gizzard Mechanical digestion Intestine Digestion and absorption Typhlosole/Dorsal fold Increase TSA for nutrient absorptionIKMAL_nik/2013 Page 5
  6. 6. BIOLOVE 2013 • Three main regions: foregut, midgut, hindgut. • Foregut consist of esophagus and crop • Food stored and moistened in crop. • Digestion occur in midgut • Gastric cecae functions in digestion and absorption • Three separate chambers – crop, stomach, gizzard • Gizzard and crop has the same function as earthworm. • Digestion and absorption occur in intestineHuman Digestive System • Consist of alimentary canal and accessory glands. • Accessory glands – salivary glands, pancreas, liver and gallbladder. • Accessory gland secrete digestive juices through duct into the canalIKMAL_nik/2013 Page 6
  7. 7. BIOLOVE 2013 Three types of salivary gland 1. Submandibular gland 2. Sublingual gland 3. Parotid gland Every gland has duct to conduct saliva • The presence of food stimulates nervous reflex – salivary gland – secrete salivaSaliva –  Initiates chemical digestion  Protecting oral cavity  Lubricates food for easier swallowing (has slippery glycoprotein, Mucin)  Aids bolus formation  Neutralize food acid – prevent tooth decay  Antibacterial agents  Contain digestive enzymesPeristalsis  Food pushed down by peristalsis  Peristalsis – alternating wave of contraction and relaxation of smooth muscle of esophagus  Peristalsis enable food to be pushed down even when we are lying down… sleepingSphincter  Muscular layer forms ring-like valves.  To close off the alimentary canal.  Regulate the passage of material between compartments.Cardiac sphincter (lower esophageal sphincter) - Limit upward movement of food from stomachPyloric sphincterIKMAL_nik/2013 Page 7
  8. 8. BIOLOVE 2013 - Control movement of food from stomach to the small intestineQuestion:Why organisms have different shapes of teeth?Dental Adaptation - Teeth help to increase Total surface area of food to be hydrolyse by enzymes (salivary amylase) Humans have  Incisors  Canines (Cuspids) Palate  2 Premolars  3 molars Used to chew, grind, smash, crush, crack food! Palate - bone reinforced structure - provide hard surface for tongue - to press food to be mixed with saliva Other organisms’ teeth Carnivores have pointed teeth for cutting and shearing Herbivores have large flat teeth for grinding celluloseIKMAL_nik/2013 Page 8
  9. 9. BIOLOVE 2013Tongue - Has taste bud (help to taste food) - Shape food into bolus - Move bolus into pharynxSwallowing foodQuestion: Explain the mechanism of swallowing food into the stomachAnswer: - The pharynx opens to the trachea and esophagus. - Normally, esophagus opening closes due to contraction of esophageal sphincter. - Air enters the larynx (opening of the trachea) - During swallowing: 1: Tongue pushes bolos to the back of oral cavity 2: Larynx moves up, epiglottis moves down; opening of trachea closes 3: Esophageal sphincter relaxes; opening of esophagus opens - After swallowing: - Epiglottis moves up - Larynx moves down - Esophageal sphincter contact - Opening of trachea opens, opening of esophagus closes Esophagus layers 1. mucosa, 2. submucosa, 3. mascularis externaIKMAL_nik/2013 Page 9
  10. 10. BIOLOVE 2013 4. serosa. Sphincter between Rectum and anus Internal sphincter – involuntary External sphincter - voluntary Feces are stored temporarily at the rectum These sphincter control movement of bowelDigestion stomachStomachCan stretch – accommodate 2L food and fluidSecrete gastric juice – mixed with food – form chimeChemical digestion in stomachCarried out by gastric juiceGastric juice has two components 1. HCl 2. PepsinWhat HCl do? - Disrupts extracellular matrix that bind cells together in meat and plant material - pH is 2 (so high) - unfolds protein in food (increase exposure to peptide bond)After HCl done its action, followed by pepsin - pepsin is a protease - work best in strong acidic environment - Protein  small polypeptidesIKMAL_nik/2013 Page 10
  11. 11. BIOLOVE 2013 - Polypeptides is further digested in the small intestineWhy doesn’t gastric juice destroy stomach cells that make it? - The ‘ingredients’ of gastric juice are kept inactive until released to the lumen of stomach - Gastric juice produced by gastric glands Gastric glands Parietal cells - Secrete hydrogen and chloride ions - H+ and Cl- then form HCl Chief cells - Secrete pepsinogen - Pepsinogen is inactive form of pepsin - Pepsinogen converted to pepsin by HCl - HCl clip off small portion of the molecule and exposing its active site - HCl and pepsin form in the lumen, not within the cells of the gastric glandsProduction of pepsin will stimulate the release of more pepsinogen. Pepsinogen thenactivated to pepsin. (Positive feedback mechanism)Wall of stomach is vulnerable to gastric juice and acid tolerant pathogen in food.Stomach lining secrete mucus to prevent self digestionStomach cell also divide every three days to replace cellsIKMAL_nik/2013 Page 11