Digestive system


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Bio 102: Fundamentals in Animal Biology. This is a handout for the digestive system.

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Digestive system

  1. 1. Functions: • Takes in food (ingests it) • Breaks it down physically and chemically into nutrient molecules (digests it) • Absorbs the nutrients into the bloodstream • It rids the body of the indigestible remains (defecates) 2 Chapter IV. The Digestive System
  2. 2. • The digestive tube can be organized into specialized regions • That carry out digestion and nutrient absorption in a stepwise fashion 3
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  5. 5. Types of animal body plans • Sac-like plans – are found in many invertebrates – have a single opening for food intake and the discharge of wastes • Tube-within-a-tube plan – found in vertebrates –food entering through one opening (the mouth) and wastes leaving through another (the anus) 6
  6. 6. Types of Digestion • Intracellular digestion –occurs in sponges, coelenterates (corals, hydras and their relatives) and most protozoans • Extracellular digestion –occurs in chordates, annelids, and crustaceans 7
  7. 7. Stages in the Digestive Process • movement: propels food through the digestive system • secretion: release of digestive juices in response to a specific stimulus • digestion: breakdown of food into molecular components small enough to cross the plasma membrane • absorption: passage of the molecules into the body's interior and their passage throughout the body • elimination: removal of undigested food and wastes 8
  8. 8. The Mammalian Digestive System • Each organ has specialized food- processing functions 9 • Alimentary canal/ GI tract - mouth - pharynx - esophagus - stomach - small intestine - large intestine • Accessory organs - salivary glands - teeth - pancreas - liver - gall bladder
  9. 9. Components of the Digestive System 10
  10. 10. Mechanics of Swallowing 11
  11. 11. 12 Peristalsis- rhythmic waves of contraction of smooth muscles in the wall of the canal
  12. 12. • Liver- regulation of amino acids in blood, production of glycogen (storage molecule) and bile • Pancreas- secretion of amylase and insulin (lack of insulin may cause diabetes) • Gallbladder- storage of bile Accessory Digestive Organs 13
  13. 13. The Stomach • Large muscular storage organ; function in storage, mixing, and secretion of gastric juice, which converts a meal to acid chyme 14
  14. 14. 15 Small intestine – is the major organ of digestion and absorption
  15. 15. • The enormous microvillar surface – Is an adaptation that greatly increases the rate of nutrient absorption 16
  16. 16. 17 • Hormones help coordinate the secretion of digestive juices into the alimentary canal
  17. 17. • reabsoption of water • Bacteria in colon produce vitamin K • The wastes of the digestive tract, the feces –Become more solid as they move through the colon –Pass through the rectum and exit via the anus The large intestine, or colon 18
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  19. 19. Chemistry of Digestion 20 Hydrolysis- digests foods: 1. Carbohydrates (starches) - become simple sugars 2. Proteins - become amino acids 3. Fats - become fatty acids & glycerol 4. Nucleic acids (RNA, DNA) - become nucleotides
  20. 20. Carbohydrate Digestion 21 • Begins in mouth - salivary amylase breaks down starch • Mostly occurs in small intestine aided by following enzymes: a. Pancreatic enzymes - breaks starch into maltose b. Maltase - breaks maltose into 2 glucoses c. Sucrase - breaks sucrose into 1 glucose and 1 fructose d. Lactase - breaks lactose into 1 glucose + 1 galactose • Last 3 enzymes produced by small intestine. Following absorbtion, glucose, fructose, & galactose transported to the liver where they are converted to glycogen.
  21. 21. Fat Digestion 22 • Gastric lipase of stomach breaks down some fats. • Most fat digestion occurs in small intestine. • bile emulsifies fat, exposing more fat to enzymes • Bile salts link fat molecules to water molecules; (normally fats are hydrophobic) • Pancreatic lipases continues fat digestion • subunits now cross into microvilli • subunits are reassembled into triglycerides, combined with cholesterol, and transported to the circulatory system
  22. 22. Protein Digestion 23 • Stomach - pepsinogen converted to pepsin in the presence of HCL. Pepsin breaks some of the peptide bonds of some proteins • Small intestine - Pancreatic enzymes trypsin & chymotrypsin break proteins into smaller and smaller units. The pancreatic enzyme carboxypeptidase breaks peptides into free amino acids. Several enzymes produced by the small intestine further break peptides into amino acids.
  23. 23. • Amino acids- absorbed and transported to the liver. − used directly by the liver to make liver proteins − others converted to acetyl coenzyme A (used in citric acid cycle) − other amino acids sent to various parts of the body for protein synthesis • Proteases must be activated before being used − Prevents them from breaking down pancreas (where they’re made & stored) − Activation occurs when they come in contact w/ certain chemicals found in the small intestine 24
  24. 24. Nucleic Acid Digestion 25 • Enzymes called nucleases break down nucleic acids such as RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) into nucleotide chains. • The pancreas produces ribonuclease and deoxyribonuclease • small intestine produces nucleases that break down nucleotides into smaller subunits.
  25. 25. Integration & Regulation of Digestive Processes 26 • Mechanical - act of chewing causes release of salivary amylase. • Neural - food in stomach stimulates vagus nerve, signal sent to brain, brain sends another signal down vagus nerve for stomach to release gastric secretions. • Hormonal - e.g. the stomach releases the hormone gastrin when a protein concentration is detected; gastrin circulates in blood, target cells are gastric glands which release gastric enzymes; similar in small intestine and pancreas.
  26. 26. Importance of Nutrition 27 • provides food for fuel • provides food for fabrication • provides food to obtain essential nutrients, water, minerals
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