Ch. 30: Digestive & Excretory Systems

  • types of tissue & their functions ⤵   * epithelial: protects, absorbs   * connective: binds   * nervous tissue: receives & transmits nerve impulses   * muscle tissue: voluntary & involuntary movements

  • body organization (smallest to biggest)   * cell ⤦   * tissue ⤦   * organ ⤦   * organ system

  • body organization (smallest to biggest)

  • homeostasis: stable internal physical & chemical conditions maintained by an organism

  • feedback inhibition (negative feedback): process where stimulus makes response that opposes original stimulus

  • jobs of the liver ⤵   * converts ammonia to urea (less toxic)     * kidneys then filter urea from blood & excrete it from body   * converts other dangerous substances into things that can be safely removed from the body   * regulates blood’s glucose levels     * too little glucose: nervous system cells slow and could lose consciousness     * too much glucose: steadily damages eye cells, kidneys, heart, & immune system       * diabetes

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Digestive System

  • breaks down food; absorbs nutrients; eliminates waste
  • {{organs involved in digestive system: mouth, pharynx, esophagus, stomach, small & large intestine, rectum{{
  • this system converts food into small usable molecules for body cells
  • mechanical digestion: the physical breakdown of large food pieces into smaller food pieces
  • chemical digestion: enzymes break down food into the small molecules the body can use
  • food is processed by the digestive system in 4 phases ⤵

     1. ingestion      * process of putting food in mouth      * opening of the digestive tract   2. digestion      * food is mechanically digested and then accessed by digestive enzymes      * chemical digestion occurs next   3. absorption      * the now small food molecules = can be absorbed in small intestine      * from small intestine, the molecules enter circulatory system & spread throughout body   4. elimination      * indigestible and unabsorbable substances (ie cellulose) travel to large intestine & out the body as feces

Full Digestive System Process (in order)
  • chewing food with teeth = first of mechanical digestion process
  • saliva from glands in mouth = first of chemical digestion process   * saliva contains enzyme called amylase that starts breaking chemical bonds in starches, forming sugars   * also contains enzyme called lysozyme that fights infection     * digests bacteria cell walls
  • tongue & throat muscles push clump of food (bolus) down throat
  • epiglottis blocks opening to trachea
  • food is moved through esophagus with peristalsis   * peristalsis: provides force to move food through the esophagus, towards the stomach
  • cardiac closes off connection between stomach & esophagus to prevent regurgitation
  • stomach: large muscular sac that continues chemical & mechanical digestion processes
  • some stomach lining glands produce hydrochloric acid, others produce pepsin, others produce mucus   * pepsin: breaks proteins into smaller polypeptide fragments     * best functioning in acidic environments   * mucus: fluid that lubricates and protects stomach wall     * prevents acid erosion & peptic ulcers
  • stomach has alternating contractions to churn bolus (mechanical digestion)   * allows enzymes greater access to bolus
  • chyme is produced from bolus   * chyme: oatmeal-like consistency mixture
  • after a couple hours, pyloric valve opens & spurts chyme into small intestine   * pyloric valve: valve located between stomach & small intestine
  • chyme enters duodenum   * duodenum: the first part of the small intestine   * where almost all digestive enzymes enter the intestine
  • small intestine: where majority of chemical digestion & absorption occurs
  • upon entering duodenum, chyme mixes with enzymes & digestive fluids from pancreas, the liver, & duodenum lining
  • pancreas: gland that serves 3 functions ⤵   * produces hormones that regulate blood sugar levels   * produces enzyme that breaks down carbs, proteins, lipids, & nucleic acids   * produces sodium bicarbonate     * sodium bicarbonate: a base that quickly neutralizes stomach acid when chyme enters duodenum       * necessary for digestion to proceed       * protects other pancreatic enzymes from being destroyed by acidic stomach acid
  • liver produces ⤵   * bile: a fluid loaded with lipids & salts     * stored in small pouchlike organ called gallbladder       * fat present in duodenum = gallbladder releases bile into small intestine     * breaks up globs of fat into smaller droplets that disperse in small intestine’s watery environment
  • most nutrients from food = absorbed through small intestine walls
  • large intestine absorbs water & several vitamins, & prepares waste for elimination from body
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