1. Feeding Methods
    1. Absorption (passive) via external surfaces - some protozoans, endoparasites, aquatic invertebrates
    2. Endocytosis - protozoans, lining of the alimentary canal
    3. Filter feeding/ suspension feeding
      1. Small food particles are "filtered" out of the water
      2. Mucus often helps trap the food
      3. Used by marine animals (sponges, brachiopods, whales)
    4. Fluid Feeding
      1. Piercing and sucking
        1. Inject anticoagulants into the host
        2. Suck blood out of host via proboscis/pharynx
        3. Used by nematodes, annelids (leech), arthropods (mosquitos, lice)
      2. Cutting and Licking
        1. Create a whole in host's integument
        2. Lick or sponge the fluid which leaks out
        3. Some use anticoagulants and/ or analgesics (eg bat)
    5. Seizing Prey
      1. Jaws, teeth, beaks - adapted to allow animals to capture prey and / or inject toxins (15-6 through 15-9)
      2. Toxins - used to paralyze / stun prey or fend off predators
    6. Herbivores/ Grazing - specialized mouths and teeth with tough enamel, or which continually grow (rodents)
  2. Alimentary Systems
    1. Types
      1. Batch reactor - food comes in, is processed, and leaves by the same opening (eg coelenterates/cnidarians: jellyfish, corals, anemones)
      2. Continuous flow, stirred-tank reactors (eg forestomach of ruminants)
        1. Food is always coming in during processing
        2. Digestive by-products leave via a different pathway
      3. Plug-flow reactor - bolus of food (plug) is digested as it flows along a long digestive reactor (eg small intestine)
    2. Headgut - food entrance point
      1. Accepts food/ begins the breakdown processes
      2. Mechanical (if food is chewed) and chemical breakdown
      3. Saliva (15-28) - main secretion (talked about in exocrine section)
        1. Moistens food - smoothes its passage
        2. Contains amylases (vertebrates and invertebrates) which breaks down starches to di and oligosaccharides
      4. Stimulated by
        1. Food in mouth
        2. Mechanical stimulation of mouth tissues
        3. Cephalic stimulation (thinking about food)
        4. When stimulated, amount of enzyme present and rate of flow increases
    3. Foregut: Food conduction, storage, and digestion
      1. Esophagus
        1. Food conduction via peristalsis (reverse is regurgitation)
        2. Storage (crop)/Fermentation - used by leeches between feedings or birds storing food to give to young
        3. Secretes mucus continually for lubrication
      2. Stomach - mono and digastric (single / many stomachs)
        1. Storage of food; major breakdown of foodstuffs
        2. Mechanical mixing of food and secretions and chemical digestion
          1. Gizzard/crop in birds contains stones to grind seeds
          2. Ruminate stomachs - rumen and reticulum used for fermentation, then passed to omasum and abomasum (the only stomach to secrete digestive enzymes)
        3. Secretions
          1. Pepsinogin
            1. Secreted by the chief cells
            2. Cleaved to pepsin which digests proteins at pH=2
            3. Stimulated by the vagus nerve and gastrin
          2. HCl
            1. Secreted by parietal/oxyntic cells
            2. Uses carbonic anhydrase and a HCO3-/Cl- exchange pump (15-32)
            3. Stimulated by vagus nerve (cephalic phase of digestion), gastrin and histamine (both needed), and caffeine, alcohol, and some spices (last 5 due to gastric phase of digestion sensed via mechano and chemo receptors)
          3. Gastric Mucus
            1. Secreted by goblet cells
            2. Contains alkaline electrolytes to neutralize the pH
          4. Inhibition of secretions
            1. Enterogastric reflex - chemo and mechanoreceptors sense food (chyme) in the duodenum and cause secretin, GIP (gastric inhibitory peptide), VIP (vasoactive intestinal peptide), and bulbogastrone to be released
            2. Sympathetic stimulation
    4. Midgut: Chemical digestion and absorption
      1. Absorption - specialization of the epithelium
        1. Large surface area (size of a doubles tennis court in humans)
          1. Mucosa is highly folded (also helps slow food down)
          2. Covered by villi
            1. lymph and blood vessels extend into the villi to transport absorbed materials
            2. digestive epithelium (absorptive and goblet cells) cover the villi
          3. brush border is formed by microvilli covering the villi
        2. cells are held together by desmosomes and tight junctions to prevent digested materials from passing between the cells
      2. Secretions
        1. Duodenum - mostly digestion
          1. Pancreatic secretions
            1. Peptidases: trypsinogen, chymotrypsinogen, carboxy and aminopeptidases
            2. Carbohydrases: amylase and maltase
            3. Lipase
            4. Nucleases
            5. Bicarbonate (neutralizes acid from the stomach)
          2. Bile (from Gallbladder)
            1. Contains fats and fatty acids, bile salts and pigments, and cholesterol
            2. Neutralizes chyme (alkaline)
            3. Breaks fats into micelles for enzymatic digestion and absorption
            4. Contains waste substances from the blood which are digested or excreted
          3. Duodenal Secretions
            1. Brunner's gland - secretes a mucoid fluid to protect duodenum before the pancreatic and gallbladder secretions can neutralize the chyme
            2. Peptidases: enterokinase, carboxy and aminopeptidases
            3. Carbohydrases: maltase, lactase, sucrase
            4. Lipase
            5. Nucleases
        2. Jejunum - secretions similar to duodenum, plus absorption
        3. Ileum - absorption
      3. Control of secretions (intestinal phase of control) (15-34)
        1. Gallbladder and pancreas are both stimulated by cholecystokinin (CCK)- released by the presence of fatty and amino acids in the duodenum
        2. Pancreas is stimulated by secretin (strong acid in stomach and small intestine)
        3. Pancreas is inhibited by
          1. Enteroglucagon (carbohydrates in the duodenum)
          2. Enkephalin (basic conditions in the stomach and intestine)
          3. Somatostatin (acid in the stomach lumen)
    5. Hindgut: water and ion absorption; defecation
      1. Stores remains of digested food where bacterial flora digest the contents
      2. Fermentation occurs in many animals (zebras, elephants, rodents)
      3. Fecal material passes through the rectum or cloaca, causing the urge to defecate
        1. If defecation occurs, feces pass through an internal sphincter and out the anus
        2. If defecation does not occur, the fecal material passes back into the colon
  3. Motility
    1. Importance/WHY?
      1. Moves food through alimentary canal
      2. Mixes food and digestive juices
      3. Provides the maximal diffusion gradient by always supplying new material to the epithelial lining
    2. Types
      1. Ciliary - used by annelids (earthworms, leeches), tunicates (look like sponges), cephalochordates (lancets)
      2. Muscular - used by most animals
        1. Peristalsis - wavelike contraction of smmoth muscle; relaxation of the circular muscle is followed by a contraction which pushes food ahead to the next relaxed area
        2. Segmentation - rhythmic contractions of circular muscle which pushes food back and forth rather than forward
    3. Control
      1. Intrinsic - myogenic muscles cause the contraction - Basal Electric Rhythm (BER)
      2. Extrinsic - neuronal/hormonal modification of the BER
        1. ACh/ parasympathetic drive increases the BER
        2. Epinephrine/ sympathetic drive decreases the BER
        3. Peptide hormones (Table 15-2) have varying effects
  4. Absorption
    1. Types: diffusion, carrier mediated, active transport, endocytosis (15-35 and 15-36)
      1. Lipids
        1. Diffuse across membrane when micelle contacts the epithelium
        2. Reassemble in the smooth endoplasmic reticulum
        3. Repackaged into chylomicrons in the Golgi
        4. Exocytoses and diffusion into central lacteal
    2. Transport in blood
      1. Fats are carried by the lymph system, added to the blood at the thoracic duct
      2. Sugars and amino acids are transported into the capillaries where they immediately go to the liver via the hepatic portal vein
      3. Vitamins are transported in both the lymphatic and circulatory system initially, depending on whether or not they are fat or water soluble