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27 digestion 2
 

27 digestion 2

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    27 digestion 2 27 digestion 2 Presentation Transcript

    • Digestion 2: Mouth throughStomachChapter 20; pages 570 - 581
    • Salivary Glands: Fig 20.9
    • Salivary Glands• Parotid– α amylase (ptyalin)– α 1 - 4 hexose linkages• Submaxillary & Sublingual–mucin (protein for lubrication)
    • Fig 5.3: Review ofSugar Structure
    • 1 4 α– linkage
    • Starch: 1 – 4 & 1 – 6 α linkages
    • Cellulose: β 1 – 4 linkages
    • Salivary GlandsAcinus type glands:Primary secretion by secretorycells and then modified by ductcells as saliva passes through onthe way to the oral cavity
    • Accessory Gland Structure: Fig 20.8Na+K+<--Cl-<-- HCO3-
    • Saliva• As saliva flows down duct:–[Na+] and [Cl-] decrease–[HCO3-] and [K+] increase– π also decreases - hypotonic• As flow rates increase, this exchange isless complete
    • Salivary pH• Saliva pH is basic (vs. plasma pH)• WHY?? (i.e., for what purpose?)
    • Excitatory Signal Molecules• ACh from Parasympathetic NSonto muscarinic receptors• VIP from enteric NS• Increased blood flow in response tokininogen activation
    • Kininogen Activation• Glands release Kallikrein whenactivated– acts on a kininogen, a plasma globulin• Results cleavage forming a peptide -->bradykinin• Bradykinin ---> local vasodilation (10Xincrease in BF)
    • Other Components of Saliva• Muramidase --> cleave muramic acid inbacterial cell walls• Lactoferrin --> binds Fe++• Epidermal growth factor --> stimulatesmucosal cell growth• IgA• Lingual lipase (small amounts)• ABO antigens (secreters)
    • Salivary Secretion• Cephalic Phase–Thought or sensory input• Gastric Phase–Distention–Secretagogues–Vagal - Vagal reflex
    • Fig 20.29Fig 20.29
    • Stomach; Figure 20.4
    • Stomach Mucosal Surface:Folds are calledRugae gastricaeAchalasia: failure to openesophageal sphincter
    • History Lesson:Alexis St. MartinandWilliam Beaumonthttp://www.james.com/beaumont/dr_life.htmhttp://www.guineapigzero.com/AlexisStMartin.html
    • Dr. William Beaumont
    • Beaumont & St. Martin
    • Stomach; Figure 20.4
    • Oxyntic Glands• Surface Epithelium - insoluble mucous• Neck Cells - soluble mucous• G cells - gastrin• Parietal (or oxyntic) Cells - HCl & IntrinsicFactor• Chief Cells - pepsinogen
    • Gastric Acid Secretion: Fig 20.22
    • PostprandialAlkaline Tide
    • http://en.wikipedia.org/wiki/File:Control-of-stomach-acid-sec.png
    • Histamine• From enterochromafin-like cells (ECLcells) in the gastric mucosa• produce, store, & release histamine• activated by ACh, gastrin, &secretagogues
    • Treatment of Hyperacidity• Atropine•Antihistamine (H2 antagonists)–Cimetidine•Proton pump inhibitors–Nexium
    • Pepsin• Pepsinogen ---> pepsin in acidicconditions of stomach• It is a family of endopeptidases• pH optima 1.8 - 3.5
    • Activation of Pepsin; Fig 20.14Activation of Pepsin; Fig 20.14
    • 1.0 3.0 5.0Gastric pHPepsinActivityµmoles/min/mg enzymeThree Different Pepsins
    • Vitamin B12• aka, cyanocobalamin• required for nucleicacid synthesis• is very labile in acid
    • Haptocorrin & Intrinsic Factor• Haptocorrin (transcobalamin) made insalivary glands• binds Vitamin B12 very tightly• protects it from gastric acid digestion
    • Haptocorrinhttp://en.wikipedia.org/wiki/Haptocorrin
    • Haptocorrin• Haptocorrin is digested by pancreaticproteolytic enzymes in the duodenum• Vit B12 now binds to Intrinsic Factor (IF)• The B12 – IF complex is taken up byendocytosis in the duodenum
    • Intrinsic Factor
    • Secretagogues• caffeine and theophylline• peptides• spices• Alcohol• aspirin
    • Digestion Review:• ANS and enteric nervous system• Smooth muscle structure - function• Saliva and regulation of flow• Stomach secretions• On to regulation of gastric secretion andmotility (emptying)…….
    • Table 20.2 Gastrointestinal Hormones
    • Hormones: GastrinHormone Site of secretion Stimuli ActionsGastrin Stomach Protein digestionproducts instomach,distention, andparasympatheticinputStimulatesgastric secretion& motility,relaxes ileocecalsphincter,stimulates massmovement ofcolon
    • Hormones: Cholecystokinin(CCK)Hormone Site of secretion Stimuli ActionsCCK Duodenum andjejunumFat or proteindigestionproducts inDuodenumInhibits gastricsecretion &motility,potentiatessecretin action,stimulatespancreaticenzymesecretion,stimulates bilesecretion, andcontracts bileduct and gallbladder
    • Hormones: SecretinHormone Site of secretion Stimuli ActionsSecretin Duodenum andjejunumAcid induodenumInhibits gastricsecretion &motility,stimulatespancreatic HCO3-secretion,potentiatesactions of CCK,and stimulatesbile secretion byliver
    • Hormones: GIP(glucose-dependent insulinotropic peptide)Hormone Site of secretion Stimuli ActionsGIP Duodenum andjejunumGlucose, fats oracid induodenum anddistention of theduodenumInhibits gastricsecretion &motility,stimulates insulinsecretion by thepancreas
    • Contol of G.I. Function: Fig. 21.21
    • GASTRIN• Peptide hormone• From G cells (stomach)• Increases HCL & pepsinogen secretion• Increases gastric motility and emptyinginto duodenum
    • Gastric Acid Secretion:Cephalic Phase Fig 20.23a• Thought of food, smell, chewing,swallowing• Vagus nerve to parietal cells (ACh)• Vagus nerve (ACh) onto G cells & thuscauses gastrin release• See TABLE 20.2 !!!!!
    • Fig 20.23aCephalicPhaseof GastricSecretion
    • Fig 20.23bGastric Phaseof GastricSecretion
    • Gastric Acid Secretion:Intestinal Phase• Stimulus - digested peptides, peptidesin duodenum, distention• G cells (gastrin)• distention -->Intestinal endocrine cellsrelease CCK, Secretin, & GIP• see Table 20-2
    • Inhibition of Gastric Secretion• Important for protection of duodenum• Acid in duodenum ---> secretin &CCK---> inhibits gastric secretion andmotilitySee Table 20.2 for sure !!!
    • Inhibition of Gastric Secretion• Acid, fats, hyper-osmotic solutions in theduodenum ---> release of enterogastrones---> inhibit gastric motility and secretion• Gastric Inhibitory Peptide or Glucose-dependent Insulinogenic Peptide (GIP) fromduodenum ---> inhibits parietal cell function–Decreases release of acid, motility, & secretion–Increases release of insulin from pancreas
    • • Ulcers - page 576–Peptic & Duodenal–Role of Helicobacter pylori• Vomit reflex - page 599–Note sympathetic symptoms