Chapter 23 Digestive System Lectures 9 & 10

1. Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 23 Digestive System Lectures 9 & 10

2. Lecture Overview (Lectures 7 & 8) • Introduction to the digestive system • General characteristics of the alimentary canal • The mouth and tongue • Salivary glands • Pharynx and esophagus • Stomach • Pancreas

3. Digestive System • Functions of Digestive System • ingestion • mechanical digestion • chemical digestion • propulsion • absorption • excretion • defecation Digestion is the mechanical and chemical breakdown of food into a form that cells can absorb

4. Major Organs of Digestive System Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 • Organs can be divided into the: • Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.) • Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas

5. The Greater and Lesser Omenta Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

6. The Mesentery Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

7. The Abdominal Cavity & Peritoneum Notice that the pancreas, duodenum, and rectum are retroperitoneal Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

8. Alimentary Canal Continuous tube modified along its length to carry out specialized, regional functions. Mouth, pharynx, esophagus, and anal canal are lined by nonkeratinized stratified squamous epithelium Stomach and intestines are lined by simple columnar epithelium. Why?

9. Alimentary Canal Wall Know the 4 layers of the alimentary canal and their order Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

10. Alimentary Canal Wall

11. Movements Through the Alimentary Canal • mixing movements (segmentation) • peristalsis - The wavelike muscular contractions of the alimentary canal or other tubular structures by which contents are forced onward toward the opening. (Triggered by pacesetter cells.)

12. Innervation of the Alimentary Canal The alimentary canal has extensive sympathetic and parasympathetic innervation - mainly in the muscularis externa - regulates its tone and the strength, rate, and velocity of muscular contractions • submucosal plexus – controls secretions/blood flow • myenteric plexus – controls gastrointestinal motility/sphincters • parasympathetic division of ANS – increases activities of digestive system and relaxes sphincters • sympathetic division of ANS – generally inhibits digestive actions and contracts sphincters

13. Mouth (Oral or Buccal cavity) (Labium) • ingestion • mechanical digestion • prepares food for further chemical digestion (Labium) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

14. Tongue Very muscular; muscles run in several directionsCovered by mucous membranes Blast from the past - Root of tongue is anchored to the hyoid bone • Tastebuds • Friction for food handling • Secretes lingual lipase

15. Palate • roof of oral cavity (adenoids) Important in separating the nasopharynx from the pharynx during swallowing

16. Secondary (Permanent) Teeth Total of 32 secondary (permanent) teeth 1 16 Watch for incoming ICBMs!!! – Or - I ‘C’ Big Molars 32 17 Know the order of these

17. Primary (Deciduous, Baby, Milk) Teeth (Mastication = chewing) • 8 incisors • 4 cuspids • 8 molars • 20 total All primary teeth are lost, generally between ages 6 and 12

18. Section of a Tooth Oh no! Not again! What type of articulation is this? Know this diagram for exam

19. Functions of Saliva • Moistens food • Binds food particles • Dissolves food for tasting • Begins chemical digestion of complex CHO (amylase) • Cleans teeth and mouth (pH = 6.5 – 7.5) • Anti-microbial (IgA and lysozyme)

20. Salivary Glands

21. Secretions of Salivary Glands Secretions are slightly acidic and continual due to basal parasympathetic stimulation, but increase after - presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume) • Parotid glands • clear • primarily water, serous fluid • rich in amylase • mumps virus typically attacks here • Submandibular glands • primarily serous fluid • some mucus, amylase • Sublingual glands • primarily mucus • most viscous

22. Pharynx Pharynx aids swallowing by grasping food and moving it toward the esophagus.

23. Three Phases of the Swallowing Reflex Only voluntary phase is the buccal (oral) phase, i.e., the initiation of swallowing, then… • soft palate and uvula raise • hyoid bone and larynx elevate Pharyngeal phase • epiglottis closes off top of trachea • longitudinal muscles of pharynx contract reflexive • inferior constrictor muscles relax and esophagus opens Esophageal phase • peristaltic waves push food through pharynx

24. Swallowing Mechanism

25. Esophagus Veins drain into hepatic portal vein (via gastric veins) Lower esophageal (cardiac) sphincter prevents reflux (backup) of stomach acid into the esophagus. Esophagus conveys food from pharynx to stomach by peristalsis

26. Stomach M Stomach can hold about 1-1.5 liters of material Gastricglands MG cellsD cells Greater curvature Stomach Functions:- Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B12 - Secretion of gastrin, somatostatin Rugae flatten as stomach fills

27. Blood Supply and Drainage of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

28. Lining and Gastric Glands of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

29. Gastric Secretions • mucus (cardia) • from goblet cells and mucous glands • protective to stomach wall • hydrochloric acid • from parietal cells • needed to convert pepsinogen to pepsin • ‘p’ in parietal and ‘p’ in pH • pepsinogen • from chief cells • inactive form of pepsin • intrinsic factor • from parietal cells • required for vitamin B12 absorption • pepsin • from pepsinogen in presence of HCl • protein splitting enzyme • mucus, gastrin, somatostatin • from pyloric glands • protective to stomach wall • gastrin and somatostatin are hormones • INFANTS ONLY • rennin (chymosin) • gastric lipase

30. Secretion of H+ by Parietal Cells Important functions of the stomach pH (1.5 – 2.0) - kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

31. Three Phases of Stomach Control • Cephalic phase • triggered by smell, taste, sight, or thought of food • begin secretion and digestion • Gastric phase • triggered by distension, presence of food, and rise in pH in stomach • enhances secretion and digestion • Intestinal phase • triggered by distension of small intestine and pH change • controls rate of gastric emptying; may slow emptying NOTE that all these phases control activity in the STOMACH Know what each phase does (shown in red)

32. Cephalic Phase of Gastric Secretion Emotional states can exaggerate or inhibit this phase Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

33. Gastric Phase of Gastric Secretion Proteins, alcohol, and caffeine can markedly increase secretions by stimulating gastric chemoreceptors Histamine stimulates acid secretion by parietal cells Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

34. Intestinal Phase of Gastric Secretion • Enterogastric reflex (inhibits gastric activity) –reduces gastric motility, stimulates contraction of pyloric sphincter (pylorus) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

35. Parasympathetic NS G cells Gastrin + Both + Key Overview of Gastric Control/Secretion + Stimulation - Mucous Cells Inhibition Emptying of Stomach ( [H+ ]) Stomach Molility (Segmentation/Peristalsis) ECL Cells Histamine Endocrine Factor + + + Exocrine Factor + (cephalic/gastric phases) + D cells Somatostatin Intrinsic Factor + B12 Parietal Cells pH < 3.0 - + H+ + Cl- HCO3- (alkaline tide) + + + + + (intestinal phase) Stretch of stomach Fats in Small Intestine pH > 3.0(dilution of H+) Peptides Chief Cells Pepsinogen Pepsin Protein Breakdown Food in Stomach Fat Breakdown Lipases

36. Mixing and Emptying Actions

37. Gastric Absorption Gastric absorption is very limited due to: - blanket of mucus covering cells - tight junctions between adjacent epithelial cells - epithelial cells lack specialized transport mechanisms - gastric lining is relatively impermeable to water - chyme usually contains only partially digested material Some substancescan be absorbed by the stomach: • some water • certain salts • certain lipid-soluble drugs, e.g., aspirin • alcohol (slowed by presence of fats)

38. Pancreas Exocrine (digestive) and endocrine (metabolic) functions Completes digestion of proteins that was started in the stomach

39. Blood Supply and Drainage of Pancreas Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

40. Pancreatic Juice • pancreatic amylase – splits glycogen into disaccharides • pancreatic lipases – break down triglycerides • pancreaticnucleases – digest nucleic acids • bicarbonate ions – make pancreatic juice alkaline (pH = 8) and neutralize acid coming from stomach • Pancreatic proteolytic enzymes…

41. Pancreatic Proteolytic Enzymes Enteropeptidase (Enterokinase)(brush border of sm. intestine) Know this chart Trypsinogen Trypsin Chymotrypsinogen Chymotrypsin Pancreas Procarboxypeptidase Carboxypeptidase Proelastase Elastase (Proenzymes, Zymogens) (Active enzymes) Dipeptides, tripeptides, amino acids Proteins Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach

42. Regulation of Pancreatic Secretions • acidic chyme stimulates release of secretin • secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to  pH)CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens

43. Key Regulation of Pancreas/Intestinal Digestion + Stimulation Acidic Chyme Enters Duodenum + (brush border) + + Enterokinase Cholecystokinin(CCK) Secretin + Trypsinogen Trypsin + + + Gallbladder Contraction Relaxation of hepatopancreatic sphincter ChymotrypsinogenProcarboxypeptidaseProelastase TrypsinogenCarboxypeptidaseElastase Pancreas Bile and Pancreatic ducts (proenzymes, zymogens) Proteins Bile Lipases HCO3-, PO43- (emulsification) Nucleases(DNA, RNA) Amylase(glycogen, starches) Di- and tripeptides TriglyceridesCholesterolFat Soluble Vitamins  pH to ≈ 8 (req. for enzyme action) Nucleotides Mono-, di-, trisaccharides Action of brush border enzymes Fatty acids,monoglycerides Lacteals Portal Vein Amino acids Conversion to chylomicrons Subclavian vein Monosaccharides

44. Review • Alimentary canal (direct contact with food) • Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal • Accessory structures (no direct contact with food, but provide secretions) • Salivary glands, liver, gall bladder, pancreas • Four layers of the alimentary canal • Mucosa – absorption, secretion, protection • Submucosa – nutrition and transport • Muscularis – movement • Serosa – protection, lubrication

45. Review • Wave-like movement of alimentary canal is called peristalsis • Results from stretching • Bowel sounds • Innervation of the alimentary canal (enteric nervous system) • Parasympathetic – increases activity • Sympathetic – decreases activity • Mouth • Mastication – mechanical processing of food and mixing with saliva

46. Review • Tongue • Lined by mucous membranes • Thick, skeletal muscle • Papillae function in food handling and taste • Lingual frenulum • Lingual tonsils • Lingual glands secrete lingual lipase • Palate (roof of oral cavity) • Hard palate (Palatine proc. of maxillary bones) • Soft palate • Uvula is suspended from this • Uvula closes opening to nasal cavity (nasopharynx)

47. Review • Tonsils • Lingual (back of tongue) • Palatine (lateral to tongue) • Pharyngeal (posterior wall of pharynx; adenoids) • Teeth • Primary teeth (deciduous teeth; baby teeth) • 6 months to 2-4 years • 20 total • Secondary (permanent teeth) • 6 yrs to 17-25 years • 32 total

48. Review • Teeth (continued) • Incisors – sharp for biting • Cuspids (canine) – for grasping/tearing • Bicuspids and molars – grinding • Structure • Crown – above gum line • Root – below gum line • Outer covering is enamel • hardest substance in body • NOT replaceable • Inner substance is dentin (alive) • Pulp cavity • Periodontal ligament

49. Review • Alimentary canal (direct contact with food) • Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal • Accessory structures (no direct contact with food) • Salivary glands, liver, gall bladder, pancreas • Four layers of the alimentary canal • Mucosa – absorption, secretion, protection • Submucosa – nutrition and transport • Muscularis – movement • Serosa – protection, lubrication

50. Review • Wave-like movement of alimentary canal is called peristalsis • Results from stretching • Bowel sounds • Innervation of the alimentary canal (enteric nervous system) • Parasympathetic – increases activity • Sympathetic – decreases activity • Mouth • Mastication – mechanical processing of food and mixing with saliva