Chapter 24 The Digestive System

1. Chapter 24The Digestive System

2. Structures and functions, fig 24.1 • Digestive System Organs • Alimentary Canal • Accessory Digestive Organs • Digestive Processes • Ingestion • Secretion • Propulsion • Digestion • Absorption • Defecation

4. Anatomy of the Digestive System • ________________ • Mouth, Pharynx, and Esophagus • Stomach • Small Intestine • Large Intestine • ___________ Digestive Organs • Teeth, Tongue, Salivary Glands • Liver and Gallbladder • Pancreas

5. Functions • _______________ taking food into the mouth • _______________ release of water, acid, buffers, & enzymes into lumen of GI tract • ___________ and __________ churning & propulsion of food thru GI tract • ______________ mechanical & chemical breakdown of food • _________________ passage of digested products from the GI tract into blood & lymph • ___________ elimination of feces from GI tract

6. Mouth, Pharynx, & Esophagus • Anatomy • Mouth • Lips and Cheeks • Palate • Tongue • Salivary Glands • Teeth • Pharynx • Esophagus • Digestive Processes • Mastication • Deglutition

7. Mouth (oral or buccal cavity) fig 24.5 • Formed by cheeks, hard & soft palate, tongue • Where mechanical AND chemical digestion begin • _____________ - chewing • Bolus- soft, flexible mass • ______________ – enzyme, initiates breakdown of starch • ______________ – enzyme in saliva, works in stomach to breakdown dietary triglycerides

9. Tongue • accessory organ • skeletal muscles covered w/ mucous membrane • Attached to hyoid, styloid process, mandible • Extrinsic muscles manuever food -chewing, form bolus, force back for swallowing • Intrinsic muscles alter shape and size during speech & swallowing • Dorsal & lateral surfaces covered w/_____________ - which are projections of lamina propria • Many contain taste buds - ______________ • Lacking taste buds - touch, increase friction • ____________ – secrete mucus, & serous fluid that contains lingual lipase

11. Teeth figure 24.7 • Accessory digestive organs in _________ __________ • Crown, neck, root – major external regions • _______________ - calcifed CT, gives shape and rigidity, harder than bone, majority of tooth • ________________- covers dentin on crown, hardest substance in body, protects tooth from wear & tear of chewing, and acids • ________________ - CT containing bv, nerves, lymphatic vessels

13. Dentitions figure 24.8 • ______________ teeth = primary, milk, or baby teeth – begin to erupt @ 6 months • 20 in full set • All are lost between age 6 to 12 • ______________ or secondary teeth • 32 teeth • 8 incisors – chisel shaped for cutting • 4 canine or cuspid – pointed to tear and shred • 8 premolars or bicuspid – crush and grind • 4 first molars (age 6) – crush and grind • 4 second molars (age 12)- crush and grind • 4 third molars or wisdom teeth (age 17)- crush and grind

15. Oral mucosa • Non-keratinized stratified squamous • ______________ – membrane that lines a body cavity that opens to the exterior • Of mouth and tongue- contain small salivary glands that open into oral cavity • Labial, buccal, palatal, and lingual • Make small contribution to saliva

16. Salivary glands figure 24.6 • Keep mouth & pharynx mucous membranes moist • Cleanse mouth & teeth • When food enters mouth, secretion  • Lubricates, dissolves, begins chemical digestion • 3 major glands (in pairs)- parotid, submandibular, sublingual glands

17. Control of salivation • ______________ stim= continuous secretion • ______________ stim= dominates during stress resulting in dryness of mouth • If body dehydrated, saliva not secreted  dry mouth  sensation of thirst • Feel & taste of food stimulate receptors in taste buds  nuclei in brain stem  parasymp impulse via facial & glossopharyngeal nerves to stimulate salivation • Smell, sight, sound or thought of food may also stim.

18. 4 basic layers of GI tract fig 24.2 • Variations, but same basic organization in esophagus, stomach, small & large intestines • From inner to outermost (starting inside the __________) • Mucosa • Submucosa • Muscularis • Serosa

20. Layers of GI tract • 1. ____________ - lines lumen, has 3 layers: • ______________- • mouth, pharynx, esophagus, & anal canal= non-keratinized stratified squamous for protective function • stomach & intestines = simple columnar, w/ tight junctions for secretion & absorption • Cells renew every 5-7 days (rapid reproduction) • Some epithelium = exocrine - mucus secreting cells • Enteroendocrine cells secrete hormones into bloodstream

21. ________________ –areolar CT, many bv & lymphatic vessels, nutrients  tissues of body • Supports epithelium & binds to muscularis mucosa • Contains most mucosa-associated lymphoid tissue (MALT) – lymphatic nodules containing immune cells • Also found in tonsils, s.i., appendix and l.i. • ________________- thin layer of smooth muscle • Puts mucous membrane of stomach & s. i. into many small folds ↑ SA for digestion & absorption • movements insure absorptive cells fully exposed

22. 2. _________________- areolar CT binds mucosa to muscularis • Highly vascular • __________________- portion of ENS- regulates movements of mucosa & bv vasoconstriction • Sensory – act as chemoreceptors & stretch receptors • Interneurons – connect myentric & submucosal • Motor - innervates secretory cells of epithelium • May contain glands and lymphatic tissue

23. 3. _____________- mouth, pharynx, & superior-mid esophagus = skeletal muscle- swallow • Skeletal muscle forms external anal sphincter • Thru rest of tract: smooth muscle- generally found in 2 sheets (exception- stomach has 3): • Inner = circular layer • outer = longitudinal layer • Involuntary contractions  breakdown food • Mix food w/ secretions & propel it along tract • Between 2 sheets: ________________ (ENS)- mostly controls GI tract motility- freq & strength of contraction

24. 4. __________- found in portions of GI tract suspended in abdominopelvic cavity • serous membrane: areolar CT & simple squamous epithelium • AKA- visceral peritoneum • Esophagus lacks this layer, has adventitia instead- single layer of areolar CT & no simple squamous

25. Peritoneum figure 24.4 • largest serous membrane of body • consists of a layer of simple squamous (mesothelium) w/ supporting areolar CT • __________________- lines abdominopelvic cavity wall • __________________- covers some organs in cavity, is serosa • peritoneal cavity- slim space between these layers • contains serous fluid

26. Peritoneum (2) • ___________________- organs lie on posterior abdominal wall • covered by peritoneum on their anterior surface • kidneys and pancreas • Bind organs to each other & walls of abdominal cavity • Contain bv, lv, & nerves -supply organs • Contains large folds between viscera: • ___________________ outward fold of serous coat of small intestine; binds to posterior ab wall • ___________________ binds large intestine to posterior ab wall; carries bv & lv to intestines *both hold intestines loosely in place

27. Peritoneum (3) • ________________- attaches liver to anterior ab wall & diaphragm, (liver = only digestive organ attached to anterior wall) • ________________- 2 folds in serosa, suspends stomach & duodenum from liver, contains some lymph nodes • _______________- largest part of peritoneum Hangs loosely like a “fatty apron” over transverse colon & coils of small intestine Contains considerable adipose & many lymph nodes, contributes macrophages & plasma cells to combat infection & prevent spread of infection

32. Esophagus figure 24.10 • Extends from laryngopharynx  esophageal hiatus (surrounded by diaphragm)  stomach • Stratified squamous epithelium • Muscularis: superior 1/3 = skeletal • Intermediate 1/3 = skeletal & smooth • Inferior 1/3 = smooth • At each end is sphincter • ____________ – skeletal, regulate pharynx  esophagus • ____________ – smooth, regulate esophagus  stomach • Adventitia- not serosa (no simple squamous cells) • Secretes mucus, transport food • No production of enzymes, no absorption

33. Deglutition (swallowing) - 3 phases • Movement of food from mouth to stomach • ________________ stage- bolus forced back into oropharynx by movement of tongue • _______________ stage- bolus stimulates receptors in oropharynx  deglutition center in medulla & pons • Soft palate & uvula close off nasal cavity • Epiglottis closes off opening to larynx • Bolus moves thru oro & laryngopharynx • ________________ stage- bolus enters esophagus • Peristalsis- progression of coordinated contractions & relaxations of circular & longitudinal layers of muscularis • Mucus to lubricate & reduce friction

37. Stomach • Functions • Anatomy • Surface Epithelium • Gastric Glands • Secretory Cells • Digestive Processes • Regulation of Gastric Secretion • Gastric Motility and Emptying

38. Stomach functions figure 24.11 • Mixes saliva, food & gastric juices to form __________ – semifluid mixture of partially digested food • reservoir for holding before release into s.i. • secretes ___________ (2-3L/day), contains: • HCl - kills bacteria & denatures proteins • Pepsin begins the digestion of proteins • Intrinsic factor- aids absorption of vitamin B12 • Gastric lipase - aids digestion of triglycerides • Secretes ___________ into blood when stomach is distended or pH is too high

41. Stomach anatomy figure 24.11 • 4 main regions: • Cardia • Fundus • Body • Pylorus • Pyloric sphincter • Lesser curvature • Greater curvature • ____________ – large folds of mucosa when stomach is empty

42. Histology of stomach fig 24.12, 13 • Mucosa – simple columnar = surface mucous cells that extend into lamina propria forming columns of ____________ secretory cells – gastric glands which line gastric pits • Mucous neck cells- secrete mucus • Parietal cells- secrete intrinsic factor & HCl • Chief cells- secrete pepsinogen & gastric lipase • ____________________ cells also part of gastric gland • G cells- secretes gastrin, which stimulates gastric acitivity, located mainly at pyloric antrum • Muscularis – 3 layers: outer-longitudinal, mid-circular, inner-oblique

46. Chemical digestion in stomach • food may remain in fundus for hr, salivary amylase works • chyme mixes w/gastric juices & lingual lipase activated • HCl denatures proteins & stimulates secretion of hormones that promote flow of bile and pancreatic juice • Also, acidity kills microbes • Enzymatic digestion of proteins begins w/pepsin • Gastric lipase breaks down short chain triglycerides (BUT, optimum pH is 5-6) • Pancreatic lipase is more important • Small amt of nutrients absorbed in stomach • Mucous cells absorb some water, ions, some f.a., drugs (such as aspirin) & alcohol

47. What prevents auto-digestion? • _____________ secreted in inactive form: pepsinogen  cannot digest proteins inside chief cells • Pepsinogen  pepsin in presence of HCl or other active pepsin • Stomach epithelium protected by 1-3 mm of _______________ secreted by surface mucous cells & mucous neck cells

48. 3 Phases of digeston, p 937 • _________________ sight, smell, thought or initial taste activates neural centers in cerebral cortex, hypothalamus, & brain stem • Facial and glossopharygeal nerves stimulate saliva secretion • Vagus nerve stimulates gastric juice secretion • (all to prep mouth & stomach for food to be eaten)

49. Phases (2) figure 24.24 • _________________ food in stomach, digestion begins • Neural regulation- when either of following occur, sets off negative feedback loop  submucosal plexus activates parasym & enteric neurons  peristalsis & gastric secretion • Stretch receptors monitor distention • Chemoreceptors monitor  pH • Hormonal regulation- gastrin regulates gastric secretions, released in response to distension, partially digested proteins,  pH (food present), caffeine, or Ach (parasymp) • Glands to secrete large amt. gastric juice • Strengthens contraction of LES •  stomach motility • Relaxes pyloric sphincter