The Digestive System

1. 23 The Digestive System

2. I. Overview of the Digestive System A. Organs are divided into two groups 1. Alimentary canal ► mouth, pharynx, and esophagus ► stomach, small intestine, and large intestine, rectum 2. Accessory digestive organs ► teeth and tongue ► gallbladder, salivary glands, liver, and pancreas i. connected to the alimentary canal by ducts ii. secretions contribute to breakdown of foodstuffs

3. Mouth (oral cavity) Parotid gland Sublingual gland Salivary glands Tongue Submandibulargland Pharynx Esophagus Stomach Pancreas (Spleen) Liver Gallbladder Transversecolon Descendingcolon Duodenum Jejunum Smallintestine Ascendingcolon Ileum Large intestine Cecum Sigmoid colon Rectum Appendix Anus Anal canal

4. II. Abdominal Regions A. Four lines divide abdominal wall into nine regions 1. Midclavicular lines - vertical lines of grid 2. Subcostal plane - superior horizontal line 3. Transtubercular plane - inferior horizontal line B. Four quadrants – cross with point in the umbilicus 1. Right upper quadrant 2. Left upper quadrant 3. Right lower quadrant 4. Left lower quadrant

5. Lefthypochondriacregion Righthypochondriacregion Epigastricregion Rightlumbarregion Leftlumbarregion Umbilicalregion Hypogastric(pubic)region Left iliac(inguinal)region Right iliac(inguinal)region Nine regions delineated by four planes

6. Diaphragm Liver Stomach Gallbladder Transverse colonof large intestine Ascending colonof large intestine Descending colonof large intestine Small intestine Cecum Initial part ofsigmoid colon Appendix Urinary bladder Anterior view of the nine regions showing the superficial organs

7. III. The Peritoneal Cavity and Peritoneum A. Imagine the digestive organs surrounded by plastic wrap 1. some of it touches the surface of the organ (“visceral”) 2. some of it touches the outer area of the organ (“parietal”) 3. like a hose that is surrounded by plastic wrapping B. Peritoneum - a serous membrane around the digestive organs 1. visceral peritoneum - surrounds digestive organs on surface 2. parietal peritoneum – part that touches the outside a. peritoneal cavity – space between these two layers

10. C. Mesentery - a double layer of peritoneum 1. holds organs in place 2. sites of fat storage 3. provides a route for circulatory vessels and nerves 4. it is the “sheet” that envelopes the intestines D. Ventral mesenteries 1. Falciform ligament - binds anterior part of liver to anterior abdominal wall; between lobes of the liver 2. Lesser omentum - attaches liver to lesser curvature of stomach

11. E. Dorsal mesenteries 1. Greater omentum - connects greater curvature of stomach to posterior abdominal wall a. a “fatty apron” flapped over the digestive organs 2. Transverse mesocolon - holds transverse colon in place 3. Sigmoid mesocolon - connects the sigmoid colon to posterior pelvic wall F. Retroperitoneal organs - behind the peritoneum G. Peritoneal organs - digestive organs that keep their mesentery

12. Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder

13. Greater omentum Transverse colon Transversemesocolon Descending colon Mesentery Sigmoidmesocolon Jejunum Sigmoid colon Ileum

14. Ligamentumteres Gallbladder Lesser omentum Spleen Liver Gastrosplenic ligament Transversemesocolon Pancreas Stomach, pyloric part Duodenum,superior part Transverse colon Duodenojejunal flexure Duodenum,horizontal part Greater omentum Descending colon Ascending colon Mesentery (cut) Sigmoidmesocolon Rectum Ileum Cecum

15. Falciform ligament Liver Gallbladder Spleen Stomach Ligamentumteres Greater omentum Small intestine Cecum

16. IV. Histology of the Alimentary Canal Wall A. Same four layers from esophagus to anus 1. mucosa—innermost layer a. epithelium b. lamina propria c. muscularis mucosae 2. submucosa—external to the mucosa a. contains blood and lymphatic vessels, nerve fibers

17. 3. muscularis externa - external to the submucosa a. circular muscularis - inner layer b. longitudinal muscularis - outer layer 4. serosa—the outermost layer – is the visceral peritoneum

18. Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Circular layer Longitudinal layer Serosa Epithelium Connective tissue Nerve Lumen Artery Vein Lymphatic vessel Mesentery Longitudinal and cross-sectional views through the small intestine

19. Mucosa Submucosa Muscularis externa Serosa Light micrograph cross section through the small intestine (85)

20. Longitudinal layer ofsmooth muscle (showssmooth muscle fibers incross section, 215) Small intestine Mucosa Circular layer of smoothmuscle (shows longitudinalviews of smooth musclefibers, 215) Cross section of the intestineshowing the smooth musclelayers (one circular and theother longitudinal) running atright angles to each other Location and plane ofsection shown in (b)

21. V. Nerve Plexuses A. Myenteric nerve plexus 1. lies between circular and longitudinal muscularis 2. controls peristalsis and segmentation B. Submucosal nerve plexus 1. lies in submucosa 2. signals glands to secrete C. Innervation - sympathetic and parasympathetic motor fibers

22. VI. The Mouth and Associated Organs A. Borders of the mouth ► Lips anteriorly ► Cheeks laterally ► Palate superiorly ► Tongue inferiorly ► Fauces of oropharynx posteriorly B. lips and cheeks - formed from orbicularis oris and buccinator C. Mucosal layer - stratified squamous epithelium

23. Soft palate Uvula Hard palate Nasopharynx Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea Sagittal section of the oral cavity and pharynx

24. Uvula Nasopharynx Oropharynx Laryngopharynx Sagittal section of the oral cavity and pharynx

25. D. labial frenulum - connects lips to gum E. palate - forms the roof of the mouth (hard and soft) F. Boundaries of the fauces ► palatoglossal arches ► palatopharyngeal arches

26. Superior labialfrenulum Palatoglossalarch Hard palate Soft palate Palatopharyngealarch Uvula Lingual frenulum Gingivae (gums) Inferior labialfrenulum Anterior view

27. VII. The Tongue A. Interlacing fascicles of skeletal muscle B. Grips food and repositions it C. Helps form some consonants D. Intrinsic muscles - within the tongue E. Extrinsic muscles - external to the tongue F. Lingual frenulum - secures tongue to floor of mouth G. Papillae – different “bumps” on the tongue for taste, etc.

28. Epiglottis Terminal sulcus Foliate papillae Vallate papilla Medial sulcusof the tongue Dorsum of tongue Fungiform papilla Filiform papilla

29. VIII. The Teeth A. Deciduous teeth – (20 teeth) - first appear at 6 months of age B. Permanent teeth – (32 teeth) - by the end of adolescence C. Types of teeth: ► Incisors (8) ► Canines (4) ► Premolars (8) ► Molars (12)

30. Incisors Central (6–8 mo) Lateral (8–10 mo) Canine (eyetooth)(16–20 mo) Molars First molar(10–15 mo) Deciduous(milk) teeth Second molar(about 2 yr) Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth)(11 yr) Premolars(bicuspids) First premolar(11 yr) Second premolar(12–13 yr) Molars First molar (6–7 yr) Second molar(12–13 yr) Permanentteeth Third molar(wisdom tooth)(17–25 yr)

31. IX. Tooth Structure A. Crown - exposed surface B. Neck – at gum line B. Root - in tooth socket C. Enamel – outer layer D. Dentin - underlies enamel E. Pulp cavity - center of tooth F. Periodontal ligament – attaches tooth to bone

32. Enamel Dentin Crown Pulp cavity (containsblood vesselsand nerves) Neck Gingiva (gum) Cement Root canal Root Periodontalligament

33. Pulp cavity (containsblood vesselsand nerves) Gingiva (gum) Cement

34. X. The Salivary Glands A. Produce saliva B. Parotid glands – in the cheeks C. Submandibular glands - along medial surface of mandible D. Sublingual glands - lie in floor of oral cavity

35. Parotidgland Ducts ofsublingualgland Parotid duct Sublingualgland Submandibularduct Submandibulargland Mucous cells Serous cellsformingdemilunes

36. XI. The Esophagus A. A long muscular tube – moves food by peristalsis B. Begins as a continuation of the pharynx C. Joins the stomach inferior to the diaphragm D. Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus E. Statified squamous epithelium F. Skeletal muscle ---- mixed skeletal/smooth ---- smooth muscle

37. Mucosa(stratified squamousepithelium) Esophagus-stomachjunction Submucosa(areolar connective tissue) Lumen Muscularis externa Simple columnarepithelium ofstomach Circular layer Longitudinal layer Adventitia (fibrousconnective tissue) Cross section throughesophagus (3) Esophagus-stomach junction,longitudinal section (85)

38. XII. The Stomach A. Site where food is churned into chyme B. Regions of the stomach ► cardiac region ► fundus ► body ► pyloric region C. Muscularis has three layers 1. circular and longitudinal and oblique layers D. Epithelium is simple columnar epithelium

39. Cardiac Region Fundus Muscularis externa Longitudinal layer Circular layer Body Oblique layer Lumen Lessercurvature Rugae ofmucosa Greatercurvature Pyloricregion Pyloric sphincter

40. E. Mucosa dotted with gastric pits with gastric glands F. Pyloric sphincter – valve that leads to small intestine G. Rugae – folds along the inner surface H. Greater and Lesser curvatures

41. Cardiac Region Fundus Muscularis externa Longitudinal layer Circular layer Body Oblique layer Lumen Lessercurvature Rugae ofmucosa Greatercurvature Pyloricregion Pyloric sphincter

42. Fundus Liver(cut) Body Spleen Lessercurvature Greatercurvature

43. A gastric ulcer lesion Bacteria Mucosalayer ofstomach H. pylori bacteria

44. XIII. The Small Intestine A. Longest portion of the alimentary canal B. Site of most enzymatic digestion and absorption C. Three subdivisions ► duodenum(1 foot) ► jejunum(next 8 feet) ► ileum(last 12 feet) D. Innervation 1. parasympathetic fibers from vagus nerve 2. sympathetic from thoracic splanchnic nerves

45. E. Duodenum 1. receives digestive enzymes and bile 2. Main pancreatic duct and common bile duct enter duodenum 3. Sphincters control entry of bile and pancreatic juices

46. Right and left hepaticducts of liver Common hepatic duct Cystic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Main pancreatic duct and sphincter Hepatopancreaticampulla and sphincter Duodenum

47. F. Modifications for absorption 1. circular folds - transverse ridges of mucosa and submucosa 2. Villi - fingerlike projections of the mucosa a. covered with simple columnar epithelium 3. microvilli - further increase surface area for absorption 4. lacteals – special lymphatic vessels of the intestine

48. Lumen Circularfolds Villi Microvilli Absorptive enterocytes Gobletcells Lacteal Villi Vilus Intestinal crypt

49. XIV. The Large Intestine A. Small amount of digestion by bacteria B. Main functions - Absorb water and electrolytes C. Mass peristaltic movements force feces toward the rectum D. Subdivided into: cecum, appendix, colon, rectum, anal canal E. Special features of large intestine 1. teniae coli - thickening of longitudinal muscularis layer 2. haustra - puckering created by teniae coli 3. epiploic appendages - fat-filled pouches of visceral peritoneum

50. Epiploic appendages Transverse colon Descending colon Haustrum Ascending colon Teniae coli Sigmoid colon Rectum Appendix Anal canal External anal sphincter