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Anatomy of the Digestive System: A Comprehensive Guide

Explore the intricate details of the digestive system, from the alimentary canal to accessory organs, digestion processes, oral cavity structure, teeth anatomy, histology of the GI tract, and more. Understand the functions and layers of the esophagus, stomach, and small intestine in this in-depth study.

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Anatomy of the Digestive System: A Comprehensive Guide

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  1. Lab Exercise 26 Anatomy of the Digestive System Portland Community College BI 233

  2. Digestive System • Alimentary Canal: hollow tube extending from mouth to anus • Technically outside the body • Covered with mucous membrane • Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas

  3. Digestion • Process by which foods are broken down into simpler forms so that nutrients can be delivered to all areas in the body. • Ingestion chewing muscular actions Enzymatic breakdown absorption excretion

  4. Oral Cavity • The lips surround the anterior opening. • Consist of skeletal muscle covered with skin. • The tongue is also made of skeletal muscle. • A major tongue muscle is the genioglossus.

  5. Papillae • 3 Types of papillae • Fungiform • Filiform • Vallate Taste buds: along the sides of fungiform and vallate papillae

  6. Muscles of Mastication • Masseter • Temporalis

  7. Teeth • Gingiva is the mucous membrane (gums) • Each region of a tooth is identified according to its relationship to the gingival margin (gum line) • Crown is visible portion • Root is below gum line • Neck is at surface of gingiva

  8. Incisor (cutting) Canine (tearing) Premolar (tearing and grinding) Molar (grinding) Teeth Adults have 32 teeth Children have 20 deciduous teeth

  9. GI Tract Histology • All of the hollow organs have the same basic 4 layers. 1. Mucosa (Lumen side) • Epithelial layer (remember from 231: stratified squamous, columnar ect…) • Lamina Propria: Base made of loose areolar connective tissue • Muscularis Mucosa: Base of smooth muscle fibers 2. Submucosa • Dense irregular connective tissue • This is where the blood vessels, nerves and the glands are.

  10. GI Tract Histology 3. Muscularis Externa • The main smooth muscle layer used for peristalsis • Longitudinal and Circular layers with myenteric plexus (parasympathetic ganglion) in between 4. Serosa (Abdominal cavity side) • Epithelial layer (usually simple squamous) • Also known as the visceral peritoneum

  11. Extends from pharynx through the diaphragm at the esophageal hiatus to the lower esophageal sphincter into the stomach Esophagus Body Diaphragm Lower Esophageal Sphincter

  12. Esophagus Histology • 3. Muscularis Externa • Upper 1/3=Skeletal • Middle 1/3=Blend • Lower 1/3=Smooth • 4. Adventitia (Rest of GI tract: Serosa) • Coarse Fibrous CT: binds/anchors Skeletal Muscle Smooth Muscle

  13. Esophagus Histology • Mucosa • Epithelium • Non-keratinized stratified squamous

  14. Esophagus Histology • Submucosa (#2) • Esophageal glands • Vessels • Submucosal Plexus

  15. Membranes • Parietal Peritoneum: Covers the wall of the abdominal cavity • Visceral Peritoneum: Covers the outside of all the abdominal organs • Mesentery: a fold of peritoneum attaching the small intestine to the posterior abdominal wall • Greater Omentum: Thick sheet of tissue (lots of fat) that hangs off the greater curvature of the stomach • Lesser Omentum: Anchors the liver to the lesser curvature of the stomach

  16. Membranes

  17. Membranes

  18. Mesentery

  19. Greater Omentum

  20. Stomach Rugae

  21. Position of Stomach

  22. StomachHistology • 4 layers: • Mucosa (inside layer) • Simple columnar epithelium • Submucosa • Muscularis Externa smooth muscle in 3 layers • Serosa (visceral peritoneum)

  23. Stomach Mucosa • Mucous neck cells • Alkaline mucus • Parietal cells • HCL • Intrinsic factor • Chief cells • Pepsinogen • Gastric lipase • G cells (in antrum) • Gastrin

  24. Stomach Histology:Mucosa (Inside layer) • Mucosa: Simple columnar epithelium

  25. Stomach Mucosa Mucus Neck Cells Gastric Pits

  26. Lamina propria Lumen of pit Parietal cell Chief cell Entroendocrine (G cell)

  27. Small Intestine: Gross Anatomy • Runs from pyloric sphincter to the ileocecal valve • Has three subdivisions: duodenum, jejunum, and ileum • The bile duct and main pancreatic duct: • Join the duodenum at the hepatopancreatic ampulla • Are controlled by the sphincter of Oddi • The jejunum extends from the duodenum to the ileum • The ileum joins the large intestine at the ileocecal valve

  28. Biliary Tree

  29. Pancreas Head Body Tail Common Bile Duct Accessory Duct Pancreatic Duct

  30. Small Intestine Minor papilla PlicaCircularis Jejunum DuodenumC-Loop Major papilla

  31. Small Intestine: Ileum Ileocecal valve

  32. Small Intestine: Histology • Structural modifications of the small intestine wall increase surface area • Plica circularis: Transverse folds on the mucosa • Villi: Fingerlike extensions of the mucosa • Microvilli (Brush border): Tiny projections of absorptive mucosal cells’ plasma membranes

  33. Small Intestine: Plica Circularis

  34. Small Intestine Histology: Mucosa • Plicae circulares: Large deep, permanent folds of the mucosa and submucosa. • Slow the movement of chyme (more time for digestion/absorption) and increase the surface area.

  35. Small Intestine Histology

  36. Small Intestine Histology: Villi • Villi: Fingerlike projections of the mucosa. • Made of simple columnar epithelium • Increase the surface area. • Within the core of each villus is a capillary bed and a lacteal for transport of the absorbed nutrients

  37. Small Intestine: Villi

  38. Small Intestine Histology: Mucosa • Microvilli: Tiny projections of the plasma membrane of the simple columnar absorptive cells. • Often called the "brush border" due to their appearance. • They further increase the available surface area and contain membrane-bound enzymes involved in digestion.

  39. Small Intestine

  40. Small Intestine Histology:Submucosa with Brunner’s Glands • Brunner’s glands in the proximal duodenum secrete alkaline mucus Brunner’s glands

  41. Small Intestine Histology:Submucosa with Peyer’s Patches • Peyer’s patches are found in the submucosa of ileum • Lymphoid tissue

  42. Large Intestine • Is subdivided into the • Cecum • Appendix • Colon • Rectum • Anal canal • The saclike cecum: • Lies below the ileocecal valve in the right iliac fossa • Contains a wormlike vermiform appendix Ileum

  43. Has distinct regions: ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon The sigmoid colon joins the rectum The anal canal, the last segment of the large intestine, opens to the exterior at the anus Colon

  44. Transverse Colon Colon Splenic Flexure Hepatic Flexure Descending Colon Ascending colon Rectum Sigmoid Colon Anal Canal

  45. Hepatic Portal Vein Aorta Large Intestine Superior Mesenteric Artery Inferior Mesenteric Artery Ileocecal valve is in here Cecum Appendix Ileum

  46. Valves and Sphincters of the Rectum and Anus • Three valves of the rectum stop feces from being passed with gas • The anus has two sphincters: • Internal anal sphincter composed of smooth muscle • External anal sphincter composed of skeletal muscle • These sphincters are closed except during defecation

  47. Structure of the Anal Canal

  48. Large Intestine: Histology • Colon mucosa is simple columnar epithelium except in the anal canal • Has numerous deep crypts lined with goblet cells • Anal canal mucosa is stratified squamous epithelium • Superficial venous plexuses are associated with the anal canal

  49. Large Intestine Histology

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