The Digestive System

1. The Digestive System

2. Functions of the Digestive System • Ingest food • Break down food into nutrient molecules • Absorb molecules into the bloodstream • Rid the body of indigestible remains

3. Summary of Digestion

4. Summary of Digestion

6. Main Divisions of the Digestive System • Alimentary Canal • Continuous, muscular digestive tube winding throughout the body • Digests and absorbs food particles • Contains the following organs: • Mouth, Pharynx, Esophagus, Stomach, Small and Large Intestines • Accessory Digestive Organs • Contains the following organs: • Teeth, Tongue, Gallbladder, Salivary Glands, Liver, and Pancreas

7. Digestive System Divisions

8. 6 Digestive Processes • Ingestion • Propulsion • Mechanical digestion • Chemical digestion • Absorption • Defecation

9. Features and Functions of the Mouth • Buccal/oral cavity • Contains stratified squamous epithelium • Vestibule: area bounded by lips and cheeks externally and teeth and gums internally • Lips: possess no sweat or oil glands • Palate: forms roof of the mouth, soft and hard palate, uvula

10. Anatomy of the Mouth

11. Features and Functions of the Tongue • Helps grind food into a bolus which contains partially digested food and saliva • Helps form words and is a sensory organ for taste • Three surface features: • Filiform papillae (roughness and grip) • Fungiform papillae (contains taste buds) • Circumvallate papillae (contains taste buds)

12. Anatomy of the Tongue

13. Features and Functions of the Salivary Glands • Main functions: • Produces and secretes saliva • Cleanses the mouth • Dissolves food chemicals so they can be tasted • Moistens food, compacting it into a bolus • Begins the chemical breakdown of food • Salivary amylase breaks down starch

14. Anatomy of the Salivary Glands

15. Composition of Saliva: 97-99.5% water • pH 6.75-7.0 • Sodium, potassium, chloride, phosphate, and bicarbonate • Mucin – large glycoproteins in mucus • Salivary amylase

16. Features and Functions of the Teeth • Break food into smaller parts, increasing surface area for digestion • Types of Teeth • Deciduous Teeth (“baby” teeth) • Permanent Teeth • Incisors- cutting and shredding • Canines- piercing and tearing • Molars- grinding • Premolars- grinding and crushing

17. Tooth Structure • Crown: exposed portion of tooth covered by enamel which covers dentin • Root: internal portion that is beneath the gums (gingiva) and is anchored by periodontal ligaments

18. Deglutition and the Pharynx • Deglutition = swallowing • Oropharynx and Laryngopharynx are common passageways for food and air • Pharynx contains stratified squamous epithelium (friction-resistant)

19. Features and Functions of the Esophagus • Muscular tube that propels food to stomach; bolus enters stomach through esophageal hiatus • Skeletal muscle (upper third for swallowing) and smooth muscle (lower third) for peristalsis • Esophageal glands – produce mucus to lubricate bolus • Esophageal sphincter – prevents backflow into oral cavity • Cardiac sphincter- prevents backflow into esophagus

20. Anatomy of the Esophagus

21. Digestive Processes in the Mouth, Pharynx, and Esophagus • Mouth processes: • Ingestion • Mechanical digestion • Initiation of Propulsion • Mastication: chewing • Pharyngeal processes: • Deglutition = swallowing • Voluntary Buccal phase • Involuntary Pharyngeal-Esophageal Phase • Esophageal processes: • Peristalsis (rhythmic contractions, involuntary)

22. Deglutition and the Pharynx

23. Peristalsis

24. Features and Functions of the Stomach • Temporary storage area for food and allows it to mix with gastric juice to produce chyme • Regions: cardiac, fundus, body, and pyloric • Greater and Lesser Curvatures: connected to greater and lesser omentums • Rugae folds: longitudinal folds in stomach wall - mucous b/w folds • Muscle layers arranged circularly, longitudinally, AND obliquely (aids in digestion)

25. Anatomy of the Stomach

26. Microscopic Anatomy of the Stomach • Simple columnar epithelium – contains gastric pits that secrete gastric juices • Goblet cells – secrete mucus that coats stomach and prevents it from being digested itself • Parietal cells – secrete hydrochloric acid (converts pepsinogen into pepsin) and intrinsic factor (necessary for absorption of vitamin B12) • Chief cells – secrete pepsinogen which is converted to pepsin to aid in protein digestion • Enteroendocrine cells – release hormones such as: • Histamine, Serotonin, Gastrin, Endorphins, and Somatostatin

27. Histamine - activates parietal cells to release HCl • Serotonin - contraction of stomach muscle • Gastrin causes - gastric glands to increase secretion • Endorphins - natural opiates • Somatostatin stimulates - sympathetic n.s. - inhibits gastric secretion - inhibits gastric emptying

28. Microscopic Anatomy of the Digestive System

29. Gastric Motility and Emptying • Peristaltic waves approach stomach and become stronger near pyloric region • Pyloric sphincter allows ~ 3 mL of chyme to pass to duodenum and the rest to return to stomach for further mixing

30. Features and Functions of the Small Intestine • Receives chyme from stomach; performs majority of digestion and absorption of nutrients • Regions: • Duodenum (upper region receiving chyme from stomach and digestive enzymes from pancreas and bile from liver and gallbladder) • Jejunum and Ileum (lower regions where absorption occurs) • Plicaecirculares (permanent folds in mucosa and submucosa that slow movement of chyme)

33. Anatomy of the Small Intestine

34. Microscopic Anatomy of Small Intestine • Villi: fingerlike projections that increase the surface area of the SI • Microvilli: tiny projections on the plasma membranes of columnar cells that appear fuzzy (i.e. brush border cells) • Crypts of Lieberkuhn: secrete intestinal juice and special lysozymes that protect against bacteria • Peyer’s Patches: aggregated lymphoid tissues containing lymphocytes

35. Microscopic Anatomy of the Small Intestine

36. Secretions of the Small Intestine • Secretin: released by enteroendocrine cells when acidic chyme enters SI; causes release of bicarbonate-rich pancreatic juices • Somatostatin: slows gastric motility and emptying and inhibits production of gastric secretions • Cholecystokinin (CCK): released when fatty, protein-rich chyme enters SI; causes release of enzyme-rich pancreatic juices and bile • Brush border enzymes: process long peptides, nucleic acids, and sugars into smaller ones

37. After Digestion: Absorption Protein Lipids

38. Functions of the Liver • Largest internal organ • Functions: • Filters and processes nutrient-rich blood of carbohydrates, proteins, and lipids from intestine • Production and regulation of cholesterol • Production of bile which emulsifies fats • Removes drugs and hormones from circulation • Storage of vitamins and minerals

39. Anatomy of the Liver • Right and Left Lobes: separated by falciform ligament • Caudate and Quadrate Lobes: found on posterior side • Blood vessels: • Hepatic artery/vein and hepatic portal vein • Gallbladder: found underneath left lobe, stores bile

41. Microscopic Anatomy of the Liver • Liver Lobules: structural unit of liver • Hepatocytes: liver cells contained within the lobules • Hepatic portal vein & Hepatic Artery: the circulation of the liver, they bring blood into the liver where it is filtered through the liver sinusoidal capillaries • Kupffer cells: remove debris • Filtered blood drains into the central vein, then to the hepatic vein, and eventually to the inferior vena cava • Bile (produced by hepatocytes) drains into the bile duct after passing through portal triad • Bile then shipped to gallbladder for storage

42. Microscopic Anatomy of the Liver

43. Microscopic Anatomy of the Liver

44. Blood supply - receives fresh O2 blood from hepatic artery (off of aorta) - receives deoxygenated blood with nutrients (from small intestine) - hepatic portal vein - From liver- hepatic vein- inferior vena cava Hepatic portal vein, hepatic artery and bile ducts make up the portal triad.

46. Features and Functions of the Pancreas • Pancreatic Juice secreted by acinar cells • Islets of Langerhans release insulin and glucagon (important in glucose metabolism) • Pancreatic Juice contains: • Sodium Bicarbonate (buffers HCl in stomach) • Proteases (break down polypeptides) • Pancreatic amylase (digests oligosaccarides and disaccharides into monosaccharides) • Pancreatic lipases (break down lipids into fatty acids and glycerol) • Pancreatic nucleases (break down nucleic acids)

47. Anatomy of the Pancreas

48. Features and Functions of the Large Intestine • Functions: • Reabsorption of remaining water and electrolytes • Production and absorption of Vitamins B and K • Elimination of feces • Diameter is only 7 cm but is larger than that of the small intestine

49. Gross Anatomy of the Large Intestine • Teniae Coli: bands of smooth muscle that create pocket-like sacs (haustra) • Cecum: sac-like connection between the small and large intestines • Appendix: small structure containing lymphoid tissue; small immune function • Ascending, Descending, Transverse, and Sigmoid Colon • Splenic and hepatic flexure • Rectum: storage area • Anus: regulates defecation with two sphincter muscles; internal and external

50. Anatomy of the Colon